CN111273290B - Three-dimensional SAR imaging method based on pre-imaging curve track - Google Patents
Three-dimensional SAR imaging method based on pre-imaging curve track Download PDFInfo
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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
- G01S13/904—SAR modes
- G01S13/9089—SAR having an irregular aperture
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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
- G01S13/9004—SAR image acquisition techniques
- G01S13/9011—SAR image acquisition techniques with frequency domain processing of the SAR signals in azimuth
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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
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/28—Details of pulse systems
- G01S7/285—Receivers
- G01S7/292—Extracting wanted echo-signals
- G01S7/2923—Extracting wanted echo-signals based on data belonging to a number of consecutive radar periods
Abstract
The invention discloses a three-dimensional SAR imaging method based on pre-imaging curve tracks, which comprises the following steps: (1) performing range-direction pulse compression on the full-aperture echo signal; (2) obtaining a distance time domain signal after the sub-aperture pulse; (3) performing two-dimensional imaging on the azimuth section with the height of 0; (4) acquiring prior directions of all targets; (5) Performing two-dimensional imaging on a distance height section with the direction as a priori direction; and (6) sorting the two-dimensional images. The invention carries out two-dimensional imaging on the full-aperture echo of the curve track by using the prior azimuth tangent plane to the prior information of all target point azimuths obtained by the two-dimensional imaging of the sub-apertures of the approximate straight line, thereby realizing the three-dimensional SAR imaging.
Description
Technical Field
The invention belongs to the technical field of communication, and further relates to a Synthetic Aperture Radar (SAR) imaging method for pre-imaging curve tracks in the technical field of radars. The method can be used for the airborne synthetic aperture radar to realize three-dimensional synthetic aperture radar SAR image imaging not only on an air scene but also on a ground scene.
Background
The traditional SAR imaging result can only obtain a two-dimensional image, and for scenes with steep terrain transformation and complex environment, the two-dimensional imaging cannot obtain the elevation resolution. In the occasions of military reconnaissance, disaster prediction, three-dimensional environment construction and the like, three-dimensional SAR image imaging is required to be adopted to restore the three-dimensional scene graph of the observation target. The three-dimensional SAR image imaging expands the SAR image imaging application range, and at present, the existing three-dimensional SAR image imaging technologies mainly comprise the following two technologies.
The first method, three-dimensional SAR image imaging using super-resolution sparse reconstruction tomography
A patent application 'maneuvering trajectory front-side view synthetic aperture radar tomography method' (application number 201910412177.5 application publication number CN 110146884A) proposed by the university of sienna electronic technology discloses a three-dimensional SAR imaging method based on super-resolution sparse reconstruction chromatography, which is realized in the technical field of engineering. According to the method, the aperture is divided into sub-apertures in three-dimensional imaging, distance and azimuth two-dimensional imaging is carried out on each sub-aperture, and then super-resolution sparse reconstruction is carried out on a two-dimensional imaging result along a plurality of basic lines of chromatography directions by adopting a compressed sensing method, so that a three-dimensional tomography result is obtained. Although the method can obtain the three-dimensional imaging result of the surveying and mapping area, the method still has the defects that the three-dimensional tomography is obtained by performing super-resolution sparse reconstruction on the two-dimensional imaging delay tomography of all the sub-apertures to a plurality of baselines, and at least dozens of baselines are needed when performing super-resolution sparse reconstruction, so that the data volume and the operation volume are large, but the three-dimensional SAR imaging result can be obtained by a carrier machine in actual engineering by performing one baseline, and the method cannot obtain the three-dimensional SAR imaging result in real time in the actual engineering.
Second, three-dimensional SAR image imaging using equidistant multi-baseline tomography
Wangceng proposes a three-dimensional SAR image imaging method of equidistant multi-baseline tomography in a published paper of "satellite-borne multi-baseline SAR imaging and moving target parameter estimation" (2018, haerbin Industrial university, doctor paper). According to the method, distance and direction two-dimensional imaging is carried out on a base line at equal intervals from low to high, then a compressed sensing method is adopted for a two-dimensional imaging result, sparse reconstruction is carried out along the height direction to obtain target height direction information, and three-dimensional image imaging is completed. Although the method can obtain the three-dimensional imaging result of the surveying and mapping area, the method still has the defects that the three-dimensional imaging is obtained on the basis of two-dimensional imaging and sparse reconstruction from the height to the equidistant base line, the carrier often shakes while moving in the actual engineering, the height of the base line is originally unchanged, the distance between the base lines is difficult to be equal along with the change of the height of the shaking base line of the carrier from top to bottom, and the three-dimensional imaging result of the method is different from the actual imaging result when distance and direction two-dimensional imaging is carried out on the equidistant base line from low to high.
Disclosure of Invention
The invention aims to provide a three-dimensional SAR imaging method based on a pre-imaging curve track aiming at the defects of the prior art, which is used for solving the problems that the space between a three-dimensional SAR imaging result obtained in real time in the actual engineering and a base line is difficult to be equal and the three-dimensional imaging result is different from the actual imaging result due to the fact that at least dozens of base lines are needed when super-resolution sparse reconstruction is carried out, and the data amount and the calculation amount are large.
The idea for realizing the purpose of the invention is to obtain the azimuth prior information of the three-dimensional imaging area by utilizing the characteristics that the target information of the three-dimensional imaging area cannot be lost and the azimuth aggregation is accurate when the two-dimensional imaging is carried out by using the approximate straight line of the sub-aperture; and then, by utilizing the characteristic that the curve track SAR has synthetic aperture in the height direction, according to azimuth prior information fed back by azimuth pre-imaging, two-dimensional imaging is carried out on the curve track full-aperture echo data on a selected azimuth section to obtain distance and height information of a target in the azimuth section, so that a three-dimensional SAR imaging result can be obtained by a carrier by making a base line, and the data amount calculation amount is small.
The method comprises the following specific implementation steps:
carrying out Fourier transform on a full-aperture echo signal of a curve track received by an SAR image imaging system in real time to obtain a range frequency domain echo signal;
performing range pulse compression on the range frequency domain echo signal by using a range pulse compression function to obtain a range frequency domain echo signal after pulse compression;
carrying out inverse Fourier transform on the pulse-compressed range frequency domain echo signal to obtain a full-aperture pulse-compressed range time domain signal;
step 2, obtaining a distance time domain signal after sub-aperture pulse compression:
intercepting the azimuth time in the distance time domain signal after full aperture pulse compression as
The signal of (a) is used as a distance time domain signal after sub-aperture pulse compression, T represents the running time of the SAR image imaging system, and the value range of a is (3, 5);
step 3, performing coherent superposition on the distance azimuth section with the height of 0 of the distance time domain signal after the sub-aperture pulse compression by using the following formula to obtain a two-dimensional image;
wherein, σ (x) i ,y i ) Representing that the target distance in the three-dimensional SAR imaging region obtained by coherent superposition of the range and azimuth section with the height of 0 is x i Orientation y i Two-dimensional image of object, [ integral ] dt 1 Representing the time t of the intercepted azimuth 1 Performing an integration operation, t 1 Has a value range of (0, T/a), s 3 (τ,t 1 ) Representing a distance time domain of tau and a bit time after truncation of t 1 After the sub-aperture pulse compression, the range of tau is
r o Representing the slant distance of a target central point in a three-dimensional SAR image imaging region, c representing the light speed, k representing the number of sampling points of an SAR image imaging system, B representing the bandwidth of the SAR image imaging system, exp (DEG) representing the exponential operation with a natural constant e as the base, j representing an imaginary unit symbol, pi representing the circumference ratio, and lambda representing the wavelength of the SAR image imaging system，R(t,x i ,y i ) The distance between the SAR image imaging system at the t moment and the three-dimensional SAR imaging area is x i Orientation y i The slant range of the target;
step 4, obtaining the prior directions of all targets:
extracting all maximum values from the two-dimensional image, wherein pixel points of each maximum value comprise distance information and azimuth information, and forming the azimuths of all the maximum value pixel points into a priori azimuth set;
wherein, σ (x) k ,y j ,z k ) Representing a pair orientation of y j After the distance elevation tangent planes are subjected to coherent superposition, the distance in the obtained three-dimensional SAR imaging area is x k Height of z k The two-dimensional image of the object,. Integral (·) dt represents the integral operation performed on the azimuthal time t, the value range of t being (0, t), s 3 (tau, t) represents a distance time domain signal after full-aperture pulse compression with the distance time domain tau and the azimuth time t, and the value range of tau is
R(t,x k ,y j ,z k ) The distance between the SAR image imaging system at the t moment and the three-dimensional SAR imaging area is x k Y in azimuth j Height of z k The slope distance of the target;
step 6, ordering the two-dimensional images:
and sequencing the two-dimensional images of the target according to the sequence of the prior azimuth set to obtain a three-dimensional image of the target in the three-dimensional SAR imaging area.
Compared with the prior art, the invention has the following advantages:
firstly, the invention carries out two-dimensional pre-imaging on the distance time domain signal after the sub-aperture pulse compression in the distance azimuth section with the height of 0 to obtain the prior azimuth of all targets, thereby overcoming the problems that the data volume and the operation volume of the three-dimensional SAR image imaging method adopting the super-resolution sparse reconstruction chromatography in the prior art are larger and the three-dimensional SAR imaging result can not be obtained in real time in the actual engineering, and leading the invention to have the advantages of smaller data volume and operation volume and being capable of obtaining the three-dimensional SAR imaging result in real time in the actual engineering.
Secondly, because the invention carries out two-dimensional imaging on the distance time domain signal after full aperture pulse compression in each azimuth section of the prior azimuth set, and obtains the three-dimensional image of the target of the three-dimensional SAR imaging region after sequencing the two-dimensional image, the invention overcomes the problem that the distance between baselines is difficult to reach the equality in the three-dimensional SAR image imaging method adopting equidistant multi-baseline chromatography in the prior art, so that the difference between the three-dimensional imaging result and the actual imaging result is caused, and the invention has the advantage that the three-dimensional imaging result is consistent with the actual imaging result.
Description of the drawings:
FIG. 1 is a flow chart of the present invention;
FIG. 2 is a plot of a stationing scene used in a simulation test of the present invention;
FIG. 3 is a graph of the results of distance-height dimension imaging of targets at different orientations of the simulation test of the present invention, wherein FIG. 3 (a) shows the results of imaging of targets at all orientations of-20; FIG. 3 (b) is a graph showing the imaging results of all targets with 0 orientation; FIG. 3 (c) shows a graph of the results of imaging all targets at orientation 20;
FIG. 4 is a sectional view of the distance and height of the imaging result of the center point target in the simulation test of the present invention, wherein FIG. 4 (a) shows a sectional view of the distance of the imaging result of the center point target; fig. 4 (b) is a height sectional view showing the imaging result of the center point target.
The specific implementation mode is as follows:
the invention is further described below with reference to the accompanying drawings.
Referring to fig. 1, the specific implementation steps of the present invention are as follows:
And carrying out Fourier transformation on the full-aperture echo signal of the curve track received by the SAR image imaging system in real time to obtain a range frequency domain echo signal.
The Fourier transform of the full-aperture echo signal of the curve track received by the SAR image imaging system in real time is completed by the following formula:
s 1 (f,t)＝∫s 0 (τ,t)exp(-j2πfτ)dτ
wherein s is 1 (f, t) represents a range frequency domain echo signal with a range frequency domain f and an azimuth time t, wherein the range of f is
f s The sampling frequency of the SAR image imaging system is represented, the value range of T is (0, T), T represents the running time of the SAR image imaging system, d tau represents the integral operation of a distance time domain tau, and tau has the value range of
r o Representing the slant range of a target central point in a three-dimensional SAR image imaging area, c representing the light speed, k representing the number of sampling points of an SAR image imaging system, B representing the bandwidth of the SAR image imaging system, s 0 (τ, t) represents the sub-aperture echo signal with distance time domain τ and azimuth time t, exp (·) represents exponential operation with natural constant e as base, j represents imaginary unit sign, and π represents circumferential ratio.
And performing range pulse pressure on the range frequency domain echo signal by using a range pulse pressure function to obtain a range frequency domain echo signal after pulse pressure.
The distance pulse pressure function is as follows:
wherein s is 2 (K, t) represents the pulse pressure back distance frequency domain echo signal with the distance frequency domain of K and the azimuth time of t, and the value range of K is
Gamma denotes the range modulation frequency of the SAR image imaging system emission signal.
And performing inverse Fourier transform on the pulse-compressed range frequency domain echo signal to obtain a full-aperture pulse-compressed range time domain signal.
The inverse Fourier transform is performed using the following equation:
s 3 (τ,t)＝∫s 2 (K,t)exp(j2πKτ)dK
wherein s is 3 (τ 1 T) represents a distance time domain signal after full aperture pulse compression with a distance time domain tau and an azimuth time t, wherein the value range of tau is
Je (·) dK represents an integration operation performed on the distance frequency domain K.
And 2, acquiring a distance time domain signal after sub-aperture pulse compression.
Intercepting the azimuth time in the distance time domain signal after full aperture pulse compression as
The value range of a is (3, 5) as the distance time domain signal after the sub-aperture pulse compression.
Step 3, performing coherent superposition on the distance azimuth section with the height of 0 of the distance time domain signal after the sub-aperture pulse compression by using the following formula to obtain a two-dimensional image:
wherein, σ (x) i ,y i ) Representing that the target distance in the three-dimensional SAR imaging region obtained by coherent superposition of the range and azimuth section with the height of 0 is x i Orientation y i Two-dimensional image of object, [ integral ] dt 1 Representing the time t of the intercepted azimuth 1 Performing an integration operation, t 1 Has a value range of (0, T/a), s 3 (τ,t 1 ) Representing the distance time domain as tau and the bit time after interceptionIs t 1 After the sub-aperture pulse compression, the range of tau is
λ represents the wavelength of the SAR image imaging system, R (t, x) i ,y i ) The distance between the SAR image imaging system at the t moment and the three-dimensional SAR imaging area is x i Y in azimuth i The slope of the target.
And 4, acquiring the prior directions of all targets.
And extracting all maximum values from the two-dimensional image, wherein the pixel point of each maximum value contains distance information and azimuth information, and forming a priori azimuth set by the azimuths of all the maximum value pixel points.
wherein, σ (x) k ,y j ,z k ) Representing a pair of orientations y j After the distance elevation tangent planes are coherently superposed, the distance in the obtained three-dimensional SAR imaging area is x k Height of z k The two-dimensional image of the object,. Integral & (·) dt represents the integration operation over an azimuthal time t, R (t, x) k ,y j ,z k ) The distance between the SAR image imaging system at the t moment and the three-dimensional SAR imaging area is x k Orientation y j Height of z k The slope of the target.
And 6, sequencing the two-dimensional images.
And sequencing the two-dimensional images of the target according to the sequence of the prior azimuth set to obtain a three-dimensional image of the target in the three-dimensional SAR imaging area.
The effect of the present invention is further explained by combining the simulation experiment as follows:
1. simulation experiment conditions are as follows:
the hardware platform of the simulation experiment of the invention is as follows: the processor is an Intel i7 5930k CPU, the main frequency is 3.5GHz, and the memory is 16GB.
The software platform of the simulation experiment of the invention is as follows: windows 10 operating system and Matlab 7.0.
The system parameter settings simulated by the present invention are shown in the following table.
| System parameter | Numerical value | System parameter | Numerical value |
| Bandwidth/Hz | 150e6 | Pulse repetition event/s | 2e-6 |
| Reference point slope distance/m | 16e3 | Carrier frequency/Hz | 10e9 |
| Oblique angle/ |
0 | Azimuthal repetition frequency/Hz | 2000 |
| Speed vector/m/s of carrier | (0,100,-100) | Airborne acceleration vector/m/s 2 | (0,0,-30) |
2. Simulation content and result analysis thereof:
the simulation experiment of the invention is to simulate the stationing scene in fig. 2 by adopting the method of the invention, and the obtained simulation result is shown in fig. 3. The X axis in FIG. 2 represents the azimuth direction, the Y axis represents the distance direction, the Z axis represents the altitude direction, the circles in FIG. 2 represent 9 point targets in the stationing scene, the circle indicated by the arrow in FIG. 2 is the target at the center, and other point targets are distributed at the edges of the stationing scene and are located at the positions of +20km and-20 km in the azimuth dimension and +8km and-8 km in the azimuth dimension.
The effect of the present invention will be further described with reference to the simulation diagram.
Fig. 3 shows the distance height dimension imaging results of targets at different azimuths, fig. 3 (a) shows three target imaging result graphs with an azimuth of-20, the abscissa shows the number of distance-direction sampling points, and the ordinate shows the number of azimuth-direction sampling points, fig. 3 (b) shows three target imaging result graphs with an azimuth of 0, the abscissa shows the number of distance-direction sampling points, and the ordinate shows the number of azimuth-direction sampling points, fig. 3 (c) shows three target imaging result graphs with an azimuth of-20, the abscissa shows the number of distance-direction sampling points, and the ordinate shows the number of azimuth-direction sampling points. As can be seen from fig. 3 (a), 3 (b) and 3 (c), the side lobes are regular, and the main side lobes are obviously separated, and both present a good cross shape, which indicates that the imaging result of the present invention has a good focusing effect.
Fig. 4 is a sectional view of the imaging result distance and height of the target at the center of the present invention, wherein fig. 4 (a) is a sectional view of the imaging result distance of the target at the center, the abscissa represents the number of sampling points in the distance direction, and the ordinate represents the normalized amplitude in dB, fig. 4 (b) is a sectional view of the imaging result height of the target at the center, the abscissa represents the number of sampling points in the height direction, and the ordinate represents the normalized amplitude in dB. As can be seen from the graphs in FIGS. 4 (a) and 4 (b), the main lobe and the side lobe of the imaging result of the target at the center can be obviously separated, the side lobe is low enough, the peak-to-side lobe ratio of the graph in FIG. 4 (a) is-13.68 dB, the peak-to-side lobe ratio of the graph in FIG. 4 (b) is-12.88 dB, the pulse pressure result is good, and the imaging performance index meets the imaging requirement. Therefore, the three-dimensional SAR imaging method can realize three-dimensional SAR imaging.
Claims (4)
1. A three-dimensional SAR imaging method based on pre-imaging curve tracks is characterized in that two-dimensional pre-imaging is carried out on distance direction tangent planes with the height of 0 on sub-aperture pulse compressed distance time domain signals to obtain prior directions of all targets, two-dimensional imaging is carried out on each direction tangent plane of a full-aperture pulse compressed distance time domain signal in a prior direction set, and three-dimensional images of three-dimensional SAR imaging area targets are obtained after the two-dimensional images are sequenced; the method comprises the following specific steps:
step 1, performing range direction pulse compression on the full aperture echo signal:
carrying out Fourier transform on a full-aperture echo signal of a curve track received by an SAR image imaging system in real time to obtain a range frequency domain echo signal;
performing range pulse compression on the range frequency domain echo signal by using a range pulse compression function to obtain a range frequency domain echo signal after pulse compression;
carrying out inverse Fourier transform on the pulse-compressed range frequency domain echo signal to obtain a full-aperture pulse-compressed range time domain signal;
step 2, obtaining a distance time domain signal after sub-aperture pulse compression:
intercepting the azimuth time in the distance time domain signal after full aperture pulse compression as
The signal of (a) is used as a distance time domain signal after sub-aperture pulse compression, T represents the running time of the SAR image imaging system, and the value range of a is (3, 5);
step 3, performing coherent superposition on the distance azimuth section with the height of 0 of the distance time domain signal after the sub-aperture pulse compression by using the following formula to obtain a two-dimensional image;
wherein, σ (x) i ,y i ) Representing that the target distance in the three-dimensional SAR imaging region obtained by coherent superposition of the range and azimuth section with the height of 0 is x i Orientation y i Two-dimensional image of object, [ integral ] dt 1 Representing the time t of the intercepted azimuth 1 Performing an integration operation, t 1 Has a value range of (0, T/a), s 3 (τ,t 1 ) Representing the distance time domain as tau and the truncated azimuth time as t 1 After the sub-aperture pulse compression, the range of tau is
r o Representing the slant distance of a target central point in a three-dimensional SAR image imaging area, c representing the light speed, k representing the number of sampling points of the SAR image imaging system, B representing the bandwidth of the SAR image imaging system, exp (DEG) representing the exponential operation with a natural constant e as the base, j representing an imaginary unit symbol, pi representing the circumference ratio, lambda representing the wavelength of the SAR image imaging system, R (t, x) i ,y i ) The distance between the SAR image imaging system at the t moment and the three-dimensional SAR imaging area is x i Y in azimuth i The slope distance of the target;
step 4, obtaining the prior directions of all targets:
extracting all maximum values from the two-dimensional image, wherein pixel points of each maximum value comprise distance information and azimuth information, and forming the azimuths of all the maximum value pixel points into a priori azimuth set;
step 5, performing coherent superposition on each azimuth section of the distance time domain signal in the prior-inspection azimuth group after full-aperture pulse compression by using the following formula to obtain a two-dimensional image of the target:
wherein, σ (x) k ,y j ,z k ) Representing a pair orientation of y j Distance height section ofAfter coherent superposition, the distance in the obtained three-dimensional SAR imaging area is x k Height of z k The two-dimensional image of the object,. Integral & (·) dt represents the integral operation on the orientation time t, the value range of t is (0, T), s 3 (tau, t) represents a distance time domain signal after full-aperture pulse compression with distance time domain tau and azimuth time t, and the value range of tau is
R(t,x k ,y j ,z k ) The distance between the SAR image imaging system at the t moment and the three-dimensional SAR imaging area is x k Y in azimuth j Height of z k The slope distance of the target;
step 6, ordering the two-dimensional images:
and sequencing the two-dimensional images of the target according to the sequence of the prior azimuth set to obtain a three-dimensional image of the target in the three-dimensional SAR imaging area.
2. The pre-imaging curve trajectory based three-dimensional SAR imaging method according to claim 1, characterized in that: the step 1 of performing fourier transform on the full-aperture echo signal of the curved track received by the SAR image imaging system in real time is completed by using the following formula:
s 1 (f,t)＝∫s 0 (τ,t)exp(-j2πfτ)dτ
wherein s is 1 (f, t) represents a range frequency domain echo signal with a range frequency domain f and an azimuth time t, wherein the range of f is
f s Represents the sampling frequency of the SAR image imaging system, and the integral operation is carried out on a distance time domain tau by integral (integral) d tau with the value range of tau
s 0 (τ, t) represents the sub-aperture echo signal at the range time domain τ and the azimuth time t.
3. The pre-imaging curve trajectory based three-dimensional SAR imaging method according to claim 2, characterized in that: the distance pulse pressure function described in step 1 is as follows:
wherein s is 2 (K, t) represents the pulse pressure back distance frequency domain echo signal with the distance frequency domain of K and the azimuth time of t, and the value range of K is
Gamma denotes the range modulation frequency of the SAR image imaging system emission signal.
4. The pre-imaging curve trajectory based three-dimensional SAR imaging method according to claim 3, characterized in that: the inverse fourier transform described in step 1 is performed using the following equation:
s 3 (τ,t)＝∫s 2 (K,t)exp(j2πKτ)dK
wherein s is 3 (τ, t) represents the distance time domain signal after full aperture pulse compression with distance time domain τ and azimuth time t, and — (dK) represents the integration operation on the distance frequency domain K.
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