CN112882031A - ISAR imaging method, device and storage medium of discrete frequency coding waveform - Google Patents
ISAR imaging method, device and storage medium of discrete frequency coding waveform Download PDFInfo
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Abstract
The invention discloses an ISAR imaging method, a device and a storage medium of a discrete frequency coding waveform, wherein the method comprises the steps of circularly transmitting a pulse group, wherein the pulse group comprises a plurality of transmitting pulses with different frequency codes; receiving echo signals returned by the response pulse group; sequentially performing matched filtering on the echo signals by using a matched filter; using a cross-correlation function to sequentially align and register each echo signal after matching and filtering; compensating the residual distance error of each echo signal after the alignment registration processing; and (5) compensating the residual distance error and then performing azimuth imaging processing. According to the invention, by circularly transmitting the transmitting pulse comprising a plurality of different frequency codes, namely using the random frequency coding waveform as the transmitting waveform of the radar, the target side lobe can be reduced, the dynamic range of the image can be enlarged, the problem that the strong point side lobe submerges the weak scattering point can be improved, and the ISAR imaging quality can be improved. The invention can be widely applied to the technical field of radars.
Description
Technical Field
The invention relates to the technical field of radars, in particular to an ISAR imaging method, device and storage medium of discrete frequency coding waveforms.
Background
In the traditional ISAR imaging method, the problem that the side lobe of a strong scattering point submerges nearby weak scattering points exists, namely in ISAR imaging, the dynamic range of echoes of different parts of an observed target can be very large due to the scattering characteristics of the target and the special shape of the parts, a linear frequency modulation signal (LFM) is used, the side lobe of the strong scattering point extremely easily submerges the target of the weak scattering point, so that target information is lost, aiming at the traditional linear frequency modulation signal ISAR imaging, low sidelobes are obtained by windowing the echoes (e.g., hamming, hanning, etc.), but the sidelobes near the main lobe are still strong (about-30 dB), moreover, the signal windowing can also bring about main lobe broadening and energy loss of a signal pulse pressure result, the pulse pressure result broadening can influence the range resolution and energy loss of a radar, the signal to noise ratio of an image can be influenced, and the signal windowing can cause side lobes to lose the performance of the signal. In the case of imaging using random frequency hopping signal ISAR, since bandwidth synthesis is performed using a plurality of pulses, inter-pulse processing is necessary to obtain a doppler result, which reduces the repetition frequency of the pulse signal, affects the doppler bandwidth, reduces the imaging bandwidth in the direction of ISAR imaging, and easily causes image superimposition. Moreover, the bandwidth synthesis needs to accurately estimate the motion parameters of the target, otherwise, insufficient phase compensation causes the synthesis error of the range profile, and the image quality is affected.
Interpretation of terms:
ISAR (inverse Synthetic Aperture radio): an inverse synthetic aperture radar;
lfm (linear Frequency modulation): linear frequency modulation;
ofdm (orthogonal Frequency Division multiplexing): orthogonal frequency division multiplexing;
SAR (synthetic Aperture radio): a synthetic aperture radar;
dfc (cognitive Frequency coding): discrete frequency encoding.
Disclosure of Invention
The present invention is directed to solving at least one of the problems of the prior art. Therefore, the invention provides an ISAR imaging method, device and storage medium of discrete frequency coding waveform.
The technical scheme adopted by the invention is as follows:
in one aspect, an embodiment of the present invention includes an ISAR imaging method of a discrete frequency encoded waveform, including:
cyclically transmitting a pulse group, wherein the pulse group comprises a plurality of transmitting pulses with different frequency codes;
receiving echo signals returned in response to the pulse group;
sequentially performing matched filtering on the echo signals by using a matched filter;
using a cross-correlation function to sequentially align and register each echo signal after matching and filtering;
compensating the residual distance error of each echo signal after the alignment registration processing;
and (5) compensating the residual distance error and then performing azimuth imaging processing.
Further, the frequency encoding of each of the transmit pulses is randomly generated by a linear congruence method.
Further, the ith transmit pulse in the pulse group is represented as:
in the formula, sl(T) is the l-th transmitted pulse in the pulse group, M is the number of frequency chips in a transmitted pulse, TspFor the width of each frequency chip, fcFor the carrier frequency of the transmitted signal, t represents time, j is an imaginary number,
a sequence of frequency codes for transmitting pulses, wherein Δ f is the frequency interval of a frequency chip and Δ f is 1/Tsp，a＝{a1,a2,…,aMIs a frequency coding coefficient, and a is a random rearrangement by an integer {0,1, …, M-1 }.
Further, the performing, by using a matched filter, sequential matched filtering on the echo signal specifically includes:
and (3) performing pulse compression on the echo signal by using a matched filter, and obtaining a pulse compression result expressed as:
in the formula, L is E [1, L ∈]Representing the sampling points of the pulse, U representing the set of scattering points of the object, U (t) representing the envelope of the scattering points after pulse compression, τl(x, y) represents the time delay of the scattering point (x, y) in the l-th transmit pulse,
represents the side lobe distribution of the scattering point (x, y) in the compression result of the l-th transmitted pulse, fcFor the transmitted signal carrier frequency, j is an imaginary number and t represents time.
Further, the compressed envelope of the scattering point pulse is represented as:
u(t)＝σ(x,y)sinc(πB(t-τl(x,y)))；
in the formula, σ(x,y)Is the echo intensity of the scattering spot (x, y), τl(x, y) represents a time delay of a scattering point (x, y) in the l-th transmission pulse, t represents time, and B represents a constant.
Further, the time delay of the scattering point (x, y) in the ith transmission pulse is calculated by the following formula:
in the formula, L is E [1, L ∈]Indicating the pulse sampling point, R0(l) Represents the translational component of the object, ω represents the equivalent rotational angular velocity of the object, c represents the speed of light, x represents the x-coordinate value of the scattering point, and y represents the y-coordinate value of the scattering point.
Further, the cross-correlation function is represented as:
in the formula (I), the compound is shown in the specification,
and
representing the real envelope of two adjacent echo signals, and tau representing the time delay between two adjacent echo signals.
Further, the performing, by using the cross-correlation function, alignment and registration processing on each echo signal after matching and filtering in sequence specifically includes:
calculating a time delay value corresponding to the peak value by using the cross-correlation function;
and according to the time delay value, sequentially aligning and registering the echo signals after matched filtering.
In another aspect, an embodiment of the present invention further includes an ISAR imaging apparatus for discrete frequency encoded waveforms, including:
at least one processor;
at least one memory for storing at least one program;
when executed by the at least one processor, cause the at least one processor to implement the method of ISAR imaging of discrete frequency encoded waveforms.
In another aspect, embodiments of the present invention further include a computer readable storage medium having stored thereon a program executable by a processor, the program executable by the processor being configured to implement the method of ISAR imaging of discrete frequency encoded waveforms as described herein.
The invention has the beneficial effects that:
according to the invention, by circularly transmitting the transmitting pulse comprising a plurality of different frequency codes, namely using the random frequency coding waveform as the transmitting waveform of the radar, the target side lobe can be reduced, the dynamic range of the image can be enlarged, the problem that the strong point side lobe submerges the weak scattering point can be improved, and the ISAR imaging quality can be improved.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
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The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a flowchart illustrating steps of a method for ISAR imaging of discrete frequency encoded waveforms according to an embodiment of the present invention;
FIG. 2 is a diagram illustrating a random frequency encoded waveform according to an embodiment of the present invention;
FIG. 3 is a diagram illustrating the result of compressing the target echo pulse according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a distance image before envelope alignment of two adjacent frames according to an embodiment of the present invention;
FIG. 5 is a diagram illustrating a correlation result between two adjacent frames of echo signals according to an embodiment of the present invention;
fig. 6 is a schematic diagram of two adjacent frames of distance images after envelope alignment according to the embodiment of the invention;
FIG. 7 is a diagram illustrating the alignment result of the range profile envelope according to the embodiment of the present invention;
FIG. 8 is a schematic diagram of a dot target set in the dot matrix target simulation according to an embodiment of the present invention;
FIG. 9 is a schematic diagram of an ISAR imaging result of transmitting an LFM waveform in the dot matrix target simulation according to the embodiment of the present invention;
FIG. 10 is a schematic diagram of an ISAR imaging result of emitting a single DFC waveform in the lattice target simulation according to the embodiment of the present invention;
FIG. 11 is a schematic diagram of an ISAR imaging result of emitting a two-dimensional random DFC waveform in lattice target simulation according to an embodiment of the present invention;
fig. 12 is a schematic diagram of a comparison result obtained by comparing doppler slices at the central points of three waveform ISAR imaging results in the dot matrix target simulation according to the embodiment of the present invention;
FIG. 13 is a schematic diagram of a point target set in an aircraft target simulation according to an embodiment of the invention;
FIG. 14 is a schematic diagram of an ISAR imaging result of transmitting an LFM waveform in an aircraft target simulation according to an embodiment of the present invention;
FIG. 15 is a schematic diagram of an ISAR imaging result for transmitting a single DFC waveform in an aircraft target simulation according to an embodiment of the present invention;
FIG. 16 is a schematic diagram of an ISAR imaging result of transmitting a two-dimensional random DFC waveform in aircraft target simulation according to an embodiment of the present invention;
fig. 17 is a schematic structural diagram of an ISAR imaging apparatus for discrete frequency encoded waveforms according to an embodiment of the present invention.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.
In the description of the present invention, it should be understood that the orientation or positional relationship referred to in the description of the orientation, such as the upper, lower, front, rear, left, right, etc., is based on the orientation or positional relationship shown in the drawings, and is only for convenience of description and simplification of description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention.
In the description of the present invention, the meaning of a plurality of means is one or more, the meaning of a plurality of means is two or more, and larger, smaller, larger, etc. are understood as excluding the number, and larger, smaller, inner, etc. are understood as including the number. If the first and second are described for the purpose of distinguishing technical features, they are not to be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated or implicitly indicating the precedence of the technical features indicated.
In the description of the present invention, unless otherwise explicitly limited, terms such as arrangement, installation, connection and the like should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above terms in the present invention in combination with the specific contents of the technical solutions.
The embodiments of the present application will be further explained with reference to the drawings.
Referring to fig. 1, an embodiment of the present invention provides an ISAR imaging method of a discrete frequency encoded waveform, including but not limited to the following steps:
s1, circularly transmitting a pulse group, wherein the pulse group comprises a plurality of transmitting pulses with different frequency codes;
s2, receiving an echo signal returned by responding to the pulse group;
s3, sequentially performing matched filtering on the echo signals by using a matched filter;
s4, using a cross-correlation function to sequentially align and register each echo signal after matching and filtering;
s5, compensating the residual distance error of each echo signal after alignment and registration processing;
and S6, compensating the residual distance error and then carrying out azimuth imaging processing.
Regarding step S1, in the present embodiment, the radar observes the target using the DFC signal, and the frequency code of each transmitted pulse is randomly generated by the linear congruence method during the observation time, and assuming that L pulse signals are transmitted in total during the observation time, L frequency code sequences need to be generated. As shown in fig. 2, each transmitted pulse is composed of a series of dot frequency narrow pulse signals which are randomly arranged and spliced, each dot frequency signal is called a chip, and the ith transmitted pulse can be represented as:
where M is the number of frequency chips in a pulse, TspFor the width of each frequency chip, fcFor transmitting the carrier frequency of the signal, the frequency-coding sequence of the transmitted pulses is flA · Δ f, Δ f is the frequency interval of the frequency chips, and Δ f is1/Tsp，a＝{a1,a2,…,aMIs a frequency coding coefficient, and a is a random rearrangement by an integer {0,1, …, M-1 }.
According to the above waveform form, the radar observes the target using L pulse signals having different frequency codes.
In this embodiment, the frequency code of each transmitted pulse is randomly generated by a linear congruence method, specifically, a set of random numbers is generated by the linear congruence method, and the required frequency code of each pulse is generated by using the random numbers. The linear congruence random number generation method can generate random numbers which are uniformly distributed in an interval [ 01 ], and the linear congruence method can generate a series of random numbers by giving three initial random numbers alpha, beta and epsilon and utilizing an iterative formula, wherein the iterative formula is as follows:
xk+1＝(αxk+ β) mod ∈ k ═ 0,1, … (formula 2);
where mod denotes the remainder, and α, β, and ε are the three initial random numbers.
With equation 2, a series of random numbers can be generated iteratively on a continuous basis by setting initial parameters. For example, a typical set of random number initial parameters is α ═ 16807, β ═ 0, and ∈ 231-1, the set of initial parameters being computer-implementable.
By setting the parameters, a set of random numbers for generating the pulse frequency code can be generated, and the generated random numbers are set as
x＝{x1,x2,…,xLM} (formula 3);
and grouping the generated random numbers, wherein each group is M random numbers, and the groups are L groups, and each group of random numbers is used for generating a group of frequency codes. The frequency code is generated by sorting the random numbers in ascending order and using the index of each value in the original array as the frequency code after sorting in ascending order. If the first group is ordered, as shown in equation 4:
sorted index { a1,a2,…,aMThe set of frequency codes a is formed. And sequencing all the L random numbers to obtain L groups of frequency codes for radar transmission.
In steps S2 and S3, in this embodiment, the radar observes the target, and the motion of the target during the observation time may be decomposed into a translational component of the overall equidirectional motion of the scattering point and a rotational component of the scattering point around a certain center. The translation component is useless for ISAR imaging, the translation component is compensated by using an envelope alignment method before the ISAR imaging, and the residual rotation component is used for target imaging processing.
Considering the translational component in the echo of the target, and assuming that the coherent processing time is the equivalent rotation angular velocity of the target is ω, the instantaneous distance of a scattering point (x, y) on the target can be expressed as:
r(l)＝R0(l) + x sin θ (l) + y cos θ (l) (formula 5);
wherein L is ∈ [1, L ∈]Indicating the pulse sampling point, R0(l) The translational component of the target is θ (l) ═ ω · l, which represents the angle of the target at each pulse sampling point. Considering a small angle rotation approximation model of the target, the distance of the rotation of the scattering point can be approximated using its first order Taylor expansion. Using the random DFC waveform signal as the transmit signal, the echo of the target can be represented as:
sR(l,t)＝∫∫(x,y)∈Uσ(x,y)sl(t-τl(x, y)) dxdy (formula 6);
where U represents the set of scattering points of the object, σ(x,y)Is the echo intensity of the scattering spot (x, y), τl(x, y) represents the time delay of the scattering point (x, y) in the ith transmit pulse, and can be expressed as:
because each pulse transmitted has different frequency codes, for each pulse echo, a corresponding matched filter is needed to be used for pulse compression of an echo signal, the intra-pulse Doppler influence possibly existing in a target echo is considered, and the matched filter for the velocity is designed according to tracking velocity information to eliminate the intra-pulse Doppler influence. Referring to fig. 3, after each echo is pulse-compressed, the pulse pressure result of the echo signal can be expressed as:
wherein u (t) represents the envelope of the scattering point pulse after compression, and can be represented as:
u(t)＝σ(x,y)sinc(πB(t-τl(x, y))) (formula 9);
In step S4, in the present embodiment, the envelope alignment of the target echo is performed by using a cross-correlation method. For two adjacent echoes, the rotation angle of the target is generally less than 0.01 degrees, so that the scattering point walk caused by the rotation angle is small, namely the change of cross terms in the two adjacent echoes is small, the real envelopes of the two echoes are very similar, and the cross correlation coefficient of the two echoes is generally more than 0.95.
It is conceivable that the time delay corresponding to the peak value is used for compensation by adopting a cross-correlation method, so that the adjacent real packets can be aligned well. If the real envelope of two adjacent echoes is respectively
And
the cross-correlation function is then:
searching tau, and calculating the time delay value corresponding to the peak value. As shown in fig. 4, a schematic diagram of a range profile before envelope alignment of two adjacent frames is shown, a target range profile of a pulse echo has a dislocation in the two adjacent frames, that is, the same scattering point is not in the same range cell, and a displacement amount of two adjacent echoes can be obtained by using a cross-correlation method, as shown in fig. 5 below, it can be seen that a peak value after correlation is in 138 cells and is deviated from a center by 9 range cells backwards, so that a range profile of two adjacent frames has a displacement amount of 9 range cells, and thus the displacement amount is compensated, and a schematic diagram of a range profile of two adjacent frames as shown in fig. 6 is obtained, and fig. 7 further shows a result of two adjacent frames after envelope alignment.
It should be noted that equation 10 is described in continuous time, while the actual radar signal is recorded in discrete time samples, with the sampling interval typically being slightly less than the pulse width (after pulse compression). As mentioned earlier, the envelope alignment accuracy requires 1/8 range resolution cells. Therefore, when the cross-correlation function is obtained, the time dispersion value is usually interpolated by 8 times.
In this embodiment, a cross-correlation method is used to sequentially perform alignment registration processing on each echo, so that the range images of the same scattering point are always in the same range unit in the observation time period.
Regarding steps S5 and S6, in this embodiment, after performing envelope alignment, the same scattering point is in the same range unit during the whole observation time, but because the accuracy of range estimation is not sufficient, it is also necessary to use the special point self-focusing manner to compensate the residual range error of each pulse, and after compensating the residual error, the translational motion of the target is completely compensated, at this time, the azimuth imaging processing may be performed.
After envelope alignment and self-focusing of each echo, the echo signal can be represented as:
where u (t) represents the envelope of the scattered point pulse after compression, which can be expressed as:
in this case, the envelope of the object changes only according to the rotation of the scattering point during the observation time, and generally, the rotation of the scattering point continues in the same range bin. And performing slow time dimension Fourier transform (FFT) on the result after the envelope alignment to complete coherent accumulation, so as to obtain the ISAR image of the target.
Substituting equation 11 into 13 yields:
the second term in the formula 14 represents the fourier transform result of the side lobe of the scattering point, and since the side lobe is random among all echo pulses, coherent accumulation gain cannot be obtained, while the main lobe position of the signal scattering point is accurately coherent accumulated, and the main lobe-side lobe ratio of the image is obviously improved; a (f)l) The envelope of the scattering points in the doppler dimension is represented as:
in equation 15, T is the coherent processing time length.
In this embodiment, a lattice target simulation is also used to perform waveform depression sidelobe verification. The radar parameters in the simulation are shown in table 1.
TABLE 1 Radar simulation parameters
In this embodiment, the set parameters are used to perform dot matrix target simulation and airplane target simulation, and there are 2048 pulses with different frequency codes in total in the observation time.
Regarding the dot matrix target simulation:
the 5 point targets set in this example are shown in fig. 8. Point target echo simulation is performed by using three waveforms, and pulse pressure and ISAR imaging processing are performed on the echoes, as shown in fig. 9-11, which are ISAR imaging results using a conventional LFM waveform, emitting a single DFC waveform, and emitting a two-dimensional random DFC waveform, respectively. Because the side lobe is higher in the traditional LFM waveform, a Hamming window of-25 dB is added in the process of distance pulse pressure, and the ISAR result shows that the side lobe with the intensity becoming smaller along with the distance is arranged near the main lobe, and if a strong scattering point and a weak scattering point exist at a close distance at the same time, the intensity of the weak scattering point is smaller than that of the strong scattering point, and the weak scattering point is submerged by the strong point side lobe. The result of the radar transmitting a single DFC waveform during the observation time is shown in fig. 10, in which there is no strong side lobe in the vicinity of the main lobe, but strong side lobes start to appear in the region far from the main lobe, and therefore, the side lobe of the strong scattering point easily swamps the weak scattering point beyond a certain distance. The result of using the two-dimensional random DFC waveform is shown in fig. 11, and in the result, the distance of the point-to-point has no obvious side lobe, and the influence caused by the side lobe of the main lobe can be significantly reduced.
To further illustrate the advantages of the method for ISAR imaging of discrete frequency coded waveforms proposed in this embodiment, doppler slices at the center point of the ISAR imaging results of three waveforms, namely, a conventional LFM waveform, a single DFC waveform and a two-dimensional random DFC waveform, are compared, and the comparison result is shown in fig. 12. The comparison result shows that the maximum side lobe of the traditional LFM waveform is about-25 dB under the action of a Hamming window, and the side lobe which is farther away from the main lobe has smaller amplitude; because the side lobe of the single DFC waveform is also subjected to coherent processing in the coherent processing among the pulses, the side lobe of the single DFC waveform is similar to the side lobe related to the single DFC waveform, the amplitude is about-30 dB, and the amplitude of the side lobe near the main lobe is lower than that of the traditional LFM waveform; with the two-dimensional random DFC waveform, the side lobe does not obtain coherent processing gain, so after the coherent processing of 2048 pulses, the normalized side lobe is smaller than-45 dB and becomes smaller with the distance becoming longer, and is lower than-50 dB beyond 5 meters. The method provided by the embodiment is obviously superior to the two waveforms in sidelobe suppression performance.
That is to say, the present embodiment uses a point target simulation experiment to verify that the side lobe suppression performance of the ISAR imaging method of the discrete frequency coded waveform of the present embodiment can reach-50 dB, obviously because of the conventional method.
Regarding aircraft target simulation:
in this example, a boeing 737 model was used for simulation verification. The airplane model was randomly selected for scattering points, which are set as a point target diagram shown in fig. 13. Likewise, in the present embodiment, isor imaging simulation was performed using three waveforms of a conventional LFM waveform, a single DFC waveform emission, and a two-dimensional random DFC waveform emission, and the imaging results are shown in fig. 14 to 16. As is apparent from fig. 14, the LFM waveform has a strong side lobe near the scattering point, and the single DFC waveform has no strong side lobe near the scattering point, but generates a strong side lobe as the distance becomes farther.
In the present embodiment, the entropy of the ISAR image is used to evaluate the imaging quality, and the better imaging result is accompanied by a decrease in the image entropy. The image quality of the three waveforms in this experiment is shown in table 2.
TABLE 2 aircraft target ISAR image entropy
| Transmit waveform | Conventional LFM | Single DFC | Two-dimensional random DFC |
| Entropy of images | 6.4551 | 6.5783 | 6.4020 |
It can also be seen from the comparison result of the image entropy in table 2 that, when the two-dimensional random DFC waveform is used, since the side lobe of the target scattering point is significantly lower than those of the other two waveforms, the signal energy is concentrated at the scattering point, and the other two waveforms are affected by the large side lobe of the scattering point, the main lobe broadening and the like, the image entropy is large, and the imaging effect using the two-dimensional random DFC waveform is superior to that of the other two waveforms. That is to say, the results of the airplane target simulation experiments verify the performance of the two-dimensional random DFC waveform provided by the embodiment on suppressing the side lobes of the scattering points.
The airplane target simulation is used in the embodiment to verify the effectiveness of the ISAR imaging method of the discrete frequency coding waveform in the embodiment on sidelobe suppression, the method remarkably improves the sidelobe problem of a strong scattering point, and the ISAR image result quality is improved.
Referring to fig. 17, an embodiment of the present invention further provides an ISAR imaging apparatus 200 for discrete frequency coded waveforms, which specifically includes:
at least one processor 210;
at least one memory 220 for storing at least one program;
when executed by the at least one processor 210, causes the at least one processor 210 to implement the method as shown in fig. 1.
The memory 220, which is a non-transitory computer-readable storage medium, may be used to store non-transitory software programs and non-transitory computer-executable programs. The memory 220 may include high speed random access memory and may also include non-transitory memory, such as at least one magnetic disk storage device, flash memory device, or other non-transitory solid state storage device. In some embodiments, memory 220 may optionally include remote memory located remotely from processor 210, and such remote memory may be connected to processor 210 via a network. Examples of such networks include, but are not limited to, the internet, intranets, local area networks, mobile communication networks, and combinations thereof.
It will be understood that the device structure shown in fig. 17 is not intended to be limiting of device 200, and may include more or fewer components than shown, or some components may be combined, or a different arrangement of components.
In the apparatus 200 shown in fig. 17, the processor 210 may retrieve the program stored in the memory 220 and execute, but is not limited to, the steps of the embodiment shown in fig. 1.
The above-described embodiments of the apparatus 200 are merely illustrative, and the units illustrated as separate components may or may not be physically separate, may be located in one place, or may be distributed over a plurality of network units. Some or all of the modules can be selected according to actual needs to achieve the purposes of the embodiments.
Embodiments of the present invention also provide a computer-readable storage medium, which stores a program executable by a processor, and the program executable by the processor is used for implementing the method shown in fig. 1 when being executed by the processor.
The embodiment of the application also discloses a computer program product or a computer program, which comprises computer instructions, and the computer instructions are stored in a computer readable storage medium. The computer instructions may be read by a processor of a computer device from a computer-readable storage medium, and executed by the processor to cause the computer device to perform the method illustrated in fig. 1.
It will be understood that all or some of the steps, systems of methods disclosed above may be implemented as software, firmware, hardware, and suitable combinations thereof. Some or all of the physical components may be implemented as software executed by a processor, such as a central processing unit, digital signal processor, or microprocessor, or as hardware, or as an integrated circuit, such as an application specific integrated circuit. Such software may be distributed on computer readable media, which may include computer storage media (or non-transitory media) and communication media (or transitory media). The term computer storage media includes volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data, as is well known to those of ordinary skill in the art. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, Digital Versatile Disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can accessed by a computer. In addition, communication media typically embodies computer readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media as known to those skilled in the art.
The embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the gist of the present invention.
Claims (10)
1. A method of ISAR imaging of discrete frequency encoded waveforms, comprising:
cyclically transmitting a pulse group, wherein the pulse group comprises a plurality of transmitting pulses with different frequency codes;
receiving echo signals returned in response to the pulse group;
sequentially performing matched filtering on the echo signals by using a matched filter;
using a cross-correlation function to sequentially align and register each echo signal after matching and filtering;
compensating the residual distance error of each echo signal after the alignment registration processing;
and (5) compensating the residual distance error and then performing azimuth imaging processing.
2. The method of ISAR imaging of discrete frequency encoded waveforms of claim 1, wherein said frequency encoding of each of said transmit pulses is randomly generated by a linear congruence method.
3. The method of ISAR imaging of discrete frequency encoded waveforms of claim 1, wherein the ith transmit pulse in said set of pulses is represented as:
in the formula, sl(T) is the l-th transmitted pulse in the pulse group, M is the number of frequency chips in a transmitted pulse, TspFor the width of each frequency chip, fcFor transmitting a signal carrier frequency, t denotes time, j is an imaginary number, flA · Δ f is a frequency-coded sequence of transmit pulses, where Δ f is the frequency spacing of the frequency chips, and Δ f is 1/Tsp，a＝{a1,a2,…,aMIs a frequency coding coefficient, and a is a random rearrangement by an integer {0,1, …, M-1 }.
4. The ISAR imaging method of claim 1, wherein the sequential matched filtering of the echo signal by using the matched filter specifically comprises:
and performing pulse compression on the echo signal by using a matched filter, wherein the obtained pulse compression result is expressed as:
in the formula, L is E [1, L ∈]Representing the sampling points of the pulse, U representing the set of scattering points of the object, U (t) representing the envelope of the scattering points after pulse compression, τl(x, y) represents the time delay of the scattering point (x, y) in the l-th transmit pulse,
represents the side lobe distribution of the scattering point (x, y) in the compression result of the l-th transmitted pulse, fcFor the transmitted signal carrier frequency, j is an imaginary number and t represents time.
5. The method of ISAR imaging of discrete frequency encoded waveforms of claim 4, wherein said pulse-compressed envelope of said scattering points is represented as:
u(t)＝σ(x,y)sinc(πB(t-τl(x,y)))；
in the formula, σ(x,y)Is the echo intensity of the scattering spot (x, y), τl(x, y) represents a time delay of a scattering point (x, y) in the l-th transmission pulse, t represents time, and B represents a constant.
6. A method of ISAR imaging of discrete frequency encoded waveforms according to any of claims 4 and 5, wherein the time delay of the scattering point (x, y) in the i-th transmit pulse is calculated by the following equation:
in the formula, L is E [1, L ∈]Indicating the pulse sampling point, R0(l) Represents the translational component of the object, ω represents the equivalent rotational angular velocity of the object, c represents the speed of light, x represents the x-coordinate value of the scattering point, and y represents the y-coordinate value of the scattering point.
7. The method of ISAR imaging of discrete frequency encoded waveforms of claim 1, wherein said cross-correlation function is represented as:
in the formula, R12(tau) represents a cross-correlation function,
and
representing the real envelope of two adjacent echo signals, and tau representing the time delay between two adjacent echo signals.
8. The ISAR imaging method of claim 7, wherein the sequentially aligning and registering the matched and filtered echo signals by using the cross-correlation function specifically comprises:
calculating a time delay value corresponding to the peak value by using the cross-correlation function;
and according to the time delay value, sequentially aligning and registering the echo signals after matched filtering.
9. An ISAR imaging apparatus for discrete frequency encoded waveforms, comprising:
at least one processor;
at least one memory for storing at least one program;
when executed by the at least one processor, cause the at least one processor to implement the method of any one of claims 1-8.
10. Computer-readable storage medium, on which a processor-executable program is stored, which, when being executed by a processor, is adapted to carry out the method according to any one of claims 1-8.
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