CN109633642B - Terahertz high-speed target radar imaging method - Google Patents

Terahertz high-speed target radar imaging method Download PDF

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CN109633642B
CN109633642B CN201811511067.6A CN201811511067A CN109633642B CN 109633642 B CN109633642 B CN 109633642B CN 201811511067 A CN201811511067 A CN 201811511067A CN 109633642 B CN109633642 B CN 109633642B
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CN109633642A (en
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王平
程妹华
肖建
钟馥鸾
郑广瑜
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Shanghai Radio Equipment Research Institute
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
    • G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
    • G01S13/9021—SAR image post-processing techniques
    • G01S13/9029—SAR image post-processing techniques specially adapted for moving target detection within a single SAR image or within multiple SAR images taken at the same time
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
    • G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
    • G01S13/904—SAR modes
    • G01S13/9064—Inverse SAR [ISAR]

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Abstract

The invention relates to a terahertz high-speed target radar imaging method, which is based on narrow-band mode radar measurement and rotation parameter estimation of data storage; the radar transmits multi-channel wide-band and narrow-band linear frequency modulation signals, pulse compression is carried out by utilizing a deskew processing mode, and detection and high-resolution imaging are carried out on a target; performing translational compensation on echo signals under different motion conditions; and (3) self-adaptive compensation imaging of the non-uniform turntable model. In the process of target movement, the relative radar field angle changes greatly, and the Doppler velocity of the target changes rapidly, so that the method adopts a rotary table model for processing. Measuring target distance, speed and angle information by using a system narrow-band working mode, estimating the angular speed and angular acceleration of the rotary table, converting the rotary table model into a constant-speed rotary table model through nonlinear phase item compensation caused by the angular acceleration, and further obtaining a target high-resolution radar image by using a conventional range-Doppler algorithm.

Description

Terahertz high-speed target radar imaging method
Technical Field
The invention relates to the technical field of terahertz active imaging, which is suitable for realizing high-resolution imaging of a moving target.
Background
The conventional radar technology gradually develops from the measurement of parameters such as distance, speed, angle and the like to the radar high-resolution imaging technology. In view of the fact that the terahertz radar has a large bandwidth and a short wavelength, the terahertz radar has a large advantage in radar imaging, the effective size of the system can be reduced, high-resolution imaging can be achieved, and rich information can be provided for target identification.
Patent CN106405550A discloses a high-speed target ISAR accurate imaging modeling method, which mainly solves the problem of model errors caused by assuming that a target is static in the radar signal transmitting, transmitting and receiving processes in a conventional imaging model, and can obtain specific expression of a target echo by combining with the specific form of a transmitting signal, thereby determining a high-speed target ISAR accurate imaging model.
The patent CN107024684A proposes an interferometric three-dimensional imaging method for a space high-speed moving target, which adopts three-antenna echo translational compensation, improved OMP algorithm based on combined parameterized sparse representation and interference phase information processing to realize three-dimensional imaging for the space target.
Patent CN104502912A discloses an inverse synthetic aperture radar imaging method for a high-speed moving target. Aiming at a high-speed moving target, firstly, estimating a target motion parameter by using a least square method and envelope alignment, then carrying out coherence processing on a demodulation line frequency modulation echo signal by using the estimated motion parameter, eliminating a phase error caused by motion parameter estimation by using a weighted eigenvector self-focusing algorithm, correcting range migration by using wedge transformation, and finally obtaining an imaging result.
The terahertz radar imaging signal processing has certain characteristics, particularly for a high-speed moving target at a certain distance, echo signals contain rich Doppler information and Doppler frequency change caused by observation angle change, and certain requirements are provided for signal processing.
Disclosure of Invention
The invention provides a terahertz high-speed target radar imaging method aiming at the problem of nonlinear change of different distances of a Doppler domain in high-speed target terahertz radar imaging, and realizes an inverse synthetic aperture high-resolution imaging technology combining system parameter measurement and constant-speed turntable model transformation.
In order to achieve the above object, the technical solution of the present invention is to provide a terahertz high-speed target radar imaging method, including the following processes:
step 1, estimating rotation parameters based on narrow-band mode radar measurement and data storage; the radar transmits multi-channel wide-band and narrow-band linear frequency modulation signals, pulse compression is carried out by utilizing a deskew processing mode, and detection and high-resolution imaging are carried out on a target;
step 2, performing translational compensation on echo signals under different motion conditions;
and 3, self-adaptive compensation imaging of the non-uniform turntable model.
Optionally, step 1 further comprises the following process:
step 1.1, emitting narrow-band signals to complete the measurement of target motion parameters and obtain the motion speed v and the distance R of a measured target relative to a radarPAnd angle θ information;
step 1.2, according to the comparison of target distance and angle information in a narrow-band working mode and data of prestored numbers, utilizing the second order approximation of the following formula and a geometric motion model of a moving target,
Figure BDA0001900793160000021
calculating instantaneous angular velocity of rotary table model
Figure BDA0001900793160000022
And angular acceleration
Figure BDA0001900793160000031
Wherein, Delta theta (t)m) Representing the rotation angle of the target relative to the radar sight line in the synthetic aperture time, theta' representing the included angle between the radar axial direction and the connecting line of the target and the radar, HpRepresenting the target-to-radar axial distance;
and 1.3, switching to a broadband signal transmitting mode, and determining the imaging duration of the broadband echo signal under different motion conditions based on the narrow-band signal measurement parameters.
Optionally, step 2 further comprises the following process:
step 2.1, carrying out envelope alignment on the echoes by using an adjacent correlation method;
and 2.2, carrying out self-focusing based on a multi-feature point comprehensive method.
Optionally, step 3 further comprises the following process:
step 3.1 selecting a compensation function from the angular velocities and angular accelerations calculated in step 1
Figure BDA0001900793160000032
Wherein, tmIs a slow time; doppler frequency modulation
Figure BDA0001900793160000033
Step 3.2, non-uniform speed turntable model is processed by utilizing non-linear phase compensationConversion to constant turntable mode, i.e. final representation of the echo signal as
Figure BDA0001900793160000034
Wherein gamma is the linear frequency modulation of the signal,
Figure BDA0001900793160000035
for a fast time, fcFor the radar operating frequency, xPRepresenting the abscissa of the object in the imaging plane;
step 3.3 Doppler center from Point target echo
Figure BDA0001900793160000036
Making distance walk caused by rotation, and then converting the distance walk into a turntable model without distance migration; and then, obtaining a high-resolution radar image by using a range-Doppler algorithm, wherein lambda is the working wavelength of the radar.
The method is used for processing the high-speed target detection echo signal aiming at terahertz high-resolution radar imaging. In the process of target movement, the relative radar field angle changes greatly, and the Doppler velocity of the target changes rapidly, and in order to solve the problem, a rotary table model is adopted for processing. Measuring target distance, speed and angle information by using a system narrow-band working mode, estimating the angular speed and angular acceleration of the rotary table, converting the rotary table model into a constant-speed rotary table model through nonlinear phase item compensation caused by the angular acceleration, and further obtaining a target high-resolution radar image by using a conventional range-Doppler algorithm.
Drawings
FIG. 1 is a radar to target coordinate system relationship;
FIG. 2 is a geometric motion model of a moving object;
FIG. 3 is a graph of the Doppler frequency variation of a complex target under high-speed motion;
figure 4 is a flow chart of adaptive inverse synthetic aperture high resolution imaging.
Detailed Description
The invention is described in detail below by way of example with reference to the accompanying drawings.
(1) Target rotation parameter estimation based on radar system measurement
For received echoes, two phase terms of residual video phase and envelope skew introduced by beat need to be eliminated, and then translation compensation is carried out. Assume that the radar transmits a chirp signal and pulse compression is performed using a deskew mode. Regardless of the target amplitude modulation, the echo model after the scattering point P on the target is deskewed is represented as:
Figure BDA0001900793160000041
wherein c is the speed of electromagnetic wave in air, gamma is the signal linear frequency modulation,
Figure BDA0001900793160000042
for a fast time, fcFor the radar operating frequency, tmFor slow time, Δ RpThe difference in distance between the scattering point P and the reference position is mainly caused by translation and rotation of the target. According to the coordinate relation between the radar and the target in the graph 1, considering that the reference distance is larger than the target dimension, the difference between the distance from the scattering point P to the radar and the reference distance and the influence of the translation of the target, neglecting a constant term, delta RpCan be expressed as:
ΔRP(tm)≈RT(tm)+xPsin[θ(tm)]+yPcos[θ(tm)](2)
wherein R isT(tm) For translation, xPAnd yPRespectively representing the coordinates of the object in the imaging plane, theta (t)m) Is the instantaneous turning angle. When the target moves at a high speed, a larger rotation angle is caused by a short distance from the detection radar (as shown in fig. 3), and the rotation not only causes a high-order phase error, but also causes envelope migration, so that the characteristics of the rotation angle caused by the target motion need to be described.
Under a narrow-band working mode, the radar measures the movement of a target and respectively gives a target speed v and a distance RPAnd angle theta' (only the pitch plane is considered here, the same applies to the conclusionsAzimuth plane). According to the geometric motion model of the target relative to the radar shown in fig. 2, the calculated target rotation angle and time are as follows:
Figure BDA0001900793160000051
wherein, Delta theta (t)m) Representing the rotation angle of the target relative to the radar sight line in the synthetic aperture time, theta' representing the included angle between the radar axial direction and the connecting line of the target and the radar, HpRepresenting the target-to-radar axial distance.
In that
Figure BDA0001900793160000052
Under unknown conditions, the time-varying errors of distance and orientation caused by angular acceleration are difficult to correct. The target rotation can be divided into uniform rotation and uniform acceleration rotation with corresponding angular velocity
Figure BDA0001900793160000053
And angular acceleration
Figure BDA0001900793160000054
Is represented by formula (4).
Figure BDA0001900793160000055
Since the inverse synthetic aperture time is short, the angular acceleration is considered to be a fixed value within a single synthetic aperture (in the near case, the effect of the angular acceleration change can be reduced by reducing the synthetic aperture time). (1) After the formula is processed by deskew and motion compensation, the formula can be approximately rewritten as
Figure BDA0001900793160000061
As can be seen from (5), since the quadratic rotation phase error affects the image focusing effect, the quadratic phase term caused by non-uniformity needs to be compensated for to achieve better imaging effect.
(2) Range-doppler algorithm for correcting range walk based on parameter estimation
The first and second derivatives of the slow time of equation (5) can be used to obtain parameters of the echo distance and phase change of the point target. Doppler center f of point target echodcAnd the Doppler modulation frequency are respectively shown as a formula (6) and a formula (7).
Figure BDA0001900793160000062
Figure BDA0001900793160000063
And eliminating the influence of angular acceleration by using azimuth quadratic term phase compensation processing. In this case, the system phase matching function is
Figure BDA0001900793160000064
After the processing, the target motion is finally converted into a constant-speed turntable model. At the moment, a good radar image can be obtained by utilizing a conventional distance-direction two-dimensional Doppler algorithm.
In summary, the terahertz high-speed target radar imaging method provided by the invention comprises the following processes:
step 1, rotation parameter estimation based on narrow-band mode radar measurement and data storage:
the radar adopts a multi-channel wide-narrow-band linear frequency modulation signal combined deskew processing mode to detect and image the target at high resolution.
Step 1.1, emitting narrow-band signals to complete the measurement of target motion parameters, namely measuring the motion speed v and the distance R of a target relative to a radarPAnd angle θ information;
step 1.2, according to the data comparison of target distance and angle information and prestored data in a narrow-band working mode, by utilizing the second-order approximation of the formula (3) and the geometric relation shown in the figure 2, the instantaneous angular velocity of the turntable model is calculated
Figure BDA0001900793160000071
And angular acceleration
Figure BDA0001900793160000072
And 1.3, switching to a broadband signal transmitting mode, and determining the imaging duration of the broadband echo signal under different motion conditions based on the narrow-band signal measurement parameters.
Step 2, performing translational compensation on echo signals under different motion conditions:
step 2.1, firstly, carrying out envelope alignment on echoes by using an adjacent correlation method;
and 2.2, carrying out self-focusing based on a multi-feature point comprehensive method.
Step 3, non-uniform turntable model self-adaptive compensation imaging:
step 3.1 selection of the compensation function from the angular rotation speed and the angular acceleration calculated in part 1
Figure BDA0001900793160000073
Step 3.2, the non-uniform turntable model is converted into the uniform turntable mode by utilizing the nonlinear phase compensation, namely the echo signal is finally expressed as
Figure BDA0001900793160000074
Step 3.3 according to formula (6),
Figure BDA0001900793160000075
making distance walk caused by rotation, and then converting the distance walk into a turntable model without distance migration; and then, obtaining a high-resolution radar image by using a range-Doppler algorithm, wherein lambda is the working wavelength of the radar.
While the present invention has been described in detail with reference to the preferred embodiments, it should be understood that the above description should not be taken as limiting the invention. Various modifications and alterations to this invention will become apparent to those skilled in the art upon reading the foregoing description. Accordingly, the scope of the invention should be determined from the following claims.

Claims (3)

1. A terahertz high-speed target radar imaging method is characterized by comprising the following processes:
step 1, estimating rotation parameters based on narrow-band mode radar measurement and data storage;
step 2, performing translational compensation on echo signals under different motion conditions;
step 3, self-adaptive compensation imaging of the non-uniform turntable model;
step 1 further comprises the following process:
step 1.1, emitting narrow-band signals to complete the measurement of target motion parameters and obtain the motion speed v and the distance R of a measured target relative to a radarPAnd angle θ information;
step 1.2, according to the comparison of target distance and angle information in a narrow-band working mode and data of prestored numbers, utilizing the second order approximation of the following formula and a geometric motion model of a moving target,
Figure FDA0002609734680000011
calculating instantaneous angular velocity of rotary table model
Figure FDA0002609734680000012
And angular acceleration
Figure FDA0002609734680000013
Wherein, Delta theta (t)m) Representing the rotation angle of the target relative to the radar sight line in the synthetic aperture time, theta' representing the included angle between the radar axial direction and the connecting line of the target and the radar, HpRepresenting the target-to-radar axial distance; t is tmIs a slow time;
and 1.3, switching to a broadband signal transmitting mode, and determining the imaging duration of the broadband echo signal under different motion conditions based on the narrow-band signal measurement parameters.
2. The terahertz high-speed target radar imaging method of claim 1,
step 2 further comprises the following processes:
step 2.1, carrying out envelope alignment on the echoes by using an adjacent correlation method;
and 2.2, carrying out self-focusing based on a multi-feature point comprehensive method.
3. The terahertz high-speed target radar imaging method as claimed in claim 2,
step 3 further comprises the following processes:
step 3.1 selecting a compensation function from the angular velocities and angular accelerations calculated in step 1
Figure FDA0002609734680000021
Wherein the Doppler frequency is adjusted
Figure FDA0002609734680000022
Step 3.2, the non-uniform turntable model is converted into the uniform turntable mode by utilizing the nonlinear phase compensation, namely the echo signal is finally expressed as
Figure FDA0002609734680000023
Wherein gamma is the linear frequency modulation of the signal,
Figure FDA0002609734680000024
for a fast time, fcFor the radar operating frequency, xPRepresenting the abscissa of the object in the imaging plane;
step 3.3 Doppler center from Point target echo
Figure FDA0002609734680000025
Making distance walk caused by rotation, and then converting the distance walk into a turntable model without distance migration; and then, obtaining a high-resolution radar image by using a range-Doppler algorithm, wherein lambda is the working wavelength of the radar.
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CN110501706B (en) * 2019-08-20 2020-03-24 中国人民解放军国防科技大学 ISAR (inverse synthetic aperture radar) imaging method for large-angle non-uniform rotation space target
CN112578382B (en) * 2020-11-13 2023-10-31 中国科学院国家空间科学中心 Echo Doppler frequency focusing method for three-dimensional rotating target
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