Satellite-borne SAR (Synthetic Aperture Radar) scene matching curve imaging wave control optimization method for overlay and shadow suppression

Abstract

The invention discloses a spaceborne SAR (Synthetic Aperture Radar) scene matching curve imaging wave control optimization method oriented to overlay and shadow suppression, which comprises the following steps of: respectively establishing a measurement and calculation model of a full-scene overlay rate and a shadow rate according to the change of a geometrical relationship such as a slant distance and a visual angle in a spaceborne SAR imaging model, and combining actually measured DEM (Digital Elevation Model) data to optimize the overlay rate and the shadow rate of the whole scene; according to the method, the initial squint angle is optimized and configured under the requirements of a specified squint range and ensuring the width of an imaging band, so that the weighted sum of the overlay rate, the shadow rate and the average width is minimum, and the overlay and shadow suppression-oriented satellite-borne SAR scene matching curve imaging wave control optimization is realized. According to the method, the problems that the existing satellite-borne SAR scene matching curve imaging does not have the capability of estimating the overlay and shadow areas and cannot suppress the overlay and shadow in the imaging task are solved, and the defects in the prior art are overcome.

Description

Technical Field

[0001] The present invention belongs to the technical field of synthetic aperture radar, and particularly relates to a method for optimizing the wave control of spaceborne SAR scene matching curve imaging for layover and shadow suppression. Background Art

[0002] Long curve scenes are an important type of scenes observed by spaceborne SAR, such as coastlines, railways, rivers, seismic faults, etc. The imaging strip of the traditional spaceborne SAR imaging mode is parallel to the satellite track. When imaging long curve scenes, the overall width of the along-track imaging strip is often increased through multi-track revisit and multi-imaging strip splicing. Spaceborne SAR scene matching curve imaging generates an imaging strip that "matches" the curve scene by continuously adjusting the pitch and azimuth beam pointing, so as to achieve high-efficiency imaging of long curve scenes.

[0003] In SAR images, layover and shadow are geometric distortions caused by the squint imaging mode, especially in areas with large terrain undulations, such as mountainous areas or urban environments. Layover is caused by the terrain slope angle being greater than the radar down-view angle, resulting in the echo signal from the top of the slope arriving at the radar receiver earlier than that from the bottom of the slope, causing the echoes from regions at different heights in the ground scene to be superimposed into the same slant range resolution cell, thus causing ground object distortion and affecting terrain mapping and target recognition; while shadow is due to the large down-view angle of the radar beam. When encountering steep mountains or tall buildings, the back slope of the target cannot be irradiated by the radar wave, so no echo can be received in this area, and finally a black "shadow" area is formed in the SAR image.

[0004] At present, there is no determination model for layover and shadow areas in spaceborne SAR scene matching curve imaging, lacking the ability to estimate layover and shadow areas in the imaging task, and unable to guarantee the quality of data acquisition. Therefore, it is necessary to carry out research on a method for optimizing the wave control of spaceborne SAR scene matching curve imaging for layover and shadow suppression according to the geometric model of spaceborne SAR scene matching curve imaging. Based on the measured DEM data, a determination model for layover and shadow is established according to the changes in radar view angle and slant range. Under the requirements of specifying the squint range and ensuring the imaging strip width, the initial squint angle of the configuration is optimized to achieve the wave control optimization of spaceborne SAR scene matching curve imaging for layover and shadow. Summary of the Invention

[0005] In view of this, the present invention provides a method for optimizing the wave control of spaceborne SAR scene matching curve imaging for layover and shadow suppression, realizing the wave control optimization of spaceborne SAR scene matching curve imaging for layover and shadow suppression.

[0006] To achieve the above invention purpose, the technical solution of the present invention is as follows:

[0007] A spaceborne SAR scene matching curve imaging wave control optimization method for layover and shadow suppression, the specific steps are as follows:

[0008] Step 1: In the geometric model of spaceborne SAR scene matching curve imaging, according to the changes of the viewing angle and the slant range, establish a layover determination model, and output the coordinates of the layover area and the full-scene layover rate;

[0009] Step 2: In the geometric model of spaceborne SAR scene matching curve imaging, according to the changes of the viewing angle and the slant range, establish a shadow determination model, and output the coordinates of the shadow area and the full-scene shadow rate;

[0010] Step 3: Based on the measured DEM data, under the requirements of the specified squint range and ensuring the imaging swath width, output the optimal initial squint angle of the configuration, so that the weighted sum of the layover rate, the shadow rate and the average swath width is the smallest.

[0011] Further, the specific method of Step 1 is as follows:

[0012] According to the geometric relationship between the incident angle θ1 and the upslope gradient γ1 when layover occurs in the spaceborne SAR scene matching curve imaging model, the condition for the occurrence of the layover area is obtained as:

[0013] 180 - γ1 - θ1 < 90 (1)

[0014] Among them, the relationship between the incident angle θ1 and the downview angle β1 is:

[0015] θ1 = 90 - β1 (2)

[0016] Substituting equation (2) into equation (1), the condition for the occurrence of the layover area can be obtained as:

[0017] β1 < γ1 (3)

[0018] Therefore, the layover area determination algorithm for spaceborne SAR scene matching curve imaging of the present invention is proposed, which is divided into the following six steps:

[0019] (1) Input the satellite flight position sequence, the beam center illumination trajectory sequence, and the range-direction beam width;

[0020] (2) At the current azimuth moment, within the zero-Doppler plane and within the range of the range-direction beam width, sample at equal angular intervals to obtain n beam pointing directions, and respectively find the first intersection points with the ground on each beam pointing direction to obtain n beam pointing vectors;

[0021] (3) Within the zero Doppler plane and within the range of the range beam width, rotate the current beam pointing vector around the satellite position. If the elevation of the end point of any rotated beam pointing vector is less than the elevation of the corresponding longitude and latitude point in the DEM data, it is determined that layover occurs. Record the longitude and latitude of the end point of the current beam pointing vector before rotation, which is the coordinate point where layover occurs;

[0022] (4) Repeat step (3) until all beam pointing vectors at the current azimuth moment are traversed;

[0023] (5) Repeat steps (2) and (3) until all azimuth moments are traversed. The ratio of the number of points where layover occurs to the number of all sampling points is the layover rate;

[0024] (6) Output the longitude and latitude of all points where layover occurs and the full-scene layover rate.

[0025] Furthermore, the specific method of step two is as follows:

[0026] According to the geometric relationship between the incident angle θ2 and the backslope gradient γ2 when shadowing occurs in the spaceborne SAR scene matching curve imaging model, the condition for the occurrence of shadowing is obtained as:

[0027] θ2 < γ2 (4)

[0028] Thus, the shadow area determination algorithm for the spaceborne SAR scene matching curve imaging of the present invention is proposed, which is divided into the following six steps:

[0029] (1) Input the satellite flight position sequence, the beam center illumination trajectory sequence, and the range beam width;

[0030] (2) At the current azimuth moment, sample at equal angular intervals within the zero Doppler plane and within the range of the range beam width to obtain n beam pointings. Respectively find the first intersection point with the ground on each beam pointing to obtain n beam pointing vectors;

[0031] (3) On the current beam pointing, extend the beam pointing vector at equal intervals to 2% of its original length. If the elevation of the end point of the extended beam pointing vector is greater than the elevation of the corresponding longitude and latitude point in the DEM data, it is determined that shadowing occurs. Record the longitude and latitude of the end point of the extended current beam pointing vector, which is the coordinate point where shadowing occurs;

[0032] (4) Repeat step (3) until all beam pointing vectors at the current azimuth moment are traversed;

[0033] (5) Repeat steps (2) and (3) until all azimuth moments are traversed. The ratio of the number of points where shadowing occurs to the number of all sampling points is the shadow rate;

[0034] (6) Output the longitude and latitude of all shaded points and the full-scene shadow rate.

[0035] Further, the specific method in Step 3 is as follows:

[0036] Under the requirements of specifying the squint range and ensuring the imaging swath width, using the initial squint angle of the configuration as the optimization variable, the wave control design is completed by the spaceborne SAR along-track multi-target imaging space-ground configuration joint design and optimization method. The output satellite flight position sequence, beam center illumination trajectory sequence, etc. are used as the input of the method proposed in this patent. Based on the measured DEM data, the algorithms described in Steps 1 and 2 are substituted for calculation. The weighted sum of the full-scene layover, shadow rate, and average swath width obtained is calculated. When the obtained sum is the smallest, this initial squint angle is the optimal initial squint angle of the configuration, as shown in the following formula:

[0037]

[0038] where φ i is the initial squint angle of the configuration, cost_i Layover , cost_i Shadow , W r represent the corresponding layover rate, shadow rate, and average swath width respectively, and α is the penalty term coefficient.

[0039] Beneficial effects:

[0040] 1. The present invention solves the problems that the existing spaceborne SAR scene matching curve imaging has no ability to estimate the layover and shadow areas and cannot suppress the layover and shadow in the imaging task. Under the requirements of specifying the squint range and ensuring the imaging swath width, by optimizing the initial squint angle of imaging, the wave control optimization of spaceborne SAR scene matching curve imaging for layover and shadow suppression is realized.

[0041] 2. In Steps 1 and 2 of the present invention, according to the changes in geometric relationships such as slant range and viewing angle in the spaceborne SAR imaging model, the measurement models of the full-scene layover rate and shadow rate are respectively established, and the calibration and estimation of the layover and shadow in the imaging task can be realized in combination with the measured DEM data.

[0042] 3. In Step 3 of the present invention, under the requirements of specifying the squint range and ensuring the imaging swath width, the initial squint angle is optimized to minimize the weighted sum of the layover rate, shadow rate, and average swath width, thereby realizing the wave control optimization of spaceborne SAR scene matching curve imaging for layover and shadow suppression. Description of the Drawings

[0043] Figure 1 is a schematic diagram of the formation of layover and shadow in the spaceborne SAR scene matching curve imaging described in the present invention;

[0044] Figure 2It is the flowchart of the method for determining layover and shadow in spaceborne SAR scene matching curve imaging according to the present invention;

[0045] Figure 3 It is the simulation result of layover and shadow in the whole scene before optimization obtained by the method proposed in the present invention in the embodiment. (a) Simulation result of layover and shadow in the whole scene before optimization, (b) Enlarged schematic diagram of Region 1, (c) Enlarged schematic diagram of Region 2;

[0046] Figure 4 It is the simulation result of layover and shadow in the whole scene after optimization obtained by the method proposed in the present invention in the embodiment. (a) Simulation result of layover and shadow in the whole scene after optimization, (b) Enlarged schematic diagram of Region 1, (c) Enlarged schematic diagram of Region 2;

[0047] Figure 5 It is the comparison diagram of the effects of layover in the whole scene before and after optimization obtained by the method proposed in the present invention in the embodiment. (a) Before optimization of layover in the whole scene, (b) After optimization of layover in the whole scene;

[0048] Figure 6 It is the comparison diagram of the effects of shadow in the whole scene before and after optimization obtained by the method proposed in the present invention in the embodiment. (a) Before optimization of shadow in the whole scene, (b) After optimization of shadow in the whole scene. Detailed implementation manners

[0049] In order to enable those skilled in the art to better understand the solution of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present application.

[0050] The flowchart of the method for optimizing the waveform control of spaceborne SAR scene matching curve imaging for layover and shadow suppression according to the present invention is as Figure 1 shown. The present invention includes the following steps:

[0051] Step 1: In the geometric model of spaceborne SAR scene matching curve imaging, according to the changes of the viewing angle and the slant range, establish a determination model for layover, and output the coordinates of the layover area and the layover rate of the whole scene;

[0052] Figure 1The schematic diagram of the formation of the layover area is given. The red dot in the upper left corner represents the position of the radar. The red dashed line represents the irradiation path of the radar beam. The black dashed line represents the isoslant range line. β and θ respectively represent the depression angle and the incidence angle of the radar signal. γ1 represents the slope of the uphill slope, and γ2 represents the slope of the downhill slope. IJAB is the target area. When the radar irradiates the uphill slope in the order of ABCDE, the slant range first decreases and then increases as the ground distance increases. This results in the phenomenon that the backscatters from different positions in the target areas AB and DE reach the radar receiver simultaneously. These backscatters from different positions are superimposed in the same range resolution cell. The superposition of the backscatter energy makes the layover area appear as a bright area in the SAR image. The area AB is the layover area. According to the geometric relationship in the figure, the condition for the slant range to gradually decrease from the bottom to the top of the uphill slope is:

[0053] 180 - γ1 - θ1 < 90 (1)

[0054] Where the relationship between the incidence angle and the depression angle is:

[0055] θ1 = 90 - β1 (2)

[0056] Substituting equation (2) into equation (1), the condition for the appearance of the layover area can be obtained as:

[0057] β1 < γ1 (3)

[0058] According to equation (3), the condition for the appearance of the layover phenomenon is that the depression angle of the radar is less than the slope of the uphill slope.

[0059] Figure 2 The algorithm flowchart for determining the layover area is given, which is divided into the following six steps:

[0060] (1) Input the satellite flight position sequence, the beam center irradiation trajectory sequence, and the range beam width.

[0061] (2) At the current azimuth moment, within the zero Doppler plane and within the range of the range beam width, sample at equal angular intervals to obtain n beam pointing directions. Respectively find the first intersection points with the ground for each beam pointing direction to obtain n beam pointing vectors.

[0062] (3) Within the zero Doppler plane and within the range of the range beam width, rotate the current beam pointing vector around the satellite position. If the elevation of the end point of any rotated beam pointing vector is less than the elevation of the corresponding longitude and latitude point in the DEM data, it is determined that the layover phenomenon has occurred. Record the longitude and latitude of the end point of the current beam pointing vector before rotation, which is the coordinate point where the layover occurs.

[0063] (4) Repeat step (3) until all beam pointing vectors at the current azimuth moment are traversed.

[0064] (5) Repeat steps (2) and (3) until all azimuth times are traversed. The ratio of the number of points with layover to the total number of sampling points is the layover rate.

[0065] (6) Output the longitude and latitude of all points with layover and the full-scene layover rate.

[0066] Step 2: In the geometric model of spaceborne SAR scene matching curve imaging, establish a shadow determination model according to the changes in viewing angle and slant range, and output the coordinates of the shadow area and the full-scene shadow rate.

[0067] Figure 1 The schematic diagram of the formation of the layover area is given. The target area IJ on the back slope is blocked by the higher area FG, resulting in no radar echo signal in this area, which is the shadow area. According to the geometric relationship in the figure, the condition for the radar signal to be blocked is:

[0068] θ2 < γ2 (4)

[0069] According to equation (4), it can be known that the condition for the shadow phenomenon to occur is that the radar incidence angle is less than the back slope gradient.

[0070] Figure 2 The algorithm flow chart for shadow area determination is given, which is divided into the following six steps:

[0071] (1) Input the satellite flight position sequence, beam center illumination trajectory sequence, and range beam width.

[0072] (2) At the current azimuth time, sample at equal angular intervals within the zero Doppler plane and within the range of the range beam width to obtain n beam directions. Respectively find the first intersection points with the ground on each beam direction to obtain n beam direction vectors.

[0073] (3) On the current beam direction, extend the beam direction vector at equal intervals to 2% of its original length. If the elevation of the end point of the extended beam direction vector is greater than the elevation of the corresponding longitude and latitude point in the DEM data, it is determined that the shadow phenomenon has occurred, and record the longitude and latitude of the end point of the current extended beam direction vector, which is the coordinate point where the shadow is generated.

[0074] (4) Repeat step (3) until all beam direction vectors at the current azimuth time are traversed.

[0075] (5) Repeat steps (2) and (3) until all azimuth times are traversed. The ratio of the number of points with shadow to the total number of sampling points is the shadow rate.

[0076] (6) Output the longitude and latitude of all shadow points and the full-scene shadow rate.

[0077] Step 3: Based on the measured DEM data, under the requirements of a specified squint range and ensuring the imaging swath width, output the optimal initial squint angle of the configuration, minimizing the weighted sum of the layover rate, shadow rate, and average swath width.

[0078] If you want to reduce the proportion of the layover area, you can increase the radar depression angle, but the cost is an increase in the shadow area; if you want to reduce the proportion of the shadow area, you can increase the radar incidence angle (decrease the depression angle), but the cost is an increase in the layover area. It can be seen that layover and shadow are a pair of contradictions. Therefore, when acquiring SAR data, both need to be considered rather than only suppressing layover or shadow.

[0079] Under the requirements of a specified squint range and ensuring the imaging swath width, using the initial squint angle of the configuration as the optimization variable, complete the wave control design using the spaceborne SAR non-track multi-target imaging space-ground configuration joint design and optimization method. Take the output satellite flight position sequence, beam center illumination trajectory sequence, etc. as the input of the spaceborne SAR scene matching curve imaging wave control optimization method for layover and shadow suppression described in this patent. Based on the measured DEM data, substitute it into the algorithms described in Steps 1 and 2 for calculation. Weightedly sum the layover, shadow rate, and average swath width of the entire scene obtained. When the sum obtained is the smallest, this initial squint angle is the optimal initial squint angle of the configuration, as shown in the following formula:

[0080]

[0081] where φ i is the initial squint angle of the configuration, cost_i Layover , cost_i Shadow , W r represent the corresponding layover rate, shadow rate, and average swath width respectively, and α is the penalty term coefficient.

[0082] The above method effectively solves the problems that the existing spaceborne SAR scene matching curve imaging has no prediction ability for layover and shadow areas and cannot suppress layover and shadow in the imaging task. Using the measured DEM data, it can accurately predict the layover rate and shadow rate of the target scene. Under the requirements of a specified squint range and ensuring the imaging swath width, optimize the initial squint angle, effectively reducing layover and shadow in the imaging process, thus expanding the existing spaceborne SAR scene matching curve imaging system and completing the spaceborne SAR scene matching curve imaging wave control optimization for layover and shadow suppression.

[0083] Simulation experiment: The simulation parameters of the spaceborne SAR scene matching curve imaging wave control optimization method for layover and shadow suppression are shown in Table 1.

[0084] Table 1 List of simulation parameters of the spaceborne SAR scene matching curve imaging wave control optimization method for layover and shadow suppression

[0085]

[0086]

[0087] To verify the effectiveness of the spaceborne SAR scene matching curve imaging wave control optimization method for layover and shadow suppression, under the parameters in Table 1, the spaceborne SAR scene matching curve imaging wave control optimization method described in this patent is used to optimize the configuration oblique viewing angle of a certain imaging task scene to achieve the suppression of layover and shadow. The results are shown in Table 2. It can be seen that the layover and shadow at the initial oblique viewing angle of 20° are effectively suppressed compared with those at 10°.

[0088] Table 2 Optimization results of layover and shadow for the squint range of about ±20°

[0089]

[0090] In Figure 3 and Figure 4 the comparison diagrams of layover and shadow before and after using the spaceborne SAR scene matching curve imaging wave control optimization method for layover and shadow suppression are given. In Figure 3 (a), the measurement results of layover and shadow for the full scene before optimization are given, where the green line is the wave foot trajectory, the blue line is the Yangtze River, and the red part is the points with layover and shadow; Figure 3 (b), Figure 3 (c) give the enlarged schematic diagrams of the yellow box area in Figure 3 (a), where the blue is the Yangtze River and the red part is the points with layover; in Figure 4 (a), the measurement results of layover and shadow for the full scene after optimization are given, where the green line is the wave foot trajectory, the blue line is the Yangtze River, and the red part is the points with layover and shadow; Figure 4 (b), Figure 4 (c) give the enlarged schematic diagrams of the yellow box area in Figure 4 (a), where the blue is the Yangtze River, and it can be seen that the points with layover and shadow are significantly reduced.

[0091] In Figure 5 (a), Figure 5 (b), the comparison diagrams of the effects before and after the full scene optimization of layover obtained by using the method described in this patent are given respectively. The horizontal axis is the length of the scene in the azimuth direction, and the vertical axis is the proportion of layover points in the range direction. The line integral value after normalizing the horizontal axis is the full scene layover rate, which is 2.30% and 0.77% before and after optimization respectively. In Figure 6 (a), Figure 6(b) shows the comparison diagrams of the effects before and after the optimization of the full-scene shadow using the method described in this patent. The horizontal axis represents the length in the azimuth direction of the scene, and the vertical axis represents the proportion of shadow points in the range direction. The line integral value after normalization of the horizontal axis is the full-scene shadow rate, which is 6.1e-4 and 3.8e-4 before and after optimization, respectively. It can be seen that the method proposed in the present invention, under the conditions of specifying the squint range and ensuring the imaging swath width, minimizes the full-scene layover rate and shadow rate by optimizing the initial squint angle of the configuration, realizing the wave control optimization of the spaceborne SAR scene matching curve imaging for layover and shadow suppression.

[0092] Therefore, the present invention provides a wave control optimization method for spaceborne SAR scene matching curve imaging for layover and shadow suppression. According to the changes in geometric relationships such as slant range and viewing angle in the spaceborne SAR imaging model, measurement models for the full-scene layover rate and shadow rate are established respectively. Combining with the measured DEM data, under the requirements of specifying the squint range and ensuring the imaging swath width, the initial squint angle of the configuration is optimized to minimize the weighted sum of the layover rate, shadow rate, and average swath width, realizing the wave control optimization of the spaceborne SAR scene matching curve imaging for layover and shadow suppression. The present invention solves the problems that the existing spaceborne SAR scene matching curve imaging has no prediction ability for layover and shadow areas and cannot suppress layover and shadow in the imaging task, making up for the deficiencies of the existing technology.

[0093] Of course, the present invention can also have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can certainly make various corresponding changes and deformations according to the present invention, but these corresponding changes and deformations should all fall within the protection scope of the appended claims of the present invention.

Claims

1. A spaceborne SAR scene matching curve imaging wave control optimization method for overlap and shadow suppression, characterized in that: The following steps are involved: Step 1: In the spaceborne SAR scene matching curve imaging geometry model, according to the changes in viewing angle and slant range, establish an overlap determination model, and output the overlap area coordinates and the overlap rate of the entire scene; Step 2: In the spaceborne SAR scene matching curve imaging geometry model, a shadow determination model is established according to the changes in viewing angle and slant range, and the shadow area coordinates and the shadow rate of the entire scene are output; Step 3: Based on the measured DEM data, under the requirements of specifying the squint range and ensuring the width of the imaging band, output the optimal configuration initial squint angle so that the weighted sum of the overlap rate, shadow rate and average width is minimized.

2. The method for optimizing the imaging waveguide of spaceborne SAR scene matching curves for overlap and shadow suppression according to claim 1, characterized in that: The conditions for the overlapped area to appear in step 1 are: 180-γ1-θ1<90 Where θ1 is the incident angle, γ1 is the slope of the slope; the relationship between the incident angle θ1 and the downward viewing angle β1 is: θ1=90-β1 The conditions for the overlapped area to appear are: β1<γ1.

3. The spaceborne SAR scene matching curve imaging wave control optimization method for overlap and shadow suppression according to claim 1, characterized in that: The conditions for the shadow phenomenon to appear in step 2 are: θ2<γ2 Where θ2 is the incident angle and γ2 is the back slope gradient.

4. The spaceborne SAR scene matching curve imaging wave control optimization method for overlap and shadow suppression according to claim 1, characterized in that: The spaceborne SAR scene matching curve imaging overlap area determination algorithm model in step 1 includes the following steps: (1) Input satellite flight position sequence, beam center illumination trajectory sequence, and range beam width; (2) At the current azimuth time, within the zero Doppler plane and within the range of the beam width, sample at equal angles to obtain n beam pointing directions, find the first intersection point of each beam pointing direction with the ground, and obtain n beam pointing vectors; (3) In the zero Doppler plane and within the range of the beam width, rotate the current beam pointing vector around the satellite position. If the elevation of any end point of the beam pointing vector after rotation is less than the elevation of the corresponding longitude and latitude point in the DEM data, it is determined that overlap occurs. The longitude and latitude of the end point of the current beam pointing vector before rotation are recorded, which are the coordinate points where overlap occurs. (4) Repeat step (3) until all beam pointing vectors at the current azimuth are traversed; (5) Repeat steps (2) and (3) until all azimuths are traversed. The ratio of the number of overlapping points to the number of all sampling points is the overlapping rate. (6) Output the latitude and longitude of all points where overlap occurs and the overlap rate of the entire scene.

5. The spaceborne SAR scene matching curve imaging wave control optimization method for overlap and shadow suppression according to claim 1, characterized in that: The spaceborne SAR scene matching curve imaging shadow area determination algorithm model in step 2 includes the following steps: (1) Input satellite flight position sequence, beam center illumination trajectory sequence, and range beam width; (2) At the current azimuth time, within the zero Doppler plane and within the range of the beam width, sample at equal angles to obtain n beam pointing directions, find the first intersection point of each beam pointing direction with the ground, and obtain n beam pointing vectors; (3) In the direction of the current beam, the beam pointing vector is extended at equal intervals to 2% of its original length. If the elevation of the end point of the beam pointing vector after extension is greater than the elevation of the corresponding longitude and latitude point in the DEM data, it is determined that a shadow phenomenon has occurred. The longitude and latitude of the end point of the current beam pointing vector after extension are recorded, which is the coordinate point where the shadow occurs. (4) Repeat step (3) until all beam pointing vectors at the current azimuth are traversed; (5) Repeat steps (2) and (3) until all azimuths are traversed. The ratio of the number of points that generate shadows to the number of all sampling points is the shadow rate. (6) Output the longitude and latitude of all shadow points and the shadow rate of the entire scene.

6. The spaceborne SAR scene matching curve imaging wave control optimization method for overlap and shadow suppression according to claim 1, characterized in that: In step 3, the initial squint angle optimization model based on the squint range and imaging band width constraints is: where φ i is the initial oblique angle of the configuration, cost_i Layover 、cost_i Shadow , W r They represent the corresponding overlap rate, shadow rate and average width respectively, and α is the penalty coefficient.

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