High-precision satellite-borne SAR walking and stopping azimuth error correction method

Abstract

According to the high-precision satellite-borne SAR walking and stopping azimuth error correction method, an analytical calculation method for analyzing and calculating point target walking and stopping errors is given for echo data based on the signal pulse emission time and by means of the reference orbit position, walking and stopping model error correction values of all observation target points in the radar signal receiving and sending process can be accurately obtained, and the accuracy of the radar signal receiving and sending process is improved. The problem of high-precision and rapid SAR walking and stopping azimuth error correction processing is solved, the correction precision can be effectively improved, the problem of azimuth defocusing of the image is avoided, and subsequent target interpretation and scattering characteristic inversion are utilized. According to the walk-stop azimuth error correction method, the walk-stop model error correction amount can be simply and directly calculated in an analysis form, Doppler parameter calculation and complex iteration steps are not involved, high calculation precision can be obtained, and the processing scheme is convenient and easy to implement. Meanwhile, the method is irrelevant to an SAR imaging algorithm, can be suitable for various imaging modes and imaging algorithms, is high in universality and practicability, can be suitable for various imaging algorithms and new-system SAR working modes, and is suitable for industrial large-scale use and popularization.

Description

Technical Field

[0001] The invention belongs to the field of signal processing and relates to a high-precision stop-and-go azimuth error correction method for satellite-borne SAR. Background Art

[0002] In order to meet the high-precision imaging and observation requirements of ultra-high-resolution spaceborne SAR payloads, it is necessary to collect the transmitted and received signals with millimeter-level accuracy within a period of nearly 1 minute. Since the satellite is far away from the surface target, it takes about 7ms after the signal is transmitted to receive the ground reflection signal. During this period, the satellite has flown forward nearly 50 meters, resulting in huge errors in satellite positioning, deviating from the millimeter-level measurement accuracy, and causing a decrease in image focusing accuracy and positioning accuracy.

[0003] In traditional low-resolution satellite ground signal processing, the signal emission time in the stop-and-go model is generally shifted by about 3ms, and the actual emission position is approximately replaced by the shifted time. This method can achieve the correction of geometric positioning errors well, but under high-resolution and long synthetic aperture time, it will produce large model approximation errors, causing image azimuth defocusing, which will lead to a serious decrease in resolution, reduce image quality, affect target interpretation and inversion of scattering characteristics, and limit the application of stop-and-go correction in actual high-resolution SAR ground observation systems. Summary of the invention

[0004] The object of the present invention is to provide a high-precision satellite-borne SAR stop-and-go azimuth error correction method to solve the problem in the prior art that the correction accuracy is insufficient when correcting the SAR stop-and-go azimuth error, resulting in azimuth defocusing of the image.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions to achieve the above problems:

[0006] A high-precision spaceborne SAR stop-and-go azimuth error correction method comprises the following steps:

[0007] Step 1: In SAR observation, the three-dimensional position of the radar is determined according to the pulse emission time, and the three-dimensional position of the observation target point is determined; the time when the signal reaches the observation target point is selected as the reference orbit time, and the reference orbit position of the radar at the reference orbit time is determined;

[0008] Step 2: According to the reference orbit position obtained in step 1, the position vector and the velocity vector of the radar are determined, and then the reflection slant distance R corresponding to the observed target point is obtained;

[0009] Step 3, using the stop-and-go model, calculate the one-way slope range error ΔR corresponding to the reflection slope range R obtained in step 3;

[0010] Step 4: Use the one-way slant range error ΔR to correct the SAR radar echo data to complete the correction of the SAR stop-go azimuth error.

[0011] The present invention also has the following features:

[0012] Furthermore, step 1 includes the following sub-steps:

[0013] Step 11: In SAR observation, let the pulse emission time be t0. The three-dimensional position of the radar in the WGS84 coordinate system at time t0 is

[0014] Step 12: Assume that the three-dimensional position of the observed target point in the WGS84 coordinate system is Expressed as

[0015]

[0016] Step 13: Use the following formula to calculate the observation vector from the radar to the observation target point:

[0017]

[0018] Step 14, based on the observation vector of the radar reaching the observation target point and the time t when the signal arrives at the observation target point r , use the following formula to calculate t r The reference orbit position of the radar at the moment:

[0019]

[0020] Among them, |·| represents the modulus value of the vector;

[0021] c represents the speed of light.

[0022] Further, step 2 includes the following sub-steps:

[0023] Step 21, according to the reference orbit position obtained in step 1, the radar position vector and the radar velocity vector are respectively and

[0024] Step 22, using the following formula, calculate the inner product D between the observation vector of the radar to the observation target point and the radar velocity vector:

[0025]

[0026] Among them, * indicates the calculation of vector inner product;

[0027] Step 23, use the following formula to calculate the reflection slope distance R corresponding to the observed target point:

[0028]

[0029] Where * represents the vector inner product operation.

[0030] Furthermore, in step 3, the one-way slope range error corresponding to the reflection slope range R under the stop-go model is calculated using the following formula:

[0031]

[0032] Wherein, ΔR represents the one-way slope range error corresponding to the reflection slope range R under the stop-go model.

[0033] Furthermore, in step 4, when the one-way slant range error ΔR is used to correct the SAR radar echo data, the SAR radar echo data is corrected in two steps of echo data interpolation and phase correction.

[0034] Furthermore, in step 4, when performing the echo data interpolation step, the Sinc interpolation algorithm in SAR processing is used to interpolate the signal originally located at R+ΔR to the position of the reflection slant range R, and obtain the position signal of the reflection slant range R after the echo data interpolation.

[0035] Furthermore, in step 4, when performing the phase correction step, the following formula is used to perform phase correction on the position signal of the reflected slant range R after the echo data is interpolated:

[0036] E crt (R)=E itp (R)e -i4πΔR / λ

[0037] Among them, E crt (R) represents the position signal of the reflected slant distance R after phase correction;

[0038] E itp (R) represents the position signal of the reflection slant range R after the echo data interpolation;

[0039] λ represents the wavelength of the radar.

[0040] Compared with the prior art, the present invention has the following technical effects:

[0041] (I) The high-precision spaceborne SAR stop-and-go azimuth error correction method of the present invention provides an analytical calculation method for the stop-and-go error of a point target based on echo data, based on the signal pulse emission time and using the reference orbit position. The stop-and-go model error correction value of each observed target point during the radar signal reception and transmission process can be accurately obtained, thereby solving the difficult problem of high-precision and rapid SAR stop-and-go azimuth error correction processing, and can effectively improve the correction accuracy, thereby avoiding the azimuth defocusing problem of the image, and utilizing the subsequent interpretation of the target and the inversion of the scattering characteristics.

[0042] (II) In the stop-and-go azimuth error correction method of the high-precision spaceborne SAR of the present invention, the stop-and-go azimuth error correction method can simply and directly calculate the stop-and-go model error correction amount in an analytical form, without involving Doppler parameter calculation and complex iterative steps, so as to obtain a higher calculation accuracy, and the processing scheme is convenient and easy. At the same time, the method is independent of the SAR imaging algorithm, and can be applied to various imaging modes and imaging algorithms. It has strong universality and practicality, can be applied to a variety of imaging algorithms and new system SAR working modes, and is suitable for large-scale use and promotion in industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a flow chart of the high-precision spaceborne SAR stop-and-go azimuth error correction method of the present invention;

[0044] Figure 2 is a schematic diagram of the geometry of radar signal transmission and reception in one embodiment of the present invention;

[0045] Figure 3 It is a schematic diagram of data interpolation in one embodiment of the present invention. DETAILED DESCRIPTION

[0046] It should be noted that, unless otherwise specified, all methods in the present invention adopt methods known in the prior art. For example, the Sinc interpolation algorithm adopts a known and commonly used Sinc interpolation algorithm.

[0047] Specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent changes made on the basis of the technical solution of this application fall within the protection scope of the present invention.

[0048] This embodiment provides a high-precision stop-and-go azimuth error correction method for spaceborne SAR, which solves the problem of high-speed and high-precision stop-and-go model correction under image azimuth defocus caused by the stop-and-go model error in ultra-high-resolution spaceborne SAR observation. Figure 1 As shown, the present invention mainly includes four parts: reference track position determination, reflection slant range calculation, stop-go model slant range error calculation, and echo stop-go azimuth error correction. The specific steps are as follows:

[0049] Step 1: In SAR observation, the three-dimensional position of the radar is determined according to the pulse emission time, and the three-dimensional position of the observation target point is determined; the time when the signal reaches the observation target point is selected as the reference orbit time, and the reference orbit position of the radar at the reference orbit time is determined;

[0050] Step 2: According to the reference orbit position obtained in step 1, the position vector and the velocity vector of the radar are determined, and then the reflection slant distance R corresponding to the observed target point is obtained;

[0051] Step 3, using the stop-and-go model, calculate the one-way slope range error ΔR corresponding to the reflection slope range R obtained in step 3;

[0052] Step 4: Use the one-way slant range error ΔR to correct the SAR radar echo data to complete the correction of the SAR stop-go azimuth error.

[0053] Furthermore, step 1 includes the following sub-steps:

[0054] Step 11: In SAR observation, let the pulse emission time be t0. The three-dimensional position of the radar in the WGS84 coordinate system at time t0 is

[0055] Step 12: Assume that the three-dimensional position of the observed target point in the WGS84 coordinate system is Expressed as

[0056]

[0057] Step 13: Use the following formula to calculate the observation vector from the radar to the observation target point:

[0058]

[0059] Step 14: according to the observation vector of the radar reaching the observation target point and the time t at which the signal reaches the observation target point r ,like Figure 2 As shown, use the following formula to calculate t r The reference orbit position of the radar at the moment:

[0060]

[0061] Among them, |·| represents the modulus value of the vector;

[0062] c represents the speed of light.

[0063] Among them, (t r )=t0+|Vp_s| / c

[0064] Further, step 2 includes the following sub-steps:

[0065] Step 21, according to the reference orbit position obtained in step 1, the radar position vector and the radar velocity vector are respectively and The radar velocity vector, like the radar position vector, is directly measured through GPS or other means.

[0066] Step 22, using the following formula, calculate the inner product D between the observation vector of the radar to the observation target point and the radar velocity vector:

[0067]

[0068] Among them, * indicates the calculation of vector inner product;

[0069] Step 23, use the following formula to calculate the reflection slope distance R corresponding to the observed target point:

[0070]

[0071] Where * represents the vector inner product operation.

[0072] Furthermore, in step 3, the one-way slope range error corresponding to the reflection slope range R under the stop-go model is calculated using the following formula:

[0073]

[0074] Wherein, ΔR represents the one-way slope range error corresponding to the reflection slope range R under the stop-go model.

[0075] Furthermore, in step 4, when the one-way slant range error ΔR is used to correct the SAR radar echo data, the SAR radar echo data is corrected in two steps of echo data interpolation and phase correction.

[0076] Further,

[0077] After obtaining the slant range error, the SAR radar echo data is corrected. The echo correction mainly includes two steps: echo data interpolation and phase compensation.

[0078] The interpolation of echo data realizes the correction of the signal envelope position caused by the stop-go error. Specifically, the original signal at R+ΔR is interpolated to the position R. Figure 3 As shown, in actual operation, the Sinc interpolation algorithm commonly used in SAR processing can be used to achieve it.

[0079] In step 4, when performing the echo data interpolation step, the Sinc interpolation algorithm in SAR processing is used to interpolate the original signal at R+ΔR to the position of the reflection slant range R to obtain the signal after the echo data interpolation.

[0080] Furthermore, phase compensation realizes the correction of signal phase deviation caused by stop-start error. Specifically, the interpolated signal is subjected to phase correction processing. In step 4, when performing the phase correction step, the phase of the signal after echo data interpolation is corrected using the following formula:

[0081] E crt (R)=E itp (R)e -i4πΔR / λ

[0082] Among them, Ecrt (R) represents the position signal of the reflected slant distance R after phase correction;

[0083] E itp (R) represents the position signal of the reflection slant range R after the echo data interpolation;

[0084] λ represents the wavelength of the radar.

[0085] This embodiment proposes a high-precision error analytical calculation and correction scheme for the in-situ "stop-and-go" model error phenomenon caused by the spaceborne SAR completing earth observation while moving at high speed.

[0086] For the spaceborne SAR system, the reference orbital position of the satellite at the time when the target is illuminated is first calculated; then based on the reference position, the precise reflection slant range is calculated by analytical method; on this basis, the stop-and-go model slant range error correction is obtained, and the slant range error correction is corrected by data interpolation and phase compensation to complete the stop-and-go error correction processing of the SAR echo data. The stop-and-go azimuth error correction method can conveniently and directly calculate the stop-and-go model error correction in an analytical form, without involving Doppler parameter calculations and complex iterative steps, and can obtain higher calculation accuracy, and the processing scheme is convenient and easy. At the same time, the method implemented in this embodiment is independent of the SAR imaging algorithm, and can be applied to various imaging modes and imaging algorithms, with strong universality and practicality.

Claims

1. A high-precision stop-and-go azimuth error correction method for spaceborne SAR, characterized in that: The following steps are involved: Step 1: In SAR observation, the three-dimensional position of the radar is determined according to the pulse emission time, and the three-dimensional position of the observed target point is determined; The time when the signal arrives at the observation target point is selected as the reference orbit time, and the reference orbit position of the radar at the reference orbit time is determined; Step 2: According to the reference orbit position obtained in step 1, the position vector and the velocity vector of the radar are determined, and then the reflection slant distance R corresponding to the observed target point is obtained; Step 3, using the stop-and-go model, calculate the one-way slope range error ΔR corresponding to the reflection slope range R obtained in step 3; Step 4: Use the one-way slant range error ΔR to correct the SAR radar echo data to complete the correction of the SAR stop-go azimuth error.

2. The high-precision spaceborne SAR stop-and-go azimuth error correction method according to claim 1, characterized in that: Step 1 The following steps are included: Step 11: In SAR observation, let the pulse emission time be t0. The three-dimensional position of the radar in the WGS84 coordinate system at time t0 is Step 12: Assume that the three-dimensional position of the observed target point in the WGS84 coordinate system is Expressed as Step 13: Use the following formula to calculate the observation vector from the radar to the observation target point: Step 14, based on the observation vector of the radar reaching the observation target point and the time t when the signal arrives at the observation target point r , use the following formula to calculate t r The reference orbit position of the radar at this moment: Among them, |·| represents the modulus value of the vector; c represents the speed of light.

3. The high-precision spaceborne SAR stop-and-go azimuth error correction method as claimed in claim 2, characterized in that: Step 2 includes the following sub-steps: Step 21, according to the reference orbit position obtained in step 1, the radar position vector and the radar velocity vector are respectively and Step 22, using the following formula, calculate the inner product D between the observation vector of the radar to the observation target point and the radar velocity vector: Among them, * indicates the calculation of vector inner product; Step 23, use the following formula to calculate the reflection slope distance R corresponding to the observed target point: Where * represents the vector inner product operation.

4. The high-precision spaceborne SAR stop-and-go azimuth error correction method as claimed in claim 3, characterized in that: In step 3, the one-way slope range error corresponding to the reflection slope range R under the stop-go model is calculated using the following formula: Wherein, ΔR represents the one-way slope range error corresponding to the reflection slope range R under the stop-go model.

5. The high-precision spaceborne SAR stop-and-go azimuth error correction method as claimed in claim 4, characterized in that: In step 4, when the one-way slant range error ΔR is used to correct the SAR radar echo data, the SAR radar echo data is corrected in two steps of echo data interpolation and phase correction.

6. The high-precision stop-and-go azimuth error correction method for spaceborne SAR as claimed in claim 5, characterized in that: In step 4, when performing the echo data interpolation step, the Sinc interpolation algorithm in SAR processing is used to interpolate the signal originally located at R+ΔR to the position of the reflection slant range R, and obtain the position signal of the reflection slant range R after the echo data interpolation.

7. The high-precision stop-and-go azimuth error correction method for spaceborne SAR as claimed in claim 5, characterized in that: In step 4, when performing the phase correction step, the following formula is used to perform phase correction on the position signal of the reflection slant range R after the echo data is interpolated: E crt (R)=E itp (R)e -i4πΔR / λ Among them, E crt (R) represents the position signal of the reflected slant distance R after phase correction; E itp (R) represents the position signal of the reflection slant range R after the echo data interpolation; λ represents the wavelength of the radar.

Images