A comprehensive acquisition method of target environment and situation based on XTI and ATI interference

Abstract

The present invention provides a method for comprehensively acquiring target environment and situation based on XTI and ATI interference, comprising the following steps: Step 1, completing data processing based on track-cutting interference data to obtain the DEM of the scene, wherein the DEM of the scene includes the lower viewing angle in the scene and the height of the position corresponding to the lower viewing angle; Step 2, performing along-track interference data processing in combination with the DEM of the scene to obtain the position of the moving target; the along-track interference data processing includes along-track data imaging processing, image registration, channel error compensation, moving target detection and motion parameter estimation. The present invention simultaneously acquires the along-track interference data of a region, and jointly processes the DEM obtained by the track-cutting interference data processing and the moving target information obtained by the along-track interference data processing, and iterates multiple times to improve the environment and situation accuracy of the region.

Description

Technical Field

[0001] The invention belongs to the technical field of radars and relates to a method for comprehensively acquiring target environment and situation based on XTI and ATI interference. Background Art

[0002] Synthetic aperture radar (SAR) can obtain scattering intensity information of ground resolution units and phase information related to slant range by actively imaging the ground with microwaves. Interferometric SAR (InSAR) obtains two imaging results of the same area in the cross-track direction or along-track direction, and then extracts the phase difference result by interferometric processing of the two images to obtain the interference pattern. Cross-track InSAR (XTI) can be used to extract surface elevation information, establish a digital elevation model (DEM), and obtain environmental information in the scene; along-track InSAR (ATI) can be used to extract the motion information of the target (scene) and obtain the situation information of the scene.

[0003] With the development of synthetic aperture radar technology, the processing technology of single on-track interferometry or single along-track interferometry data has become very mature, but there has been no relevant report on the joint processing of along-track interferometry data. In order to improve the accuracy of obtaining moving target information and the accuracy of obtaining elevation environment, it is necessary to improve the comprehensive acquisition accuracy of target environment and situation through along-track joint processing. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a method for comprehensively acquiring target environment and situation based on XTI and ATI interference, comprising the following steps:

[0005] Step 1: completing data processing based on the track cutting interference data to obtain the DEM of the scene, wherein the DEM of the scene includes a lower viewing angle in the scene and the height of the position corresponding to the lower viewing angle;

[0006] Step 2: Perform along-track interferometric data processing in combination with the DEM of the scene to obtain the position of the moving target; the along-track interferometric data processing includes along-track data imaging processing, image registration, channel error compensation, moving target detection and motion parameter estimation.

[0007] Furthermore, after the step of estimating motion parameters, the method further includes:

[0008] Step 3: Based on the result of moving target parameter estimation, the track cutting interferometry data is processed, and the residual point phase error caused by the moving target is compensated according to the obtained target position, so as to obtain the DEM information of the new scene.

[0009] Furthermore, after obtaining the DEM of the new scene, it also includes:

[0010] Step 4: Repeat steps 2 and 3 to improve the scene target information and situation accuracy through multiple iterations until the scene elevation change or the moving target parameter estimation result change between two iterations is less than the set threshold.

[0011] Furthermore, the method is implemented based on an antenna system, which includes antenna 1 and antenna 2, each of which includes at least one antenna channel, wherein at least one antenna includes at least two antenna channels; a track-along baseline is formed between two adjacent channels of the same antenna, and a track-off baseline is formed between antenna channels symmetrically axially along the nose direction of the carrier aircraft between different antennas, and antenna 1 and antenna 2 are loaded on the carrier aircraft.

[0012] Furthermore, assuming that the height of all positions in the scene is h and the downward angle is θ, B is the baseline between the cutting track antennas, H is the flight altitude of the carrier, r1 and r2 are the distances between the two antennas and the target, α is the roll angle of the carrier, θ is the downward angle corresponding to the target, Φ is the interferometric phase after unwrapping obtained by the two antennas through cutting track interferometry, and λ is the signal wavelength, then

[0013]

[0014] Since the interference phase Φ after the scene is unwrapped, the track baseline B, the roll angle α and the wavelength λ are known, the downward viewing angle θ of each position in the scene is calculated by the above formula, and the height of all positions in the scene is obtained as follows:

[0015] h=Hr cosθ

[0016] Among them, H is the flight altitude of the carrier aircraft, and r is the position of the target in the scene from the antenna.

[0017] Furthermore, in the presence of a drift angle β, the along-track baseline is decomposed into the along-track baseline By along the flight trajectory direction and the off-track baseline Bx perpendicular to the flight trajectory direction, wherein the phase introduced by the off-track baseline Bx perpendicular to the flight trajectory direction is When detecting moving targets, it is an interference term. The phase caused by the baseline along the flight trajectory is The phase required for actual moving target detection;

[0018] The track-cutting baseline Bx in the vertical flight trajectory direction is obtained by the drift angle β and the track-cutting baseline Bs between the channels:

[0019] Bx=Bs·sinβ

[0020] The phase introduced by the track-cutting baseline Bx in the vertical flight trajectory direction in the scene It is obtained by the following formula:

[0021]

[0022] Then the actual phase caused by the along-track baseline Bs is:

[0023]

[0024] in, is the phase obtained by interfering the two antenna channels along the baseline, is the phase brought by the track-cutting baseline due to the deviation angle β.

[0025] Furthermore, the relationship between the pixel points of the moving target T on the image and the earth coordinate system is established through the distance equation between the moving target T and the sensor S of the carrier, the range Doppler positioning equation and the earth ellipsoid model equation, and the relationship between the target and the platform is established as follows:

[0026]

[0027] Among them, (X S ,Y S ,Z S ) and (V SX ,V SY ,V SZ ) represent the position vector and velocity vector of the carrier in the earth coordinate system respectively; slant range R = R0 + x·d r , R0 is the perigee slant distance, d r is the slant range resolution, x is the number of points along the range axis from the perigee R0 of the moving target in the image; f DC is the Doppler frequency, estimated through the image; λ is the wavelength of the radar, R e is the Earth’s equatorial radius, R p is the polar radius, h is the height of the moving target;

[0028] According to the above three equations, solve the position of the moving target (X t ,Y t ,Z t ).

[0029] Furthermore, in step 3, the residual point phase error caused by compensating the moving target according to the obtained target position is specifically:

[0030] The phase difference loop integral R(i,j) starting from the pixel point (i,j) in the DEM of the definition scene is:

[0031]

[0032] Among them, Δ nrepresents the phase gradient in the loop; if R(i,j)=0, it means that point (i,j) is a continuous point. If |R(i,j)|=2π, then the point is a residual point. Then the phase derivative variance is used to compensate the residual point phase. The phase derivative variance is expressed by z i,j Indicates, specifically:

[0033]

[0034] in, and represents the gradient in the row and column directions, and express The mean value in the k×k window; in order to compensate for the residual point phase, Define the compensation factor φ n for:

[0035]

[0036] Among them, z n Represents the phase derivative variance of a pixel on the residual point loop integral, then:

[0037]

[0038] Among them, (i, j) represents the position of the residual point caused by the moving target detected by GMTI in the interference graph.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] The present invention provides a method for comprehensively acquiring target environment and situation based on XTI and ATI interference, which combines the information of moving target and elevation in two dimensions, and continuously improves the accuracy of moving target and elevation information through iterative optimization. Compared with the traditional single along-track interference or single off-track interference to obtain moving target and elevation information respectively, this method can improve the accuracy of target environment and comprehensive situation acquisition. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is the flow chart of conventional track cutting interferometry DEM inversion.

[0042] Figure 2 This is a DEM map of the scene according to an embodiment of the present invention.

[0043] Figure 3 This is a DEM inversion result diagram of an embodiment of the present invention.

[0044] Figure 4 This is a schematic diagram of the principle of rail cutting interferometry height measurement according to an embodiment of the present invention.

[0045] Figure 5Flowchart for obtaining moving target information during along-track interferometric motion.

[0046] Figure 6 It is a schematic diagram of the decomposition of the along-track interferometric baseline in the presence of a drift angle according to an embodiment of the present invention.

[0047] Figure 7 This is the principle diagram of target range Doppler positioning.

[0048] Figure 8 The present invention is a flowchart of a method for comprehensively acquiring a target environment and a situation in combination with track-cutting interference according to an embodiment of the present invention.

[0049] Fig. 9 It is a schematic diagram of the along-track interference phase after inter-channel error compensation and filtering processing according to an embodiment of the present invention.

[0050] Fig.10 Result diagram of target detection according to an embodiment of the present invention.

[0051] Fig.11 This is a target detection position diagram of an embodiment of the present invention. DETAILED DESCRIPTION

[0052] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0053] The purpose of the present invention is to provide a method for comprehensively acquiring target environment and situation based on XTI and ATI interference, by simultaneously acquiring along-track interference data and off-track interference data of a region, jointly processing the DEM (Digital Elevation Model) obtained by processing the off-track interference data and the moving target information obtained by processing the along-track interference data, and iterating multiple times to improve the accuracy of the environment and situation of the region. The method is implemented based on an antenna system, the antenna system includes antenna 1 and antenna 2, the antenna 1 and antenna 2 each include at least one antenna channel, wherein at least one antenna includes at least two antenna channels; the two adjacent channels of the same antenna constitute a along-track antenna, and the corresponding antenna channels between different antennas constitute a off-track antenna. In a specific embodiment, the antenna 1 and antenna 2 are loaded on a carrier, the antenna 1 includes three antenna channels from channel 1 to channel 3, and the antenna 2 includes three antenna channels from channel 1 to channel 3. The antenna channels of the antenna 1 or antenna 2 constitute a along-track baseline, and the antenna channels symmetrical along the nose direction of the carrier between the antenna 1 and the antenna 2 constitute a off-track baseline, such as Figure 4 shown.

[0054] The target environment and situation comprehensive acquisition method based on XTI and ATI interference implemented by the above antenna system specifically includes the following steps: Figure 8 As shown:

[0055] Step 1: Based on the track interferometry data, complete the track interferometry data processing to obtain the DEM of the scene. The specific process of track interferometry data processing includes track interferometry data imaging processing, image registration, phase filtering, phase unwrapping and DEM inversion. The DEM of the scene is obtained through the above conventional processing process. The conventional processing process is as follows: Figure 1 The DEM of the scene is shown as Figure 2 As shown in Figure 2, the DEM inversion results are as follows: Figure 3 shown.

[0056] The principle diagram of height measurement in rail cutting interference data processing is as follows Figure 4 As shown, B is the track cutting baseline, H is the aircraft flight altitude, r1 and r2 are the distances between antenna 1 and antenna 2 and the target, α is the aircraft roll angle, θ is the downward viewing angle corresponding to the target, Φ is the unwrapped interference phase obtained by the two antennas through track cutting interference, and λ is the signal wavelength. Then we have

[0057]

[0058] Since the interference phase Φ after the scene is unwrapped, the track baseline B, the roll angle α and the wavelength λ are known, the downward viewing angle θ of each position in the scene can be calculated by the above formula, and the height of all positions in the scene is obtained as

[0059] h=Hr cosθ

[0060] Where H is the aircraft's flight altitude, and r is the position of the target in the scene from the antenna, which can be accurately calculated using the gate and the number of points.

[0061] Step 2: Combine the DEM of the scene to perform along-track interferometry data processing to assist in improving the accuracy of channel error compensation, thereby improving the accuracy of moving target detection and reducing the probability of false alarms. The along-track interferometry data processing process includes along-track data imaging processing, image registration, channel error compensation, moving target detection and motion parameter estimation, such as Figure 5 shown.

[0062] After acquiring the DEM data of the scene, the known three-dimensional information can be used to remove the inter-channel phase error caused by the off-track interference baseline in the along-track interferometric data alignment, thereby improving the accuracy of channel error compensation, thereby increasing the probability of moving target detection and reducing the probability of false alarm.

[0063] Figure 6The schematic diagram of dual-antenna down-track interferometry is given. Channel 2 of antenna 1 and channel 2 of antenna 2 constitute the down-track baseline. Each antenna contains three channels, and each channel of each antenna constitutes the down-track baseline. In the presence of a drift angle β, the down-track baseline between channel 1 and channel 2 can be decomposed into the down-track baseline By along the flight trajectory and the down-track baseline Bx in the direction perpendicular to the flight trajectory. The phase introduced by the down-track baseline Bx in the direction perpendicular to the flight trajectory is When detecting moving targets, it is an interference term. The phase caused by the baseline along the flight trajectory is It is the phase required for actual moving target detection.

[0064] The track-cutting baseline Bx in the vertical flight trajectory direction can be obtained from the drift angle β and the track-cutting baseline Bs between the channels:

[0065] Bx=Bs·sinβ

[0066] Through step 1, the downward viewing angle θ of all positions in the scene is obtained. Then the phase introduced by the track-cutting baseline Bx in the vertical flight trajectory direction in the scene is It can be obtained by the following formula:

[0067]

[0068] Then the actual phase caused by the along-track baseline is:

[0069]

[0070] in, is the phase obtained by interfering the two antenna channels along the baseline, is the error phase caused by the track cutting baseline due to the deviation angle.

[0071] When performing channel error compensation in the process of processing along-track interferometric data, removing the error phase caused by the track-cutting baseline due to the deviation angle can make the moving target detection more accurate and reduce the false alarm rate. At the same time, it can also help improve the positioning accuracy of moving targets, eliminate obviously unrealistic targets, and reduce the false alarm probability of moving targets based on terrain information matching, such as eliminating moving targets whose positioning results are between mountain roads and moving targets in gullies.

[0072] Finally, by combining terrain information, coherence coefficient, backscatter coefficient and other information, the scene content is judged to further reduce the probability of false alarms, such as eliminating targets moving in forests, lakes, farmlands or narrow residential areas.

[0073] Use the DEM of the scene to accurately locate the moving target and improve the positioning accuracy of the moving target.

[0074] like Figure 7As shown in the figure, S is the sensor, T represents the moving target, and XOYOZ is the earth coordinate system. The relationship between the pixel points of the moving target on the image and the earth coordinate system can be established through the distance equation between the moving target T and the sensor S, the range Doppler positioning equation, and the earth ellipsoid model equation. The relationship between the target and the platform can be established as follows:

[0075]

[0076] Among them, (X S ,Y S ,Z S ) and (V SX ,V SY ,V Sz ) represent the position vector and velocity vector of the aircraft in the earth coordinate system respectively; slant range R = R0 + x·d r , R0 is the perigee slant distance, d r is the slant range resolution, x is the number of points along the range axis of the target in the image at the slant range R0; f DC is the Doppler frequency, estimated through the image; λ is the wavelength of the radar, R e is the Earth’s equatorial radius, R p is the polar radius, and h is the terrain height at the target location.

[0077] According to the above three equations, the moving target position (X t ,Y t ,Z t ) three unknown quantities. Since the target positioning result is closely related to the elevation h of the scene where the target is located, the DEM of the scene obtained by track cutting interferometry can improve the positioning accuracy of the moving target.

[0078] The along-track interference phase after inter-channel error compensation and filtering is as follows Fig. 9 As shown, combined with target positioning, the target detection results and positions are obtained as follows Fig.10 and Fig.11 shown.

[0079] Step 3 processes the track cutting interferometry data according to the moving target position obtained in step 2, compensates for the residual point phase caused by the moving target, reduces the track cutting interferometry phase unwrapping error, obtains a new DEM of the scene, and improves the DEM inversion accuracy. Since the moving target cannot be focused, the position of the moving target in the interference pattern is inaccurate when processing the track cutting interferometry data, which affects the interference phase of the area and produces the residual point position of the phase unwrapping, which has a certain impact on the accuracy of the phase unwrapping.

[0080] The area affected by the moving target can be obtained through accurate parameter estimation of the moving target. The phases of these residual points can be compensated during the phase unwrapping of the track-crossing interferometer to reduce the probability of unwrapping errors, thereby improving the accuracy of DEM inversion.

[0081] The phase difference loop integral starting from the pixel point (i, j) in the DEM of the definition scene is:

[0082]

[0083] Among them, Δ n Represents the phase gradient in the loop. If R(i,j)=0, it means that point (i,j) is a continuous point. If |R(i,j)|=2π, then the point is a residual point. The phase of the residual point can be compensated by the phase derivative variance, which can be expressed as:

[0084]

[0085] in, and represents the gradient in the row and column directions, and express The mean and variance of the phase derivative in the k×k window can reflect the quality of the phase map. In order to compensate the residual point phase, The compensation factor is defined as:

[0086]

[0087] Among them, z n Represents the phase derivative variance of a pixel on the residual point loop integral, then:

[0088]

[0089] Where (i, j) represents the position of the residual point caused by the moving target detected by GMTI (Ground moving target indication) in the interferogram. The residual point is compensated and then phase unwrapped to improve the unwrapping accuracy, thereby improving the height measurement accuracy.

[0090] Step 4: Repeat steps 2 and 3 to improve the accuracy of scene target information and situation through multiple iterations until the change in scene elevation or the change in the estimated result of the moving target parameter between two iterations is less than the set threshold, and output the results of the moving target environment and situation.

[0091] The DEM auxiliary information is used to comprehensively improve the accuracy of target acquisition during on-track interferometry. The improvement of target acquisition accuracy will also improve the DEM inversion accuracy during off-track interferometry and improve the accuracy of target environment acquisition. Therefore, through multiple iterative optimizations, the comprehensive acquisition accuracy of target environment and situation can be continuously improved.

[0092] The invention discloses a method for comprehensively acquiring target environment and situation based on XTI and ATI interference. For the on-track baseline and along-track baseline interference data simultaneously acquired in the same scene, the on-track interference data is firstly processed to obtain DEM data of the scene. Then, channel error compensation is performed in combination with DEM while processing the along-track interference data, so as to improve the detection probability of moving targets and suppress the false alarm rate. Then, the detailed position information of the moving targets is solved by the RD principle. Finally, the moving target parameter estimation result acquired by the along-track interference is fed back to the on-track interference data processing flow. During phase unwrapping, the residual points caused by the moving targets are avoided, so as to improve the phase unwrapping accuracy and thus optimize the DEM inversion accuracy. The final target environment and situation of the scene are acquired through multiple iterations.

[0093] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for comprehensive acquisition of target environment and situation based on XTI and ATI interference, characterized in that: The method is implemented based on an antenna system, wherein the antenna system includes an antenna 1 and an antenna 2, wherein the antenna 1 and the antenna 2 each include at least one antenna channel, wherein at least one antenna includes at least two antenna channels; two adjacent channels of the same antenna constitute a track-along baseline, and antenna channels symmetrical along the nose direction of the carrier aircraft between different antennas constitute a track-off baseline, wherein the antenna 1 and the antenna 2 are loaded on the carrier aircraft, and the method includes the following steps: Step 1: Complete data processing based on the track cutting interference data to obtain the DEM of the scene. The DEM of the scene includes the lower viewing angle in the scene and the height of the position corresponding to the lower viewing angle. Assume that the height of all positions in the scene is and the lower viewing angle is , B is the baseline between the cutting track antennas, H is the flight altitude of the carrier aircraft, and are the distances between the two antennas and the target, is the aircraft roll angle, is the lower viewing angle corresponding to the target, is the unwrapped interference phase obtained by the two antennas through the cut-track interferometry, is the signal wavelength, then ; Due to the interference phase after scene unwrapping , track cutting baseline B, rolling angle and wavelength As a known quantity, the downward viewing angle of each position in the scene is calculated by the above formula , and the height of all positions in the scene is: Where H is the flight altitude of the aircraft, is the position of the target in the scene from the antenna; Step 2: Performing along-track interferometric data processing in combination with the DEM of the scene to obtain the position of the moving target; the along-track interferometric data processing includes along-track data imaging processing, image registration, channel error compensation, moving target detection and motion parameter estimation; In the presence of a drift angle In the case of and the track-tangent baseline perpendicular to the flight path , where the vertical flight trajectory direction is the track baseline Phase introduced It is an interference item in the detection of moving targets, and the baseline along the flight trajectory The phase brought The phase required for actual moving target detection; The vertical flight path direction By the drift angle The baseline between the channels get: ; The track baseline in the scene due to the vertical flight trajectory direction Phase introduced It is obtained by the following formula: ; then the along-track baseline The actual phase caused is: ;in, is the phase obtained by interfering the two antenna channels along the track baseline, Due to the deviation angle The phase caused by the track cutting baseline; The relationship between the pixel points of the moving target T on the image and the earth coordinate system is established through the distance equation between the moving target T and the sensor S of the carrier, the range Doppler positioning equation and the earth ellipsoid model equation. The relationship between the target and the platform is established as follows: ;in, and Respectively represent the position vector and velocity vector of the carrier in the earth coordinate system; slant range , is the perigee slant distance, is the slant range resolution, The slant distance from the perigee to the moving target in the image The number of points; is the Doppler frequency, estimated from the image; is the wavelength of the radar, is the Earth's equatorial radius, is the polar radius, is the height of the moving target; According to the above three equations, solve the position of the moving target ; Step 3: Based on the result of moving target parameter estimation, the track cutting interferometry data is processed, and the residual point phase error caused by the moving target is compensated according to the obtained target position, so as to obtain the DEM information of the new scene; the residual point phase error caused by the moving target is compensated according to the obtained target position as follows: The pixels in the DEM that define the scene The phase difference loop integral with the starting point for: ;in, represents the phase gradient in the loop; if , explain the point For continuous points, if , then this point is the residual point, and the phase derivative variance is used to compensate the residual point phase. The phase derivative variance is expressed as Indicates, specifically: ;in, and represents the gradient in the row and column directions, and express , exist The mean of the window; in order to compensate for the residual point phase, , define the compensation factor for: ;in, Represents the phase derivative variance of a pixel on the residual point loop integral, then: ;in, It indicates the position of the residual point in the interference pattern caused by the moving target detected by GMTI.

2. The method for comprehensive acquisition of target environment and situation based on XTI and ATI interference according to claim 1, characterized in that: After obtaining the DEM of the new scene, it also includes: Step 4: Repeat steps 2 and 3 to improve the scene target information and situation accuracy through multiple iterations until the scene elevation change or the moving target parameter estimation result change between two iterations is less than the set threshold.

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