A Fast Simulation Method and Device for Airborne SAR Images

Abstract

The present invention relates to the field of image simulation, in particular to a method and device for rapid simulation of airborne SAR images. After importing or constructing a 3D scene model, the present invention calculates the imaging area and other related parameters, and after adding a point light source on the aircraft, an optical image is collected and processed to output a SAR simulation image; the simulation image has the effects of top view, shadow, light spot and cross cursor of strong reflection target, greatly accelerating the simulation speed and effectively improving the simulation effect; it also avoids the problem that the SAR image is separated from the real-time simulated unmanned aerial vehicle and SAR state and cannot reflect the ground object characteristics of the area pointed by the radar during the real-time simulation process.

Description

Technical Field

[0001] The present invention relates to the field of image simulation, and particularly to a method and device for rapid simulation of airborne SAR images. Background Art

[0002] An unmanned aerial vehicle (UAV) simulation training system usually consists of parts such as flight platform simulation, payload simulation, link simulation, battlefield situation simulation, and ground display and control, and is mainly used for operation training such as flight monitoring, mission monitoring, and link monitoring of UAV operators. Synthetic aperture radar (hereinafter referred to as SAR) simulation is a type of payload simulation, which usually includes two parts: logic simulation and image simulation. The logic simulation completes functions such as working mode management, command response, and parameter feedback of the SAR, and is used to generate SAR image data.

[0003] There are usually two implementation methods for airborne SAR image simulation in UAV simulation training:

[0004] 1) Establish a SAR image library by using the real-shot SAR images accumulated daily. When the simulation training system enters the image working mode, the SAR images are retrieved from the image library according to a certain strategy for display.

[0005] 2) Establish a three-dimensional model of the scene and the target, calculate the radar scattering field information of the target model according to the incident signal and scene information, and then generate a SAR simulation image based on the SAR imaging principle.

[0006] Among them, the main disadvantage of the first method is that the SAR image is separated from the real-time simulated UAV and SAR status, and cannot reflect the ground object characteristics in the area pointed by the radar during the real-time simulation process; the main disadvantage of the second method is that the SAR image generation speed is slow, and the SAR imaging resolution is high, which cannot meet the rapid requirements of real-time simulation (i.e., the requirement of processing 4K*4K pixel images within 30S). The currently disclosed patent CN111462012A provides a SAR image simulation method based on a conditional generative adversarial network, but this method mainly solves the problem of noise interference and does not solve the above problems. Therefore, there is a need for a simulation method and device with better simulation effects now. Summary of the Invention

[0007] The purpose of the present invention is to overcome the problem that the simulation speed in the prior art does not meet the actual use requirements, and to provide a method and device for rapid simulation of airborne SAR images.

[0008] To achieve the above invention purpose, the present invention provides the following technical solutions:

[0009] An airborne SAR image rapid simulation method includes the following steps:

[0010] S1: Import the 3D scene model or construct the 3D scene model, and initialize the aircraft and optical sensor models; the 3D scene model includes the environment model, the reflection target model, and the model material;

[0011] S2: Dynamically receive the position parameters of the aircraft, and calculate the imaging area of the SAR image in the 3D scene model;

[0012] S3: Set a point light source on the aircraft, and determine the state parameters of the optical sensor; the state parameters include the position, attitude, and field of view angle;

[0013] S4: Collect the optical image of the imaging area through the optical sensor;

[0014] S5: Grayscale and add noise to the optical image, and obtain and output the SAR simulation image;

[0015] Among them, the method uses an optical real-time 3D engine (such as unity, unreal engine, Unigine or any other engine) for simulation. By adding a point light source on the aircraft, the simulation image has the effects of top view, shadow, light spot, and cross cursor of strong reflection target, which greatly speeds up the simulation speed and effectively improves the simulation effect; at the same time, by simulating in the pre-established or imported model and formulating simulation parameters according to the actual situation of SAR and the aircraft, the problem that the SAR image is separated from the real-time simulated UAV and SAR state and cannot reflect the ground object characteristics in the area pointed by the radar during the real-time simulation process is avoided, and the effect of fast simulation (that is, processing a 4K*4K pixel image within 30S) is also achieved.

[0016] As a preferred solution of the present invention, the step S2 includes:

[0017] S21: Dynamically receive the position parameters of the aircraft, and calculate the azimuth angle of the geographical system in which the aircraft points to the reflection target model;

[0018] S22: Calculate the longitude and latitude of the four corner points of the imaging area according to the longitude and latitude of the reflection target model, the azimuth angle of the geographical system, and the length and width of the imaging area, so as to obtain the imaging area; among them, the length and width of the imaging area are obtained by looking up a table, and the table in the look-up table corresponds to the performance of the airborne SAR. The present invention calculates the longitude and latitude of the four corner points of the imaging area according to the longitude and latitude of the reflection target model, the azimuth angle of the geographical system, and the length and width of the imaging area, so as to obtain the imaging area, thereby ensuring that the SAR imaging area in the simulation is consistent with the real airborne SAR imaging area.

[0019] As a preferred solution of the present invention, the calculation of the azimuth angle of the geographical system includes the following steps:

[0020] S211: Obtain the position parameters of the aircraft and the position parameters of the reflection target model;

[0021] S212: Convert the position parameters of the aircraft and the reflection target model from the geodetic coordinate system to the geodetic rectangular coordinate system according to the following formula;

[0022]

[0023] where, (x g , y g , z g ) are the coordinates in the geodetic rectangular coordinate system, H, B, and L are respectively the altitude, latitude, and longitude of the position parameters, e is the first eccentricity of the ellipsoid, and a is the semi-major axis of the ellipsoid;

[0024] S213: Convert the position parameters of the aircraft and the reflection target model from the geodetic rectangular coordinate system to the geographic coordinate system according to the following formula;

[0025]

[0026] where, (x s , y s , z s ) are the coordinates in the geographic coordinate system;

[0027] S214: Calculate the azimuth angle in the geographic coordinate system of the aircraft pointing to the reflection target model according to the following formula;

[0028] θ saz = arctan((y s目标 - y s飞机 ) / (x s目标 - x s飞机 ))

[0029] where, θ saz is the azimuth angle in the geographic coordinate system, (x s飞机 , y s飞机 , z s飞机 ) are the coordinates of the aircraft in the geographic coordinate system, and (x s目标 , y s目标 , z s目标 ) are the coordinates of the target in the geographic coordinate system.

[0030] As a preferred solution of the present invention, in step S22, the imaging area is obtained according to the longitude and latitude of the reflection target model, the azimuth angle in the geographic coordinate system, and the length and width of the imaging area based on the following formula:

[0031] B 2 = arcsin(sin(B 1) * cos(d / a) + cos(B 1 ) * sin(d / a) * cos(θ))

[0032] L 2 = L 1 + atan((cos(d / a) - sin(B 1 ) * sin(B 2 )) / (sin(θ) * sin(d / a) * cos(B 1 ))))

[0033] Wherein, L 1 is the longitude of point 1, B 1 is the latitude of point 1, θ is the azimuth of point 2 relative to point 1, d is the distance from point 1 to point 2, and L 2 is the longitude of point 2, B 2 is the latitude of point 2.

[0034] As a preferred solution of the present invention, the state parameters of the optical sensor model are as follows:

[0035] Position parameter: The optical sensor is located directly above the imaging area and at the same height as the aircraft;

[0036] Attitude parameter: The azimuth angle of the optical sensor in the geographical coordinate system = the azimuth angle of the aircraft pointing to the reflection target model in the geographical coordinate system; The Wherein, L is the length of the imaging area, ΔH = H 飞机 - H 目标 , H 飞机 , H 目标 are the heights of the aircraft and the reflection target model respectively;

[0037] Field of view angle: Wherein, W is the width of the imaging area.

[0038] As a preferred solution of the present invention, the step S4 further includes setting a corresponding delay time according to the pixel size of the optical image. Since the time consumed by simulating the SAR image is less than the actual generation time of the SAR image of the same size, the present invention makes the imaging time of the SAR simulation image basically consistent with the actual imaging time of the airborne SAR by setting different delay times to achieve synchronization.

[0039] As a preferred solution of the present invention, when the reflection target model is a strong reflection target, a crosshair model is used to replace the reflection target model.

[0040] As a preferred solution of the present invention, the step S4 further includes adjusting the brightness, saturation, and contrast parameters of the optical image.

[0041] As a preferred embodiment of the present invention, the reflection intensity of the reflection target model is positively correlated with the brightness of the optical image.

[0042] An electronic device includes at least one processor and a memory communicatively connected to the at least one processor; the memory stores instructions executable by the at least one processor, and when the instructions are executed by the at least one processor, the at least one processor is enabled to execute the method described in any one of the above.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] 1. By adding point light sources on the aircraft, the simulation image of the present invention has the effects of top view, shadow, light spot and strong reflection target crosshair, greatly enhancing the authenticity of the simulation image and effectively improving the simulation effect; at the same time, the present invention conducts simulation in a pre-established or imported model and formulates simulation parameters according to the actual situation of SAR and the aircraft, thereby avoiding the problem that the SAR image is separated from the real-time simulated unmanned aerial vehicle and the SAR state and cannot reflect the ground object characteristics in the area pointed by the radar during the real-time simulation process.

[0045] 2. The present invention calculates the latitudes and longitudes of the four corner points of the imaging area according to the latitude and longitude of the reflection target model, the azimuth angle of the geographic coordinate system and the length and width of the imaging area, so as to obtain the imaging area, thereby ensuring that the SAR imaging area in the simulation is consistent with the real airborne SAR imaging area.

[0046] 3. Since the time consumed by simulating the SAR image is less than the actual generation time of the SAR image of the same size, the present invention sets different delay times to make the imaging time of the SAR simulation image basically the same as the actual imaging time of the airborne SAR, achieving synchronization. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic flow chart of a method for rapid simulation of airborne SAR images according to Embodiment 1 of the present invention;

[0048] Figure 2 It is a top view schematic diagram of SAR simulation imaging of a method for rapid simulation of airborne SAR images according to Embodiment 1 of the present invention;

[0049] Figure 3 It is a side view schematic diagram of SAR simulation imaging of a method for rapid simulation of airborne SAR images according to Embodiment 1 of the present invention;

[0050] Figure 4 It is a top view schematic diagram of the imaging area of a method for rapid simulation of airborne SAR images according to Embodiment 1 of the present invention;

[0051] Figure 5 Schematic diagram A of the final simulation graph of an airborne SAR image rapid simulation method described in Embodiment 2 of the present invention;

[0052] Figure 6 Schematic diagram B of the final simulation graph of an airborne SAR image rapid simulation method described in Embodiment 2 of the present invention;

[0053] Figure 7 An electronic device that utilizes the airborne SAR image rapid simulation method described in Embodiment 1 of the present invention as described in Embodiment 3 of the present invention. Specific embodiments

[0054] The present invention will be further described in detail below in conjunction with test examples and specific embodiments. However, this should not be construed as limiting the scope of the above-mentioned subject matter of the present invention to the following embodiments. Any technology implemented based on the content of the present invention belongs to the scope of the present invention.

[0055] Embodiment 1

[0056] As Figure 1 shown, an airborne SAR image rapid simulation method includes the following steps:

[0057] S1: Import a 3D scene model or construct a 3D scene model, and initialize the aircraft and optical sensor models; the 3D scene model includes an environment model, a reflection target model, and model materials;

[0058] Adjust the model reflection effect according to the material reflection intensity. The principle is: the brightness is positively correlated with the target reflection intensity, and the target reflection intensity is related to the material and shape;

[0059] Among them, for strong reflection targets, a crosshair model is established: that is, the reflection target model is replaced by a crosshair structure, and the crosshair reflectivity is increased.

[0060] S2: Dynamically receive the position parameters of the aircraft, and calculate the imaging area of the SAR image in the 3D scene model. The spatial relationship is as Figures 2 to 4 shown.

[0061] There are determinations of antenna attitude parameters (antenna azimuth angle, antenna elevation angle) and position parameters of the center point of the target area (hereinafter referred to as the target point) (longitude, latitude, altitude). When the antenna attitude parameters are determined, first calculate the position parameters of the center point of the target area through the aircraft position, attitude parameters, and map elevation data, and then calculate according to the determination of the target point position parameters. The following will elaborate on the determination of the target point position parameters:

[0062] S21: Dynamically receive the position parameters of the aircraft, and calculate the direction of the aircraft pointing to the target point ( Figure 3Geographical azimuth of midpoint T):

[0063] S211: Acquire the position parameters of the aircraft and the position parameters of the reflection target model;

[0064] S212: Convert the aircraft position parameters and target position parameters from the earth coordinate system to the earth rectangular coordinate system. The conversion method is as follows:

[0065]

[0066] Among them, (x g ,y g , z g ) is the coordinate in the geodetic rectangular coordinate system, H, B, L are the altitude, latitude and longitude of the position parameter respectively, e is the first eccentricity of the ellipsoid, and a is the major radius of the ellipsoid;

[0067] S213: Convert the aircraft position and target position from the geodetic rectangular coordinate system to the geographic system. The conversion method is as follows:

[0068]

[0069] in, (x s ,y s , z s ) are geographic coordinates;

[0070] S214: Calculate the geographic system azimuth of the aircraft pointing to the reflective target model according to the following formula;

[0071] θ saz =arctan((y s目标 -y s飞机 ) / (x s目标 -x s飞机 )),

[0072] Among them, θ saz is the azimuth of the geographic system, (x s飞机 ,y s飞机 , z s飞机 ) is the coordinate of the aircraft in the geographic system, (x s目标 ,y s目标 z s目标 ) are the coordinates of the target in the geographic system.

[0073] S22: According to the latitude and longitude of the target point, θ saz And the length and width of the imaging area L, W (known parameters, bound to the SAR imaging mode, obtained by looking up the table) calculate the four corner points of the imaging area ( Figure 4 The longitude and latitude of the four points A, B, C, and D in the figure are obtained to obtain the SAR imaging area.

[0074] The table in the look-up table is related to the simulated SAR. When the simulated SAR is TerraSAR-X, the table is as follows:

[0075] Serial number Mode Resolution Imaging coverage 1 Beamforming 1m 5 * 10 km 2 Strip 3m 30 * 50 km

[0076] After looking up the table, the longitude and latitude of the four corner points can be calculated based on the following formula.

[0077] B 2 = arcsin(sin(B 1 ) * cos(d / a) + cos(B 1 ) * sin(d / a) * cos(θ))

[0078] L 2 = L 1 + atan((cos(d / a) - sin(B 1 ) * sin(B 2 )) / (sin(θ) * sin(d / a) * cos(B 1 ))))

[0079] Among them, L 1 is the longitude of point 1, B 1 is the latitude of point 1, θ is the azimuth angle of point 2 relative to point 1, d is the distance from point 1 to point 2, L 2 is the longitude of point 2, and B 2 is the latitude of point 2.

[0080] Therefore, the longitude and latitude of the four corner points of the imaging area can be calculated through the longitude and latitude of the center point T of the imaging area, the azimuth angle of the aircraft pointing to the imaging center in the geographical system, and the length and width of the imaging area.

[0081] For example, the longitude and latitude of A can be obtained by moving point T in the (+180°) direction by L / 2 and then in the (+270°) direction by W / 2, as Figure 2 shown.

[0082] S3: Determine the light source position parameters and emit light rays around the light source position; and determine the spatial parameters such as the position, attitude, and field of view angle of the optical sensor model;

[0083] Light source position parameters: The same as the aircraft position parameters (changing with the movement of the aircraft);

[0084] Light ray simulation: Completed by the 3D engine.

[0085] Position: The height is the same as the aircraft height; the horizontal position is the same as the midpoint of points A and B.

[0086] Attitude: The geographical azimuth angle of the optical sensor = the geographical azimuth angle of the aircraft pointing to the reflection target model; the where L is the length of the imaging area, and ΔH = H 飞机 -H 目标 ,H 飞机 、H 目标 ,are the heights of the aircraft and the reflection target model respectively;

[0087] Field of view angle: where W is the width of the imaging area.

[0088] S4: Adjust the brightness, saturation, and contrast of the optical image.

[0089] S5: Perform graying and noise addition processing on the optical image formed in step S4 to obtain the final SAR simulation image.

[0090] Among them, any method can be used for graying, such as:

[0091] I(x, y) = aI R (x, y) + bI G (x, y) + cI B (x, y)

[0092] where I(x, y) is the gray value at (x, y) after graying;

[0093] I R (x, y), I G (x, y), I B (x, y) are the gray values of the R, G, and B channels at (x, y) before graying respectively. Any noise such as Gaussian noise and salt-and-pepper noise can be added during the noise addition processing.

[0094] Embodiment 2

[0095] This embodiment is an actual implementation example of using the method of the present invention to receive aircraft position and attitude data, target information, and imaging mode information, calculate light source parameters and camera parameters according to flight data and target data, drive the 3D engine to generate a reference image, and the image processing module performs gray and noise processing on the received reference image to generate the final SAR simulation image.

[0096] Input parameters:

[0097] Aircraft position: 105.63658° east longitude, 36.698° north latitude, altitude 7000m.

[0098] Attitude parameters of the aircraft: roll 0°, pitch 0°, heading 270°.

[0099] Target location: 105.63658° E longitude, 36.94524° N latitude, altitude 1700 m (a refinery model is placed at the target location).

[0100] Imaging mode: spotlight, 0.3 m resolution, imaging area range 2.4 km x 2.4 km, imaging time controlled to be 13 s.

[0101] The output parameters of the imaging parameter calculation module are:

[0102] Light source location: 105.63658° E longitude, 36.698° N latitude, altitude 7000 m.

[0103] Camera parameters: 105.63658° E longitude, 36.92365° N latitude, altitude 7000 m, horizontal field of view: 25.5°, vertical field of view 24.4°.

[0104] The final simulation images under different brightness parameters output in this embodiment are as Figure 5 and Figure 6 shown.

[0105] Embodiment 3

[0106] As Figure 7 shown, an electronic device includes at least one processor and a memory communicatively connected to the at least one processor; the memory stores instructions executable by the at least one processor, and when the instructions are executed by the at least one processor, the at least one processor is enabled to execute an airborne SAR image fast simulation method as described in the foregoing embodiment. The input / output interface may include a display, a keyboard, a mouse, and a USB interface for inputting and outputting data; the power supply is used to supply electrical energy to the electronic device.

[0107] Those skilled in the art can understand that all or part of the steps for implementing the foregoing method embodiments can be completed by hardware related to program instructions. The foregoing program can be stored in a computer-readable storage medium. When the program is executed, it executes the steps including the foregoing method embodiments; and the foregoing storage medium includes: various media such as a removable storage device, a read-only memory (ROM), a magnetic disk, or an optical disc that can store program codes.

[0108] When the above integrated unit of the present invention is implemented in the form of a software functional unit and sold or used as an independent product, it can also be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the embodiments of the present invention essentially or the part that contributes to the prior art can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the methods described in the various embodiments of the present invention. The foregoing storage medium includes: various media that can store program codes such as a removable storage device, a ROM, a magnetic disk, or an optical disc.

[0109] The foregoing is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for rapid simulation of airborne SAR images, characterized in that, it includes the following steps: S1: Import a 3D scene model or construct a 3D scene model, and initialize the aircraft and optical sensor models; the 3D scene model includes an environmental model, a reflection target model, and model materials; S2: Dynamically receive the position parameters of the aircraft, and calculate the imaging area of the SAR image in the 3D scene model; S3: Set a point light source on the aircraft, and determine the spatial parameters of the optical sensor; the spatial parameters include position, attitude, and field of view angle; S4: Collect the optical image of the imaging area through the optical sensor; S5: Grayscale and add noise to the optical image, and obtain and output the SAR simulation image; wherein, the method uses an optical real-time 3D engine for simulation.

2. The method for rapid simulation of airborne SAR images according to claim 1, characterized in that, the step S2 includes: S21: Dynamically receive the position parameters of the aircraft, and calculate the azimuth angle in the geographic coordinate system of the aircraft pointing to the reflection target model; S22: Calculate the longitude and latitude of the four corner points of the imaging area according to the longitude and latitude of the reflection target model, the azimuth angle in the geographic coordinate system, and the length and width of the imaging area, so as to obtain the imaging area; wherein, the length and width of the imaging area are obtained by looking up a table, and the table in the look-up table corresponds to the performance of the airborne SAR.

3. The method for rapid simulation of airborne SAR images according to claim 2, characterized in that, the calculation of the azimuth angle in the geographic coordinate system includes the following steps: S211: Obtain the position parameters of the aircraft and the position parameters of the reflection target model; S212: Convert the position parameters of the aircraft and the reflection target model from the geodetic coordinate system to the geodetic rectangular coordinate system according to the following formula; Among them, (x g , y g , z g ) are coordinates in the geodetic rectangular coordinate system, H, B, and L are the height, latitude, and longitude of the position parameters respectively, e is the first eccentricity of the ellipsoid, and a is the semi-major axis of the ellipsoid; S213: Convert the position parameters of the aircraft and the reflection target model from the geodetic rectangular coordinate system to the geographic coordinate system according to the following formula; Among them, (x s , y s , z s ) is the coordinate under the geosystem; S214: Calculate the azimuth angle in the geographic coordinate system of the aircraft pointing to the reflection target model according to the following formula; θ saz = arctan((y s目标 - y s飞机 ) / (x s目标 - x s飞机 )), where θ saz is the azimuth angle of the geographical system, (x s飞机 , y s飞机 , z s飞机 ) is the coordinate of the aircraft in the geographical system, and (x s目标 , y s目标 , z s目标 ) is the coordinate of the target in the geographical system.

4. The method for rapid simulation of airborne SAR images according to claim 3, characterized in that, in the step S22, the imaging area is obtained based on the longitude and latitude of the reflection target model, the azimuth angle in the geographic coordinate system, and the length and width of the imaging area according to the following formula: B 2 = arcsin(sin(B 1 ) * cos(d / a) + cos(B 1 ) * sin(d / a) * cos(θ)) L 2 = L 1 + atan((cos(d / a) - sin(B 1 )) * sin(B 2 )) / (sin(θ) * sin(d / a) * cos(B 1 )))) Among them, L 1 is the longitude of point 1, B 1 is the latitude of point 1, θ is the azimuth of point 2 relative to point 1, d is the distance from point 1 to point 2, L 2 is the longitude of point 2, B 2 is the latitude of point 2.

5. The method for rapid simulation of airborne SAR images according to claim 3, characterized in that, the state parameters of the optical sensor model are: Position parameter: The optical sensor is located directly above the imaging area and at the same height as the aircraft; Attitude parameters: The azimuth angle of the optical sensor in the geographical coordinate system = the azimuth angle of the aircraft pointing to the reflection target model in the geographical coordinate system; The where L is the length of the imaging area, and ΔH = H 飞机 -H 目标 , H 飞机 , H 目标 are the heights of the aircraft and the reflection target model respectively; Field of view: where W is the width of the imaging area.

6. The method for rapid simulation of airborne SAR images according to claim 1, characterized in that, the step S4 further includes setting a corresponding delay time according to the pixel size of the optical image.

7. The method for rapid simulation of airborne SAR images according to claim 1, characterized in that, when the reflection target model is a strong reflection target, the reflection target model is replaced with a crosshair model.

8. The method for rapid simulation of airborne SAR images according to claim 1, characterized in that, The step S4 further includes adjusting the brightness, saturation, and contrast parameters of the optical image.

9. An airborne SAR image fast simulation method according to claim 1, wherein, the reflection intensity of the reflection target model is positively correlated with the brightness of the optical image.

10. An electronic device, wherein, it includes at least one processor and a memory communicatively connected to the at least one processor; the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the method according to any one of claims 1 to 9.

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