CN118011397B

CN118011397B - Echo abnormality detection and compensation method

Info

Publication number: CN118011397B
Application number: CN202410412366.3A
Authority: CN
Inventors: 陈龙永; 谢燚; 栾禹辰; 王大伟; 颜千程
Original assignee: Aerospace Information Research Institute of CAS
Current assignee: Aerospace Information Research Institute of CAS
Priority date: 2024-04-08
Filing date: 2024-04-08
Publication date: 2024-06-11
Anticipated expiration: 2044-04-08
Also published as: CN118011397A

Abstract

The invention provides an echo anomaly detection and compensation method which can be applied to the technical field of radars. The method comprises the following steps: respectively performing fast Fourier transform on any two adjacent echo sampling sequences in the N echo sampling sequences to obtain a first spectrogram and a second spectrogram; determining autocorrelation normalized cross power spectrums between two adjacent echo sampling sequences according to the first spectrogram and the second spectrogram; normalizing the cross power spectrum solution phase of the autocorrelation to obtain a power spectrum phase sequence; fitting each power spectrum phase included in the power spectrum phase sequence to determine a phase slope; determining the number of offset pixels according to the phase slope; and carrying out time delay compensation on the post echo sampling sequence according to the offset pixel number to obtain a time delay compensation sequence.

Description

Echo abnormality detection and compensation method

Technical Field

The invention relates to the technical field of radars, in particular to an echo anomaly detection and compensation method.

Background

Synthetic aperture radar (SAR, SYNTHETIC APERTURE RADAR) is widely used in the fields of military reconnaissance, topographic mapping, environmental monitoring, etc., because of its all-day all-weather operational capability.

In the related art, a time difference between two adjacent received echoes is detected by using an echo correlation method, that is, a cross-correlation operation is performed on the two adjacent echoes, and the time difference between the two adjacent echoes is corrected by searching for a peak point position difference after the cross-correlation operation. However, it can only detect and correct the difference of an integer number of sampling points, but cannot detect the difference of a small number of sampling points and the difference of initial phases, which will have negative effects on the quality of the image corresponding to the echo, so that the image is defocused and the like, which affects the image quality.

Disclosure of Invention

In view of the foregoing, the present invention provides an echo anomaly detection and compensation method, apparatus, device, medium, and program product.

According to a first aspect of the present invention, there is provided an echo abnormality detection and compensation method, the method comprising:

Respectively performing fast Fourier transform on any two adjacent echo sampling sequences in the N echo sampling sequences to obtain a first spectrogram and a second spectrogram, wherein N is a positive integer;

Determining an autocorrelation normalized cross power spectrum between two adjacent echo sampling sequences according to the first spectrogram and the second spectrogram;

the autocorrelation normalized cross power spectrum is subjected to phase resolution to obtain a power spectrum phase sequence;

Fitting each power spectrum phase included in the power spectrum phase sequence to determine a phase slope;

Determining the offset pixel number according to the phase slope, wherein the offset pixel number represents the pixel number of the later echo sampling sequence in the two adjacent echo sampling sequences, which is offset compared with the pixel number of the earlier echo sampling sequence, and the offset pixel number corresponding to the first echo sampling sequence is a first preset value;

And carrying out time delay compensation on the post-echo sampling sequence according to the offset pixel number to obtain a time delay compensation sequence.

A second aspect of the present invention provides an echo abnormality detection and compensation device, the device including:

the first obtaining module is used for respectively carrying out fast Fourier transform on any two adjacent echo sampling sequences in the N echo sampling sequences to obtain a first spectrogram and a second spectrogram, wherein N is a positive integer;

The first determining module is used for determining an autocorrelation normalized cross power spectrum between two adjacent echo sampling sequences according to the first spectrogram and the second spectrogram;

the second obtaining module is used for obtaining a power spectrum phase sequence by resolving the autocorrelation normalized cross power spectrum;

The second determining module is used for fitting each power spectrum phase included in the power spectrum phase sequence to determine a phase slope;

A third determining module, configured to determine an offset pixel count according to the phase slope, where the offset pixel count characterizes a pixel count of a subsequent echo sampling sequence in the two adjacent echo sampling sequences that is offset from a preceding echo sampling sequence, and an offset pixel count corresponding to the first echo sampling sequence is a first preset value;

And a third obtaining module, configured to perform time delay compensation on the post-echo sampling sequence according to the offset pixel number, to obtain a time delay compensation sequence.

A third aspect of the present invention provides an electronic device comprising: one or more processors; storage means for storing one or more computer programs. The one or more processors execute the one or more computer programs to implement the steps of the methods described above.

The fourth aspect of the present invention also provides a computer-readable storage medium having a computer program stored thereon. Which computer program, when being executed by a processor, carries out the steps of the method described above.

The fifth aspect of the invention also provides a computer program product comprising a computer program. The computer program as described above, when executed by a processor, implements the steps of the method as described above.

According to the embodiment of the invention, after the autocorrelation normalized cross power spectrum between two echo sampling sequences is obtained, a power spectrum phase sequence is obtained by resolving the phase of the autocorrelation normalized cross power spectrum; fitting each power spectrum phase included in the power spectrum phase sequence to determine a phase slope; according to the phase slope, the offset pixel number is determined, so that the small offset pixel number, namely the offset pixel number of the sub-pixel level, can be obtained, then the time delay compensation is carried out on the post-echo sampling sequence according to the offset pixel number, so that the time delay compensation sequence is obtained, the time delay compensation of the sub-pixel level can be realized, the influence of the time delay on the compensated time delay compensation sequence is greatly reduced, and the quality of the image corresponding to the time delay compensation sequence is improved.

Drawings

The foregoing and other objects, features and advantages of the invention will be apparent from the following description of embodiments of the invention with reference to the accompanying drawings, in which:

FIG. 1 shows an application scenario diagram of an echo anomaly detection and compensation method according to an embodiment of the present invention;

FIG. 2A shows a schematic diagram of the coherence exhibited between two adjacent pulses transmitted by a SAR system in the presence of both a time delay and an initial phase difference between the two adjacent pulses;

FIG. 2B shows a schematic diagram of the coherence exhibited between two adjacent pulses transmitted by a SAR system in the absence of a time delay between the two adjacent pulses but with an initial phase difference;

FIG. 2C shows a schematic diagram of the coherence exhibited between two adjacent pulses transmitted by a SAR system in the presence of a time delay between the two adjacent pulses but no initial phase difference;

FIG. 2D shows a schematic diagram of the coherence exhibited between two adjacent pulses in an ideal case;

FIG. 3A shows a schematic diagram of the NCPS folding phase and ANCPS folding phase of two adjacent echoes prior to unwrapping;

FIG. 3B shows a schematic diagram of the NCPS phase and ANCPS phases of two adjacent echoes after unwrapping;

FIG. 3C shows a schematic diagram of NCPS phases and ANCPS phases corresponding to region 301 of FIG. 3B;

FIG. 4 is a flow chart of an echo anomaly detection and compensation method according to an embodiment of the present invention;

FIG. 5A shows a schematic diagram of the number of individual offset sample points corresponding to an N-frame echo sample sequence, according to an embodiment of the invention;

FIG. 5B illustrates a schematic diagram of the number of individual offset sample points corresponding to the echo sample sequence in region 501 of FIG. 5A, in accordance with an embodiment of the present invention;

FIG. 6 is a flow chart of an echo anomaly detection and compensation method according to another embodiment of the present invention;

FIG. 7A shows a schematic diagram of all unwrapped phase differences included in a phase difference sequence in accordance with an embodiment of the present invention;

FIG. 7B illustrates a schematic diagram of respective unwrapped phase differences corresponding with region 701 of FIG. 7A in accordance with an embodiment of the present invention;

FIG. 8A is a schematic diagram showing the variation of the phase error with frame number for each constant term corresponding to an N-frame echo sample sequence in accordance with an embodiment of the invention;

FIG. 8B is a graph showing the variation of the phase error with frame number for each constant term corresponding to region 801 of FIG. 8A, in accordance with an embodiment of the present invention;

FIG. 9 is a schematic diagram showing the number of hops and the abnormal positions detected by the echo abnormality detection and compensation method according to the embodiment of the present invention;

FIG. 10 is a schematic diagram showing a jump point error after performing time delay compensation on an echo sampling sequence according to an echo anomaly detection and compensation method according to an embodiment of the present invention;

FIG. 11 is a schematic diagram showing abnormal positions and differences detected by the echo abnormality detection and compensation method according to the embodiment of the present invention;

Fig. 12 is a schematic diagram showing a phase difference after performing phase compensation on an echo sampling sequence according to an echo anomaly detection and compensation method provided by an embodiment of the present invention;

FIG. 13 is a block diagram showing the configuration of an echo abnormality detection and compensation device according to an embodiment of the present invention;

Fig. 14 shows a block diagram of an electronic device adapted to implement the echo anomaly detection and compensation method according to an embodiment of the present invention.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be understood that the description is only illustrative and is not intended to limit the scope of the invention. In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention. It may be evident, however, that one or more embodiments may be practiced without these specific details. In addition, in the following description, descriptions of well-known structures and techniques are omitted so as not to unnecessarily obscure the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The terms "comprises," "comprising," and/or the like, as used herein, specify the presence of stated features, steps, operations, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, or components.

All terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art unless otherwise defined. It should be noted that the terms used herein should be construed to have meanings consistent with the context of the present specification and should not be construed in an idealized or overly formal manner.

Where a convention analogous to "at least one of A, B and C, etc." is used, in general such a convention should be interpreted in accordance with the meaning of one of skill in the art having generally understood the convention (e.g., "a system having at least one of A, B and C" would include, but not be limited to, systems having a alone, B alone, C alone, a and B together, a and C together, B and C together, and/or A, B, C together, etc.).

In the technical scheme of the invention, the related user information (including but not limited to user personal information, user image information, user equipment information, such as position information and the like) and data (including but not limited to data for analysis, stored data, displayed data and the like) are information and data authorized by a user or fully authorized by all parties, and the related data are collected, stored, used, processed, transmitted, provided, disclosed, applied and the like, all comply with related laws and regulations and standards, necessary security measures are adopted, no prejudice to the public order is provided, and corresponding operation entries are provided for the user to select authorization or rejection.

Ideally, the chirped pulses transmitted and received by the radar system are considered to remain highly coherent in the SAR imaging algorithm. However, in practical situations, the radar system may have abnormal linear coherence between the transmitted and received chirps due to a defect of the system design, so that an image corresponding to the SAR echo is defocused, which affects the image quality. Drawbacks of radar system design may be, for example: the digital system time sequence design is not robust, so that the transmitted or received pulse sampling sequence is misplaced, namely, the adjacent pulses generate time movement, or the DAC chip and the radio frequency transceiver module are reset by the electromagnetic environment interference of the total system, so that the transmitted or received pulses have larger phase difference, namely, the adjacent pulses generate time movement and the initial phase change.

SAR systems typically undergo extensive testing and iteration before shipment to avoid this, but not completely. Thus, once this occurs, it will have a serious negative impact on SAR image quality. And as technology advances, SAR tends to be low cost, which is more pronounced in low cost SAR systems. To solve this problem, it is necessary to detect and correct the coherent anomalies brought about by the system by means of an algorithm, i.e. to detect the anomalies by analyzing the echoes and to compensate them.

In the related art, a time difference between two adjacent received echoes is detected by using an echo correlation method, that is, a cross-correlation operation is performed on the two adjacent echoes, and the time difference between the two adjacent echoes is corrected by searching for a peak point position difference after the cross-correlation operation. However, it can only detect and correct the difference of an integer number of sampling points, but cannot detect the difference of a small number of sampling points and the difference of initial phases, which will have negative effects on the quality of the image corresponding to the SAR echo, so that the image is defocused and the like, which affects the image quality.

In order to at least partially solve the technical problems in the related art, embodiments of the present invention provide an echo anomaly detection and compensation method, apparatus, device, medium, and program product, which can be applied to the radar technical field.

The embodiment of the invention provides an echo abnormity detection and compensation method, which comprises the following steps: respectively performing fast Fourier transform on any two adjacent echo sampling sequences in the N echo sampling sequences to obtain a first spectrogram and a second spectrogram, wherein N is a positive integer; determining autocorrelation normalized cross power spectrums between two adjacent echo sampling sequences according to the first spectrogram and the second spectrogram; normalizing the cross power spectrum solution phase of the autocorrelation to obtain a power spectrum phase sequence; fitting each power spectrum phase included in the power spectrum phase sequence to determine a phase slope; determining the number of offset pixels according to the phase slope, wherein the number of offset pixels represents the number of pixels offset by a later echo sampling sequence in two adjacent echo sampling sequences compared with the previous echo sampling sequence, and the number of offset pixels corresponding to the first echo sampling sequence is a first preset value; and carrying out time delay compensation on the post echo sampling sequence according to the offset pixel number to obtain a time delay compensation sequence.

Fig. 1 shows an application scenario diagram of an echo anomaly detection and compensation method according to an embodiment of the present invention.

As shown in fig. 1, an application scenario 100 according to this embodiment may include a first terminal device 101, a second terminal device 102, a third terminal device 103, a network 104, and a server 105. The network 104 is a medium used to provide a communication link between the first terminal device 101, the second terminal device 102, the third terminal device 103, and the server 105. The network 104 may include various connection types, such as wired, wireless communication links, or fiber optic cables, among others.

The user may interact with the server 105 through the network 104 using at least one of the first terminal device 101, the second terminal device 102, the third terminal device 103, to receive or send messages, etc. Various communication client applications, such as a shopping class application, a web browser application, a search class application, an instant messaging tool, a mailbox client, social platform software, etc. (by way of example only) may be installed on the first terminal device 101, the second terminal device 102, and the third terminal device 103.

The first terminal device 101, the second terminal device 102, the third terminal device 103 may be various electronic devices having a display screen and supporting web browsing, including but not limited to smartphones, tablets, laptop and desktop computers, and the like.

The server 105 may be a server providing various services, such as a background management server (by way of example only) providing support for websites browsed by the user using the first terminal device 101, the second terminal device 102, and the third terminal device 103. The background management server may analyze and process the received data such as the user request, and feed back the processing result (e.g., the web page, information, or data obtained or generated according to the user request) to the terminal device.

It should be noted that the echo anomaly detection and compensation method provided in the embodiments of the present invention may be generally executed by the server 105. Accordingly, the echo anomaly detection and compensation device provided by the embodiment of the present invention may be generally disposed in the server 105. The echo anomaly detection and compensation method provided by the embodiment of the invention may also be performed by a server or a server cluster which is different from the server 105 and is capable of communicating with the first terminal device 101, the second terminal device 102, the third terminal device 103 and/or the server 105. Accordingly, the echo anomaly detection and compensation device provided by the embodiment of the present invention may also be provided in a server or a server cluster that is different from the server 105 and is capable of communicating with the first terminal device 101, the second terminal device 102, the third terminal device 103 and/or the server 105.

It should be understood that the number of terminal devices, networks and servers in fig. 1 is merely illustrative. There may be any number of terminal devices, networks, and servers, as desired for implementation.

Based on formulas (1) to (5) and fig. 2A to 2D, the coherence between two adjacent pulses sent by the SAR system is analyzed under ideal conditions and under unstable conditions, and the time and phase difference and change rule between two adjacent pulses after the coherence between two adjacent pulses is changed are given.

In accordance with an embodiment of the present invention, ideally, the nth chirp s _n (t) and the n+1th chirp s _n+1 (t) emitted by the SAR system satisfy the expression in equation (1) (assuming the initial phase is 0):

（1）

Wherein T _r is pulse width, prf is pulse repetition frequency, rect () is gate function, f ₀ is carrier frequency, K is frequency modulation, T is absolute time, and j is imaginary unit.

As can be seen from the formula (1), the relation in the formula (2) is satisfied between two adjacent pulses emitted by the SAR system:

（2）

As can be seen from equation (2), there is a fixed time delay of 1/prf between two adjacent pulses sent by the SAR system. Order the The method can obtain: τ _n and τ _n+1 have the same value range. Thus, τ _n= τ_n+1 =τ, and ideally two adjacent pulses can be equivalent to the expression in equation (3) while ignoring the carrier frequency and window function part in equation (1):

(3)

where τ is referred to as fast time according to SAR rationale.

From equation (3), two adjacent pulses transmitted by the SAR system should have a high degree of consistency, i.e., ignoring amplitude variations, and phase-coincident.

According to the embodiment of the invention, in the case of unstable system, such as time sequence dislocation of a digital system or reset of a DA chip and a radio frequency system under the interference of electromagnetic environment, the pulse transmitted by the SAR system can change from one pulse, and in the case of neglecting the carrier frequency and window function part in the formula (1), the change between two adjacent pulses can be equivalently expressed as the expression in the formula (4):

(4)

At this time, the relationship between two adjacent pulses is as shown in formula (5):

(5)

Wherein τ ₀ and To be constant, the transmitted pulse is characterized by a time delay τ ₀ and an initial phase/>, starting from a certain pulseIs a variation of (c).

In accordance with an embodiment of the present invention, equation (5) is approximately equal because the rf signal is noisy across the transmit and receive chains and it is not possible to completely agree even if the time delay and initial phase error between two adjacent pulses are eliminated.

Fig. 2A shows a schematic diagram of the coherence exhibited between two adjacent pulses transmitted by a SAR system in the presence of both a time delay and an initial phase difference between the two adjacent pulses.

In fig. 2A, the waveforms between two adjacent pulses are both changed and there is an offset in the time axis.

Fig. 2B shows a schematic diagram of the coherence exhibited between two adjacent pulses transmitted by a SAR system in the absence of a time delay between the two adjacent pulses, but in the presence of an initial phase difference.

In fig. 2B, the waveform between two adjacent pulses is changed, but there is no shift in the time axis.

Fig. 2C shows a schematic diagram of the coherence exhibited between two adjacent pulses transmitted by a SAR system in the presence of a time delay between the two adjacent pulses but no initial phase difference.

In fig. 2C, the waveforms of two adjacent pulses are identical with an offset on the time axis.

Fig. 2D shows a schematic diagram of the coherence presented between two adjacent pulses in an ideal case.

As can be seen from fig. 2D, in an ideal case, two adjacent pulses emitted by the SAR system have a high degree of consistency.

In accordance with an embodiment of the present invention, for convenience in describing these two types of linear coherence anomalies, the time delay may be referred to simply as "time delay" (or "jump point"), and the initial phase difference may be referred to simply as "phase difference". Wherein "jump point" is another way of describing "delay",

As can be seen from fig. 2A and 2C, after AD sampling is performed on two adjacent pulses transmitted by the SAR system, if a "delay" occurs, the echo sampling sequence corresponding to the two adjacent pulses is shifted as shown in fig. 2A or 2C. This offset profile may be described as a jump, simply "jump point", in units of "one", with a time offset of 1/f _s per jump, where f _s is the sample rate, which may be a fraction.

The reason why the phenomena shown in fig. 2A, 2B and 2C described above occur is various according to the embodiment of the present invention, and the system abnormality may exist at the transmitting end or the receiving end, and may be different according to different systems, but the nature may be abstracted as represented by the formula (5). At this time, the radar system performs static self-closed loop sampling, and an abnormal situation as shown in fig. 2A, 2B or 2C is observed.

In accordance with an embodiment of the present invention, τ ₀ and in the case of linear coherence anomalies due to system instabilityThe phase errors with different degrees are introduced into the azimuth direction of the SAR image due to the change along with the change of time (namely the number n of pulses), so that defocusing and artifacts of the image occur, and the imaging quality is seriously reduced. However, this variation is not irregular, and in general, τ ₀ and/>After each change, the pulse is kept unchanged for a certain period of time (i.e. a certain number of pulses), and after a period of time, the change occurs again, and tau ₀ and/>, between every two pulses, hardly occurAre inconsistent. I.e.. Tau ₀ and/>In a stepwise fashion rather than an irregular noise-like variation.

The basic principle of the echo anomaly detection and compensation method according to the embodiment of the present invention will be described based on equations (6) to (18) and fig. 3A to 3C.

According to the embodiment of the invention, as can be seen from formulas (1) to (5) and fig. 2A to 2D, the essence of SAR echo abnormality detection and compensation is detection and compensation τ ₀ and. However, when a pulse is irradiated onto a ground object, reflected by the ground object, and received, a chirp signal at the time of transmission is not always obtained any more, and therefore τ ₀ and/>, can be estimated only by using echo signals corresponding to the transmitted pulseAnd compensates for this.

According to an embodiment of the present invention, when the SAR system transmits the first pulse and is acquired, its echo can be described as expressed as equation (6):

(6)

Wherein S _n (τ) is the echo of the first transmitted pulse, S _n (τ) is the nth transmitted chirp, h _n (τ) is the transfer function of a system when the ground object is considered as the system, Is a convolution symbol.

According to an embodiment of the present invention, equation (6) shows that: the echo is the convolution of the transmit pulse with the feature system transfer function. Similarly, the echo S _n+1 (τ) of the n+1th transmit pulse can be obtained according to equation (7).

(7)。

According to an embodiment of the present invention, in the case where the n+1th transmission pulse is abnormal in linear coherence due to system reasons, equation (5) may be substituted into equation (7) to obtain equation (8).

(8)。

According to the embodiment of the invention, since the repetition time interval of two adjacent pulses is extremely short, the change of the ground system in the time period is not great, and the ground system corresponding to the echo of the first transmitting pulse and the ground system corresponding to the echo of the +1st transmitting pulse can be considered to be approximately equal, and the relationship in the formula (9) is satisfied.

(9)。

According to the embodiment of the invention, according to algebraic property and time shift property of convolution, the relation of two adjacent echoes in the formula (10) can be further obtained by substituting the formula (6) into the formula (8).

(10)。

According to the embodiment of the invention, according to the formula (10), there is a time delay τ ₀ between two adjacent waves and a constant phase error。

According to the embodiment of the invention, the echo abnormality detection and compensation method provided by the embodiment of the invention can respectively estimate and compensate tau ₀ and tau ₀ between two adjacent echoes in two steps based on the formula (10)The purposes of SAR echo linear coherence anomaly detection and compensation are achieved.

According to an embodiment of the present invention, let the fourier transform of the echo S _n (τ) be F _n (ω), the fourier transform of the echo S _n+1 (τ) be F _n+1 (ω), and take the time shift property of the fourier transform into equation (10) to obtain equation (11).

(11)。

Normalized Cross-Power Spectrum (NCPS) between echo S _n (τ) and echo S _n+1 (τ)May be expressed as formula (12).

(12)

Wherein,Representing taking the complex conjugate.

According to an embodiment of the invention, let，Bringing equation (11) into equation (12) yields equation (13).

（13）

Wherein,

(14)

Wherein A _n (omega) is the amplitude of the echo of the nth transmitted pulse in the frequency domain,For the phase of the echo of the nth transmit pulse in the frequency domain, A _n+1 (ω) is the amplitude of the echo of the n+1th transmit pulse in the frequency domain,/>For the phase of the echo of the (n+1) th transmit pulse in the frequency domain, H _n (ω) is the ideal normalized cross-power spectrum,/>For a gaussian white noise sequence with respect to ω, N _p (ω) is the noise term phase generated by the gaussian white noise sequence.

In accordance with an embodiment of the present invention, the ideal normalized cross power spectrum phase H _n (ω) satisfies equation (15) ignoring the constant term phase error Φ ₀ in the ideal normalized cross power spectrum phase H _n (ω).

(15)

Where μ is the offset of frequency ω.

According to the embodiment of the present invention, as shown in the formula (14), the ideal normalized cross power spectrum NCPS, i.e., H _n (ω), has a phase of a straight line about the frequency axis ω and a slope of τ ₀. From the time shift property of fourier transform, the time domain shift is equivalent to the frequency domain phase shift, and the detection and compensation of the time delay can be performed in the frequency domain as long as the slope τ ₀ of the straight line can be estimated.

According to the embodiment of the invention, according to the formula (9), the ground object systems at different moments are not completely equal, although they are very similar in practical situations. In addition, according to the formula (5), even if the time delay and the initial phase error are eliminated, the waveforms of the two adjacent transmitted pulses are not completely consistent due to the noise of the transceiving link. Therefore, in the formula (13)I.e. there will be some noise in the actual NCPS phase, i.e. there will be more N _p (ω) terms, where in the N _p (ω) term,/>Typically a Gaussian white noise sequence for ω, pair/>After unwrapping the phase of (c) it is hardly restored to a straight line. It is necessary to denoise its phase.

According to an embodiment of the present invention, the autocorrelation operation of equation (13) may be performed to obtain an autocorrelation normalized cross-Power Spectrum (ANCPS, autocorrelated Normalized Cross-Power Spectrum) in equation (16)。

(16)。

According to an embodiment of the present invention, formula (13) and formula (15) are substituted into formula (16) to obtain formula (17).

（17）。

According to an embodiment of the present invention, as can be seen from equation (17),Is the complex conjugate of the ideal normalized cross-power spectrum H _n (ω). The expression in square brackets of the formula (17) is the autocorrelation of Gaussian noise signals, and the Gaussian white noise signals are an impact function with an origin of sigma ² after the autocorrelation, so that noise energy can be compressed to a point, and the purpose of denoising can be indirectly achieved. At this time,/>Complex conjugation to an ideal NCPS/>Almost equivalently, therefore, only need toThe phase extraction and unwrapping are performed to obtain approximately the phase of the ideal NCPS.

According to an embodiment of the present invention, to obtain ANCPS quickly, the property of convolution can be obtained by using a fourier transform to multiply complex conjugate in the frequency domain.

Fig. 3A shows a schematic diagram of NCPS folding phase and ANCPS folding phase of two adjacent echoes prior to unwrapping. Fig. 3B shows schematic diagrams of NCPS phases and ANCPS phases of two adjacent echoes after unwrapping. Fig. 3C shows a schematic diagram of NCPS phases and ANCPS phases corresponding to region 301 of fig. 3B.

As can be seen from fig. 3A to 3C, after the NCPS is obtained ANCPS through autocorrelation, the normalized cross power spectrum phase noise is significantly removed. As can be seen from fig. 3B and 3C, the ANCPS phases after unwinding can observe a distinct straight line.

According to the embodiment of the invention, ANCPS is obtainedThe folded phase can then be extracted and unwrapped to yield the autocorrelation normalized cross power spectral phase phi (omega) in equation (18).

(18)

Wherein,Representing taking a complex sequence of folding phases and unwrapping.

According to the embodiment of the present invention, the linear phase Φ (ω) can be optimally estimated by using the least square method, resulting in a linear expression corresponding to the linear phase Φ (ω). Wherein, the slope of phi (omega) with respect to omega can be set as a _n, the sequence of a _n can be obtained by traversing all adjacent pulses, if the SAR system works normally, a _n can be converged in a smaller range and slowly change in the range, when an abnormal value occurs in the SAR system, the linear coherence abnormality can be determined to occur at the position, thus completing the detection of the coherence abnormality, and the time delay can be compensated based on the abnormal value.

The specific steps of the echo anomaly detection and compensation method according to the embodiment of the present invention will be described in detail based on the formulas (19) to (37) and fig. 4 to 8B, starting from the actual echo samples.

Fig. 4 shows a flowchart of an echo anomaly detection and compensation method according to an embodiment of the present invention.

As shown in fig. 4, the echo anomaly detection and compensation method of the embodiment includes operations S410 to S460.

In operation S410, fast fourier transform is performed on any two adjacent echo sampling sequences in the N echo sampling sequences, respectively, to obtain a first spectrogram and a second spectrogram, where N is a positive integer.

According to an embodiment of the invention, the echo sampling sequence characterizes a digital signal which is discrete in the time domain and is obtained after each pulse of SAR emission is received and sampled.

According to the embodiment of the invention, the first spectrogram represents a spectrogram obtained after performing fast Fourier transform on a preceding echo sampling sequence in two adjacent echo sampling sequences. And the second spectrogram representation is used for carrying out fast Fourier transform on the post echo sampling sequences in the two adjacent echo sampling sequences to obtain a spectrogram.

According to an embodiment of the invention, the time of receiving the pre-echo sample sequence is earlier than the time of receiving the post-echo sample sequence.

According to an embodiment of the present invention, the n-th frame echo sampling sequence of SAR reception may be: s _n (M), n=1, 2,3, …, N, m=1, 2,3, …, M. Wherein N is the number of pulses received, M is the number of samples per pulse, N and M are integers greater than 1, N is an integer greater than or equal to 1 and less than or equal to N, and M is an integer greater than or equal to 1 and less than or equal to M.

According to the embodiment of the present invention, N and M may be selected according to practical situations, and are not limited herein. For example, N may be 10000, 30000, 50000, or the like, and M may be 20000, 60000, 100000, or the like.

According to an embodiment of the present invention, after obtaining the adjacent two echo sampling sequences S _n (m) and S _n+1 (m), FFT (fast fourier transform) may be performed according to equation (19), respectively, to obtain a first spectrogram F _n (m) corresponding to the nth frame echo sampling sequence S _n (m) (i.e., the preceding echo sampling sequence) and a second spectrogram F _n+1 (m) corresponding to the (n+1) th frame echo sampling sequence S _n+1 (m) (i.e., the following echo sampling sequence).

(19)。

In operation S420, an autocorrelation normalized cross-power spectrum between two adjacent echo sample sequences is determined from the first and second spectrograms.

According to the embodiment of the invention, the normalized cross power spectrum between the first spectrogram and the second spectrogram can be calculated first, then the FFT is utilized to perform autocorrelation operation on the normalized cross power spectrum in the frequency domain, and the autocorrelation normalized cross power spectrum is obtained through calculation.

In operation S430, the cross power spectrum solution phase is normalized for the autocorrelation, resulting in a power spectrum phase sequence.

According to the embodiment of the invention, the folding phase of the autocorrelation normalized cross power spectrum can be calculated first, and then the folding phase is unwound to obtain a power spectrum phase sequence.

In operation S440, each power spectrum phase included in the power spectrum phase sequence is fitted, and a phase slope is determined.

According to the embodiment of the invention, each power spectrum phase included in the power spectrum phase sequence can be fitted by utilizing least square to obtain a linear expression corresponding to the power spectrum phase sequence, and the phase slope is determined according to the linear expression.

According to an embodiment of the invention, the phase slope is in radians in units of change of phase slope in the frequency domain, reflecting the time delay of the post-echo sample sequence compared to the pre-echo sample sequence in the time domain.

In operation S450, an offset pixel number is determined according to the phase slope, wherein the offset pixel number characterizes a pixel number of a subsequent echo sampling sequence in two adjacent echo sampling sequences, which is offset from a preceding echo sampling sequence, and the offset pixel number corresponding to the first echo sampling sequence is a first preset value.

According to the embodiment of the invention, after the period phase is divided by the sampling number M of the pulses, the unit slope change amount of the post echo sampling sequence is obtained compared with the time length corresponding to one sampling point of each delay of the prior echo sampling sequence. Then, the phase slope is divided by the unit slope variation to obtain the offset pixel number.

According to embodiments of the present invention, the number of offset pixels is determined based on the phase slope, and it is possible to determine how many pixels the post-echo sample sequence is "offset", i.e., the number of "hops", from the pre-echo sample sequence.

According to the embodiment of the invention, the offset pixel number is determined according to the phase slope, and the small offset pixel number of the offset between the two adjacent echo sampling sequences, namely the offset pixel number smaller than the integral number of sampling points, can be determined. Since the number of offset pixels multiplied by 1/f _s is the time delay between adjacent two echo sample sequences, a fractional number of offset pixels can reflect the amount of time delay corresponding to a duration less than an integer number of sample points.

According to an embodiment of the present invention, the first preset value may be selected according to practical situations, which is not limited herein. For example, the first preset value may be 0.

In operation S460, the post-echo sampling sequence is time-delay-compensated according to the offset pixel number, resulting in a time-delay-compensated sequence.

According to an embodiment of the present invention, for operation S420 as shown in fig. 4, determining an autocorrelation normalized cross-power spectrum between two adjacent echo sample sequences from the first spectrogram and the second spectrogram may include the following operations:

determining a normalized cross power spectrum according to the first spectrogram and the second spectrogram;

And carrying out autocorrelation operation on the normalized cross power spectrum, and determining the autocorrelation normalized cross power spectrum.

According to the embodiment of the invention, under the condition that n is more than or equal to 2, the autocorrelation normalized cross power spectrum between two adjacent echo sampling sequences can be calculated according to the formula (20)。

(20)。

According to the embodiment of the invention, when n is greater than or equal to 2, the normalized cross power spectrum calculated by the formula (20) can be subjected to autocorrelation operation according to the formula (21) to obtain an autocorrelation normalized cross power spectrum。/>

（21）。

According to the embodiment of the invention, when n is greater than or equal to 2, the folding phase can be calculated and unwrapped according to the formula (22) on the autocorrelation normalized cross power spectrum calculated by the formula (21) to obtain a power spectrum phase sequence phi _n (m).

(22)。

According to embodiments of the invention, least squares may be utilized for the power spectrum phase sequenceFitting to obtain a phase slope.

According to an embodiment of the present invention, the phase slope may be calculated according to equation (23).

（23）。

According to an embodiment of the present invention, for operation S450 shown in fig. 4, determining the offset pixel number according to the phase slope may include the following operations:

Determining a unit slope variation according to the sampling point number and the period phase of each echo sampling sequence;

the number of offset pixels is determined based on the phase slope and the unit slope conversion amount.

According to an embodiment of the present invention, the unit slope change amount Δa may be calculated according to the formula (24).

(24)

Wherein the period phase is 2 pi.

According to the embodiment of the invention, based on the time shifting property of the discrete Fourier transform, the unit slope change delta a represents the change of the slope of the post-echo sampling sequence every time a sampling point moves rightwards, namely, the post-echo sampling sequence is delayed by a time length corresponding to one sampling point compared with the pre-echo sampling sequence.

According to the embodiment of the present invention, as shown in the formula (24), each change Δa of the slope of the linear phase of the frequency domain information corresponding to the echo sampling sequence, the sequence S _n (m) is shifted to the right by one sampling point, i.e. the time delay is 1/f _s.

According to an embodiment of the present invention, to reduce the scaling process, the number of "hops" between two echo sample sequences, i.e., the number of offset pixels, may be calculated in units of sample points, where the number of offset pixels may be a fraction.

According to an embodiment of the present invention, in the case where n is 2 or more, the offset pixel number may be calculated from the phase slope based on the formula (25).

(25)。

According to an embodiment of the present invention, since there is no preceding echo sample sequence corresponding to the 1 st echo sample sequence, the offset pixel number corresponding to the 1 st echo sample sequence may be defined as 0, i.e., P (1) =0.

According to the embodiment of the invention, after all echo sampling sequences in the N echo sampling sequences are traversed, the number of pixels, namely the number of 'jumping points', of each echo sampling sequence which is offset relative to the previous echo sampling sequence can be obtained, and the number of N offset pixels, namely the number of N offset sampling points, is obtained.

According to the embodiment of the invention, the unit slope variation is determined according to the sampling point number and the period phase of each echo sampling sequence; and determining the offset pixel number according to the phase slope and the unit slope conversion quantity, and determining the offset pixel number smaller than the whole sampling point number and determining the pixel offset quantity of the sub-pixel level.

Fig. 5A shows a schematic diagram of the number of respective offset sampling points corresponding to an N-frame echo sampling sequence according to an embodiment of the present invention. Fig. 5B shows a schematic diagram of the number of individual offset sampling points corresponding to the echo sampling sequence in region 501 of fig. 5A, according to an embodiment of the invention.

In fig. 5A and 5B, the dash-dot line is a schematic diagram of the number of respective offset sampling points in the case where two adjacent echo sampling sequences are both normal echoes. The solid line is a schematic diagram of the number of each offset sampling point in the case where there is a time delay between two adjacent echo sampling sequences, i.e. an abnormal echo.

As can be seen from fig. 5A and 5B, in the case of stable system operation, the offset of the relative sampling points between the pulses is relatively stable, i.e. the offset pixel number between two adjacent echo sampling sequences is relatively stable, and is generally within 0.1 sampling points, i.e. within 0.1 pixel, although it varies according to the actual operating parameters and features thereof. When the system is unstable in operation, the offset number of the sampling points is in very obvious jump, namely the offset pixel number is in very obvious jump, and at the moment, the anomaly detection and compensation can be carried out according to the characteristic.

According to an embodiment of the present invention, for operation S460 as described in fig. 4, performing time delay compensation on the post-echo sampling sequence according to the number of offset pixels to obtain a time delay compensation sequence may include the following operations:

Determining an offset pixel number variance and an offset pixel number average value according to N offset pixel numbers which are in one-to-one correspondence with the N echo sampling sequences;

Determining abnormal offset pixel numbers from N offset pixel numbers according to the offset pixel number variance and the offset pixel number average value;

Performing linear difference on two offset pixel numbers adjacent to the abnormal offset pixel number to obtain a corrected offset pixel number;

Replacing the abnormal offset pixel number in the N offset pixel numbers with the correction offset pixel number to obtain a correction offset pixel number sequence;

Determining a target compensation pixel number sequence according to the N offset pixel numbers and the correction offset pixel number sequence;

and carrying out time delay compensation on the post-echo sampling sequence according to the target compensation pixel number which is included in the target compensation pixel number sequence and corresponds to the post-echo sampling sequence, so as to obtain a time delay compensation sequence.

According to the embodiment of the invention, the abnormal offset pixel number can be positioned on the basis of the 3 sigma principle, namely the variance of the offset pixel number of the N offset pixel numbers is calculatedAnd an offset pixel number average μ _p, and then performing anomaly offset pixel number localization according to σ _p and μ _p.

According to the embodiment of the present invention, in the case where any one of the N offset pixel numbers P (k) satisfies the formula (26), the offset pixel number may be determined as the abnormal offset pixel number.

(26)

Wherein N _σp is a first scaling factor, and k is an integer greater than or equal to 1 and less than or equal to N.

According to the embodiment of the present invention, n _σp may be selected according to practical situations, which is not limited herein. For example, n _σp can be 3, 5, 7, or the like.

In accordance with an embodiment of the present invention, there is a "skip" phenomenon in the case where P (k) satisfies equation (26), i.e., represents the frame-wise echo sample sequence.

According to an embodiment of the present invention, the number of offset pixels corresponding to each echo sampling sequence is traversed, if equation (26) is satisfied, the value of P (k) is deleted, the number of pixels to which the point should actually be offset, i.e., the corrected offset pixel number, is estimated by linear interpolation, and the abnormal offset pixel number of the point is replaced with the corrected offset pixel number, thereby generating a corrected offset pixel number sequence。

According to an embodiment of the present invention, determining a target compensation pixel number sequence from the N offset pixel numbers and the correction offset pixel number sequence includes:

constructing an offset pixel number sequence according to the N offset pixel numbers;

Subtracting the offset pixel number sequence from the correction offset pixel number sequence to obtain an initial compensation pixel number sequence;

And determining a target compensation pixel number corresponding to the nth post-echo sampling sequence according to the first N initial compensation pixel numbers included in the initial compensation pixel number sequence aiming at the nth post-echo sampling sequence, wherein N is an integer greater than or equal to 1 and less than or equal to N.

According to the embodiment of the invention, the N offset pixel numbers corresponding to the N echo sampling sequences can be sequenced according to the time of receiving the N echo sampling sequences, so that an offset pixel number sequence is obtained, wherein the earlier the receiving time is, the earlier the sequencing is.

According to an embodiment of the present invention, the initial compensated pixel number sequence P _e (n) can be obtained according to equation (27).

(27)。

According to the embodiment of the invention, the position where the linear coherence anomaly occurs can be obtained according to the initial compensation pixel number sequence P _e (n), namely, the linear coherence occurs from the first frame echo sampling sequence and the number of the jump points, and the position can be used as the basis of algorithm compensation.

According to the embodiment of the invention, for the nth post-echo sampling sequence, the first n initial compensation pixel numbers included in the initial compensation pixel number sequence P _e (n) can be summed to obtain the target compensation pixel number corresponding to the nth post-echo sampling sequence.

According to an embodiment of the present invention, the target compensation pixel number P _c (n) corresponding to the nth post-echo sampling sequence may be obtained according to equation (28).

(28)

Wherein i is an integer of 1 or more and n or less.

According to an embodiment of the present invention, time delay compensating the post-echo sampling sequence according to a target compensation pixel number corresponding to the post-echo sampling sequence included in the target compensation pixel number sequence, and obtaining the time delay compensation sequence includes obtaining the time delay compensation sequence according to formula (29)。

（29）

Wherein,In the case of S _n (m) as the post-echo sampling sequence, the time delay compensation sequence after the time delay compensation is performed on S _n (m).

According to the embodiment of the invention, after the time delay compensation is performed on the N frame echo sampling sequences according to the formula (29), the time delay compensation sequences corresponding to the N frame echo sampling sequences are obtained, and N time delay compensation sequences are obtained.

According to an embodiment of the present invention, after performing time delay compensation on the post-echo sampling sequence according to formula (29) to obtain a time delay compensation sequence, sub-pixel level time delay compensation on the post-echo sampling sequence may be implemented, and transition from fig. 2A to fig. 2B may be implemented.

Fig. 6 is a flowchart of an echo anomaly detection and compensation method according to another embodiment of the present invention.

As shown in fig. 6, the echo anomaly detection and compensation method of the embodiment includes operations S610 to S630.

According to an embodiment of the present invention, for the echo anomaly detection and compensation method shown in fig. 4, operations S610 to S630 may be further included.

In operation S610, complex conjugate multiplication is performed on any two adjacent time delay compensation sequences in the N time delay compensation sequences, and a phase difference sequence is determined, where each phase difference included in the phase difference sequence characterizes a phase of a subsequent time delay compensation sequence in the two adjacent time delay compensation sequences, compared to a phase amount shifted by a preceding time delay compensation sequence, and each phase difference included in the phase difference sequence corresponding to the 1 st time delay compensation sequence is a second preset value.

According to an embodiment of the present invention, the second preset value may be selected according to practical situations, which is not limited herein. For example, the second preset value may be 0.

According to an embodiment of the present invention, in the adjacent two time delay compensation sequences, the acquisition time of the echo sampling sequence corresponding to the subsequent time delay compensation sequence is later than the acquisition time of the echo sampling sequence corresponding to the preceding time delay compensation sequence.

According to an embodiment of the present invention, the 1 st time delay compensation sequence characterizes a time delay compensation sequence corresponding to the 1 st echo sampling sequence among the N time delay compensation sequences.

According to an embodiment of the present invention, the phase difference sequence includes phase differences corresponding to the respective sampling points. Each phase difference characterizes a phase of a subsequent time delay compensation sequence of the two adjacent time delay compensation sequences compared to a phase of a preceding time delay compensation sequence offset at a sampling point corresponding to the phase difference.

According to an embodiment of the present invention, after time delay compensation is performed on the echo sampling sequence, based on the formula (10), it is known that two adjacent time delay compensation sequences satisfy the relationship in the formula (30).

(30)

Wherein,For the time delay compensation sequence corresponding to the n+1th echo sampling sequence,/>And compensating the sequence for the time delay corresponding to the nth echo sampling sequence. The phase error of the constant term between two adjacent time delay compensation sequences is/>。

According to the embodiment of the invention, according to the formula (30), after linear coherence anomalies exist between adjacent echo sampling sequences and 'jump point' compensation (time delay compensation) is carried out, only a constant term phase error exists between the two obtained adjacent time delay compensation sequencesI.e. "phase difference".

According to the embodiment of the present invention, in the case where n is equal to or greater than 2, the phase difference sequence between the adjacent two time delay compensation sequences can be calculated according to the formula (31).

(31)。

According to the embodiment of the present invention, in the case where n is equal to 1, since there is no preceding time delay compensation sequence corresponding to the 1 st time delay compensation sequence, each phase difference in the phase difference sequence corresponding to the 1 st time delay compensation sequence can be defined as 0, that is。

In operation S620, each phase difference included in the phase difference sequence is averaged to obtain a constant term phase error.

According to the embodiment of the invention, under the normal condition of the system operation, analysis of a large number of time delay compensation sequences actually corresponding to SAR echo sampling sequences finds that if complex conjugate multiplication is carried out between adjacent time delay compensation sequences, the phase difference value in the obtained phase difference sequence obviously has a main value although the phase difference value contains a large amount of noise.

Fig. 7A shows a schematic diagram of all unwrapped phase differences included in a phase difference sequence in accordance with an embodiment of the present invention. Fig. 7B illustrates a schematic diagram of respective unreeled phase differences corresponding to the region 701 of fig. 7A according to an embodiment of the present invention.

As can be seen from fig. 7A and 7B, the phase difference of each sampling point wander around the mean value. Thus, it is possible toAs a constant term phase difference between the two echoes.

For example, the phase difference sequence corresponding to the 1 st time delay compensation sequence can beAnd averaging the included phase difference values to obtain a constant term phase error corresponding to the 1 st time delay compensation sequence, wherein the constant term phase error corresponding to the 1 st time delay compensation sequence is 0. For the phase difference sequence/>, corresponding to the 2 nd time delay compensation sequenceAnd averaging the included phase difference values to obtain a constant term phase error corresponding to the 2 nd time delay compensation sequence.

According to an embodiment of the present invention, the constant term phase error may be calculated according to equation (32).

（32）。

In operation S630, the subsequent time delay compensation sequence is phase-compensated according to the constant term phase error, resulting in a target echo sampling sequence.

According to the embodiment of the invention, the phase difference sequence is determined to average each phase difference included in the phase difference sequence by performing complex conjugate multiplication on any two adjacent time delay compensation sequences in the N time delay compensation sequences, so as to obtain a constant term phase error, obtain an average phase quantity of the phase of the subsequent time delay compensation sequence in the two adjacent time delay compensation sequences compared with the offset of the preceding time delay compensation sequence, perform phase compensation on the subsequent time delay compensation sequence according to the constant term phase error, obtain a target echo sampling sequence, and improve the quality of an image corresponding to the target echo sampling sequence.

According to an embodiment of the present invention, performing phase compensation on a subsequent time delay compensation sequence according to a constant term phase error, obtaining a target echo sampling sequence includes:

determining an offset phase variance and an offset phase mean according to N constant term phase errors in one-to-one correspondence with the N echo sampling sequences;

Determining an abnormal phase error from the N constant term phase errors according to the offset phase variance and the offset phase mean;

performing linear difference on two constant term phase errors adjacent to the abnormal phase error to obtain a corrected phase error;

replacing abnormal phase errors in the N constant term phase errors with corrected phase errors to obtain a corrected phase error sequence;

determining a target compensation phase sequence according to the N constant term phase errors and the corrected phase error sequence;

And carrying out phase compensation on the later time delay compensation sequence according to the target compensation phase corresponding to the later time delay compensation sequence included in the target compensation phase sequence to obtain a target echo sampling sequence.

Fig. 8A shows a schematic diagram of the variation of the phase error with the number of frames of each constant term corresponding to a sequence of N-frame echo samples according to an embodiment of the invention. Fig. 8B shows a schematic diagram of the variation of the phase error with the number of frames for each constant term corresponding to the region 801 of fig. 8A, according to an embodiment of the present invention.

In fig. 8A and 8B, the dash-dot line indicates the change of the constant term phase error with the number of echo sampling sequence frames n in the case where the system operates normally, and the solid line indicates the change of the constant term phase error with the number of echo sampling sequence frames n in the case where the linear coherence abnormality occurs.

As can be seen from fig. 8A and 8B, the change of c (n) is similar to the change of P (n), i.e., the change of c (n) with the number of frames n is not severe and regular, and is basically within a few degrees when the radar system is operating normally. When the radar system works abnormally to generate linear coherence abnormality, the c (n) sequence can generate jump, and outliers can be found by comparing various values in the c (n) sequence. But unlike P (n), c (n) is within an acceptable range, the variation of which does not tend to be straight. That is, the 3 sigma principle is directly used when screening outliers, so that non-outliers can be detected by mistake, and when the outliers are properly relaxed to 5 sigma, a plurality of outliers can be missed. Therefore, the low frequency component of the curve formed by c (n) can be filtered first, the high frequency component is reserved, the curve is straightened, outliers are screened, and then the phase is compensated according to the outliers.

According to an embodiment of the present invention, determining the offset phase variance and the offset phase mean from N constant term phase errors in one-to-one correspondence with the N time delay compensation sequences includes:

constructing a constant term phase difference sequence according to the N constant term phase errors;

high-pass filtering is carried out on the constant term phase difference sequence to obtain a high-frequency phase sequence;

And determining an offset phase variance and an offset phase mean value according to the high-frequency phase sequence.

According to the embodiment of the invention, since the N time delay compensation sequences are in one-to-one correspondence with the N echo sampling sequences, the N constant term phase errors are in one-to-one correspondence with the N time delay compensation sequences, and therefore the N constant term phase errors are in one-to-one correspondence with the N echo sampling sequences.

According to the embodiment of the invention, the N constant term phase errors corresponding to the N echo sampling sequences one by one can be sequenced according to the time of receiving the N echo sampling sequences, so that the constant term phase difference sequences are obtained, wherein the earlier the receiving time is, the earlier the sequencing is.

According to an embodiment of the present invention, the constant term phase difference sequence C (n) may be high-pass filtered according to formula (33) to obtain a high-frequency phase sequence.

（33）

Wherein rect () is a gate function, D is a gate width, D is 1.ltoreq.D.ltoreq.N, and C _h (N) is a filtered high-frequency phase sequence.

According to the embodiment of the present invention, D may be selected according to practical situations, and is not limited herein. For example, D may be 0.8XN, 0.85 XN, or 0.9 XN.

According to an embodiment of the present invention, a variance of the high frequency phase sequence C _h (N) including N high frequency phases can be calculatedAnd the mean μ _c, then the variance/>, of the high-frequency phase sequence C _h (n)As the offset phase variance, the mean μ _c of the high-frequency phase sequence C _h (n) is taken as the offset phase mean.

According to the embodiment of the invention, the constant term phase difference sequence is subjected to high-pass filtering to obtain a high-frequency phase sequence, the low-frequency component of the C (N) curve is filtered to keep the high-frequency component, the curve C (N) is straightened, and then the offset phase variance and the offset phase mean value are determined according to the high-frequency phase sequence, so that the offset phase variance and the offset phase mean value which are more suitable for screening abnormal phase errors from N constant term phase errors can be obtained, and the missing detection or the false detection of the abnormal phase errors is avoided.

According to an embodiment of the present invention, determining an abnormal phase error from the N constant term phase errors based on the offset phase variance and the offset phase mean comprises:

And determining an abnormal phase error from the N constant term phase errors according to the high-frequency phase, the offset phase variance and the offset phase mean value which are respectively corresponding to the N constant term phase errors and are included in the high-frequency phase sequence.

According to an embodiment of the present invention, the localization of the abnormal phase error can be performed on the N constant term phase errors based on the 3σ principle according to σ _c and μ _c.

According to an embodiment of the present invention, determining an abnormal phase error from the N constant term phase errors based on the high frequency phase, the offset phase variance, and the offset phase mean value, which each correspond to the N constant term phase errors, included in the high frequency phase sequence includes determining the abnormal phase error according to equation (34).

(34)

Where n _σc is the second scaling factor and C _h (k) is any one of the high frequency phases of the high frequency phase sequence.

According to the embodiment of the present invention, n _σc may be selected according to practical situations, which is not limited herein. For example, n _σc can be 3,4,5, 7, or the like.

According to an embodiment of the present invention, in the case where n _σc satisfies the formula (34), it is characterized that there is a linear coherence anomaly in the echo sample sequence of the frame, that is, the constant term phase error C (k) corresponding to the echo sample sequence of the k frame is an anomalous phase error.

According to an embodiment of the present invention, if C _h (k) satisfies the formula (34), deleting the value of C (k) in C (n), estimating the phase error that the k point should actually be offset, i.e., correcting the phase error, by using linear interpolation, and replacing the abnormal phase error of the point with the corrected phase error, thereby generating a new offset sequence, i.e., corrected phase error sequence C _r (k).

According to an embodiment of the present invention, the positions where two linear coherence anomalies occur are calculated by equation (26) and equation (34), essentially because: equation (26) is a position where a deviation of the calculated time delay occurs, and equation (34) is a position where an abnormal phase error occurs, which may be inconsistent, so that the calculation is performed alone.

According to an embodiment of the present invention, determining a target compensated phase sequence from the N constant term phase errors and the modified phase error sequence comprises:

Constructing a constant term phase error sequence according to the N constant term phase errors;

Subtracting the constant term phase error sequence from the corrected phase error sequence to obtain an initial compensation phase sequence;

For the nth subsequent time delay compensation sequence, determining a target compensation phase corresponding to the nth subsequent time delay compensation sequence according to the first N initial compensation phases included in the initial compensation phase sequence, wherein N is an integer greater than or equal to 1 and less than or equal to N.

According to the embodiment of the invention, the N constant term phase errors corresponding to the N echo sampling sequences can be sequenced according to the time of receiving the N echo sampling sequences, so that a constant term phase error sequence is obtained, wherein the earlier the receiving time is, the earlier the sequencing is.

According to an embodiment of the present invention, the initial compensated phase sequence C _e (n) may be derived according to equation (35).

(35)。

According to the embodiment of the invention, the position (namely, abnormal phase error position) where the linear coherence abnormality occurs can be obtained according to the formula (34), the error amount is determined according to the formula (35), and the error amount is taken as the basis of algorithm compensation.

According to an embodiment of the present invention, the first n initial compensation phases included in the initial compensation phase sequence C _e (n) may be summed for the nth subsequent time delay compensation sequence to obtain a target compensation phase corresponding to the nth subsequent time delay compensation sequence.

According to an embodiment of the present invention, the target compensation phase C _c (n) corresponding to the nth subsequent time delay compensation sequence may be obtained according to equation (36).

(36)。

According to an embodiment of the present invention, phase compensating the subsequent time delay compensation sequence according to a target compensation phase included in the target compensation phase sequence and corresponding to the subsequent time delay compensation sequence, obtaining the target echo sampling sequence includes obtaining the target echo sampling sequence according to formula (37)。

(37)。

According to an embodiment of the present invention, the transition from fig. 2B to fig. 2D may be implemented after the phase compensation of the subsequent time delay compensation sequence according to equation (37) resulting in the target echo sample sequence.

The echo anomaly detection and compensation method according to the embodiment of the present invention is experimentally verified according to table 1 and fig. 9 to 12.

In an experiment, the effectiveness and performance index of the echo anomaly detection and compensation method provided by the embodiment of the invention are verified by adopting a semi-physical simulation mode, namely, a known random delay parameter and a known random phase difference parameter are added to a real radar echo to enable the echo to generate linear coherence anomaly, then the echo anomaly detection and compensation method provided by the embodiment of the invention is used for compensation, and the detected delay parameter and the detected phase difference parameter and the compensated imaging quality are observed.

The simulation parameters are shown in table 1.

TABLE 1

From table 1, it can be seen that, in the experiment, 32768 pulses emitted by the SAR system in total are simulated in the whole operation process of the SAR system, and 40960 points are sampled for each pulse, wherein linear coherence anomalies occur 15 times in total, the number of "jump points" each time is randomly distributed in-10 to 10 inequality, and the "phase difference" each time is randomly distributed in-180 ° to 180 ° inequality.

Fig. 9 is a schematic diagram showing an abnormal position and a jump number detected by the echo abnormal detection and compensation method according to an embodiment of the present invention. Fig. 10 is a schematic diagram showing the number of hops after performing time delay compensation on an echo sampling sequence according to the echo anomaly detection and compensation method provided by the embodiment of the invention. Fig. 11 is a schematic diagram showing abnormal positions and phase differences detected by the echo abnormality detection and compensation method according to an embodiment of the present invention. Fig. 12 is a schematic diagram showing a phase difference after performing phase compensation on an echo sampling sequence according to the echo anomaly detection and compensation method provided by the embodiment of the invention.

In fig. 9 and 10, the abscissa indicates the frame number (i.e., the number of frames) of the echo sampling sequence, and the ordinate indicates the number of hops. In fig. 11 and 12, the abscissa is the frame number of the echo sampling sequence, and the ordinate is the phase difference.

In fig. 9, the dot-dash line is the added hop count, the solid line is the compensated hop count, and the difference is taken to obtain the solid line diagram in fig. 10, i.e., the compensated hop count.

As can be seen from fig. 10, after the compensation, the number of hops after the compensation can be controlled within ±0.02 points, i.e., within 0.02 pixels. Similarly, the compensation result of the phase difference can be seen in fig. 11 and 12, and the phase difference after compensation is divided by 4 degrees respectively, and most of the phase differences are controlled within +/-1 degree.

As can be seen from fig. 9 to fig. 12, the echo anomaly detection and compensation method provided by the embodiment of the invention detects the linear coherence anomaly emission position and degree according to the high similarity of adjacent SAR echoes, and finally can realize the jump point compensation and phase difference compensation of sub-pixel level, wherein the jump point is controlled within ±0.02 sampling points, and the phase error is controlled within ±1°. The method can meet the detection and correction requirements of linear coherence anomalies generated by echoes due to SAR system defects, namely, the problems caused by hardware are solved by using an algorithm, and powerful support can be provided for low-cost SAR application, so that the echo anomaly detection and compensation method provided by the embodiment of the invention has strong practicability and applicability.

It should be noted that, unless there is an execution sequence between different operations or an execution sequence between different operations in technical implementation, the execution sequence between multiple operations may be different, and multiple operations may also be executed simultaneously.

Based on the echo abnormality detection and compensation method, the invention also provides an echo abnormality detection and compensation device. The device will be described in detail below in connection with fig. 13.

Fig. 13 is a block diagram showing the configuration of an echo abnormality detection and compensation device according to an embodiment of the present invention.

As shown in fig. 13, the echo anomaly detection and compensation device 1300 of this embodiment includes a first obtaining module 1310, a first determining module 1320, a second obtaining module 1330, a second determining module 1340, a third determining module 1350, and a third obtaining module 1360.

The first obtaining module 1310 is configured to perform fast fourier transform on any two adjacent echo sampling sequences in the N echo sampling sequences, to obtain a first spectrogram and a second spectrogram, where N is a positive integer. In an embodiment, the first obtaining module 1310 may be configured to perform the operation S410 described above, which is not described herein.

A first determining module 1320 is configured to determine an autocorrelation normalized cross-power spectrum between two adjacent echo sample sequences according to the first spectrogram and the second spectrogram. In an embodiment, the first determining module 1320 may be used to perform the operation S420 described above, which is not described herein.

A second obtaining module 1330, configured to perform phase decomposition on the autocorrelation normalized cross power spectrum to obtain a power spectrum phase sequence. In an embodiment, the second obtaining module 1330 may be used to perform the operation S430 described above, which is not described herein.

A second determining module 1340 is configured to fit each power spectrum phase included in the power spectrum phase sequence to determine a phase slope. In an embodiment, the second determining module 1340 may be used to perform the operation S440 described above, which is not described herein.

The third determining module 1350 is configured to determine an offset pixel count according to the phase slope, where the offset pixel count represents a pixel count of a later echo sampling sequence in the two adjacent echo sampling sequences that is offset from a preceding echo sampling sequence, and the offset pixel count corresponding to the first echo sampling sequence is a first preset value. In an embodiment, the third determining module 1350 may be used to perform the operation S450 described above, which is not described herein.

A third obtaining module 1360 is configured to perform time delay compensation on the post-echo sampling sequence according to the offset pixel number, so as to obtain a time delay compensation sequence. In an embodiment, the third obtaining module 1360 may be used to perform the operation S460 described above, which is not described herein.

According to an embodiment of the present disclosure, the third obtaining module includes a first determining sub-module, a second determining sub-module, a first obtaining sub-module, a second obtaining sub-module, a third determining sub-module, and a third obtaining sub-module.

The first determining submodule is used for determining an offset pixel number variance and an offset pixel number mean value according to N offset pixel numbers corresponding to N echo sampling sequences one by one.

And the second determination submodule is used for determining the abnormal offset pixel number from the N offset pixel numbers according to the offset pixel number variance and the offset pixel number average value.

And the first obtaining submodule is used for carrying out linear difference on two offset pixel numbers adjacent to the abnormal offset pixel number to obtain the corrected offset pixel number.

And the second obtaining submodule is used for replacing the abnormal offset pixel number in the N offset pixel numbers with the correction offset pixel number to obtain a correction offset pixel number sequence.

And the third determining submodule is used for determining a target compensation pixel number sequence according to the N offset pixel numbers and the correction offset pixel number sequence.

And the third obtaining submodule is used for carrying out time delay compensation on the post-echo sampling sequence according to the target compensation pixel number which is included in the target compensation pixel number sequence and corresponds to the post-echo sampling sequence, so as to obtain a time delay compensation sequence.

According to an embodiment of the present disclosure, the third determination submodule includes a first building unit, a first obtaining unit, and a first determination unit.

And the first construction unit is used for constructing an offset pixel number sequence according to the N offset pixel numbers.

The first obtaining unit is used for subtracting the offset pixel number sequence from the correction offset pixel number sequence to obtain an initial compensation pixel number sequence.

A first determining unit, configured to determine, for an nth subsequent echo sampling sequence, a target compensation pixel number corresponding to the nth subsequent echo sampling sequence according to a first N initial compensation pixel numbers included in the initial compensation pixel number sequence, where N is an integer greater than or equal to 1 and less than or equal to N.

According to an embodiment of the present disclosure, the third determination module includes a fourth determination sub-module and a fifth determination sub-module.

And the fourth determination submodule is used for determining the unit slope change amount according to the sampling point number and the period phase of each echo sampling sequence.

And a fifth determining sub-module for determining the offset pixel number according to the phase slope and the unit slope conversion amount.

According to an embodiment of the present disclosure, the first determination module includes a sixth determination sub-module and a seventh determination sub-module.

A sixth determining submodule, configured to determine a normalized cross power spectrum according to the first spectrogram and the second spectrogram;

and the seventh determination submodule is used for carrying out autocorrelation operation on the normalized cross power spectrum and determining the autocorrelation normalized cross power spectrum.

According to an embodiment of the disclosure, the echo abnormality detection and compensation device further includes a fourth determination module, a fourth obtaining module, and a fifth obtaining module.

And a fourth determining module, configured to perform complex conjugate multiplication on any two adjacent time delay compensation sequences in the N time delay compensation sequences, and determine a phase difference sequence, where each phase difference included in the phase difference sequence represents a phase amount of a phase of a subsequent time delay compensation sequence in the two adjacent time delay compensation sequences compared with a phase amount of a phase offset of a preceding time delay compensation sequence, and each phase difference included in the phase difference sequence corresponding to the 1 st time delay compensation sequence is a second preset value.

And a fourth obtaining module, configured to average each phase difference included in the phase difference sequence to obtain a constant term phase error.

And a fifth obtaining module, configured to perform phase compensation on the later time delay compensation sequence according to the constant term phase error, to obtain a target echo sampling sequence.

According to an embodiment of the disclosure, the fifth obtaining module includes an offset phase variance and mean determining sub-module, an abnormal phase error determining sub-module, a corrected phase error obtaining sub-module, a corrected phase error sequence obtaining sub-module, a target compensating phase sequence determining sub-module, and a target echo sampling sequence obtaining sub-module.

And the offset phase variance and mean value determining submodule is used for determining the offset phase variance and the offset phase mean value according to N constant term phase errors which are in one-to-one correspondence with the N time delay compensation sequences.

The abnormal phase error determining submodule is used for determining abnormal phase errors from N constant term phase errors according to the offset phase variance and the offset phase mean value.

And the corrected phase error obtaining submodule is used for carrying out linear difference on the phase errors of two constant terms adjacent to the abnormal phase error to obtain the corrected phase error.

The corrected phase error sequence obtaining submodule is used for replacing abnormal phase errors in the N constant term phase errors with corrected phase errors to obtain a corrected phase error sequence;

The target compensation phase sequence determining submodule is used for determining a target compensation phase sequence according to the N constant term phase errors and the corrected phase error sequence;

The target echo sampling sequence obtaining submodule is used for carrying out phase compensation on the later time delay compensation sequence according to the target compensation phase corresponding to the later time delay compensation sequence included in the target compensation phase sequence to obtain the target echo sampling sequence.

According to an embodiment of the present disclosure, the target compensation phase sequence determination submodule includes a second building unit, a second obtaining unit, and a second determining unit.

And the second construction unit is used for constructing a constant term phase error sequence according to the N constant term phase errors.

And the second obtaining unit is used for subtracting the constant term phase error sequence from the corrected phase error sequence to obtain an initial compensation phase sequence.

And a second determining unit configured to determine, for the nth subsequent time delay compensation sequence, a target compensation phase corresponding to the nth subsequent time delay compensation sequence according to the first N initial compensation phases included in the initial compensation phase sequence, where N is an integer greater than or equal to 1 and less than or equal to N.

According to an embodiment of the present disclosure, the offset phase variance and mean determination submodule includes a third construction unit, a third obtaining unit, and a third determination unit.

And the third construction unit is used for constructing a constant term phase difference sequence according to the N constant term phase errors.

And the third obtaining unit is used for carrying out high-pass filtering on the constant term phase difference sequence to obtain a high-frequency phase sequence.

And a third determining unit for determining an offset phase variance and an offset phase mean value according to the high-frequency phase sequence.

According to an embodiment of the present disclosure, the abnormal phase error determination submodule includes a fourth determination unit.

And a fourth determining unit configured to determine an abnormal phase error from the N constant term phase errors according to a high frequency phase, an offset phase variance, and an offset phase mean value, which are included in the high frequency phase sequence and correspond to the N constant term phase errors, respectively.

According to an embodiment of the present invention, any of the first obtaining module 1310, the first determining module 1320, the second obtaining module 1330, the second determining module 1340, the third determining module 1350, and the third obtaining module 1360 may be combined in one module to be implemented, or any of the modules may be split into a plurality of modules. Or at least some of the functionality of one or more of the modules may be combined with, and implemented in, at least some of the functionality of other modules. According to an embodiment of the invention, at least one of the first obtaining module 1310, the first obtaining module 1320, the second obtaining module 1330, the second determining module 1340, the third determining module 1350 and the third obtaining module 1360 may be implemented at least partially as a hardware circuit, for example, a Field Programmable Gate Array (FPGA), a Programmable Logic Array (PLA), a system on a chip, a system on a substrate, a system on a package, an Application Specific Integrated Circuit (ASIC), or may be implemented in hardware or firmware in any other reasonable way of integrating or packaging the circuits, or in any one of or a suitable combination of three of software, hardware and firmware. Or at least one of the first obtaining module 1310, the first determining module 1320, the second obtaining module 1330, the second determining module 1340, the third determining module 1350 and the third obtaining module 1360 may be at least partially implemented as a computer program module, which may perform corresponding functions when being executed.

As shown in fig. 14, an electronic device 1400 according to an embodiment of the present invention includes a processor 1401 that can perform various appropriate actions and processes according to a program stored in a Read Only Memory (ROM) 1402 or a program loaded from a storage section 1408 into a Random Access Memory (RAM) 1403. The processor 1401 may include, for example, a general purpose microprocessor (e.g., a CPU), an instruction set processor and/or an associated chipset and/or a special purpose microprocessor (e.g., an Application Specific Integrated Circuit (ASIC)), or the like. The processor 1401 may also include on-board memory for caching purposes. The processor 1401 may comprise a single processing unit or a plurality of processing units for performing different actions of the method flows according to embodiments of the invention.

In the RAM 1403, various programs and data necessary for the operation of the electronic device 1400 are stored. The processor 1401, ROM 1402, and RAM 1403 are connected to each other through a bus 1404. The processor 1401 performs various operations of the method flow according to the embodiment of the present invention by executing programs in the ROM 1402 and/or the RAM 1403. Note that the program may be stored in one or more memories other than the ROM 1402 and the RAM 1403. The processor 1401 may also perform various operations of the method flow according to embodiments of the present invention by executing programs stored in the one or more memories.

According to an embodiment of the invention, the electronic device 1400 may also include an input/output (I/O) interface 1405, the input/output (I/O) interface 1405 also being connected to the bus 1404. The electronic device 1400 may also include one or more of the following components connected to an input/output (I/O) interface 1405: an input section 1406 including a keyboard, a mouse, and the like; an output portion 1407 including a Cathode Ray Tube (CRT), a Liquid Crystal Display (LCD), and the like, a speaker, and the like; a storage section 1408 including a hard disk or the like; and a communication section 1409 including a network interface card such as a LAN card, a modem, and the like. The communication section 1409 performs communication processing via a network such as the internet. The drive 1410 is also connected to an input/output (I/O) interface 1405 as needed. Removable media 1411, such as magnetic disks, optical disks, magneto-optical disks, semiconductor memory, and the like, is installed as needed on drive 1410 so that a computer program read therefrom is installed as needed into storage portion 1408.

The present invention also provides a computer-readable storage medium that may be embodied in the apparatus/device/system described in the above embodiments; or may exist alone without being assembled into the apparatus/device/system. The computer-readable storage medium carries one or more programs which, when executed, implement methods in accordance with embodiments of the present invention.

According to embodiments of the present invention, the computer-readable storage medium may be a non-volatile computer-readable storage medium, which may include, for example, but is not limited to: a portable computer diskette, a hard disk, a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. For example, according to embodiments of the invention, the computer-readable storage medium may include ROM 1402 and/or RAM 1403 described above and/or one or more memories other than ROM 1402 and RAM 1403.

Embodiments of the present invention also include a computer program product comprising a computer program containing program code for performing the method shown in the flowcharts. When the computer program product runs in a computer system, the program code is used for enabling the computer system to realize the echo abnormity detection and compensation method provided by the embodiment of the invention.

The above-described functions defined in the system/apparatus of the embodiment of the present invention are performed when the computer program is executed by the processor 1401. The systems, apparatus, modules, units, etc. described above may be implemented by computer program modules according to embodiments of the invention.

In one embodiment, the computer program may be based on a tangible storage medium such as an optical storage device, a magnetic storage device, or the like. In another embodiment, the computer program can also be transmitted, distributed over a network medium in the form of signals, and downloaded and installed via the communication portion 1409, and/or installed from the removable medium 1411. The computer program may include program code that may be transmitted using any appropriate network medium, including but not limited to: wireless, wired, etc., or any suitable combination of the foregoing.

In such an embodiment, the computer program can be downloaded and installed from a network via the communication portion 1409 and/or installed from the removable medium 1411. The above-described functions defined in the system of the embodiment of the present invention are performed when the computer program is executed by the processor 1401. The systems, devices, apparatus, modules, units, etc. described above may be implemented by computer program modules according to embodiments of the invention.

According to embodiments of the present invention, program code for carrying out computer programs provided by embodiments of the present invention may be written in any combination of one or more programming languages, and in particular, such computer programs may be implemented in high-level procedural and/or object-oriented programming languages, and/or in assembly/machine languages. Programming languages include, but are not limited to, such as Java, c++, python, "C" or similar programming languages. The program code may execute entirely on the user's computing device, partly on the user's device, partly on a remote computing device, or entirely on the remote computing device or server. In the case of remote computing devices, the remote computing device may be connected to the user computing device through any kind of network, including a Local Area Network (LAN) or a Wide Area Network (WAN), or may be connected to an external computing device (e.g., connected via the Internet using an Internet service provider).

The flowcharts and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams or flowchart illustration, and combinations of blocks in the block diagrams or flowchart illustration, can be implemented by special purpose hardware-based systems which perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

Those skilled in the art will appreciate that the features recited in the various embodiments of the invention can be combined in a variety of combinations and/or combinations, even if such combinations or combinations are not explicitly recited in the present invention. In particular, the features recited in the various embodiments of the invention can be combined and/or combined in various ways without departing from the spirit and teachings of the invention. All such combinations and/or combinations fall within the scope of the invention.

The embodiments of the present invention are described above. These examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Although the embodiments are described above separately, this does not mean that the measures in the embodiments cannot be used advantageously in combination. The scope of the invention is defined by the appended claims and equivalents thereof. Various alternatives and modifications can be made by those skilled in the art without departing from the scope of the invention, and such alternatives and modifications are intended to fall within the scope of the invention.

Claims

1. An echo anomaly detection and compensation method, the method comprising:

determining autocorrelation normalized cross power spectrums between two adjacent echo sampling sequences according to the first spectrogram and the second spectrogram;

Carrying out cross power spectrum phase decomposition on the autocorrelation normalization to obtain a power spectrum phase sequence;

Determining the offset pixel number according to the phase slope, wherein the offset pixel number represents the pixel number of the later echo sampling sequence in the two adjacent echo sampling sequences, which is offset compared with the earlier echo sampling sequence, and the offset pixel number corresponding to the first echo sampling sequence is a first preset value;

and carrying out time delay compensation on the post echo sampling sequence according to the offset pixel number to obtain a time delay compensation sequence.

2. The method of claim 1, wherein time delay compensating the sequence of post-echo samples according to the number of offset pixels to obtain a time delay compensated sequence comprises:

And carrying out time delay compensation on the post-echo sampling sequence according to the target compensation pixel number which is included in the target compensation pixel number sequence and corresponds to the post-echo sampling sequence, so as to obtain the time delay compensation sequence.

3. The method of claim 2, wherein said determining a target sequence of compensated pixel numbers based on N of said offset pixel numbers and said modified offset pixel number sequence comprises:

And determining a target compensation pixel number corresponding to an nth post-echo sampling sequence according to the first N initial compensation pixel numbers included in the initial compensation pixel number sequence aiming at the nth post-echo sampling sequence, wherein N is an integer greater than or equal to 1 and less than or equal to N.

4. A method according to any one of claims 1 to 3, wherein said determining an offset pixel number from said phase slope comprises:

And determining the offset pixel number according to the phase slope and the unit slope conversion amount.

5. A method according to any one of claims 1 to 3, wherein said determining an autocorrelation normalized cross-power spectrum between two adjacent echo sample sequences from said first and second spectrograms comprises:

6. A method according to any one of claims 1 to 3, further comprising:

performing complex conjugate multiplication on any two adjacent time delay compensation sequences in the N time delay compensation sequences to determine a phase difference sequence, wherein each phase difference included in the phase difference sequence represents the phase difference of a later time delay compensation sequence in the two adjacent time delay compensation sequences, compared with the phase quantity of the offset of the earlier time delay compensation sequence, and each phase difference included in the phase difference sequence corresponding to the 1 st time delay compensation sequence is a second preset value;

averaging all phase differences included in the phase difference sequence to obtain a constant term phase error;

And carrying out phase compensation on the later time delay compensation sequence according to the constant term phase error to obtain a target echo sampling sequence.

7. The method of claim 6, wherein phase compensating the subsequent time delay compensation sequence based on the constant term phase error to obtain a target echo sample sequence comprises:

Determining an offset phase variance and an offset phase mean according to N constant term phase errors in one-to-one correspondence with the N time delay compensation sequences;

replacing abnormal phase errors in the N constant term phase errors with the corrected phase errors to obtain a corrected phase error sequence;

Determining a target compensation phase sequence according to N constant term phase errors and the corrected phase error sequences;

And carrying out phase compensation on the later time delay compensation sequence according to the target compensation phase corresponding to the later time delay compensation sequence included in the target compensation phase sequence to obtain the target echo sampling sequence.

8. The method of claim 7, wherein said determining a target compensated phase sequence based on N of said constant term phase errors and said modified phase error sequence comprises:

Constructing a constant term phase error sequence according to N constant term phase errors;

And determining a target compensation phase corresponding to an nth subsequent time delay compensation sequence according to the first N initial compensation phases included in the initial compensation phase sequence aiming at the nth subsequent time delay compensation sequence, wherein N is an integer greater than or equal to 1 and less than or equal to N.

9. The method of claim 7, wherein determining the offset phase variance and the offset phase mean from the N constant term phase errors in one-to-one correspondence with the N time delay compensation sequences comprises:

constructing a constant term phase difference sequence according to N constant term phase errors;

Performing high-pass filtering on the constant term phase difference sequence to obtain a high-frequency phase sequence;

And determining the offset phase variance and the offset phase mean value according to the high-frequency phase sequence.

10. The method of claim 9, wherein said determining an abnormal phase error from N of said constant term phase errors based on said offset phase variance and said offset phase mean comprises:

and determining the abnormal phase error from the N constant term phase errors according to the high-frequency phase, the offset phase variance and the offset phase mean value, which are respectively corresponding to the N constant term phase errors, included in the high-frequency phase sequence.