GEO satellite-ground bistatic SAR imaging processing method

Abstract

The invention belongs to the technical field of synthetic aperture radars, and particularly relates to a GEO satellite-ground bistatic SAR imaging processing method. The method specifically comprises the following steps: step 1, acquiring related parameters of a GEO satellite-ground bistatic SAR system, and estimating direct wave parameter information; 2, judging the starting time of the GEO SAR by using the parameter information, obtaining radar data of an echo channel, and obtaining sub-aperture echo data and ephemeris information through sub-aperture division processing; 3, constructing a back lobe direct wave signal of an echo channel by using the echo data and ephemeris information, performing phase synchronization and time synchronization, performing slant range and phase compensation on the synchronized signal, and performing sub-aperture imaging processing; and step 4, performing fusion processing on the imaging results of the sub-apertures by adopting a coherent accumulation algorithm, and finally obtaining a focusing imaging result within the complete synthetic aperture time.

Description

Technical Field

[0001] This invention belongs to the field of synthetic aperture radar technology, and particularly relates to a GEO bistatic SAR imaging processing method. Background Technology

[0002] Spaceborne Synthetic Aperture Radar (SAR) is a microwave remote sensing device mounted on a satellite that uses synthetic aperture technology to achieve high-resolution Earth observations day and night, in all weather conditions. However, this technology still has several limitations in practical applications: First, in complex terrain areas (such as steep mountains) and densely built-up urban areas, insufficient geometric information leads to limited deformation monitoring accuracy and poor 3D reconstruction results; second, due to the fixed observation geometry of the spaceborne platform, local areas are prone to shadowing and occlusion effects, making it difficult to obtain effective imaging data in these areas.

[0003] Bistatic SAR (SS-BiSAR) systems are a novel type of radar observation system that utilizes a satellite as the transmission platform and separates transmission and reception by deploying receiving devices on the ground. The significant advantages of this system are: the ground receiving system only needs to handle echo signal reception, greatly reducing system construction costs; simultaneously, by deploying distributed receiving stations on the ground, multi-angle observation data can be acquired, effectively compensating for the shortcomings of traditional spaceborne SAR systems in terms of their ability to observe key areas. This system has attracted widespread attention from scholars both domestically and internationally, with countries such as the UK, Italy, and China successively conducting systematic experimental research and achieving significant progress in key technological areas such as synchronous imaging technology and double-orbit interferometry processing.

[0004] Currently, experimental research and signal processing methods for bistatic SAR mainly rely on two types of satellite platforms: communication satellites (such as the BeiDou and Galileo systems) and low-Earth orbit (LEO) SAR satellites (such as LT-1). However, both types of platforms have significant limitations: LEO SAR satellites are limited by their orbital altitude, resulting in long revisit periods and limited imaging swaths in their bistatic systems; while communication satellites, constrained by signal bandwidth and transmission power, produce imaging results with low signal-to-noise ratios and poor resolution. In contrast, high-Earth orbit (GEO) SAR satellites operating in a 36,000 km geostationary orbit exhibit unique advantages: they possess shorter revisit periods and larger imaging swaths. Therefore, constructing a GEO bistatic SAR system using GEO SAR as the observation source provides a feasible technical path to overcome existing technological bottlenecks.

[0005] However, due to the long illumination time of GEO SAR, the GEO bistatic SAR system still faces two major technical challenges in actual imaging processing: First, during signal transmission, time drift and radio frequency interference inevitably occur between the direct wave channel and the echo channel, which introduces significant synchronization errors when using the direct wave channel for synchronization; second, the amount of data that the ground receiving system needs to process is extremely large, which poses a severe challenge to the imaging processing system. Summary of the Invention

[0006] To address the aforementioned issues, this invention provides a GEO bistatic SAR imaging processing method. This method extracts the back lobe direct wave signal from the echo channel, thereby minimizing synchronization errors caused by time drift between channels during long-term acquisition. By eliminating and fitting singular values ​​through the back lobe direct wave peak index, radio frequency interference during synchronization is eliminated. Furthermore, based on sub-aperture coherent accumulation processing technology, imaging processing of long-term observation data is achieved.

[0007] The technical solution for implementing the present invention is as follows:

[0008] A GEO bistatic SAR imaging processing method includes:

[0009] Step 1: Obtain relevant parameters of the GEO satellite-to-ground bistatic SAR system and estimate direct wave parameter information;

[0010] Step 2: Use the parameter information to determine the power-on time of GEO SAR, obtain radar data of the echo channel, and obtain sub-aperture echo data and ephemeris information through sub-aperture segmentation processing.

[0011] Step 3: Using the echo data and ephemeris information, construct the back lobe direct wave signal of the echo channel, and perform phase synchronization and time synchronization. Then, after slant range and phase compensation of the synchronized signal, perform sub-aperture imaging processing.

[0012] Step 4: The coherent accumulation algorithm is used to fuse the imaging results of each sub-aperture to finally obtain the focused imaging results within the complete synthetic aperture time.

[0013] Optionally, the phase synchronization and time synchronization described in this invention are as follows:

[0014] Phase synchronization: based on the peak index [V] of each azimuth pulse. pf [n;k)], extract the peak phase information of each azimuth signal, compensate it into the azimuth signal, and complete the peak phase synchronization;

[0015] Time synchronization: based on the peak index [V] of each azimuth pulse. pf[n;k)], the back lobe direct wave signal is compensated to the first column of the signal after peak phase synchronization, the signal time synchronization is completed, and finally the signal after the kth sub-aperture is synchronized is obtained.

[0016] Optionally, the specific process of step 3 in this invention is as follows:

[0017] Step 3.1: Using the parameter information from Step 1, process the k-th two-dimensional sub-aperture echo data S. e (n,f r k) Perform range pulse compression processing to obtain the signal S after compression of the k-th sub-aperture pulse in the frequency domain. pc (n,f r ;k);For signal S pc (n,f r k) Extract the peak index at each azimuth time point to obtain the peak index array V within the k-th sub-aperture. p (n; k), the index array is fitted to obtain the fitting curve V of the peak index. pf (n;k);

[0018] Step 3.2, fit the curve V pf The peak index value of (n; k) is rounded down to obtain the peak index of each azimuth pulse [V]. pf [n; k], extract the direct peak value information of the echo channel according to the index, perform phase synchronization and time synchronization, and obtain the synchronized signal S. syn (n,f r ;k);

[0019] Step 3.3: Based on the echo antenna coordinates and ephemeris, calculate the slant range history of the direct wave within the echo channel, and apply this to the synchronized signal S. syn (n,f r ;k) Perform slant range and phase compensation to obtain the compensated signal S c (n,f r ;k);

[0020] Step 3.4: Use the bistatic BP algorithm to analyze the sub-aperture signal S. c (n,f r ;k) is used for imaging to obtain the imaging result s of the kth sub-aperture. sub (k).

[0021] Optionally, in step 3.1 of the present invention, for signal S pc (n,f r k) Extract the peak index at each azimuth time point to obtain the peak index array V within the k-th sub-aperture. p(n; k), outlier removal is performed on the peak index vector, and a fourth-order fit is performed using the least squares method to obtain the fitting curve V of the peak index. pf (n;k).

[0022] Optionally, the back lobe direct wave signal S in the frequency domain echo channel of the present invention dpc (n,f r ;k) is:

[0023]

[0024] Among them, f r For faster time and frequency, B w K is the signal bandwidth. r Let Δf be the signal modulation frequency, Δf be the difference between the carrier frequencies of the illumination source and the receiver, A be a complex coefficient, ΔPRT be the difference between the pulse repetition times of the illumination source and the receiver, n be the azimuth pulse number, and τ be the signal frequency. d (n; k) represents the direct wave delay in the echo channel of the k-th sub-aperture, τ m The initial data collection time. f is the pulse repetition time at the receiving end. c The center frequency.

[0025] Optionally, the peak phase of the present invention for:

[0026]

[0027] Optionally, the compensated signal S described in this invention c (n,f r ;k) is:

[0028]

[0029] S c (n,f r ;k) corresponds to the time-domain expression s of the range direction. c (n,τ;k) is:

[0030] s c (n,τ;k)=A′(n;k)·B w ·sinc(B w ·(τ-τ e (n;k)))

[0031] ·exp(j2πΔf(τ-τ e (n;k)))exp(-j2πf c τ e (n;k))

[0032] In the formula, A′(n;k) are complex coefficients, and τ e (n; k) represents the echo delay of the k-th sub-aperture.

[0033] Optionally, step 3.4 of the present invention obtains the k-th sub-aperture imaging result s. sub (k)

[0034]

[0035] Optionally, step 1 of the present invention includes:

[0036] Step 1.1: Obtain the ephemeris information of the GEO SAR and the center frequency f of the payload parameters. c Time width T p And the pulse repetition frequency (PRF) and the signal modulation frequency (K) r The estimated range [K] rmin ,K rmax ];

[0037] Step 1.2: Obtain the receiver's sampling information, including the sampling rate f. s Receiver carrier frequency f c,r Receiver intermediate frequency f IF Receiver latitude and longitude coordinates and echo acquisition length T all ; Obtain the latitude, longitude, and altitude coordinates of the echo antenna in the ground receiving system, the imaging range, and the grid size;

[0038] Step 1.3, extract the middle part τ of the sampling es Echo channel data within a time period, denoted as s es (t), traverse the signal frequency modulation estimation range, and for the i-th signal frequency modulation K within the estimation range... r (i) Construct the reference signal s ref (t;K r (i)), using the reference signal for s es (t) is subjected to matched filtering to obtain the pulse-compressed signal s epc (t;K r (i) extract each signal s epc (t;K r (i) The peak value is used to obtain the pulse pressure peak map result. The peak position of the pulse pressure peak map is extracted, and the horizontal axis of the peak position is used as the frequency modulation frequency of the signal. Based on the known signal duration T p The bandwidth B of the signal is obtained. w .

[0039] Optionally, step 2 of the present invention specifically involves the following process:

[0040] Step 2.1, traverse the echo acquisition length T all Interval ΔTj Extract the 0.1-second echo channel data, where j represents the extracted data set. Use the parameter information obtained in step 1 to perform pulse compression to obtain... One-dimensional pulse pressure images are generated; during the power-on period, the one-dimensional pulse pressure images reflect equally spaced peak pulses, while during the power-off period, the one-dimensional pulse pressure images reflect equally amplitude noise signals.

[0041] Step 2.2, in the initial stage of data collection, the j-th... left Group j represents the data in the power-off state. left +1 data represents the device being powered on. During the later stages of data acquisition, the j-th data... right Group j represents the power-on status. right +1 data represents the power-off state; during the acquisition time of the two data segments, the echo channel data is extracted at 1-second intervals, and the operation in step 2.1 is repeated to finally obtain the power-on time range T. s ;

[0042] Step 2.3, based on the power-on time range T in Step 2.2 s Extract the kth sub-aperture echo data S every 2 seconds. e (n,f r ;k), and generate satellite position coordinates P for the power-on period based on ephemeris information. s The satellite position coordinates P corresponding to the sub-aperture were extracted. s (t;k).

[0043] Beneficial effects:

[0044] This invention addresses the issues of time drift, radio frequency interference, and memory limitations caused by long-term observations of GEO bistatic SAR systems. By extracting the back lobe direct wave signal from the echo channel, this method can minimize synchronization errors caused by time drift between channels during long-term acquisition. Furthermore, by eliminating and fitting singular values ​​through the back lobe direct wave peak index, radio frequency interference during synchronization is eliminated, enabling accurate imaging of GEO bistatic SAR systems under long-term observation. Attached Figure Description

[0045] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 It is a GEO bistatic SAR system configuration.

[0047] Figure 2 This is a flowchart illustrating the overall processing of the present invention;

[0048] Figure 3 This represents the relative position of the GEO SAR and the receiver.

[0049] Figure 4 The original echo signal is 0.1 seconds long;

[0050] Figure 5 The peak pulse pressure graph obtained from parameter estimation;

[0051] Figure 6 It is a one-dimensional signal after pulse compression (at a certain location and time);

[0052] Figure 7 To determine the image results upon power-on;

[0053] Figure 8 The original echo and slant range images for the first sub-aperture;

[0054] Figure 9 This is the pulse compression image of the first sub-aperture;

[0055] Figure 10 The graph shows the original peak index curve and the fitted peak index curve for the first sub-aperture.

[0056] Figure 11 This is a two-dimensional pulse compression image after time synchronization of the first sub-aperture;

[0057] Figure 12 The image shows the two-dimensional pulse compression after compensation for the slant range and phase of the first sub-aperture.

[0058] Figure 13 This is the imaging result for the first sub-aperture.

[0059] Figure 14 This is the overall imaging result. Detailed Implementation

[0060] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0061] It should be noted that, unless otherwise specified, the following embodiments and features can be combined with each other; and, based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0062] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this disclosure, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0063] Figure 1 The configuration of a GEO bistatic SAR system is shown, in which the ground receiving system includes a direct wave antenna and an echo antenna. The GEO SAR illuminates the observation scene, and the scattered signal from the scene is received by the echo channel. At the same time, the echo back lobe can receive the direct wave signal.

[0064] like Figure 2 As shown in the figure, an embodiment of this application provides a GEO satellite-to-ground bistatic SAR imaging processing method, comprising:

[0065] Step 1: Obtain relevant parameters of the GEO satellite-to-ground bistatic SAR system and estimate direct wave parameter information;

[0066] Step 2: Use the parameter information to determine the power-on time of GEO SAR, obtain radar data of the echo channel, and obtain sub-aperture echo data and ephemeris information through sub-aperture segmentation processing.

[0067] Step 3: Using the echo data and ephemeris information, construct the back lobe direct wave signal of the echo channel, and perform phase synchronization and time synchronization. Then, after slant range and phase compensation of the synchronized signal, perform sub-aperture imaging processing.

[0068] Step 4: The coherent accumulation algorithm is used to fuse the imaging results of each sub-aperture to finally obtain the focused imaging results within the complete synthetic aperture time.

[0069] This embodiment extracts the back lobe direct wave signal from the echo channel to minimize synchronization errors caused by time drift between channels during long-term acquisition. By eliminating and fitting singular values ​​through the back lobe direct wave peak index, radio frequency interference during synchronization is eliminated. Furthermore, based on the sub-aperture coherent accumulation processing technology, imaging processing of long-term observation data is achieved.

[0070] The invention will now be described in detail with reference to the accompanying drawings.

[0071] Step 1: Obtain relevant parameters of the GEO satellite-ground bistatic SAR system and estimate the direct wave parameter information.

[0072] Step 1.1: Obtain the ephemeris information and payload parameters (center frequency f) of the GEO SAR. c Time width T p Pulse repetition frequency (PRF), signal modulation frequency (K) r Estimated range [K] rmin ,K rmax ];

[0073] Step 1.2: Obtain the receiver's sampling information, including the sampling rate f. s Receiver carrier frequency f cr Receiver intermediate frequency f IF Receiver latitude and longitude coordinates and echo acquisition length T all ; Obtain the latitude, longitude, and altitude coordinates of the echo antenna in the ground receiving system, as well as the imaging range and grid size.

[0074] Step 1.3, extract the middle part τ of the sampling es Echo channel data within a time period, denoted as s es (t), traverse the signal frequency modulation estimation range, and for the i-th signal frequency modulation K within the estimation range... r (i) Construct the reference signal s ref (t;K r (i)), using the reference signal for s es (t) is subjected to matched filtering to obtain the pulse-compressed signal s epc (t;K r (i) extract each signal s epc (t;K r (i) The peak value is used to obtain the pulse pressure peak map result. The peak position of the pulse pressure peak map is extracted, and the horizontal axis of the peak position is used as the frequency modulation frequency of the signal. Based on the known signal duration T p The bandwidth B of the signal is obtained. w .

[0075] Step 2: Use parameter information to determine the power-on time of GEO SAR, obtain radar data of the echo channel, and obtain sub-aperture echo data and ephemeris information through sub-aperture segmentation processing.

[0076] Step 2.1, traverse the echo acquisition length T all (Turkey) all >500 seconds), interval ΔT j (ΔT j Extract 0.1-second echo channel data (>0.1 seconds), where j represents the extracted data set. Use the parameter information obtained in step 1 to perform pulse compression to obtain... Group one-dimensional pulse pressure image ( (Represents rounding down). During the power-on period, the one-dimensional pulse pressure image reflects equally spaced peak pulses, while during the power-off period, the one-dimensional pulse pressure image reflects a noise signal of equal amplitude.

[0077] Step 2.2: GEO SAR transmits signals continuously, therefore there must be two data segments: in the initial stage of acquisition, the j-th segment... left Group j represents the data in the power-off state. left +1 data set is in an offline state; during the later stages of data acquisition, the j-th data set... right Group j represents the data in the power-off state. right +1 data set indicates the device is not powered on. During the acquisition time of the two data segments, the echo channel data is extracted at 1-second intervals. Step 2.1 is repeated to obtain the power-on time range T. s .

[0078] Step 2.3: Based on the power-on time range in Step 2.2, extract the k-th sub-aperture echo data S every 2 seconds. e (n,f r ;k), and generate satellite position coordinates P for the power-on period based on ephemeris information. s The satellite position coordinates P corresponding to the sub-aperture were extracted. s (t;k).

[0079] Step 3: Using the echo data and ephemeris information, construct the back lobe direct wave signal of the echo channel, and perform phase synchronization and time synchronization. Then, perform slant range and phase compensation on the synchronized signal, and perform sub-aperture imaging processing.

[0080] Step 3.1: Using the parameter information from Step 1, process the k-th two-dimensional sub-aperture echo data S. e (n,f r k) Perform range pulse compression processing to obtain the signal S after compression of the k-th sub-aperture pulse in the frequency domain. pc (n,f r ;k) is:

[0081]

[0082] Where n is the azimuth pulse number, f r For fast time frequency, A is a complex coefficient related to the satellite antenna pattern, Δf = f c -f c,r This is the difference between the carrier frequencies of the illumination source and the receiver, i.e., the corresponding frequency error. τ is the difference in pulse repetition time between the illumination source and the receiver, corresponding to the time synchronization error of a bistatic SAR system. e (n; k) represents the echo delay of the k-th sub-aperture, τm This is the initial data collection time.

[0083] Back lobe direct wave signal S in the echo channel in the frequency domain dpc (n,f r ;k) can be represented as:

[0084]

[0085] In the formula, τ d (n; k) represents the direct wave delay in the echo channel of the k-th sub-aperture.

[0086] Extract the peak index at each azimuth time point to obtain the peak index array V within the k-th sub-aperture. p (n; k), outlier removal is performed on the peak index vector, and a fourth-order fit is performed using the least squares method to obtain the fitting curve V of the peak index. pf (n;k).

[0087] Step 3.2: Round the peak index value of the fitted curve to obtain the peak index [V] of each azimuth pulse. pf (n;k)]([*] represents rounding), extract the direct peak value information of the echo channel according to the index, perform phase synchronization and time synchronization, and obtain the synchronized signal S. syn (n,f r ;k).

[0088] Specifically, based on the peak index information, the peak phase information of each azimuth signal is extracted and compensated into the azimuth signal to complete peak phase synchronization. It can be expressed according to equation (2):

[0089]

[0090] Next, the two-dimensional signals are synchronized in time, based on the peak index [V] of each azimuth pulse. pf [n; k)], the back lobe direct wave signal is compensated to the first column, and finally the signal S after synchronization of the kth sub-aperture is obtained. syn (n,f r ;k) is:

[0091]

[0092] Step 3.3: Calculate the slant range history of the direct wave within the echo channel based on the echo antenna coordinates and ephemeris. Compensate for the slant range and phase of the synchronized signal to obtain the compensated signal S. c (n,f r ;k).

[0093] Specifically, based on the satellite position coordinates P of the k-th sub-aperture obtained in step 2.3 s Using (t; k) and the receiving antenna coordinates, the slant range history information of the direct wave is obtained. The time delay and phase of the direct wave introduced by pulse compression are compensated to obtain the compensated signal S. c (n,f r ;k) is:

[0094]

[0095] S c (n,f r ;k) corresponds to the time-domain expression s of the range direction. c (n,τ;k) is:

[0096]

[0097] In the formula, A′(n;k) are complex coefficients.

[0098] Step 3.4: Use the bistatic BP algorithm to analyze the subaperture signal s. c Imaging is performed on (n, τ; k) to obtain the k-th sub-aperture imaging result s. sub (k).

[0099]

[0100] Step 4: The coherent accumulation algorithm is used to fuse the imaging results of each sub-aperture to finally obtain the focused imaging result s within the complete synthetic aperture time. im for:

[0101] s im =∫s sub (k)dk (8)

[0102] This completes all the steps.

[0103] The following provides an implementation example with specific parameters.

[0104] In this example, we simulated the imaging process of a GEO bistatic SAR system, constructing 1800 seconds of sub-aperture echo data. In step 1, the simulated system parameters are shown in Table 1, the simulated GEO SAR orbit elements are shown in Table 2, and the relative positions of the GEO SAR and receiver are shown in Table 3. Figure 3 As shown, for the GEO SAR trajectory, we selected 1800 seconds of trajectory data within the time period from 23:45:00 to 00:15:00 based on the orbital elements.

[0105] Table 1 System Parameter Information

[0106]

[0107]

[0108] Table 2 Simulation Track Element Information

[0109]

[0110] We set up three point targets in the scene. The first point target is located at the receiver position, with an amplitude of 1, representing the direct wave signal. The second point target is located 100m north of the receiver (the actual distance should be very small for easy distinction), with the amplitude of each azimuth pulse set to a random number between 0 and 2, to represent direct wave interference. The third point target is located 250m east and 250m north of the receiver, with an amplitude of 0.5, representing the echo signal, indicating that the receiving antenna is pointing northeast for observation.

[0111] First, we simulated the echo information for each sub-aperture, and added 0.1 seconds of noise before and after the overall signal echo to simulate the power-on and power-off time. The 0.1-second echo signal is shown below. Figure 4 As shown.

[0112] After performing step 1.3, the result is as follows: Figure 5 The pulse pressure peak plot obtained from the parameter estimation shown shows a modulation frequency of 4 × 10⁻⁶. 10 Hz / s, consistent with simulation parameters. Figure 6 The one-dimensional signal after pulse compression is shown, where the signal on the left represents the dorsal lobe direct wave, the signal in the middle represents interference, and the signal on the right represents the echo.

[0113] After performing steps 2.1 and 2.2, the following result is obtained: Figure 7 The power-on judgment image shown shows that the power-on time period is from 0.1 seconds after the start of the acquisition to 0.1 seconds before the last echo of the whole system, with a total power-on time of approximately 30 minutes.

[0114] The following analysis will take the first sub-aperture as an example.

[0115] Perform step 2.3 to obtain the following result: Figure 8 The original echo and slant range images are shown.

[0116] Execute step 3.1 to obtain the following result: Figure 9 The sub-aperture pulse compression image shown shows the back lobe direct wave signal at the red box location. The original peak index curve and the corrected peak index curve are obtained as follows: Figure 10 As shown.

[0117] Perform step 3.2 to obtain the time-synchronized two-dimensional pulse compression image as shown below. Figure 11 As shown.

[0118] Perform step 3.3 to obtain the two-dimensional pulse compression image after slant range and phase compensation, as shown below. Figure 12 As shown.

[0119] Perform step 3.4 to obtain the sub-aperture imaging results as follows: Figure 13 As shown.

[0120] Perform step 4 to obtain the final imaging result as follows: Figure 14 As shown.

[0121] contrast Figure 10 The proposed method, using both the original and fitted indices, can eliminate the vast majority of outliers, effectively removing radio frequency interference and synchronization errors. Figure 13 and Figure 14 It can be seen that the proposed method can obtain images of the area to be imaged even with large amounts of data. The above results demonstrate the effectiveness of this patent in GEO bistatic SAR imaging processing.

[0122] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

Claims

1. A GEO (Geographic-Oriented Oscillator) bistatic SAR imaging processing method, characterized in that, include: Step 1: Obtain relevant parameters of the GEO satellite-to-ground bistatic SAR system and estimate direct wave parameter information; Step 2: Use the parameter information to determine the power-on time of GEO SAR, obtain radar data of the echo channel, and obtain sub-aperture echo data and ephemeris information through sub-aperture segmentation processing. Step 3: Using the echo data and ephemeris information, construct the back lobe direct wave signal of the echo channel, and perform phase synchronization and time synchronization. Then, after slant range and phase compensation of the synchronized signal, perform sub-aperture imaging processing. Step 4: The coherent accumulation algorithm is used to fuse the imaging results of each sub-aperture to finally obtain the focused imaging results within the complete synthetic aperture time.

2. The GEO satellite-to-ground bistatic SAR imaging processing method according to claim 1, characterized in that, The phase synchronization and time synchronization are as follows: Phase synchronization: based on the peak index [V] of each azimuth pulse. pf [n;k)], extract the peak phase information of each azimuth signal, compensate it into the azimuth signal, and complete the peak phase synchronization; Time synchronization: based on the peak index [V] of each azimuth pulse. pf [n;k)], the back lobe direct wave signal is compensated to the first column of the signal after peak phase synchronization, the signal time synchronization is completed, and finally the signal after the kth sub-aperture is synchronized is obtained.

3. The GEO satellite-to-ground bistatic SAR imaging processing method according to claim 2, characterized in that, The specific process of step 3 is as follows: Step 3.1: Using the parameter information from Step 1, process the k-th two-dimensional sub-aperture echo data S. e (n,f r k) Perform range pulse compression processing to obtain the signal S after compression of the k-th sub-aperture pulse in the frequency domain. pc (n,f r ;k);For signal S pc (n,f r k) Extract the peak index at each azimuth time point to obtain the peak index array V within the k-th sub-aperture. p (n; k), the index array is fitted to obtain the fitting curve V of the peak index. pf (n;k); Step 3.2, fit the curve V pf The peak index value of (n; k) is rounded down to obtain the peak index of each azimuth pulse [V]. pf [n; k], extract the direct peak value information of the echo channel according to the index, perform phase synchronization and time synchronization, and obtain the synchronized signal S. syn (n,f r ;k); Step 3.3: Based on the echo antenna coordinates and ephemeris, calculate the slant range history of the direct wave within the echo channel, and apply this to the synchronized signal S. syn (n,f r ;k) Perform slant range and phase compensation to obtain the compensated signal S c (n,f r ;k); Step 3.4: Use the bistatic BP algorithm to analyze the sub-aperture signal S. c (n,f r ;k) is used for imaging to obtain the imaging result s of the kth sub-aperture. sub (k).

4. The GEO satellite-to-ground bistatic SAR imaging processing method according to claim 3, characterized in that, In step 3.1, for signal S pc (n,f r k) Extract the peak index at each azimuth time point to obtain the peak index array V within the k-th sub-aperture. p (n; k), outlier removal is performed on the peak index vector, and a fourth-order fit is performed using the least squares method to obtain the fitting curve V of the peak index. pf (n;k).

5. The GEO satellite-to-ground bistatic SAR imaging processing method according to claim 2 or 4, characterized in that, The back lobe direct wave signal S in the frequency domain echo channel dpc (n,f r ;k) is: Among them, f r For faster time and frequency, B w K is the signal bandwidth. r Let Δf be the signal modulation frequency, Δf be the difference between the carrier frequencies of the illumination source and the receiver, A be a complex coefficient, ΔPRT be the difference between the pulse repetition times of the illumination source and the receiver, n be the azimuth pulse number, and τ be the signal frequency. d (n; k) represents the direct wave delay in the echo channel of the k-th sub-aperture, τ m The initial data collection time. f is the pulse repetition time at the receiving end. c The center frequency.

6. The GEO satellite-to-ground bistatic SAR imaging processing method according to claim 5, characterized in that, The peak phase for:

7. The GEO satellite-to-ground bistatic SAR imaging processing method according to claim 3, characterized in that, The compensated signal S c (n,f r ;k) is: S c (n,f r ;k) corresponds to the time-domain expression s of the range direction. c (n,τ;k) is: In the formula, A′(n;k) are complex coefficients, and τ e (n; k) represents the echo delay of the k-th sub-aperture.

8. The GEO satellite-to-ground bistatic SAR imaging processing method according to claim 3, characterized in that, Step 3.4 obtains the k-th sub-aperture imaging result s sub (k) 。 9. The GEO satellite-to-ground bistatic SAR imaging processing method according to claim 1, characterized in that, Step 1 includes: Step 1.1: Obtain the ephemeris information of the GEO SAR and the center frequency f of the payload parameters. c Time width T p And the pulse repetition frequency (PRF) and the signal modulation frequency (K) r The estimated range [K] rmin ,K rmax ]; Step 1.2: Obtain the receiver's sampling information, including the sampling rate f. s Receiver carrier frequency f c,r Receiver intermediate frequency f IF Receiver latitude and longitude coordinates and echo acquisition length T all ; Obtain the latitude, longitude, and altitude coordinates of the echo antenna in the ground receiving system, the imaging range, and the grid size; Step 1.3, extract the middle part τ of the sampling es Echo channel data within a time period, denoted as s es (t), traverse the signal frequency modulation estimation range, and for the i-th signal frequency modulation K within the estimation range... r (i) Construct the reference signal s ref (t;K r (i)), using the reference signal for s es (t) is subjected to matched filtering to obtain the pulse-compressed signal s epc (t;K r (i) extract each signal s epc (t;K r (i) The peak value is used to obtain the pulse pressure peak map result. The peak position of the pulse pressure peak map is extracted, and the horizontal axis of the peak position is used as the frequency modulation frequency of the signal. Based on the known signal duration T p The bandwidth B of the signal is obtained. w .

10. The GEO satellite-to-ground bistatic SAR imaging processing method according to claim 1, characterized in that, The specific process of step 2 is as follows: Step 2.1, traverse the echo acquisition length T all Interval ΔT j Extract the 0.1-second echo channel data, where j represents the extracted data set. Use the parameter information obtained in step 1 to perform pulse compression to obtain... One-dimensional pulse pressure images are generated; during the power-on period, the one-dimensional pulse pressure images reflect equally spaced peak pulses, while during the power-off period, the one-dimensional pulse pressure images reflect equally amplitude noise signals. Step 2.2, in the initial stage of data collection, the j-th... left Group j represents the data in the power-off state. left +1 data represents the device being powered on. During the later stages of data acquisition, the j-th data... right Group j represents the power-on status. right +1 data represents the power-off state; during the acquisition time of the two data segments, the echo channel data is extracted at 1-second intervals, and the operation in step 2.1 is repeated to finally obtain the power-on time range T. s ; Step 2.3, based on the power-on time range T in Step 2.2 s Extract the kth sub-aperture echo data S every 2 seconds. e (n,f r ;k), and generate satellite position coordinates P for the power-on period based on ephemeris information. s The satellite position coordinates P corresponding to the sub-aperture were extracted. s (t;k).

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