A high-precision stop-and-go azimuth error correction method for spaceborne SAR

Abstract

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. This method can accurately obtain the stop-and-go model error correction value for each observed target point during the radar signal transmission and reception process, solving the problem of high-precision and rapid SAR stop-and-go azimuth error correction processing, effectively improving the correction accuracy, and thus avoiding the azimuth defocus problem of the image, utilizing subsequent target interpretation and scattering characteristic inversion. The stop-and-go azimuth error correction method can simply and directly calculate the stop-and-go model error correction value in an analytical form, without involving Doppler parameter calculation and complex iterative steps, thus achieving high calculation accuracy and a convenient and easy processing scheme. Furthermore, the method is independent of the SAR imaging algorithm and can be applied to various imaging modes and imaging algorithms. It has high universality and practicality, can be applied to multiple imaging algorithms and new system SAR operating modes, and is suitable for large-scale industrial use and promotion.

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 spaceborne SAR. Background Art

[0002] To meet the high-precision imaging and observation requirements of ultra-high-resolution spaceborne SAR payloads, transmission and reception signals must be acquired with millimeter-level accuracy within a period of nearly 1 minute. Due to the satellite's considerable distance from surface targets, it takes approximately 7 milliseconds after signal transmission for the ground-reflected signal to be received. During this time, the satellite has traveled nearly 50 meters, resulting in significant errors in satellite positioning, deviating from millimeter-level measurement accuracy and causing a decrease in image focusing and positioning accuracy.

[0003] In traditional low-resolution satellite ground signal processing, the signal emission time in the stop-and-go model is typically shifted by approximately 3 milliseconds, and the shifted time is used to approximate the actual emission position. This method can effectively correct geometric positioning errors, but at high resolution and long synthetic aperture times, it can produce large model approximation errors, causing azimuth defocusing of the image. This leads to a significant loss of resolution, degrades image quality, and affects target interpretation and scattering characteristic inversion. This limits the application of stop-and-go correction in practical high-resolution SAR Earth observation systems. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-precision stop-and-go azimuth error correction method for spaceborne SAR, so as to solve the problem in the prior art that the correction accuracy of the SAR stop-and-go azimuth error is insufficient, resulting in azimuth defocusing of the image.

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

[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 based on 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: Determine the radar position vector and the radar velocity vector based on the reference orbit position obtained in step 1, and then obtain the reflection slant range R corresponding to the observed target point;

[0009] Step 3: Using the stop-and-go model, calculate the one-way slant range error ΔR corresponding to the reflection slant 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 observation 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 at which the signal reaches the observation target point r , calculate t using the following formula r The reference orbit position of the radar at this moment:

[0019]

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

[0021] c represents the speed of light.

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

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

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

[0025]

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

[0027] Step 23: Calculate the reflection slant distance R corresponding to the observed target point using the following formula:

[0028]

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

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

[0031]

[0032] Wherein, ΔR represents the one-way slant range error corresponding to the reflection slant range R under the stop-and-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 sequentially using two steps: 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 original signal 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 phase correction is performed on the position signal of the reflected slant range R after the echo data interpolation using the following formula:

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

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

[0038] E itp (R) represents the position signal of the reflected slant range R after 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. This method can accurately obtain the stop-and-go model error correction value of each observed target point during the radar signal transmission and reception process, solving the difficult problem of high-precision and rapid SAR stop-and-go azimuth error correction processing, effectively improving the correction accuracy, and thus avoiding the azimuth defocus problem of the image, and utilizing the subsequent interpretation of the target and the inversion of the scattering characteristics.

[0042] (II) The high-precision stop-and-go azimuth error correction method of the present invention can directly and analytically calculate the stop-and-go model error correction value without involving Doppler parameter calculations and complex iterative steps, thereby achieving high computational accuracy and a convenient and easy-to-implement processing scheme. Furthermore, the method is independent of the SAR imaging algorithm and is applicable to various imaging modes and algorithms. It has high universality and practicality, can be applied to a variety of imaging algorithms and new SAR operating modes, and is suitable for large-scale industrial use and promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This 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 commonly known 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 modifications 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 observations. 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 based on 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: Determine the radar position vector and the radar velocity vector based on the reference orbit position obtained in step 1, and then obtain the reflection slant range R corresponding to the observed target point;

[0051] Step 3: Using the stop-and-go model, calculate the one-way slant range error ΔR corresponding to the reflection slant 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 observation 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: Based on 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 this 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] Furthermore, step 2 includes the following sub-steps:

[0065] Step 21, based on 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, calculate the inner product D between the radar's observation vector to the observed target point and the radar's velocity vector using the following formula:

[0067]

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

[0069] Step 23: Calculate the reflection slant distance R corresponding to the observed target point using the following formula:

[0070]

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

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

[0073]

[0074] Wherein, ΔR represents the one-way slant range error corresponding to the reflection slant range R under the stop-and-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 sequentially using two steps: echo data interpolation and phase correction.

[0076] Furthermore,

[0077] After obtaining the slant range error, the SAR radar echo data is corrected. 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 this.

[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 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 echo data interpolated signal 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 range R after phase correction;

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

[0084] λ represents the wavelength of the radar.

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

[0086] For a spaceborne SAR system, the satellite's reference orbital position at the moment the target is illuminated is first calculated. Based on this reference position, the precise reflection slant range is analytically calculated. This is then used to obtain the stop-and-go model slant range error correction, which is then corrected through data interpolation and phase compensation, completing the stop-and-go error correction process for the SAR echo data. This stop-and-go azimuth error correction method allows for the convenient and direct calculation of the stop-and-go model error correction using an analytical approach. It does not involve Doppler parameter calculations or complex iterative steps, resulting in high computational accuracy and a convenient and easy-to-implement processing scheme. Furthermore, the method is independent of the SAR imaging algorithm and can be applied to various imaging modes and algorithms, demonstrating its 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 moment when the signal reaches the observation target point is selected as the reference orbit moment, and the reference orbit position of the radar at the reference orbit moment is determined; Step 2: Determine the radar position vector and the radar velocity vector based on the reference orbit position obtained in step 1, and then obtain the reflection slant range R corresponding to the observed target point; Step 3: Using the stop-and-go model, calculate the one-way slant range error ΔR corresponding to the reflection slant range R obtained in step 2; 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 stop-and-go azimuth error correction method for spaceborne SAR 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 observation 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 at which the signal reaches the observation target point r , calculate t using the following formula 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 stop-and-go azimuth error correction method for spaceborne SAR according to claim 2, characterized in that: Step 2 includes the following sub-steps: Step 21, based on the reference orbit position obtained in step 1, the radar position vector and the radar velocity vector are respectively and Step 22, calculate the inner product D between the radar's observation vector to the observed target point and the radar's velocity vector using the following formula: Among them, * indicates the calculation of vector inner product; Step 23: Calculate the reflection slant distance R corresponding to the observed target point using the following formula: Where * represents the vector inner product operation.

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

5. The high-precision stop-and-go azimuth error correction method for spaceborne SAR according to 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: echo data interpolation and phase correction.

6. The high-precision stop-and-go azimuth error correction method for spaceborne SAR according to 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 original signal 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 according to 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 reflected slant range R after the echo data interpolation: E crt (R)=E itp (R)e -i4πΔR / λ Among them, E crt (R) represents the position signal of the reflected slant range R after phase correction; E itp (R) represents the position signal of the reflected slant range R after echo data interpolation; λ represents the wavelength of the radar.

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