CN112799062A - High-resolution wide swath SAR motion compensation method based on prior information - Google Patents
High-resolution wide swath SAR motion compensation method based on prior information Download PDFInfo
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- CN112799062A CN112799062A CN202110395192.0A CN202110395192A CN112799062A CN 112799062 A CN112799062 A CN 112799062A CN 202110395192 A CN202110395192 A CN 202110395192A CN 112799062 A CN112799062 A CN 112799062A
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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
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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
Abstract
The invention discloses a high-resolution wide swath SAR motion compensation method based on prior information, which comprises the following steps: step S1: distance partitioning is carried out, the distance in each distance block is guaranteed not to be changed in a space mode, and the distance is used for subsequent estimation of RD phase errors; step S2: estimating the phase error of each distance block by using PGA (programmable Gate array), and carrying out azimuth pulse pressure; step S3: the output parameter P is 1 if the phase error is estimated correctly, otherwise P is 0. The method has the advantages of simple principle, capability of improving the estimation precision, more complete and accurate expression of the RD phase error curve and the like.
Description
Technical Field
The invention mainly relates to the technical field of radars, in particular to a high-resolution wide swath SAR motion compensation method based on prior information.
Background
Due to the influence of various factors such as atmospheric motion, the motion trajectory of an airborne Synthetic Aperture Radar (SAR) is changed from an ideal straight-line trajectory to a nonlinear trajectory, and during SAR imaging, motion compensation (MOCO) is often required to compensate the nonlinear trajectory to a linear trajectory. While the RD phase error is a factor that must be considered for motion compensation of high-resolution and wide-band airborne SAR, since the PGA estimation is based on strong scattering points, a situation of erroneous phase error estimation may occur for some observation scenarios without strong scattering points.
In the conventional scheme, after phase error data is obtained, a phase error curve is generally estimated by using a fitting method, which includes a least square method (hereinafter, referred to as LS) and a weighted least square method (hereinafter, referred to as WLS). But the estimation curve has a certain deviation due to the existence of wrong estimation points. The existing methods for estimating the RD phase error comprise LS and WLS, because of the existence of wrong phase error estimation points, a large estimation error occurs when the LS is used, a phase error curve cannot be accurately represented, although the WLS passes through weighting processing, an estimation error which cannot be ignored still exists, and the two methods cannot automatically identify and remove the wrong phase error estimation points, so that the estimation accuracy is poor. In summary, because there are wrong phase error estimation points, both LS and WLS have no function of self-detecting and eliminating the wrong estimation points, firstly, a single use of LS will result in a large estimation error when estimating RD phase error, and secondly, while WLS can reduce the error through weighting processing, but cannot completely eliminate the influence of the wrong phase error, and also will result in a non-negligible estimation error.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: aiming at the technical problems in the prior art, the invention provides the high-resolution wide swath SAR motion compensation method based on the prior information, which has a simple principle, can improve the estimation precision and more completely and accurately express the RD phase error curve.
In order to solve the technical problems, the invention adopts the following technical scheme:
a high-resolution wide swath SAR motion compensation method based on prior information comprises the following steps:
step S1: distance partitioning is carried out, the distance in each distance block is guaranteed not to be changed in a space mode, and the distance is used for subsequent estimation of RD phase errors;
step S2: estimating the phase error of each distance block by using PGA (programmable Gate array), and carrying out azimuth pulse pressure;
step S3: the output parameter P is 1 if the phase error is estimated correctly, otherwise P is 0.
As a further improvement of the process of the invention: the elimination of the estimated points of possible error in the estimated phase error in step S2 includes:
step S201: each distance block is subjected to two imaging processes, namely imaging after PGA estimation and compensation and imaging without PGA estimation and compensation;
step S202: the imaging quality is expressed by specific numerical quantization, and the entropy value of imaging is selected as the standard for judging the imaging quality; setting the entropy value of the imaging image estimated and compensated by using PGA as E1, and the entropy value of the imaging image estimated and compensated by using PGA as E2;
step S203: comparing the image entropy values of the two cases in step S202, if E1> E2, it indicates that the imaging quality estimated by PGA is better, i.e. the phase error of the range block is correctly estimated, otherwise, the phase error of the range block is incorrectly estimated.
As a further improvement of the process of the invention: the higher the entropy value of the image, the worse the imaging quality.
As a further improvement of the process of the invention: estimating an error phase point from the variance in step S2, including: calculating the variance of the estimated phases of the adjacent distance blocks, and if the variance of a certain distance block and the variance of two adjacent distance blocks exceed the set threshold value
Then the phase of this distance block is estimated incorrectly.
As a further improvement of the process of the invention: estimating an error phase point according to a threshold in step S2, including: setting a maximum threshold for phase estimation, the estimated phase exceeding the threshold
Then the phase of the distance block is deemed to be erroneously estimated.
As a further improvement of the process of the invention: the distance blocking in step S1 means: a certain distance range is evenly divided into a plurality of distance sections.
As a further improvement of the process of the invention: in step S3, when all the distance blocks are completely estimated, the WLS is used to estimate the RD phase error, and the wrong estimation point is affected by the parameter P and filtered out, so that only the correct estimation point is left, thereby obtaining an accurate RD phase error estimation curve.
As a further improvement of the process of the invention: before the step S1, data with RCM residues eliminated is obtained.
Compared with the prior art, the invention has the advantages that:
the invention discloses a high-resolution wide swath SAR motion compensation method based on prior information, which is developed around how to improve the estimation accuracy of RD phase errors. The method can effectively solve the influence of insufficient RD error estimation precision caused by the existence of error phase errors.
Drawings
FIG. 1 is a schematic flow diagram of the process of the present invention.
Fig. 2 is a schematic diagram of phase errors estimated by different methods in a specific application example of the present invention.
Detailed Description
The invention will be described in further detail below with reference to the drawings and specific examples.
For ease of understanding, the present invention makes clear the important key terms and standard names mentioned below. PGA: a phase gradient autofocus algorithm. The algorithm can be used to estimate and compensate for low order, high order, and random phase errors. LS: the least squares method. WLS: a weighted least squares method. PI-WLS: weighted least squares method based on prior information (method of the invention). RD: the distances are related. RCM: and (4) moving distance. The change of the distance between the airborne synthetic aperture radar and the target due to the relative motion between the two is called range migration.
As shown in fig. 1, the high resolution wide swath SAR motion compensation method based on prior information of the present invention includes the steps of:
step S1: distance partitioning is carried out; in order to estimate the RD phase error, distance blocking must be performed to ensure that the distance in each distance block does not change spatially, so as to be used for subsequent RD phase error estimation;
step S2: estimating the phase error of each distance block by using PGA (programmable Gate array), and carrying out azimuth pulse pressure;
step S3: the output parameter P is 1 if the phase error is estimated correctly, otherwise P is 0.
In a specific application example, the distance blocking in step S1 means: a certain distance range is evenly divided into a plurality of distance sections. For example, the range of 0-200m is divided into two blocks, the first block is 0-100m, and the second block is 100-200 m. The distance blocking is carried out according to actual needs, and the number and the size of the blocks are selected according to the actual needs.
In a specific application example, in the phase error estimated in step S2, there may be a wrong estimation point, and the present invention further adopts the following procedure to eliminate the wrong estimation point:
determining a criterion: if the estimated point is estimated correctly, the imaging quality after estimation and compensation using the PGA should be better than that without the PGA, but if the estimated point is estimated incorrectly, the imaging quality with the PGA is worse than that without the PGA due to the incorrect estimation point.
Step S201: each distance block is subjected to two imaging processes, namely imaging after PGA estimation and compensation and imaging without PGA estimation and compensation;
step S202: the imaging quality is expressed by specific numerical quantification, and the entropy value of imaging is selected as a standard for judging the imaging quality. Note that: the higher the entropy value of the image, the worse the imaging quality. The entropy value of the imaging image estimated and compensated by the PGA is set as E1, the entropy value of the imaging image estimated and compensated by the PGA is set as E2;
step S203: comparing the image entropy values of the two cases in step S202, if E1> E2, it indicates that the imaging quality estimated by PGA is better, i.e. the phase error of the range block is correctly estimated, otherwise, the phase error of the range block is incorrectly estimated.
Compared with the traditional method of directly estimating the phase error by using LS or WLS, the method has the advantages that a detection function is generated in advance, namely whether the phase error estimation point is correct or not is judged, the wrong estimation point can be effectively filtered, the estimation precision is improved, and the RD phase error curve is expressed more completely and accurately.
In another embodiment, further, the present invention can also estimate the error phase point according to the variance, as follows:
according to the variance: calculating the variance of the estimated phases of the adjacent distance blocks, and if the variance of a certain distance block and the variance of two adjacent distance blocks exceed the set threshold value
Then the phase of this distance block is estimated incorrectly. Here, the problem is illustrated by an example: a, B, C are three adjacent distance blocks. The invention can calculate the variance of two adjacent distance blocks, if the B point is estimated by error, the variance of two adjacent distance blocks can be calculated
And
are all greater than
And if not, the step (B),
and
are all less than
。
In another embodiment, further, the present invention may also estimate the error phase point according to a threshold, specifically as follows:
setting a maximum threshold for phase estimation, the estimated phase exceeding the threshold
Then the phase of the distance block is deemed to be erroneously estimated.
In a specific application example, in step S3, further, when all the distance blocks are completely estimated, the WLS may be used to estimate the RD phase error, and the wrong estimation point may be filtered out due to the influence of the parameter P, and only the correct estimation point is left, so as to obtain an accurate RD phase error estimation curve.
In a specific application example, before step S1, the residual RCM data may be further eliminated.
Referring to fig. 2, a schematic diagram of curves for estimating phase errors by using various methods is shown, it is apparent from the diagram that phase estimation errors at abscissa 5 and abscissa 10 are erroneous, and LS and WLS are both affected by erroneous estimation points to some extent.
Therefore, by adopting the scheme of the invention, the estimated phase errors of the distance blocks can be detected to be wrong, wrong phase error estimation points are removed when the phase errors are estimated, and only correct phase error estimation points are reserved, so that the precision of the estimated curve can be greatly improved, and the RD phase error curve can be completely and accurately represented.
The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. It should be noted that modifications and embellishments within the scope of the invention may be made by those skilled in the art without departing from the principle of the invention.
Claims (6)
1. A high-resolution wide swath SAR motion compensation method based on prior information is characterized by comprising the following steps:
step S1: distance partitioning is carried out, the distance in each distance block is guaranteed not to be changed in a space mode, and the distance is used for subsequent estimation of RD phase errors;
step S2: estimating the phase error of each distance block by using PGA (programmable Gate array), and carrying out azimuth pulse pressure;
step S3: if the phase error is estimated correctly, the output parameter P is 1, otherwise, P is 0;
estimating an error phase point from the variance in step S2, including: calculating the variance of the estimated phases of the adjacent distance blocks, and if the variance of a certain distance block and the variance of two adjacent distance blocks exceed the set threshold value
Then the phase of this distance block is estimated incorrectly; alternatively, estimating the error phase point according to the threshold in step S2 includes: setting a maximum threshold for phase estimation, the estimated phase exceeding the threshold
Then the phase of the distance block is deemed to be erroneously estimated.
2. The a priori information based high resolution wide swath SAR motion compensation method of claim 1, wherein the removing of possible erroneous estimated points in the estimated phase error in step S2 comprises:
step S201: each distance block is subjected to two imaging processes, namely imaging after PGA estimation and compensation and imaging without PGA estimation and compensation;
step S202: the imaging quality is expressed by specific numerical quantization, and the entropy value of imaging is selected as the standard for judging the imaging quality; setting the entropy value of the imaging image estimated and compensated by using PGA as E1, and the entropy value of the imaging image estimated and compensated by using PGA as E2;
step S203: comparing the image entropy values of the two cases in step S202, if E1> E2, it indicates that the imaging quality estimated by PGA is better, i.e. the phase error of the range block is correctly estimated, otherwise, the phase error of the range block is incorrectly estimated.
3. The method for motion compensation of high-resolution wide-swath SAR based on the prior information as claimed in claim 2, wherein the higher the entropy of the image, the worse the imaging quality.
4. The method for motion compensation of a high-resolution wide swath SAR according to any of claims 1-3, wherein the distance blocking in step S1 is: a certain distance range is evenly divided into a plurality of distance sections.
5. The method for motion compensation of high-resolution wide swath SAR based on prior information according to any of claims 1-3, wherein in step S3, when all distance blocks are completely estimated, the WLS is used to estimate the RD phase error, and the wrong estimation point is affected by the parameter P and filtered out, and only the correct estimation point is left, so as to obtain an accurate RD phase error estimation curve.
6. The method for motion compensation of high-resolution wide swath SAR based on prior information according to any of claims 1-3, characterized in that before step S1, data with RCM residual eliminated is obtained.
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| CN113702974A (en) * | 2021-09-01 | 2021-11-26 | 上海无线电设备研究所 | Method for quickly optimizing airborne/missile-borne synthetic aperture radar image |
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