Ground distance geometric imaging grid division method and system for back projection of synthetic aperture radar

Abstract

The embodiment of the invention provides a ground distance geometric imaging grid division method and system for back projection of a synthetic aperture radar, and belongs to the technical field of radars. According to the scheme, satellite orbit parameters, radar parameters and radar echo data are acquired; center coordinate information of a scene center point is determined according to the satellite orbit parameters and the radar parameters, and the scene center point represents a geometric center point of the imaging area; dividing grids on the three-dimensional ground distance plane according to the central coordinate information and the imaging resolution by combining a digital elevation model to obtain a ground distance geometric imaging grid; and performing backward projection imaging processing on the ground distance geometric imaging grid according to the radar echo data to obtain an imaging result. According to the method, the process of terrain correction after conversion from a slant distance imaging plane to a ground distance imaging plane is not needed, the processing efficiency can be improved, and the synthetic aperture radar image with geocoding can be directly generated.

Description

Technical Field

[0001] The present application relates to the field of radar technology, and in particular to a method and system for ground-range geometric imaging grid division for synthetic aperture radar backprojection. Background Art

[0002] Spaceborne synthetic aperture radar (SAR) is a means of remote sensing and Earth observation. Its all-weather, all-day, long-range, and large-scale imaging capabilities make it extremely valuable. Radar systems transmit pulses at a specific frequency, and the received echo data is defocused. This data requires imaging algorithms to focus. Focusing imaging algorithms are primarily categorized into two types: time-domain and frequency-domain.

[0003] Frequency domain algorithms in related technologies generally first image on the slant range plane and then project it onto the ground range plane to correct the terrain. This method involves many processing steps and has low processing efficiency. Moreover, the conversion from slant range to ground range is not true geocoding or terrain geometry correction, and cannot directly generate synthetic aperture radar images with geocoding. Summary of the Invention

[0004] The main purpose of the embodiments of the present application is to propose a method and system for ground-range geometric imaging grid division for synthetic aperture radar backprojection, aiming to improve processing efficiency and directly generate synthetic aperture radar images with geocoding without the need for a process of converting from a slant-range imaging plane to a ground-range imaging plane and then performing terrain correction.

[0005] To achieve the above objectives, an embodiment of the present application provides a method for ground-level geometric imaging grid division for synthetic aperture radar backprojection, the method comprising:

[0006] Obtain satellite orbit parameters, radar parameters and radar echo data;

[0007] Determining central coordinate information of a scene center point according to the satellite orbit parameters and the radar parameters, wherein the scene center point represents a geometric center point of an imaging area;

[0008] In combination with the digital elevation model, a grid is divided according to the imaging resolution on the three-dimensional ground-distance plane based on the center coordinate information to obtain a ground-distance geometric imaging grid;

[0009] Back-projection imaging processing is performed on the ground-distance geometric imaging grid according to the radar echo data to obtain an imaging result.

[0010] In some embodiments, determining the center coordinate information of the scene center point according to the satellite orbit parameters and the radar parameters includes the following steps:

[0011] Performing geometric processing based on the satellite orbit parameters and the radar parameters to obtain a scene center point and a satellite-ground geometric relationship model, wherein the satellite-ground geometric relationship model includes an Earth-centered Earth-fixed coordinate system model, a satellite platform coordinate system model, and a longitude-latitude high-coordinate system model;

[0012] Rotate the center point of the scene to the longitude of the satellite to obtain the scene projection point;

[0013] Performing data analysis based on the geometric relationship between the scene projection point and the satellite-ground geometric relationship model to obtain projection coordinate information and a rotation angle of the scene projection point;

[0014] Coordinate transformation is performed according to the projection coordinate information and the rotation angle to obtain central coordinate information of the scene center point.

[0015] In some embodiments, performing data parsing based on the geometric relationship between the scene projection point and the satellite-ground geometric relationship model to obtain the projection coordinate information and rotation angle of the scene projection point includes the following steps:

[0016] Performing coordinate inverse processing according to the geometric relationship between the scene projection point and the satellite to obtain the first projection coordinates of the scene projection point in the Earth-centered Earth-fixed coordinate system model;

[0017] Based on the first projection coordinates, performing a first coordinate system conversion process on the scene projection point to obtain a second projection coordinate of the scene projection point in the satellite platform coordinate system model, and using the second projection coordinates as the projection coordinate information of the scene projection point;

[0018] Perform rotation inverse processing on the second projection coordinates to obtain a rotation angle.

[0019] In some embodiments, performing coordinate transformation according to the projection coordinate information and the rotation angle to obtain the center coordinate information of the scene center point includes the following steps:

[0020] Rotate the second projection coordinates according to the rotation angle to obtain the first center coordinates of the scene center point in the satellite platform coordinate system model;

[0021] Based on the first center coordinates, the scene center point is converted into a second coordinate system to obtain the second center coordinates of the scene center point in the latitude and longitude high coordinate system model, and the second center coordinates are used as the center coordinate information of the scene center point.

[0022] In some embodiments, combining the digital elevation model and dividing the grid according to the imaging resolution on the three-dimensional ground-distance plane based on the center coordinate information to obtain the ground-distance geometric imaging grid includes the following steps:

[0023] Performing grid division processing on a three-dimensional ground distance plane according to the center coordinate information and imaging resolution to obtain a latitude and longitude ground distance grid;

[0024] The latitude and longitude ground distance grid is given elevation information in combination with a digital elevation model to obtain a ground distance geometric imaging grid.

[0025] In some embodiments, performing grid division processing on a three-dimensional ground distance plane according to the center coordinate information and the imaging resolution to obtain a latitude and longitude ground distance grid includes the following steps:

[0026] Determine the grid spacing based on the imaging resolution;

[0027] Performing a grid division process on a three-dimensional ground plane according to the grid spacing to obtain a plurality of grid points;

[0028] Taking the center coordinate information as a reference, determining the grid coordinate information of each of the grid points according to the grid spacing;

[0029] A latitude and longitude distance grid is obtained according to the grid points and the corresponding grid coordinate information.

[0030] In some embodiments, performing backprojection imaging processing on the ground-level geometric imaging grid according to the radar echo data to obtain an imaging result includes the following steps:

[0031] Processing the radar echo data to obtain a plurality of sub-aperture data;

[0032] Calculating the slant distance corresponding to each sub-aperture according to the sub-aperture data;

[0033] Back-projection imaging processing is performed on the ground-range geometric imaging grid according to the sub-aperture data and the corresponding slant range to obtain an imaging result.

[0034] In some embodiments, processing the radar echo data to obtain a plurality of sub-aperture data includes the following steps:

[0035] Performing sub-aperture division processing on the radar echo data to obtain a plurality of pre-processed data;

[0036] A two-dimensional interpolation process is performed on each of the pre-processed data on an inclined plane to obtain a plurality of sub-aperture data.

[0037] To achieve the above-mentioned objectives, another aspect of the present application provides a virtual system for ground-range geometric imaging grid division for synthetic aperture radar backprojection, the virtual system comprising:

[0038] The first module is used to obtain satellite orbit parameters, radar parameters and radar echo data;

[0039] A second module is configured to determine central coordinate information of a scene center point according to the satellite orbit parameters and the radar parameters, wherein the scene center point represents a geometric center point of an imaging area;

[0040] The third module is used to divide the grid according to the imaging resolution on the three-dimensional ground-distance plane based on the central coordinate information in combination with the digital elevation model to obtain a ground-distance geometric imaging grid;

[0041] The fourth module is used to perform back-projection imaging processing on the ground-distance geometric imaging grid according to the radar echo data to obtain an imaging result.

[0042] To achieve the above-mentioned purpose, another aspect of an embodiment of the present application proposes a hardware system for ground-range geometric imaging grid division of synthetic aperture radar backprojection, the hardware system including a memory and a processor, the memory storing a computer program, and the processor implementing the above-mentioned method when executing the computer program.

[0043] To achieve the above-mentioned purpose, another aspect of an embodiment of the present application provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and the computer program implements the above-mentioned method when executed by a processor.

[0044] Embodiments of the present application include at least the following beneficial effects: A method and system for ground-range geometric imaging grid division using synthetic aperture radar backprojection is provided. This solution obtains satellite orbit parameters, radar parameters, and radar echo data; determines the center coordinate information of a scene center point based on the satellite orbit parameters and radar parameters, where the scene center point represents the geometric center point of the imaging area; combines the center coordinate information with a digital elevation model, and divides the grid according to the imaging resolution on a three-dimensional ground-range plane to obtain a ground-range geometric imaging grid; and performs backprojection imaging processing on the ground-range geometric imaging grid based on the radar echo data to obtain an imaging result. This application eliminates the need for a conversion process from a slant-range imaging plane to a ground-range imaging plane followed by terrain correction, thereby improving processing efficiency and directly generating a geocoded synthetic aperture radar image. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is a schematic diagram of a three-dimensional ground-distance plane grid provided in an embodiment of the present application;

[0046] Figure 2 Schematic diagram of airborne SAR ground-range grid imaging results provided in an embodiment of the present application;

[0047] Figure 3A flowchart of a method for ground-level geometric imaging grid division for synthetic aperture radar backprojection provided in an embodiment of the present application;

[0048] Figure 4 Schematic diagram of the satellite-ground geometric relationship provided in the embodiment of the present application;

[0049] Figure 5 Schematic diagram of the satellite-ground geometric cross-section relationship provided in the embodiments of the present application;

[0050] Figure 6 A schematic diagram of the ground distance grid division result provided in an embodiment of the present application;

[0051] Figure 7 Schematic diagram of the geometric relationship between scene elevation and slant range provided in the embodiment of the present application;

[0052] Figure 8 A flowchart of a method for ground-range geometric imaging grid division for synthetic aperture radar backprojection provided in another embodiment of the present application;

[0053] Figure 9 A schematic diagram of the strip mode provided in an embodiment of the present application at zero elevation ground distance grid imaging results;

[0054] Figure 10 A digital elevation map of a stripe-mode imaging scene provided in an embodiment of the present application;

[0055] Figure 11 A schematic diagram of the imaging results of the strip mode provided in an embodiment of the present application on a ground-distance grid with elevation;

[0056] Figure 12 An optical remote sensing image of a stripe pattern imaging scene provided in an embodiment of the present application;

[0057] Figure 13 1 is a structural diagram of a virtual system for ground-range geometric imaging grid division of synthetic aperture radar backprojection provided in an embodiment of the present application;

[0058] Figure 14 This is a hardware structure diagram of the ground-range geometric imaging grid division hardware system for synthetic aperture radar backprojection provided in an embodiment of the present application. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the embodiments of the present application. They are merely examples of devices and methods consistent with some aspects of the embodiments of the present application as detailed in the appended claims.

[0060] It will be understood that the terms "first", "second", etc. used in this application may be used herein to describe various concepts, but unless otherwise specified, these concepts are not limited by these terms. These terms are only used to distinguish one concept from another. For example, without departing from the scope of the embodiments of the present application, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the words "if" and "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining".

[0061] The terms "at least one", "plurality", "each", "any", etc. used in this application include "at least one", "two" or more, "plurality" or "each", "any" or "any one", "each" or "any one" as used herein.

[0062] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein are for the purpose of describing the embodiments of this application only and are not intended to limit this application.

[0063] Before describing the embodiments of the present application in detail, the nouns involved in the embodiments of the present application and some related technologies are first described.

[0064] (1) Synthetic Aperture Radar (SAR): Synthetic aperture radar is an active earth observation system that can be installed on aircraft, satellites, spacecraft and other flying platforms. It can observe the earth around the clock and in all weather conditions, and has a certain surface penetration capability. Therefore, the SAR system has unique advantages in disaster monitoring, environmental monitoring, ocean monitoring, resource exploration, crop yield estimation, surveying and mapping, and military applications, and can play a role that other remote sensing methods cannot play.

[0065] (2) Back-projection (BP): The back-projection algorithm refers to the idea of "delay-superposition". In radar applications, it performs distance matching on the echo signal received by the radar receiving antenna to obtain the phase and amplitude information contained in the echo data, and then performs inverse Fourier transform through IFFT to obtain the delay of the transmitting and receiving antenna combination. Finally, the accumulated signals are coherently added to obtain the target function.

[0066] (3) Earth-Centered Earth-Fixed (ECEF) coordinate system: referred to as the geocentric coordinate system, it is an earth-fixed coordinate system (also called the earth coordinate system) with the center of the earth as the origin. The origin O is the center of mass of the earth. The z-axis is parallel to the earth's axis and points to the North Pole. The x-axis points to the intersection of the prime meridian and the equator. The y-axis is perpendicular to the xOz plane (that is, the intersection of 90 degrees east longitude and the equator), forming a right-handed coordinate system.

[0067] (4) WGS-84: WGS-84 is the most widely used earth coordinate system. It gives the latitude, longitude and altitude of a point and tells us the position of the point on the earth more intuitively, so it is also called the longitude, latitude and altitude (LLA) coordinate system.

[0068] (5) Digital Elevation Model (DEM): It is a digital simulation of the ground terrain (i.e., a digital expression of the terrain surface morphology) achieved through limited terrain elevation data. It is a physical ground model that represents the ground elevation in the form of a set of ordered numerical arrays and is a branch of the digital terrain model.

[0069] Radar systems transmit pulses at a constant frequency, and the received echo data is defocused. This data needs to be focused using imaging algorithms, which are primarily categorized as time-domain and frequency-domain. Existing frequency-domain algorithms typically first image the image in the slant-range plane, then project it onto the ground-range plane to correct for terrain. These existing solutions are inefficient, involve numerous processing steps, and cannot directly generate geocoded SAR imagery products.

[0070] Specifically, spaceborne SAR typically compresses acquired echo data and transmits it to a ground station for data processing. Different spaceborne SAR satellite data products vary depending on their application scenarios and intended use, but are generally similar. Taking the Sentinel-1 SAR satellite as an example, data products are categorized into three levels: Level-0 (L0), Level-1 (L1), and Level-2 (L2). L0 products are raw, unfocused compressed SAR echo data, including noise, calibration, and attitude data, and serve as the foundation for generating other higher-level data products. L1 products are L0-focused data, including single-look complex (SLC) images and ground range detected (GRD) images. SLC images are the result of radiometric calibration and imaging on the slant range plane at natural pixel spacing. GRD images are the result of projecting the multi-look processed SLC data onto a ground range grid with approximately square pixel spacing, as defined by the WGS-84 ellipsoid model. Pixel values represent the amplitude of the region, while phase information is discarded. Due to multi-look processing, the resolution of GRD is lower than that of SLC. L2 products are derivatives of L1 products and include information such as ocean wind field, ocean expansion spectrum, and surface radial velocity.

[0071] For many scientific applications in remote sensing, the geometric accuracy of data products is crucial. Geometric distortion errors primarily originate from ephemeris, elevation estimation, and signal processing. Therefore, SAR imaging focused images require geometric correction or rectification to resample the geometrically distorted projected images to the true ground-range geometry. Geocoding is then performed to assign the images their actual geographic coordinates. Geometric correction and geocoding are generally referred to collectively as orthocorrection, which corrects SAR images from their original range-azimuth coordinate system to a geographic latitude-longitude coordinate system (or map projection coordinate system). It should be noted that the Sentinel-1 L1 GRD product merely projects the multi-look processed SLC data onto the WGS-84 ellipsoid model. The conversion from slant range to ground range does not constitute true geocoding or terrain geometric rectification.

[0072] like Figure 1 As shown in the figure, the spaceborne SAR is back-projected onto a ground-based grid with known elevation. The effect of DEM on the focusing of airborne SAR imaging is shown in the figure. Figure 2 shown. Figure 2 (a) shows the imaging result of zero-altitude ground-distance plane imaging. Due to the motion error of the SAR platform, the target above the center point of the scene appears defocused. Figure 2 (b) is the imaging result of combining DEM with the ground grid, and the orthorectification result is obtained, which solves the problem. Figure 2 There is a defocus problem in (a).

[0073] Although two methods for reconstructing scenes at ground distance planes have been proposed in related technologies, these two methods are based on airborne SAR scenes. The assumption that the ground surface is approximately flat will lead to errors in spaceborne SAR scenes. Therefore, spaceborne SAR requires a more accurate ground distance grid division method.

[0074] In view of this, an embodiment of the present application provides a method and system for dividing a ground-range geometric imaging grid by back-projection of a synthetic aperture radar. The scheme obtains satellite orbit parameters, radar parameters, and radar echo data; determines the center coordinate information of the scene center point based on the satellite orbit parameters and radar parameters, where the scene center point represents the geometric center point of the imaging area; combines the digital elevation model, and divides the grid according to the imaging resolution on the three-dimensional ground-range plane based on the center coordinate information to obtain a ground-range geometric imaging grid; performs back-projection imaging processing on the ground-range geometric imaging grid based on the radar echo data to obtain an imaging result. The present application does not require the process of converting from the slant-range imaging plane to the ground-range imaging plane and then performing terrain correction, which can improve processing efficiency and directly generate a synthetic aperture radar image with geocoding.

[0075] The embodiment of the present application provides a method for dividing the ground-range geometric imaging grid of the synthetic aperture radar back projection, which relates to the field of radar technology. The embodiment of the present application provides a method for dividing the ground-range geometric imaging grid of the synthetic aperture radar back projection, which can be applied to a terminal, a server, or software running in a terminal or a server. In some embodiments, the terminal can be a smart phone, a tablet computer, a laptop computer, a desktop computer, a smart speaker, a smart watch, and a car terminal, etc., but is not limited to this; the server side can be configured as an independent physical server, or as a server cluster or distributed system composed of multiple physical servers, or as a cloud server that provides basic cloud computing services such as cloud services, cloud databases, cloud computing, cloud functions, cloud storage, network services, cloud communications, middleware services, domain name services, security services, CDN, and big data and artificial intelligence platforms. The server can also be a node server in a blockchain network; the software can be an application that implements the method for dividing the ground-range geometric imaging grid of the synthetic aperture radar back projection, etc., but is not limited to the above forms.

[0076] The present application can be used in many general or special computer system environments or configurations. For example: personal computers, server computers, handheld or portable devices, tablet devices, multiprocessor systems, microprocessor-based systems, set-top boxes, programmable consumer electronics, network PCs, minicomputers, mainframe computers, distributed computing environments including any of the above systems or devices, and the like. The present application can be described in the general context of computer-executable instructions executed by a computer, such as program modules. Generally, program modules include routines, programs, objects, components, data structures, and the like that perform specific tasks or implement specific abstract data types. The present application can also be practiced in distributed computing environments in which tasks are performed by remote processing devices connected via a communication network. In a distributed computing environment, program modules can be located in local and remote computer storage media, including storage devices.

[0077] Figure 3 This is an optional flow chart of the method for ground-range geometric imaging grid division of synthetic aperture radar backprojection provided in an embodiment of the present application. Figure 3 The method may include but is not limited to steps S101 to S104.

[0078] Step S101: Acquire satellite orbit parameters, radar parameters, and radar echo data.

[0079] Step S102: determining the center coordinate information of the scene center point according to the satellite orbit parameters and the radar parameters, wherein the scene center point represents the geometric center point of the imaging area.

[0080] Step S103 , combining the digital elevation model and dividing the grid on the three-dimensional ground-distance plane according to the imaging resolution based on the center coordinate information, to obtain a ground-distance geometric imaging grid.

[0081] Step S104 , performing back-projection imaging processing on a ground-range geometric imaging grid according to the radar echo data to obtain an imaging result.

[0082] In this embodiment, satellite orbit data describes the motion of a satellite in orbit. It can be obtained from satellite ephemeris data and is used to determine the geometric relationship between the satellite and the ground. It primarily includes satellite position, satellite velocity, orbital inclination, right ascension of the ascending node, argument of perigee, true perigee angle, orbital ascending node, orbital perigee, subsatellite point track, and satellite elevation. Satellite motion and Earth's rotation cause the subsatellite point to move across the Earth's surface, forming a subsatellite point track. For a ground observer located at the subsatellite point, the subsatellite point appears to be at the zenith. When a satellite passes through the ascending node, the subsatellite point is at the equator. Plotting the subsatellite point track on a map creates a subsatellite point track diagram. The subsatellite point track diagram shows that the satellite is near the zenith of a given location at a given time, and the line connecting the subsatellite point to the satellite is the normal to the Earth's surface. The ascending node is the point where the satellite's orbital plane intersects the Earth's equatorial plane when the satellite is traveling from south to north. The intersection of a celestial body's orbital plane and a reference plane is called the nodal line. The celestial point where a celestial body passes through the nodal line when traveling from south to north is called the ascending node. Commonly used reference planes include the equatorial plane and the ecliptic plane. In this embodiment, the equator is used as the reference plane.

[0083] Radar parameters describe the operating status of a radar system, primarily including beam coverage and slant range. As a satellite platform moves forward, it transmits pulses of electromagnetic energy toward the ground at regular intervals. During the transmission of a pulse, the radar antenna's beam projects onto a specific area on the ground, representing the beam coverage. Slant range, which indicates the distance from the satellite to a ground target, is used to determine the distance between the satellite and the ground target.

[0084] Radar echo data is the scattered signal received by the radar antenna after the electromagnetic wave pulse emitted by the radar system interacts with the ground target. The radar echo data is projected onto each pixel in the imaging area through the back-projection algorithm. The echo data corresponding to different azimuths and times are coherently accumulated, and finally a complete image of the target area can be reconstructed.

[0085] Before discussing the generation of the ground-range grid for spaceborne SAR, we will briefly explain the method for dividing the slant-range plane grid. First, the scene center is determined, typically by calculating the reference slant range and slant angle of the central sampling point in azimuth. Next, the imaging resolution in azimuth and range, i.e., the spacing between reconstructed pixels, is determined. Finally, a grid is generated in the imaging coordinate system based on the imaging resolution, and the grid center is translated to the scene center. The division of the ground-range geometric imaging grid in this embodiment is similar, differing in the determination of the scene center.

[0086] The Earth is an irregular sphere that is slightly flattened at the poles and slightly bulging at the equator. Due to the curvature of the Earth's surface, the Earth-satellite geometry is different from the airborne geometry, and the approximation of the Earth's surface as a plane has certain errors. To reduce the error, the reference ellipsoid of the World Geodetic System is used as the Earth model. Figure 4In this embodiment, the WGS-84 model is used as the earth model. In the WGS-84 model, the scene center coordinates are calculated based on the geometric relationship between the satellite and the earth according to the satellite orbit parameters and radar parameters. Figure 4 As shown in the figure, the near point of the satellite-borne SAR beam coverage area is A, the far point is C, point B is the scene reference center, and point G is the projection point of the satellite position S on the surface. Figure 4 The satellite position S is the azimuth sampling center point, and point B is the scene center point.

[0087] In order to determine the coordinates of point B in WGS-84, we also need to use two basic coordinate systems in the satellite-earth geometric relationship: the Earth-centered Earth-fixed coordinate system and the satellite platform coordinate system. The Earth-centered Earth-fixed coordinate system can be used as a bridge from the WGS-84 coordinate system to the satellite platform coordinate system. Conversely, the transition from the satellite platform coordinate system to the WGS-84 coordinate system is also completed in two steps using the Earth-centered Earth-fixed coordinate system as a transition.

[0088] Since the intersection line between the satellite beam and the ground surface in the WGS-84 model is a complex spatial curve, in order to simplify the solution process, the three-dimensional spatial curve problem can be reduced to a two-dimensional plane problem.

[0089] Specifically, the coordinates of point B in the satellite platform coordinate system can be converted to the coordinates of point B'. Point B' is the position of point B rotated around the z-axis of the satellite platform coordinate system to the meridian where point G is located. After the coordinates of point B' are obtained, they are rotated to the original position of point B in the satellite platform coordinate system and finally converted to WGS-84 coordinates.

[0090] Combined with the digital elevation model, the spaceborne SAR imaging grid is divided into a three-dimensional ground-range plane of the WGS-84 ellipsoid model using the scene center coordinates (latitude and longitude) calculated in step S102 and a preset imaging resolution, generating a ground-range geometric imaging grid. A backprojection imaging algorithm projects each pulse echo data back onto the ground-range geometric imaging grid after pulse compression, coherently integrating them within the synthetic aperture time to produce a geocoded synthetic aperture radar image as the imaging result.

[0091] This embodiment utilizes the advantage of the back-projection imaging algorithm in that it can image on any imaging grid and can image directly on the ground-distance geometric imaging grid. Back-projecting imaging is performed on the ground-distance geometric imaging grid combined with the DEM, and the output result directly completes the orthorectification including terrain geometric correction and geocoding. In related technologies such as SNAP and other SAR processing software, taking the Sentinel-1IW mode as an example (imaging width is 250km), the processing of SLC orthorectification takes about one hour, and the entire process from SLC to orbit file correction, noise removal, multi-view processing, radiation calibration, terrain correction, geocoding and image cropping takes several hours, of which terrain correction and geocoding are the most time-consuming. In contrast, this embodiment directly completes the orthorectification during the imaging process through the back-projection algorithm, avoiding a series of tedious and time-consuming operations such as the conversion from the range-azimuth coordinate system to the geographic longitude and latitude coordinate system, and is more efficient overall.

[0092] In some embodiments, step S102 may include but is not limited to steps S201 to S204.

[0093] Step S201 , geometric processing is performed based on satellite orbit parameters and radar parameters to obtain a scene center point and a satellite-ground geometric relationship model, wherein the satellite-ground geometric relationship model includes an Earth-centered Earth-fixed coordinate system model, a satellite platform coordinate system model, and a longitude-latitude high-coordinate system model.

[0094] Step S202: Rotate the center point of the scene to the longitude of the satellite to obtain the scene projection point.

[0095] Step S203 , performing data analysis based on the geometric relationship between the scene projection point and the satellite-ground geometric relationship model to obtain projection coordinate information and rotation angle of the scene projection point.

[0096] Step S204: performing coordinate transformation according to the projection coordinate information and the rotation angle to obtain the center coordinate information of the scene center point.

[0097] In this embodiment, the parameters of the WGS-84 model are shown in Table 1.

[0098] Table 1 WGS-84 model parameters

[0099] parameter Numerical unit <![CDATA[The semi-major axis a of the reference ellipsoid e > 6378137.0 m <![CDATA[The minor radius b of the reference ellipsoid e > 6356752.31424518 M The extreme flattening f of the reference ellipsoid 1 / 298.257223565 -

[0100] Reference Figure 4Based on the WGS-84 model, with the center of mass of the Earth as the origin O, the direction of the intersection of the prime meridian and the equator as the x-axis direction, the direction of the Earth's rotation angular momentum as the z-axis direction, and the y-axis, x-axis, and z-axis forming a right-handed coordinate system, the Earth-centered Earth-fixed coordinate system model is established, including: Earth-centered Earth-fixed coordinate system O-xyz, orbit perigee D, orbit ascending node E, orbit inclination i, ascending node right ascension Ω, perigee argument ω, semi-major axis a o , eccentricity e o and the true pericentric angle v, J is the intersection of the prime meridian and the equator, and the satellite position is depicted as point S (the semi-major axis and eccentricity are not in Figure 4 The unit vector from the center of the Earth O to the satellite position S is l, the unit vector of the satellite velocity is t, and the unit vector of the satellite angular momentum (i.e., the unit normal vector of the orbital plane) is n. Point G is the projection position of the satellite position S on the Earth's surface, and its longitude and latitude are and

[0101] The satellite position S is the origin of the satellite platform coordinate system, and the velocity direction t is x s axis, direction of angular momentum n is y s Axis, z s Axis and x s axis and y s The axes form a right-hand coordinate system and establish the satellite platform coordinate system Sx s y s z s , there is the following relationship:

[0102] x s =t (1);

[0103] y s =l×t (2);

[0104] z s =x s ×y s (3).

[0105] In formula (3), “×” represents a vector cross multiplication operation.

[0106] Let WGS-84 coordinates be ECEF coordinates are (x, y, z), and WGS-84 coordinates can be converted to ECEF coordinates using the following formula:

[0107]

[0108] In formula (4), e e is the eccentricity of the ellipsoid, N e is the radius of curvature of the reference ellipsoid, which can be calculated as follows:

[0109]

[0110] Since the extreme flattening of the reference ellipsoid f=(a e -b e ) / a e , eccentricity e e There is the following relationship with f:

[0111]

[0112] Therefore, formula (4) can be written as:

[0113]

[0114] in,

[0115] ECEF coordinates can be converted to WGS-84 coordinates using the following formula:

[0116]

[0117] Assume that the position vector of satellite position S in ECEF coordinate system is r S First, align the origin S of the satellite platform coordinate system with the origin O of the ECEF coordinate system. The transformation of the translated satellite platform coordinates to the ECEF coordinate system is equivalent to the basis transformation of the vector in the linear space. The transition matrix from the ECEF coordinate system basis to the translated satellite platform coordinate system basis is as follows:

[0118]

[0119] Assume that the satellite platform coordinates r SAT =(x SAT ,y SAT ,z SAT ), the corresponding ECEF coordinate is r ECEF =(x ECEF ,y ECEF ,z ECEF ), the satellite platform coordinates to ECEF coordinates can be converted using the following formula:

[0120] r ECEF =Pr SAT +r S (11).

[0121] The conversion from ECEF coordinates to satellite platform coordinates is the inverse process of formula (11) (the matrix P is reversible), as follows:

[0122] r SAT =P -1 (r ECEF -r S ) (12).

[0123] The scene center point B is determined based on the near point A and the far point C in the spaceborne SAR beam coverage area, and then the scene center point B is revolved around z s The axis rotates to the position on the meridian of point G (rotating towards the southern hemisphere) to obtain the scene projection point B', as shown Figure 4 As shown, |SB|=|SB'|.

[0124] Point F is the intersection of the meridian of point G and the equator. Since the scene projection point B' obtained by rotation is in the plane formed by points S, O, and F, data analysis can be performed in the two-dimensional plane based on the geometric relationship between the scene projection point and the satellite-ground geometric relationship model. Since the scene projection point B' is on the meridian of point G, the longitude of the scene projection point B' is known, and it is only necessary to solve the latitude of the scene projection point B'. Figure 5 In the earth cross-section diagram where points S, O, and F are located, the latitude of the scene projection point B' can be calculated using the slant range and satellite elevation through the cosine theorem, and then the projection coordinate information of the scene projection point B' can be obtained.

[0125] Furthermore, after obtaining the projection coordinate information of the scene projection point, the spaceborne SAR beam sight and projection coordinate information are used to calculate the projection coordinate information of the scene projection point. s y s The data analysis is continued in the plane, and the rotation angle from the scene center point B to the scene projection point B' is obtained by inverse analysis.

[0126] The center coordinate information of the scene center point can be obtained by reverse deduction from the coordinate information of the scene projection point B' using the known rotation angle.

[0127] In some embodiments, step S201 may include but is not limited to steps S301 to S303.

[0128] Step S301 : performing coordinate inverse processing based on the geometric relationship between the scene projection point and the satellite to obtain the first projection coordinates of the scene projection point in the Earth-centered Earth-fixed coordinate system model.

[0129] Step S302: Based on the first projection coordinates, the scene projection point is converted into a first coordinate system to obtain a second projection coordinate of the scene projection point in the satellite platform coordinate system model, and the second projection coordinates are used as the projection coordinate information of the scene projection point.

[0130] Step S303: Perform rotation inverse processing on the second projection coordinates to obtain a rotation angle.

[0131] In this embodiment, in order to maintain generality, it is assumed that the intersection line of the beam sight plane and the ground surface ( Figure 4 The slope distance of a point X on the curve AB in the figure is Rs , after rotating the point to the meridian of point G, it becomes point X' (assuming the satellite is locally a spherical model), and the relationship |SX'|=|SX|=R s '=R s , |SG| is the satellite elevation h, R G and R X ' are the distances between point G and point X and point O, respectively. The calculation formula is as follows:

[0132]

[0133] In formula (13), function g() represents the transformation of WGS-84 coordinates into ECEF coordinates using formula (4) or formula (7).

[0134] set up Figure 5 In the equation, ∠SOX'=ψ, then the latitude of point X' can be expressed as:

[0135]

[0136] Therefore, the slope distance calculation formula of point X' is as follows:

[0137]

[0138] exist Figure 5 According to the cosine theorem, △SOX' in the equation can be obtained as follows:

[0139]

[0140] Substituting equations (13) to (15) into equation (16) to obtain the angle (minimum value) by numerical calculation, the ECEF vector of point X' is:

[0141]

[0142] The ECEF coordinates (i.e., the first projection coordinates) are converted to satellite platform coordinates (i.e., the second projection coordinates) by formula (12):

[0143] Next, determine the angle of rotation from point X' to point X around the axis. First, determine In Sx s y s Projection vector to the plane:

[0144]

[0145] Next, determine the spaceborne SAR beam line of sight at Sx s y s Projected unit vector of the plane:

[0146] w=(sinθsq ,ι·cosθ sq ,0) (19);

[0147] In formula (19), ι represents the look side, which is 1 when viewed from the left and -1 when viewed from the right.

[0148] The rotation angle is the vector The angle between θ and vector w is calculated as follows:

[0149]

[0150] In formula (20), the function -sign() is used to determine the positive or negative sign of the rotation angle, that is, the rotation direction.

[0151] It is understandable that when point X coincides with point B, the coordinate information and rotation angle solved for point X' are the coordinate information and rotation angle of the scene projection point B'.

[0152] In some embodiments, step S204 may include but is not limited to steps S401 to S402.

[0153] Step S401 : rotating the second projection coordinates according to the rotation angle to obtain the first center coordinates of the scene center point in the satellite platform coordinate system model.

[0154] Step S402: Based on the first center coordinates, the scene center point is converted to the second coordinate system to obtain the second center coordinates of the scene center point in the latitude and longitude coordinate system model, and the second center coordinates are used as the center coordinate information of the scene center point.

[0155] In this embodiment, the rotation angle obtained in step S303 is used to construct a rotation matrix. The rotation matrix is multiplied by the projection coordinate information of the scene projection point obtained in step S302. The vector expression of point X in the satellite platform coordinate system can be obtained as follows:

[0156]

[0157] Using formula (11), we can get the vector of point X in the ECEF coordinate system as:

[0158]

[0159] It can be understood that when point X coincides with point B, the coordinates obtained by formula (21) are the first center coordinates of the scene center point in the satellite platform coordinate system model. The first center coordinates are then subjected to a second coordinate system conversion process. The second coordinate system conversion process includes converting the coordinates from the satellite platform coordinate system to the ECEF coordinate system, and converting the ECEF coordinate system to the latitude and longitude coordinate system.

[0160] Specifically, the first center coordinate of the scene center point in the satellite platform coordinate system is converted to the transition center coordinate in the ECEF coordinate system using formula (11), and then the transition center coordinate is converted to the second center coordinate in the latitude and longitude coordinate system using formula (9). The second center coordinate is used as the center coordinate information of the scene center point.

[0161] In some embodiments, step S103 may include but is not limited to steps S501 to S502.

[0162] Step S501 : performing grid division processing on a three-dimensional ground-range plane according to the center coordinate information and the imaging resolution to obtain a latitude and longitude ground-range grid.

[0163] Step S502: assigning elevation information to the latitude and longitude ground distance grid in combination with the digital elevation model to obtain a ground distance geometric imaging grid.

[0164] In this embodiment, the grid division only requires calculating the coordinates of the scene center. According to the center coordinate information (latitude and longitude) and the imaging resolution, the output imaging grid can be directly divided on the three-dimensional ground-distance plane. At this time, the imaging grid is a latitude and longitude ground-distance grid.

[0165] If a digital elevation model (DEM) exists, the elevation value of each point in the latitude and longitude ground distance grid is replaced with the elevation data of the corresponding position in the DEM to obtain the ground distance geometric imaging grid.

[0166] In step S502 of some embodiments, if there is no DEM data in the digital elevation model, the elevation defaults to zero.

[0167] In some embodiments, step S501 may include but is not limited to steps S601 to S604.

[0168] Step S601: determining the grid spacing according to the imaging resolution.

[0169] Step S602: performing grid division processing on the three-dimensional ground plane according to the grid spacing to obtain a plurality of grid points.

[0170] Step S603: Taking the center coordinate information as a reference, the grid coordinate information of each grid point is determined according to the grid spacing.

[0171] Step S604: Obtaining a longitude and latitude distance grid based on the grid points and the corresponding grid coordinate information.

[0172] In this embodiment, the imaging resolutions in the azimuth and range directions are extracted from the radar system parameters, and the grid spacing of the reconstructed pixel points is determined according to the imaging resolutions.

[0173] Based on the WGS-84 ellipsoid model, a three-dimensional ground distance plane is established on the surface of the WGS-84 ellipsoid model. On the latitude and longitude plane, the center point of the scene is used as the origin, and grid points are generated by expanding to the surrounding areas according to the grid spacing. Then, based on the central coordinate information of the scene center point, the grid coordinate information of each grid point is determined by adding and subtracting the grid spacing in the longitude and latitude directions. A uniform longitude and latitude ground distance grid is formed based on the grid points and the corresponding grid coordinate information, as shown in the following example: Figure 6 shown.

[0174] In some embodiments, step S104 may include but is not limited to steps S701 to S703 .

[0175] Step S701: Process the radar echo data to obtain a plurality of sub-aperture data.

[0176] Step S702: Calculate the slant distance corresponding to each sub-aperture according to the sub-aperture data.

[0177] Step S703 : performing back-projection imaging processing on the ground-range geometric imaging grid according to the sub-aperture data and the corresponding slant range to obtain an imaging result.

[0178] In this embodiment, the entire synthetic aperture is divided into multiple sub-apertures, each corresponding to a period of radar data. For each sub-aperture, the projection range of the ground-range geometric imaging grid during the final fusion stage is determined, and the slant range between each sub-aperture data and the grid is calculated. Using the slant range as a bridge, the data is mapped to the ground-range geometric imaging grid through a back-projection imaging algorithm to directly obtain the imaging result, completing the ground-range grid imaging processing.

[0179] In some embodiments, step S701 may include but is not limited to steps S801 to S802.

[0180] Step S801 : performing sub-aperture division processing on radar echo data to obtain a plurality of pre-processed data.

[0181] Step S802 : performing two-dimensional interpolation processing on each pre-processed data on an oblique plane to obtain a plurality of sub-aperture data.

[0182] In this embodiment, a method for determining the longitude and latitude position of the ground is used with reference to any range gate value in the direction of sight of a given spaceborne SAR to determine the longitude and latitude position of the imaging scene center, and to divide the three-dimensional imaging grid accordingly. It is not difficult to imagine that the sub-aperture polar coordinate imaging grid can also be divided into a three-dimensional imaging grid on the surface of the earth according to this method, and then fusion is achieved through three-dimensional interpolation. This technical route is feasible in theory, but it is actually difficult to achieve in programming. Because compared with the two-dimensional interpolation of the oblique plane, although the three-dimensional interpolation has only one more dimension, its computational complexity increases exponentially, and the computational time is dozens of times that of the oblique plane imaging, which in turn leads to inefficient algorithm and poor practicality.

[0183] In fact, from the perspective of radar systems, it is not necessary to image the subaperture on a cylindrical grid (a polar grid with altitude and latitude added). APC is a key point in GNSS measurement. It is defined as the theoretical spatial position where pseudorange and carrier phase can be observed. For APC, the back projection value of a certain position only concerns the azimuth and distance. Figure 7 As shown, point P is the actual position of the scene point, and the corresponding zero elevation position is point P'. Their corresponding slope distances are R P and R P ', the positions on the inclined plane are P slant and P' slant Therefore, the influence of elevation is reflected in the slant range. To avoid the high computational complexity of three-dimensional interpolation, the polar coordinate imaging grid is still divided on the oblique plane during sub-aperture imaging processing. The intermediate fusion process of sub-aperture imaging is also performed on the oblique plane. Since the image will be distorted in the polar coordinate system, the distortion between different polar coordinates is different. Therefore, interpolation processing is required during image coherence fusion so that the two-dimensional interpolation can be projected onto the final imaging grid.

[0184] It should be noted that, from the sampling perspective, the callback signal is sampled in two-dimensional space at fast time and slow time, which also means that there is no need for imaging in three-dimensional space.

[0185] The following describes and explains the solution of the embodiment of the present invention in detail with reference to specific application examples.

[0186] It should be noted that because the assumption that the surface is approximately flat is inaccurate in spaceborne SAR scenarios, spaceborne SAR requires a more accurate ground-range gridding method. The ground-range geometric imaging gridding method for synthetic aperture radar backprojection provided in the embodiments of this application is specifically designed for spaceborne SAR. The backprojection imaging algorithm has the advantage of imaging on any imaging grid. Combined with a digital high-level model, the image obtained by backprojection imaging processing on the grid obtained by this method is naturally geocoded. Therefore, there is no need to convert from the slant-range imaging plane to the ground-range imaging plane, improving processing efficiency.

[0187] Specifically, refer to Figure 8 In the embodiment of the present application, the orbit parameters and radar parameters are first obtained, and the coordinates of the scene center point B are calculated based on the orbit parameters and radar parameters.

[0188] Specifically, refer to Figure 4 , let the slope distance R s The slant distance corresponding to the center moment of the satellite sampling time window is set as B', and the slant distance corresponding to the scene projection point is R. s ', then there exists a relation |SB'|=|SB|=R s '=R s |SG| is the satellite height h, R G is the distance between point G and point O, and the calculation formula is as follows:

[0189]

[0190] In formula (23), the function represents the conversion of WGS-84 coordinates to ECEF coordinates, which is achieved by formula (4) or formula (7).

[0191] Next, refer to Figure 5 , point B' is equivalent to Figure 5 For point X' in the figure, according to the satellite-ground geometric profile relationship, the latitude of point B' can be calculated according to formula (14), which is as follows:

[0192]

[0193] Therefore, the calculated latitude Substituting into formula (15) we can get:

[0194]

[0195] According to the cosine theorem:

[0196]

[0197] According to the above calculation results, the ECEF coordinates of point B' are:

[0198]

[0199] Convert point B' to satellite platform coordinates using formula (12)

[0200] After obtaining the satellite platform coordinates of the scene projection point B', the rotation angle from the scene projection point B' to the scene center point B is determined.

[0201] For example, according to In Sx s y s Projection vector of the plane And the spaceborne SAR beam line of sight is at Sx s y s The projection vector of the plane w=(sinθ sq ,ι·cosθ sq ,0), calculate the angle between the vectors, the angle between the two vectors is the rotation angle θ rot , the calculation formula is as follows:

[0202]

[0203] Calculate the vector of point B in the satellite platform coordinate system based on the satellite platform coordinates and rotation angle of point B':

[0204]

[0205] According to formula (11), the scene center point B is first converted from the satellite platform coordinate system to the coordinates of the ECEF coordinate system. The conversion formula is as follows:

[0206]

[0207] Then, according to formula (9), the scene center point B is converted from the ECEF coordinate system to the LLA coordinate system.

[0208] Set the range and spacing of the ground-based geometric imaging grid. Divide the ground-based geometric imaging grid by the LLA coordinates of the scene center point calculated in the previous steps and the set grid range and spacing. At this time, the imaging grid is a longitude and latitude grid. Combined with the digital elevation model, use formula (4) to convert the longitude and latitude grid into an ECEF coordinate grid for backprojection imaging.

[0209] It should be noted that since WGS-84 is an ellipsoid model, there is a certain deviation from the actual scene center. However, this deviation does not cause an error between the imaging result and the geocoded location, that is, an error between the pixel value and the corresponding geographic location. There is no positional "error" in the grid location. The algorithm strictly follows the grid pixel coordinates for imaging, and there is no deviation between the reconstructed pixel value and the location. The error only exists between the reconstructed pixel value and the true value due to factors such as signal processing, ground range error, atmospheric radiation, and thermal noise. However, the traditional method of imaging on an oblique plane and then projecting it onto a ground range plane can cause errors between the pixel value and the geographic location. This is because errors in sensor and platform ephemeris, target positioning, and distance can all lead to deviations in the projected position. Imaging on a ground range grid can fundamentally avoid this model error.

[0210] Spaceborne radars use multiple range gates for range sampling. The ground-range position of each range gate value can be determined based on the intersection of the beamline of sight and the ground surface, and the ground-range imaging grid can be divided accordingly. However, this is unnecessary because the grid is not uniform in the range direction. The algorithm still needs to calculate the range and interpolate the echoes during the backward processing. This has no advantages over grid processing based solely on the scene center and the imaging resolution, and can even introduce geometric distortion in the image.

[0211] Furthermore, in order to verify the method provided in the embodiment of the present application, the actual imaging parameters of the Sentinel-1 strip mode are used to divide the imaging grid on the ground range geometry. The results are as follows: Figure 6 shown.

[0212] The measured data of Sentinel-1 satellite strip mode are intercepted. Assuming the scene is at zero elevation, the imaging results on the ground plane are as follows: Figure 9 shown.

[0213] The following is an image taken on a ground-based grid in combination with DEM data. The SIR-C / X-SAR was sent into space by the space shuttle to perform an 11-day mission. A 60m-long boom was installed on the outside of the space shuttle to carry an external antenna to simultaneously receive C-band and X-band signals. Temporal decorrelation has brought the technical level of spaceborne interferometric SAR to a new level, and a digital elevation model from 56°S to 60°N has been obtained. The DEM dataset is named SRTM, with an original resolution of 1 arc second (about 30m along the equator). The distributed data are in two versions, SRTM 1 and SRTM 3. The former has an accuracy of 1 arc second and the latter has an accuracy of 3 arc seconds (about 90m along the equator). The original SRTM elevation is calculated based on the WGS84 ellipsoid model, and the vertical error at a 90% confidence level in EGM96 is less than 16m. The DEM model used in this embodiment is SRTM 3 data. Figure 9The DEM corresponding to the area is as follows Figure 10 shown.

[0214] Combine Figure 10 The DEM data is divided into ground-distance imaging grids on the earth's surface, and the height of each point of zero elevation latitude and longitude is set to the corresponding DEM elevation (interpolation may be required), and the oblique plane imaging projection is performed. The imaging result is as follows Figure 11 As shown, Figure 9 Comparing the imaging results on the ground-distance grid with elevation, it is obvious that the imaging results on the mountainous part have been terrain corrected.

[0215] Figure 9 and Figure 11 The corresponding optical remote sensing image is as follows Figure 12 As shown, compared with imaging in the oblique plane, ground-range grid imaging also completes geocoding.

[0216] In the above imaging process, processing the same data, the average imaging time on the slant plane is 621 seconds, and the average imaging time on the ground-range grid is 662 seconds. Therefore, there is not much difference in the computational complexity and algorithm performance of imaging on the slant-range plane and the ground-range plane, which reflects a major advantage of the backprojection time-domain algorithm.

[0217] In summary, the method for ground-distance geometric imaging grid division of synthetic aperture radar backprojection provided in the embodiment of the present application utilizes the advantage that the backprojection imaging algorithm can be imaged on any grid, and divides the spaceborne SAR imaging grid on the surface of the WGS-84 ellipsoid model. By using the satellite-earth geometric configuration as a model, the scene center coordinates are calculated. The grid division only requires calculating the coordinates of the scene center, while the coordinates of other grid points are generated based on the grid range and grid spacing. In this way, other points do not need to be obtained through complex calculations. At the same time, the generation of the grid can be combined with the data elevation model to generate a ground-distance geometric imaging grid, so that terrain correction and geocoding can be completed simultaneously with backprojection imaging.

[0218] The backprojection imaging results obtained based on the embodiments of the present application are terrain-corrected and geocoded products, eliminating the need for a conversion from the slant-range plane to the ground-range plane followed by terrain correction. Furthermore, compared to backprojecting directly onto the slant-range plane, backprojecting onto the ground-range geometric imaging grid created by the embodiments of the present application does not significantly increase the time required, significantly impacting the efficiency of the algorithm.

[0219] Reference Figure 13 The present application also provides a virtual system for ground-range geometric imaging grid division of synthetic aperture radar backprojection, which can implement the above-mentioned ground-range geometric imaging grid division method of synthetic aperture radar backprojection. The virtual system includes:

[0220] The first module is used to obtain satellite orbit parameters, radar parameters and radar echo data.

[0221] The second module is used to determine the central coordinate information of the scene center point according to the satellite orbit parameters and the radar parameters, wherein the scene center point represents the geometric center point of the imaging area.

[0222] The third module is used to combine the digital elevation model and divide the grid according to the imaging resolution on the three-dimensional ground-distance plane based on the center coordinate information to obtain the ground-distance geometric imaging grid.

[0223] The fourth module is used to perform back-projection imaging processing on the ground-range geometric imaging grid according to the radar echo data to obtain the imaging result.

[0224] It can be understood that the contents of the above method embodiments are applicable to this virtual system embodiment, the functions specifically implemented by this virtual system embodiment are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

[0225] The present application also provides a hardware system for ground-range geometric imaging grid division for synthetic aperture radar backprojection. The hardware system includes a memory and a processor. The memory stores a computer program, and the processor, when executing the computer program, implements the aforementioned method for ground-range geometric imaging grid division for synthetic aperture radar backprojection. The hardware system can be any intelligent terminal, including a tablet computer and an in-vehicle computer.

[0226] It can be understood that the contents of the above method embodiments are all applicable to the present hardware system embodiment, the functions specifically implemented by the present hardware system embodiment are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

[0227] Reference Figure 14 , Figure 14 The hardware structure of the hardware system of another embodiment is shown, and the hardware system includes:

[0228] The processor 901 can be implemented using a general-purpose CPU (Central Processing Unit), a microprocessor, an application-specific integrated circuit (ASIC), or one or more integrated circuits, and is used to execute relevant programs to implement the technical solutions provided in the embodiments of the present application.

[0229] The memory 902 can be implemented in the form of a read-only memory (ROM), a static storage device, a dynamic storage device, or a random access memory (RAM). The memory 902 can store an operating system and other application programs. When the technical solutions provided in the embodiments of this specification are implemented through software or firmware, the relevant program code is stored in the memory 902 and is called by the processor 901 to execute the ground-range geometric imaging grid division method for synthetic aperture radar backprojection according to the embodiments of the present application.

[0230] The input / output interface 903 is used to implement information input and output.

[0231] The communication interface 904 is used to realize the communication interaction between the hardware system and other devices. Communication can be achieved through wired means (such as USB, network cable, etc.) or wireless means (such as mobile network, WIFI, Bluetooth, etc.).

[0232] The bus 905 transmits information between various components of the hardware system (eg, the processor 901 , the memory 902 , the input / output interface 903 , and the communication interface 904 ).

[0233] The processor 901 , the memory 902 , the input / output interface 903 and the communication interface 904 are connected to each other in communication within the hardware system via a bus 905 .

[0234] An embodiment of the present application also provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, it implements the above-mentioned ground-range geometric imaging grid division method for synthetic aperture radar backprojection.

[0235] It can be understood that the contents of the above method embodiments are all applicable to the present storage medium embodiment, the functions specifically implemented by the present storage medium embodiment are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

[0236] The memory, as a non-transient computer-readable storage medium, can be used to store non-transient software programs and non-transient computer executable programs. In addition, the memory may include a high-speed random access memory and may also include a non-transient memory, such as at least one disk storage device, a flash memory device, or other non-transient solid-state storage device. In some embodiments, the memory may optionally include a memory remotely arranged relative to the processor, and these remote memories may be connected to the processor via a network. Examples of the above-mentioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0237] The embodiments described in the embodiments of this application are intended to more clearly illustrate the technical solutions of the embodiments of this application and do not constitute a limitation on the technical solutions provided by the embodiments of this application. Those skilled in the art will appreciate that with the evolution of technology and the emergence of new application scenarios, the technical solutions provided in the embodiments of this application are also applicable to similar technical problems.

[0238] Those skilled in the art will understand that the technical solutions shown in the figures do not constitute a limitation on the embodiments of the present application, and may include more or fewer steps than shown in the figures, or a combination of certain steps, or different steps.

[0239] The system embodiment described above is merely illustrative. The units described as separate components may or may not be physically separate, i.e., they may be located in one place or distributed across multiple network units. Some or all of the modules may be selected based on actual needs to achieve the objectives of this embodiment.

[0240] Those skilled in the art will appreciate that all or some of the steps in the methods, systems, and functional modules / units in the devices disclosed above may be implemented as software, firmware, hardware, or appropriate combinations thereof.

[0241] The terms "first", "second", "third", "fourth", etc. (if any) in the specification of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0242] The preferred embodiments of the present invention are described above with reference to the accompanying drawings, but are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and essence of the present invention should be within the scope of the present invention.

Claims

1. A method for ground-level geometric imaging grid division for synthetic aperture radar backprojection, characterized in that: The method comprises the following steps: Obtain satellite orbit parameters, radar parameters and radar echo data; Determining central coordinate information of a scene center point according to the satellite orbit parameters and the radar parameters, wherein the scene center point represents a geometric center point of an imaging area; In combination with the digital elevation model, a grid is divided according to the imaging resolution on the three-dimensional ground-distance plane based on the center coordinate information to obtain a ground-distance geometric imaging grid; Back-projection imaging processing is performed on the ground-distance geometric imaging grid according to the radar echo data to obtain an imaging result.

2. The method according to claim 1, characterized in that Determining the center coordinate information of the scene center point according to the satellite orbit parameters and the radar parameters includes the following steps: Performing geometric processing based on the satellite orbit parameters and the radar parameters to obtain a scene center point and a satellite-ground geometric relationship model, wherein the satellite-ground geometric relationship model includes an Earth-centered Earth-fixed coordinate system model, a satellite platform coordinate system model, and a longitude-latitude high-coordinate system model; Rotate the center point of the scene to the longitude of the satellite to obtain the scene projection point; Performing data analysis based on the geometric relationship between the scene projection point and the satellite-ground geometric relationship model to obtain projection coordinate information and a rotation angle of the scene projection point; Coordinate transformation is performed according to the projection coordinate information and the rotation angle to obtain central coordinate information of the scene center point.

3. The method according to claim 2, characterized in that The step of performing data parsing based on the geometric relationship between the scene projection point and the satellite-ground geometric relationship model to obtain projection coordinate information and a rotation angle of the scene projection point includes the following steps: Performing coordinate inverse processing according to the geometric relationship between the scene projection point and the satellite to obtain the first projection coordinates of the scene projection point in the Earth-centered Earth-fixed coordinate system model; Based on the first projection coordinates, performing a first coordinate system conversion process on the scene projection point to obtain a second projection coordinate of the scene projection point in the satellite platform coordinate system model, and using the second projection coordinates as the projection coordinate information of the scene projection point; Perform rotation inverse processing on the second projection coordinates to obtain a rotation angle.

4. The method according to claim 3, characterized in that The step of performing coordinate transformation according to the projection coordinate information and the rotation angle to obtain the center coordinate information of the scene center point includes the following steps: Rotate the second projection coordinates according to the rotation angle to obtain the first center coordinates of the scene center point in the satellite platform coordinate system model; Based on the first center coordinates, the scene center point is converted into a second coordinate system to obtain the second center coordinates of the scene center point in the latitude and longitude high coordinate system model, and the second center coordinates are used as the center coordinate information of the scene center point.

5. The method according to claim 1, wherein The method of combining the digital elevation model and dividing the grid according to the imaging resolution on the three-dimensional ground-distance plane according to the center coordinate information to obtain the ground-distance geometric imaging grid includes the following steps: Performing grid division processing on a three-dimensional ground distance plane according to the center coordinate information and imaging resolution to obtain a latitude and longitude ground distance grid; The latitude and longitude ground distance grid is given elevation information in combination with a digital elevation model to obtain a ground distance geometric imaging grid.

6. The method according to claim 5, characterized in that The method of performing grid division processing on a three-dimensional ground distance plane according to the center coordinate information and the imaging resolution to obtain a latitude and longitude ground distance grid comprises the following steps: Determine the grid spacing based on the imaging resolution; Performing a grid division process on a three-dimensional ground plane according to the grid spacing to obtain a plurality of grid points; Taking the center coordinate information as a reference, determining the grid coordinate information of each of the grid points according to the grid spacing; A latitude and longitude distance grid is obtained according to the grid points and the corresponding grid coordinate information.

7. The method according to claim 1, characterized in that The step of performing backprojection imaging processing on the ground-distance geometric imaging grid according to the radar echo data to obtain an imaging result comprises the following steps: Processing the radar echo data to obtain a plurality of sub-aperture data; Calculating the slant distance corresponding to each sub-aperture according to the sub-aperture data; Back-projection imaging processing is performed on the ground-range geometric imaging grid according to the sub-aperture data and the corresponding slant range to obtain an imaging result.

8. The method according to claim 7, characterized in that The processing of the radar echo data to obtain a plurality of sub-aperture data comprises the following steps: Performing sub-aperture division processing on the radar echo data to obtain a plurality of pre-processed data; A two-dimensional interpolation process is performed on each of the pre-processed data on an inclined plane to obtain a plurality of sub-aperture data.

9. A ground-level geometric imaging grid division virtual system for synthetic aperture radar backprojection, characterized in that: The virtual system includes: The first module is used to obtain satellite orbit parameters, radar parameters and radar echo data; A second module is configured to determine central coordinate information of a scene center point according to the satellite orbit parameters and the radar parameters, wherein the scene center point represents a geometric center point of an imaging area; The third module is used to divide the grid according to the imaging resolution on the three-dimensional ground-distance plane based on the central coordinate information in combination with the digital elevation model to obtain a ground-distance geometric imaging grid; The fourth module is used to perform back-projection imaging processing on the ground-distance geometric imaging grid according to the radar echo data to obtain an imaging result.

10. A hardware system for ground-range geometric imaging grid division for synthetic aperture radar backprojection, characterized in that: The hardware system includes a memory and a processor, the memory stores a computer program, and the processor implements the method according to any one of claims 1 to 8 when executing the computer program.

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