CN114609628A - Long-synthetic-aperture-time sea surface moving object imaging processing method - Google Patents

Long-synthetic-aperture-time sea surface moving object imaging processing method Download PDF

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CN114609628A
CN114609628A CN202111438748.6A CN202111438748A CN114609628A CN 114609628 A CN114609628 A CN 114609628A CN 202111438748 A CN202111438748 A CN 202111438748A CN 114609628 A CN114609628 A CN 114609628A
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target
equivalent
shaking
total equivalent
motion
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丁泽刚
张天意
高永澎
龙腾
曾涛
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Beijing Institute of Technology BIT
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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
    • G01S13/9041—Squint mode
    • 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
    • G01S13/9052—Spotlight mode
    • 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
    • G01S7/41—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
    • G01S7/415—Identification of targets based on measurements of movement associated with the target

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  • Radar, Positioning & Navigation (AREA)
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  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Radar Systems Or Details Thereof (AREA)

Abstract

The invention discloses a long-synthetic aperture time sea surface moving target imaging processing method, which can quickly judge the sea condition, and adopts algorithms based on different imaging systems aiming at targets under different sea conditions and different moving states to realize refocusing of the targets and obtain fine imaging results of the targets; the target two-dimensional imaging result under the long synthetic aperture time can be obtained, and the target high-resolution image under the long synthetic aperture time is obtained.

Description

Long-synthetic-aperture-time sea surface moving object imaging processing method
Technical Field
The invention relates to a long synthetic aperture time sea surface moving target imaging processing method, and belongs to the technical field of synthetic aperture radars.
Background
The radar imaging technology of sea surface moving targets is an important branch of the synthetic aperture radar imaging technology. The traditional sea surface moving target imaging technology can be divided into the imaging technology based on the traditional SAR system and the imaging technology based on the ISAR system according to different systems.
The sea surface moving target imaging technology based on the SAR system is essentially that a moving target echo and a static target echo are divided according to the echo characteristics or the image characteristics difference between the moving target and the static target, and various Doppler parameters or a motion parameter estimation method is utilized to realize the fine imaging of the moving target on the basis. The method has good performance under the conditions of low sea state and stable target motion, and can obtain an image with good two-dimensional focusing of the target; however, under the constraints of high sea conditions and long synthetic aperture time, because the self-shaking is obvious, the motion states of all scattering units on the target are different, and at the moment, the method based on the SAR imaging system cannot compensate the inconsistent motion parts among all scattering units caused by the shaking of the target, and finally the SAR image of the target is defocused.
The moving target imaging technology based on the ISAR system is to perform translation compensation on a target, remove a uniform motion (translation of the target) part among scattering units, and then utilize non-uniform motion caused by shaking of the target by specific means such as: and realizing ISAR imaging of the target by means of imaging time window selection, time-frequency analysis, parameter estimation and the like. The imaging technology based on the ISAR system has good performance under the conditions of high sea condition and obvious target shaking; although the imaging method of the ISAR system is not limited by long synthetic aperture time, when the sea state is low and the target is in a stable motion state, the ISAR system fails at this time because non-uniform motion components do not exist among the scattering units, and a two-dimensional high-resolution image of the target cannot be obtained.
In summary, there is no effective imaging method for different sea conditions and different target motion states in a long synthetic aperture time.
Disclosure of Invention
In view of this, the invention provides a long synthetic aperture time sea surface moving object imaging processing method, which can select imaging technologies of corresponding systems under different sea conditions and different object moving states.
A long synthetic aperture time sea surface moving target imaging processing method regards echo signals as a result of superposition of echoes of a plurality of scattering points, analyzes equivalent speed and equivalent acceleration of the echo signals, and judges whether equivalent speed errors and equivalent acceleration errors caused by target shaking due to sea conditions exist or not; when the error caused by target shaking does not exist, the method considers that the method is suitable for low sea state imaging processing; when there is an error caused by the target shake, it is considered that the selection is suitable for the high sea state imaging process.
Preferably, the specific method for analyzing the equivalent velocity and the equivalent acceleration of the echo signal and determining whether the error caused by the target shaking exists is as follows:
performing Taylor series expansion on echo signals subjected to pulse compression at any scattering point under the constraint of sub-aperture, and estimating by adopting a target motion parameter estimation algorithm to obtain the total equivalent velocity and the total equivalent acceleration of the scattering point; wherein, the total equivalent speed is equal to the sum of the equivalent speed caused by the self motion of the target and the radar platform and the equivalent speed caused by the shaking of the target; the total equivalent acceleration is equal to the sum of equivalent acceleration caused by the target and the radar platform self-motion and equivalent acceleration caused by target shaking; if the total equivalent speeds obtained by the scattering points are the same and the total equivalent accelerations obtained by the scattering points are also the same, the error caused by target shaking does not exist; if the total equivalent speeds obtained by the scattering points are different and the total equivalent accelerations obtained by the scattering points are also different, an error caused by target shaking exists.
Preferably, the method for obtaining the total equivalent speed and the total equivalent acceleration comprises the following steps:
and performing Taylor series expansion on echo signals subjected to pulse compression at any scattering point under the constraint of sub-apertures, performing motion parameter estimation by using generalized radon-Fourier transform as an estimation means of motion parameters, and after the motion parameter estimation of the target is realized, detecting by using a constant false alarm rate to obtain the number of the scattering points of the target and the total equivalent speed and the total equivalent acceleration of each scattering point.
Preferably, when there is no error caused by target shaking, selecting SAR imaging technology; when there is an error caused by the shaking of the target, the ISAR imaging technique is selected.
Preferably, when satisfied
Figure BDA0003379188990000031
Judging that the total equivalent speeds obtained by all scattering points are the same, and judging that the total equivalent accelerations obtained by all scattering points are the same;
wherein
Figure BDA0003379188990000032
And
Figure BDA0003379188990000033
are each vSiAnd aSiDifference between maximum and minimum, vSiIs the total equivalent velocity of the ith scattering point, aSiTotal equivalent acceleration of the ith scattering point, TobIs the sub-aperture time length, λ is the system wavelength, fsIs the system sampling rate and c is the speed of light.
Advantageous effects
The invention can quickly judge the sea state condition, and adopts algorithms based on different imaging systems aiming at targets under different sea states and different motion states to realize the refocusing of the targets and obtain the fine imaging result of the targets; the target two-dimensional imaging result under the long synthetic aperture time can be obtained, and the target high-resolution image under the long synthetic aperture time is obtained.
Drawings
FIG. 1 is a diagram of radar imaging geometric model of sea surface moving object
FIG. 2 is a schematic diagram of ISAR imaging geometric model of sea surface moving target
FIG. 3 shows the results of compressing the range-wise pulse of three point targets in the translational motion state
FIG. 4 shows the distance direction pulse compression results of three point targets in the shaking motion state
Fig. 5(a) -5 (f) GRFT results of three point targets in translational motion, where fig. 5(a) is a range-velocity plane projection; FIG. 5(b) distance-acceleration plane projection; FIG. 5(c) velocity-acceleration planar projection; FIG. 5(d) distance plane projection; FIG. 5(e) velocity plane projection; FIG. 5(f) acceleration plane projection
FIG. 6(a) -FIG. 6(f) shows GRFT results of three point targets under shaking motion, wherein FIG. 6(a) is a distance-velocity plane projection, FIG. 6(b) is a distance-acceleration plane projection, FIG. 6(c) is a velocity-acceleration plane projection, FIG. 6(d) is a distance plane projection, FIG. 6(e) is a velocity plane projection, and FIG. 6(f) is an acceleration plane projection
FIG. 7 shows CFAR detection results of three point targets in the translational motion state
FIG. 8 shows CFAR detection results of three point targets in a shaking motion state
FIG. 9 imaging results of three point targets in translational motion
FIG. 10 imaging results of three point targets under shaking motion
FIG. 11(a) to FIG. 11(c) are schematic diagrams showing a simulation target model, in which FIG. 11(a) is a three-dimensional model, FIG. 11(b) is a plan view, and FIG. 11(c) is a side view
FIG. 12 results of pulse compression in the target distance direction in the translational motion state
FIG. 13(a) -FIG. 13(f) results of GRFT of a simulated target under translational motion, wherein FIG. 13(a) is a range-velocity plane projection, FIG. 13(b) is a range-acceleration plane projection, FIG. 13(c) is a velocity-acceleration plane projection, FIG. 13(d) is a range plane projection, FIG. 13(e) is a velocity plane projection, and FIG. 13(f) is an acceleration plane projection
FIG. 14 SAR imaging results of a simulation target under translational motion
FIG. 15 shows the target distance direction pulse compression results in the shaking motion state
FIG. 16(a) -FIG. 16(f) GRFT results for simulated targets under shaking motion, where FIG. 16(a) is distance-velocity plane projection, FIG. 16(b) is distance-acceleration plane projection, FIG. 16(c) is velocity-acceleration plane projection, FIG. 16(d) is distance plane projection, FIG. 16(e) is velocity plane projection, and FIG. 16(f) is acceleration plane projection
FIG. 17 ISAR imaging results of simulation target under shaking motion
FIG. 18 is a flow chart of the present invention.
Detailed Description
The following description of embodiments of the method of the present invention is given with reference to the accompanying drawings and examples.
The idea of the invention is that as shown in fig. 18, by analyzing the equivalent motion parameters of the echo signals, the equivalent motion parameters can be divided into two parts, namely a part caused by the motion of the target and the radar itself and a part caused by the sea state; when the sea state is poor (i.e., high sea state), there is a portion caused by the sea state since the wave motion of the sea surface necessarily affects the movement of the object. When the sea state is good (i.e. low sea state), the fluctuation of the sea surface is small, and the part caused by the sea state is negligible. The specific analysis process is as follows:
suppose the slant distance course R between the ith scattering point and the radar on the moving targeti(t) the expression is:
Ri(t)≈R0i+RT(t)+ri(t) (1)
when only translation of the target exists (low sea state), the slope distance course of the target can be obtained by combining the following formula with the attached figure 1:
Figure BDA0003379188990000051
wherein t is the azimuth time of the radar echo,
Figure BDA0003379188990000052
Figure BDA0003379188990000053
(xp,0,zp) And (x)0i,y0i,z0i) The coordinates of the platform and the target in the xyz coordinate system at time t ═ 0, respectively. Taylor expansion is carried out on the above formula to obtain vTAnd aTThe expression of (a) is as follows:
Figure BDA0003379188990000061
wherein v isTAnd aTFor equivalent velocities and equivalent accelerations, v, caused by the motion of the target and the platform itselfpIs the speed of movement of the platform, vrIs the target radial velocity, vaIs the azimuth velocity of the target. It is worth mentioning that since R0iIs larger and much larger than the moving speed of the platform and the target, so that the moving parameter a of different targets can be consideredTSubstantially consistent.
When there is shaking of the target, v is measured in conjunction with the ISAR imaging geometry shown in FIG. 2RiAnd aRiThe expression of (a) is analyzed. With reference to fig. 2, the slope history caused by shaking can be obtained as follows:
ri(t)＝ρ0icos(θ0+θe(t))＝r0icos(θe(t))+d0isin(θe(t)) (4)
wherein ρ0iIs the distance from the ith scattering point of the target to the shaking center of the target, (r)0i,d0i) Is the coordinate, theta, of the ith scattering point of the target in the ISAR imaging plane0Is the initial angle theta between the line connecting the scattering point to the center of rotation and the R axise(t) is the effective rotation angle of the target, and in a short synthetic aperture time, the target can be considered to be at an angular velocity ω0Rotate at a constant speed and with a small rotation angle
θe(t)＝ω0t (5)
sin(θe)≈ω0t (6)
cos(θe)≈1-0.5(ω0t)2 (7)
Bringing formulas (5) to (7) into formula (4) or
ri(t)≈r0i+ω0d0it-0.5r0i(ω0t)2 (8)
V is obtained from formula (8)RiAnd aRiThe expression of (a) is as follows:
Figure BDA0003379188990000062
comparing the formula (3) with the formula (9), it can be found that when the target only has translation, the slope course between scattering points of the target is consistent, so the motion parameter v of each scattering point is consistentTIs the same, a of each scattering pointTAre the same; when the target shakes, the slope distance histories of all scattering points of the target are inconsistent, and v introduced by different scattering pointsRiAnd aRiAre different from each other. Further, it can be considered that the total velocity v when each scattering point of the object isSi(vSi＝vRi+vT) Substantially the same, and the total acceleration a of each scattering pointSi(aSi＝aRi+aT) When the two are substantially the same, the target can be considered to have only translational motion; v when each scattering point of the objectSiAnd aSiObviously different, the target is considered to have shaking motion.
Based on the conclusion, the existing echo signal is subjected to subaperture interception, the subaperture echo signal is subjected to pulse compression and then subjected to GRFT and CFAR detection, the detection result is analyzed based on the conclusion, and an SAR imaging technology and an ISAR imaging technology are selected according to the analysis result.
To explain the specific implementation method of the present technology in detail, the following will be explained with reference to the computer simulation results of three motion point targets in different motion states:
first, a geometric model and an echo signal model of sea surface moving target radar imaging are introduced. FIG. 1 is a schematic diagram of a radar imaging geometric model of a sea surface moving target, wherein an origin O of an OXYZ coordinate system is a moving target mass center, a Y axis is a radar platform moving direction, a Z axis is perpendicular to a sea level, and an X axis is determined by a right-hand rule. The origin of the OBWZ coordinate system and the OHRV coordinate system is also the moving object centroid. The B-axis and the W-axis represent the length and width of the target, respectively, the R-axis represents the radar line of sight (RLOS) direction, the H-axis belongs to the XOY plane and is perpendicular to the R-axis, the H-axis coincides with the Y-axis in the front side view case, and the V-axis is determined by the right-hand rule. The angle psi is the angle of the ground wiping part
Figure BDA0003379188990000071
Is the included angle between the B axis and the X axis, and G is the plumb line of the radar platform and the seaThe intersection of the planes. Height is the Height of the platform and the moving speed of the platform. v. ofxIs the translational velocity, v, of the object along the X-axisyIs the translational velocity, v, of the object along the Y-axisrThe targeted radial velocity, i.e. vxProjection on the R axis. OmegaR、ωPAnd omegaZThe instantaneous angular velocities of the target wobbling along the three axes B, W, Z, respectively. For a sea surface moving object, since the echo can be regarded as a result of superposition of echoes of a plurality of scattering points, the following analysis takes any scattering point on the sea surface moving object to expand. On the basis of the geometric model, through a series of coordinate transformation, the slope distance process R between the ith scattering point and the radar on the moving target can be obtainedi(t) the expression is:
Ri(t)≈R0i+RT(t)+ri(t) (10)
wherein R is0iDistance of moving object centroid to radar, RT(t) is the slant distance introduced by the motion of the moving target and the radar platform, and is the same for all scattering points on the moving target, ri(t) the skew introduced by the three-dimensional shaking of a sea-wave-driven object, r for different scattering pointsi(t) are different from each other.
On the basis, under the sub-aperture constraint, a second-order slant-range model more suitable for actual imaging processing and an echo signal model after corresponding distance pulse compression are obtained by using Taylor series expansion:
Ri(t)≈R0i+vRit+aRit2+vTt+aTt2＝R0i+vSit+aSit2 (11)
wherein v isSi＝vRi+vT，aSi＝aRi+aT。
According to equation (10), the signal expression of the target distance after pulse compression can be obtained as follows:
Figure BDA0003379188990000081
wherein t isrIs the range time of the SAR signal, t is the azimuth time of the SAR signal, R0iIs the equivalent slope constant, v, of the radar to the ith scattering pointRiAnd aRiFor the equivalent velocity and equivalent acceleration of the i-th scattering point caused by object shaking, vTAnd aTFor equivalent velocity and equivalent acceleration, v, caused by the motion of the target and the platform itselfSiAnd aSiIs the sum of the two types of velocity and acceleration. λ is the system wavelength, M is the number of scattering points constituting the target, Arc＝TpB is the signal gain brought by the distance to the pulse compression, where TpIs the pulse width, B is the signal bandwidth, σiIs the intensity of the ith scattering point. The results of pulse compression in the direction of the distance of three point targets in the translational motion state and the shaking motion state are shown in fig. 3 and fig. 4 respectively.
Before determining the motion state of the target, the motion parameters of each scattering point of the target, namely, R shown in formula (12), are first required0i，vSiAnd aSiAnd (6) estimating. At present, a plurality of mature target motion parameter estimation algorithms exist, generalized radon-fourier transform (GRFT) is taken as a motion parameter estimation means in the patent, and the specific implementation process is not described herein again. The results of parameter estimation of three point targets in translation and shaking by using the GRFT are shown in fig. 5(a) - (f) and fig. 6(a) - (f), and since the estimation result is a 4-dimensional matrix, the maximum value of the target is selected from the distance-velocity plane, the distance-acceleration plane, the velocity-acceleration plane, the distance axis, and the projections of the velocity axis and the acceleration axis to display the GRFT results.
After the motion parameter estimation of the target is realized, the number of scattering points of the target can be obtained by adopting constant false-alarm rate (CFAR) detection
Figure BDA0003379188990000091
And motion parameters of scattering points
Figure BDA0003379188990000092
Figure BDA0003379188990000093
And
Figure BDA0003379188990000094
the CFAR detection results of three point targets in translation and shaking are shown in fig. 7 and 8, and the peak values circled by circles in the two figures are the CFAR detection results.
After the motion parameter estimation of the target is completed, the motion state of the target can be judged. From the former analysis, it can be known that, when the sea state is low and the target is in a translational motion state, the motion parameters of the scattering points of the target are the same except for the constant term distance because the shaking component of the target can be ignored, that is, the v between the scattering points of the targetSiAnd a between the scattering pointsSiThere was no significant difference; when the sea state is high and the target is in shaking motion, the motion parameters of scattering points of the target are different because the target has obvious shaking components, namely v between the scattering points of the target is differentSiAnd a between the scattering pointsSiThere are significant differences. This is the basis for judging the motion state of the target and adopting the corresponding algorithm. The total equivalent velocity obtained by each scattering point is the same, and the total equivalent acceleration obtained by each scattering point is the same, or the following condition is satisfied.
Figure BDA0003379188990000095
In the above formula, the first and second carbon atoms are,
Figure BDA0003379188990000096
Figure BDA0003379188990000097
are each vSiAnd aSiDifference between maximum and minimum, TobIs the sub-aperture time length, λ is the system wavelength, fsIs the system sampling rate and c is the speed of light. As shown in FIG. 7The three point targets have the same motion parameter vSiAnd aSiThe condition shown in the formula (13) is satisfied, so that an SAR imaging algorithm is adopted to complete imaging; v for the three point target for the CFAR detection results shown in FIG. 8SiAnd aSiThe difference is large, and the condition shown in the formula (13) is not satisfied, so that an ISAR imaging algorithm is adopted to complete imaging.
Finally, according to the motion state judgment result, an SAR imaging algorithm is adopted for the three point targets in the translation state, and the processing result is shown in the attached figure 9; the ISAR imaging algorithm is adopted for the three point targets in the shaking state, and the processing result is shown in the attached figure 10. It can be seen that the imaging process results are good.
Example 1
And the target model SAR imaging processing under the translation motion is realized by utilizing computer simulation. The simulation parameters and motion parameters are shown in tables 1 and 2, respectively.
TABLE 1 computer simulation parameters
Figure BDA0003379188990000101
TABLE 2 computer simulation of translational motion parameters
Parameter/unit Numerical value Parameter/unit Numerical value
Platform velocity/(m.s)-1) 150 TargetVelocity/(m.s)-1) 5
Amplitude/deg of rolling movement - Amplitude/deg of pitching motion -
Amplitude/deg of yawing movement - Angular frequency/Hz of rolling movement -
Angular frequency/Hz of pitching motion - Angular frequency of yaw motion/Hz -
Initial phase/deg of rolling movement - Pitching motion initial phase/deg -
Yaw motion onset/deg -
The target model used for the computer simulation is shown in fig. 11(a) - (c).
Firstly, range pulse compression is carried out on the target echo with translational motion. The results of the range-wise pulse compression are shown in fig. 12.
And then selecting a sub-aperture for GRFT of the pulse compression result, wherein the GRFT result is shown in the attached figures 13(a) to 13 (f). Since the GRFT results are now a four-dimensional matrix, for simplicity, the GRFT results are shown in the form of projections of the GRFT at its maximum into three two-dimensional planes (range-velocity, range-acceleration and velocity-acceleration) and three one-dimensional planes (range, velocity and acceleration).
And (3) extracting the motion parameters of the target, judging the motion state of the target by using the condition shown in the formula (13), and finding that the target conforms to the condition shown in the formula (13) and is in a translational motion state.
On the basis, GRFT parameter estimation is carried out on each sub-aperture, SAR imaging processing is carried out by using the fused target motion parameters, and the target imaging result based on translational motion is obtained as shown in figure 14. Obviously, the focusing effect is good.
Example 2
And the ISAR imaging processing of the target model under the shaking motion is realized by utilizing computer simulation. The simulation parameters and motion parameters are shown in tables 1 and 3, respectively.
TABLE 3 computer simulation shaking motion parameters
Figure BDA0003379188990000111
Figure BDA0003379188990000121
Similar to example 1, the target model used in the computer simulation is shown in FIGS. 11(a) to (c).
First, range pulse compression is performed on a target echo in a shaking motion. The results of the range-wise pulse compression are shown in fig. 15.
And then selecting a sub-aperture for GRFT of the pulse compression result, wherein the GRFT result is shown in the attached figures 16(a) to 16 (f). The drawing is the same as that shown in FIGS. 13(a) to 13 (f).
And (3) extracting the motion parameters of the target, judging the motion state of the target by using the condition shown in the formula (13), and finding that the target meets the condition shown in the formula (13) and is in a shaking motion state.
On the basis, the imaging time is selected to be the synthetic aperture center time 0s by using the parameter estimation result of the sub-aperture, and the obtained target ISAR imaging result based on the shaking motion is shown in the attached figure 17. Obviously, the focusing effect is good.
In summary, the above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (5)

1. A long synthetic aperture time sea surface moving object imaging processing method regards echo signals as a result of superposition of echoes of a plurality of scattering points, and is characterized in that: analyzing the equivalent speed and the equivalent acceleration of the echo signal, and judging whether an equivalent speed error and an equivalent acceleration error caused by target shaking caused by sea conditions exist or not; when the error caused by target shaking does not exist, the method considers that the method is suitable for low sea state imaging processing; when there is an error caused by the target shake, it is considered that the selection is suitable for the high sea state imaging process.
2. The imaging processing method of claim 1, wherein: the specific method for analyzing the equivalent speed and the equivalent acceleration of the echo signal and judging whether the error caused by the target shaking exists is as follows:
performing Taylor series expansion on echo signals subjected to pulse compression at any scattering point under the constraint of sub-aperture, and estimating by adopting a target motion parameter estimation algorithm to obtain the total equivalent velocity and the total equivalent acceleration of the scattering point; wherein, the total equivalent speed is equal to the sum of the equivalent speed caused by the self motion of the target and the radar platform and the equivalent speed caused by the shaking of the target; the total equivalent acceleration is equal to the sum of equivalent acceleration caused by the target and the self motion of the radar platform and equivalent acceleration caused by the shaking of the target; if the total equivalent speeds obtained by the scattering points are the same and the total equivalent accelerations obtained by the scattering points are also the same, the error caused by target shaking does not exist; if the total equivalent speeds obtained by the scattering points are different and the total equivalent accelerations obtained by the scattering points are also different, an error caused by target shaking exists.
3. The imaging processing method of claim 2, wherein: the method for obtaining the total equivalent speed and the total equivalent acceleration comprises the following steps:
and performing Taylor series expansion on echo signals subjected to pulse compression at any scattering point under the constraint of sub-apertures, performing motion parameter estimation by using generalized radon-Fourier transform as an estimation means of motion parameters, and after the motion parameter estimation of the target is realized, detecting by using a constant false alarm rate to obtain the number of the scattering points of the target and the total equivalent speed and the total equivalent acceleration of each scattering point.
4. The imaging processing method of claim 1, wherein: when the error caused by target shaking does not exist, selecting an SAR imaging technology; when there is an error caused by the shaking of the target, the ISAR imaging technique is selected.
5. The imaging processing method of claim 2, 3 or 4, characterized by:
when it is satisfied with
Figure FDA0003379188980000021
Judging that the total equivalent speeds obtained by all scattering points are the same, and judging that the total equivalent accelerations obtained by all scattering points are the same;
wherein
Figure FDA0003379188980000022
Are each vSiAnd aSiDifference between maximum and minimum, vSiIs the total equivalent velocity of the ith scattering point, aSiTotal equivalent acceleration of the ith scattering point, TobIs the sub-aperture time length, λ is the system wavelength, fsIs the system sampling rate, c isThe speed of light.
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