Satellite-borne double-antenna interference SAR block adjustment method

Abstract

The invention discloses a space-borne double-antenna interference SAR block adjustment method. The method comprises the steps that a plurality of adjacent unwrapping interferograms and additional data which are produced by a space-borne double-antenna interference SAR in a research area and have overlapped areas are acquired; the method comprises the following steps: acquiring an initial DSM of a radar coordinate system based on a satellite-borne double-antenna interference SAR interference baseline model and phase elevation conversion, and acquiring an initial DSM of a geographic coordinate system through geocoding; calculating the row and column numbers and elevation of the control points in the initial DSM of the radar coordinate system; determining the adjacency relation of each initial DSM, uniformly selecting homonymy points in the overlapping area of the adjacent initial DSM as connection points, and determining the row and column numbers and elevation of the connection points in the initial DSM of the corresponding radar coordinate system; and establishing a block adjustment model based on elevation constraints of the control points and the connection points, carrying out block adjustment correction on the radar coordinate system initial DSM, and obtaining an adjusted geographic coordinate system DSM through geocoding. According to the invention, the precision of an initial DSM product produced by a satellite-borne double-antenna X-band interference SAR system can be further improved.

Description

Technical Field

[0001] This invention relates to a method for adjusting a spaceborne dual-antenna interferometric SAR regional network, belonging to the field of interferometric synthetic aperture radar altimetry. Background Technology

[0002] A Digital Surface Model (DSM) is a digital description of the elevation information of a terrain surface. Obtaining DSMs of ground scenes has significant application value in military and national economic construction. How to obtain high-precision DSMs of observation scenes is currently one of the hot topics in surveying and remote sensing technology. Spaceborne Synthetic Aperture Radar Interferometry (InSAR), as an important geodetic observation method, can quickly, efficiently, and over a large area achieve global topographic mapping and obtain high-precision DSMs of the Earth's surface.

[0003] The new dual-antenna X-band interferometric SAR satellite is the world's first high-precision dual-antenna interferometric synthetic aperture radar satellite. Building upon the all-weather, all-time topographic measurement advantages of the US Space Shuttle Radar Topography Mission (SRTM), this satellite extends the platform from the Space Shuttle to a satellite. Combined with a longer interferometric baseline, it reduces InSAR elevation ambiguity and improves the elevation accuracy of digital surface models. The research objective of the dual-antenna X-band interferometric SAR system is to acquire observational data with a unified reference frame and a unified data source through dual-antenna X-band interferometric SAR, construct a global digital surface model with uniform accuracy, and ultimately prepare a digital elevation model (DEM) to promote the development and application of interferometric SAR.

[0004] Interferometric baseline errors are the primary cause of initial DSM elevation errors during the generation of the Distance Standard Model (DSM) by interferometric SAR. To achieve longer interferometric baselines, spaceborne dual-antenna interferometric SAR satellites mount antennas at the ends of flexible antenna arms approximately 60 meters long at each end. This novel method of constructing interferometric baselines complicates the time-varying characteristics of the baselines, rendering traditional linear interferometric baseline models insufficient to describe these variations. This can lead to complex systematic errors in DSM elevation, making it difficult for existing regional network adjustment methods to effectively correct these initial DSM elevation systematic errors. Therefore, there is an urgent need to develop a regional network adjustment method suitable for spaceborne dual-antenna interferometric SAR (SARDSM). Summary of the Invention

[0005] The technical problem solved by this invention is to overcome the shortcomings of the prior art. This invention provides a method for adjusting the regional network of spaceborne dual-antenna interferometric SAR, which can solve the limitations of the prior art in adjusting the regional network of spaceborne dual-antenna interferometric SAR DSM, effectively improve the initial DSM elevation accuracy of spaceborne dual-antenna interferometric SAR, eliminate data edge-joining errors, and achieve consistency of DSM accuracy within the region.

[0006] The present invention adopts the following technical solution: A method for adjusting a spaceborne dual-antenna interferometric SAR regional network includes the following steps: Step S1: Obtain unwrapped interferograms and additional data for multiple adjacent and overlapping regions generated by spaceborne dual-antenna interferometric SAR in the study area; Step S2: Obtain the initial DSM of the radar coordinate system based on the interferometric baseline model of the spaceborne dual-antenna interferometric SAR and the phase elevation transformation, and obtain the initial DSM of the geographic coordinate system through geocoding; Step S3: Calculate the row and column numbers and elevation of the control points in the initial DSM of the radar coordinate system; Step S4: Determine the adjacency relationship of each initial DSM, uniformly select the same points in the overlapping area of ​​adjacent initial DSMs as connection points, and determine the row and column number and elevation of the connection points in the corresponding radar coordinate system initial DSM. Step S5: Establish a regional network adjustment model based on the elevation constraints of control points and connection points, perform regional network adjustment correction on the initial radar coordinate system DSM, and obtain the adjusted geographic coordinate system DSM through geocoding.

[0007] Furthermore, in step S2, the initial DSM of the radar coordinate system is obtained based on the interferometric baseline model of the spaceborne dual-antenna interferometric SAR and the phase elevation transformation, and the initial DSM of the geographic coordinate system is obtained through geocoding, including: Step S2.1: Construct an interferometric baseline model based on the time-varying characteristics of the interferometric baseline of a spaceborne dual-antenna interferometric SAR. Step S2.2: Based on the view vector decomposition method and the transformation relationship from spatial rectangular coordinate system to geodetic coordinate system, the unwrapped interferometric phase to elevation transformation is realized to obtain the initial DSM of radar coordinate system, and the initial DSM of geographic coordinate system is obtained through geocoding.

[0008] Furthermore, in step S2.1, an interferometric baseline model is constructed based on the time-varying characteristics of the interferometric baseline of the spaceborne dual-antenna interferometric SAR, including: The interferometric baseline in the Earth-centered, Earth-fixed space rectangular coordinate system is: ; in, Let be the transformation matrix from the TCN coordinate system to the geocentric rectangular coordinate system. Let be the interferometric baseline vector represented in the TCN coordinate system. The three-dimensional position of the phase center of the main antenna in the Earth-centered, Earth-fixed space rectangular coordinate system. The velocity vector of the main antenna phase center in the Earth-centered, Earth-fixed space rectangular coordinate system. The unit vector along the C-axis of the TCN coordinate system. The unit vector along the N-axis of the TCN coordinate system; Based on the time-varying characteristics of the spaceborne dual-antenna interferometric SAR flexible antenna, the interferometric baseline vector in the TCN coordinate system is: ; in, , and The components of the interferometric baseline vector along the T-axis, C-axis, and N-axis in the TCN coordinate system. , and for , and The constant part in The view from the main antenna radar side. This refers to the change in the azimuth direction of the auxiliary antenna's phase center caused by the vibration of the antenna support arm. The change in the phase center of the auxiliary antenna in the slant range direction caused by the jitter of the antenna support arm. The main antenna arm roll bending amplitude. The damping coefficient of the main antenna arm. The main antenna arm jitter angular frequency. For direction and time, Main antenna arm rolls and bends reference phase. To measure the roll bending amplitude of the auxiliary antenna arm, The damping coefficient of the auxiliary antenna arm, To reduce the angular frequency of the auxiliary antenna arm jitter, The auxiliary antenna arm rolls and bends to reference the phase.

[0009] For cross-track interferometry, the baseline along the T-axis after SAR registration and resampling... It is 0, and The error has a negligible impact on InSAR altimetry measurements. Therefore, the interferometric baseline components along the T-axis can be set to constants that do not change with time; the specific value can be the average of all low-frequency interferometric baseline observations along the T-axis. For the C-axis and N-axis of the interferometric baseline, the parameters in the interferometric baseline model need to be adjusted using the low-frequency baseline vector measurement data from the baseline parameter file. Make an estimate, and then determine the time based on the azimuth. Calculate the C-axis and N-axis components of the interference baseline corresponding to each pixel. Let: ; Assuming the baseline parameter file contains For each low-frequency interferometric baseline measurement data point, there is an error equation:

[0010] in, Indicates the first Interferometric baseline observation data, . , It represents the observation data error at points Bci and bni.

[0011] Expressed in matrix form as follows: ; in, ; ; ; , , The equation takes initial values ​​for the interferometric baseline parameters. The value of time, , For the first C-axis and N-axis components of low-frequency interferometric baseline observations; By iteratively solving for the corrections to the model parameters using the least squares criterion as the adjustment criterion, we obtain: ; The root mean square of the difference between the baseline vectors of the TCN coordinate system before and after each iteration is: ; In the formula, Indicates the first The measurement data is the first one. The interferometric baseline vector in the TCN coordinate system is calculated using the adjusted parameters in the next iteration. The iteration stops when the value is less than the set value. This yields the adjusted interferometric baseline model parameters. ; After obtaining the parameters of the interferometric baseline model, the azimuth time of each row of pixels in the unwrapped interferogram can be determined. Calculate the interferometric baseline vector corresponding to each row of pixels. .

[0012] Furthermore, in step S3, the row and column numbers and elevations of the control points in the initial DSM of the radar coordinate system are calculated, including: Step S3.1: Obtain the row and column numbers of the control points in the initial DSM of the geographic coordinate system based on the geographic information of the control point data; Step S3.2: Use the lookup table data to obtain the row and column numbers of the control points on the initial DSM of the radar coordinate system. The initial DSM elevation of the radar coordinate system at the corresponding row and column number is calculated using the bilinear interpolation algorithm.

[0013] Furthermore, in step S4, the adjacency relationship of each initial DSM is determined, and corresponding points within the overlapping area of ​​adjacent initial DSMs are uniformly selected as connection points. The row, column, and elevation of the connection points in the corresponding radar coordinate system initial DSM are then determined, including: Step S4.1: Determine whether two DSMs are adjacent and overlap based on the latitude and longitude range of the initial DSM; Step S4.2: Uniformly select corresponding points within the overlapping area of ​​adjacent initial DSMs as connection points, and determine the row and column numbers and elevations of the connection points in the corresponding radar coordinate system initial DSM.

[0014] Furthermore, in step S4.1, determining whether two DSMs are adjacent and overlap based on the latitude and longitude range of the initial DSM includes: Let the longitude range of an initial DSM be... The latitude range is Another scene requires determination of the longitude range of the initial DSM. The latitude range is denoted as ; if or or or This indicates that there is no overlapping area between the two DSMs; otherwise, there is an overlapping area between the two DSMs. in, Indicates the degree of overlap along the longitude axis. Indicates the degree of overlap in the latitudinal direction.

[0015] Furthermore, in step S5, a regional network adjustment model is established based on the elevation constraints of control points and connection points. The initial radar coordinate system (DSM) is then adjusted using regional network adjustment, and the adjusted geographic coordinate system (DSM) is obtained through geocoding, including: Step S5.1: Establish the initial DSM elevation regional network adjustment model of the radar coordinate system based on the elevation constraints at the control points and connection points; Step S5.2: Perform regional network adjustment correction on the initial radar coordinate system DSM, and obtain the adjusted geographic coordinate system DSM through geocoding.

[0016] Furthermore, in step S5.1, an initial DSM elevation regional network adjustment model for the radar coordinate system is established based on the elevation constraints at control points and connection points, including: One connection point, One control point, The matrix form of the error equation for the initial DSM elevation area network adjustment model can be written as: ; in, ; ; ; in, It is the elevation residual vector. The coefficient matrix, Let be the coefficient vector of the initial DSM elevation system error correction model for the radar coordinate system to be solved. Let be the elevation difference vector at the control point and the connection point. This refers to the column number of the control point or tie point on the initial DSM of the radar coordinate system. This refers to the row number of the control point or connection point on the initial DSM of the radar coordinate system. For the Kth initial DSM, the th The column number of each control point For the Kth initial DSM, the th The row number of each control point For the second initial DSM The column number of each connection point For the second initial DSM The row number of each connection point For the first initial DSM that is adjacent to the second initial DSM On the first initial DSM The column number of each connection point For the first initial DSM that is adjacent to the second initial DSM On the first initial DSM The row number of each connection point , , The coefficients of the initial DSM elevation system error correction model for the Kth radar coordinate system are: For the first scene of radar coordinate system initial DSM, the first The initial DSM elevation of each control point location. For the first scene of radar coordinate system initial DSM, the first Elevation of each control point For the first initial DSM The initial DSM elevation of each connection point. For the first initial DSM that is adjacent to the first initial DSM, the first initial DSM is the first initial DSM. Initial DSM elevation at each connection point.

[0017] Furthermore, under the least squares criterion, the solution to the above error equation is: ; in, Represents the coefficient matrix Transpose The weight matrix is ​​the observation weight matrix. The initial weight matrix can be the identity matrix. This is the parameter vector for the error correction model of all initial DSM elevation systems.

[0018] To improve the stability and accuracy of model parameter estimation, an iterative reweighted least squares algorithm is used to solve the error equation. Substitute into the error equation to calculate the elevation residual vector Then, the new weights are calculated using the following formula: ; in, For the first The second iteration The weights corresponding to each observation. For the first The second iteration The weights corresponding to each observation. For the first The second iteration The elevation residuals corresponding to each observation value For the first The unit weight mean square error at the next iteration.

[0019] The newly calculated weights are combined into a weight matrix and re-introduced into the error equation to iteratively calculate the model parameters until the [number]th ...]. Second and third If the unit weight error difference is less than a certain threshold, the iteration stops, and the final initial DSM elevation system error correction model coefficient vector is obtained.

[0020] The above-described solution of the present invention has the following beneficial effects: To address the issues of inconsistent initial DSM accuracy, significant edge-joining errors, and the inability of existing regional network adjustment methods to effectively compensate for complex initial DSM elevation system errors caused by interference parameter errors such as the interferometric baseline of spaceborne dual-antenna interferometric SAR, this invention proposes a regional network adjustment method for spaceborne dual-antenna interferometric SAR. This method is based on the time-varying characteristics of the interferometric baseline of the spaceborne dual-antenna interferometric SAR system. It uses an interferometric baseline model that better matches the system to estimate baseline parameters, avoiding complex DSM elevation errors caused by the combined effects of interferometric parameter errors. Subsequently, a DSM regional network adjustment model is established based on the elevation constraints of control points and tie points. The initial DSM in the radar coordinate system is corrected using regional network adjustment, and the adjusted geographic coordinate system DSM is obtained through geocoding. This effectively improves the initial DSM elevation accuracy of spaceborne dual-antenna interferometric SAR, eliminates edge-joining errors, and achieves consistent DSM accuracy within the region. Attached Figure Description

[0021] Figure 1 The flowchart is a process for adjusting the spaceborne dual-antenna interferometric SAR regional network provided by the present invention. Figure 2 This is a schematic diagram of the radar coordinate system and radar coordinate system image in this invention.

[0022] Figure 3 This is a schematic diagram of the rolling and yaw bending projection of the support arm of the spaceborne dual-antenna interferometric SAR interferometric baseline antenna in this invention. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0025] like Figure 1 As shown, this invention provides a method for adjusting a spaceborne dual-antenna interferometric SAR regional network, which includes the following steps: Step S1: Obtain unwrapped interferograms and additional data for multiple adjacent and overlapping regions generated by spaceborne dual-antenna interferometric SAR in the study area; Step S2: Obtain the initial DSM of the radar coordinate system based on the interferometric baseline model of the spaceborne dual-antenna interferometric SAR and the phase elevation transformation, and obtain the initial DSM of the geographic coordinate system through geocoding; Step S3: Calculate the row and column numbers and elevation of the control points in the initial DSM of the radar coordinate system; Step S4: Determine the adjacency relationship of each initial DSM, uniformly select the same points in the overlapping area of ​​adjacent initial DSMs as connection points, and determine the row and column number and elevation of the connection points in the corresponding radar coordinate system initial DSM. Step S5: Establish a regional network adjustment model based on the elevation constraints of control points and connection points, perform regional network adjustment correction on the initial radar coordinate system DSM, and obtain the adjusted geographic coordinate system DSM through geocoding.

[0026] To more clearly explain the spaceborne dual-antenna interferometric SAR regional network adjustment method of the present invention, the following will be combined with... Figure 1 The steps of each embodiment of the present invention will be described in detail below.

[0027] The spaceborne dual-antenna interferometric SAR regional network adjustment method provided in this embodiment of the invention includes steps S1-S5, each step of which is described in detail below: Step S1: Obtain unwrapped interferograms and additional data for multiple adjacent and overlapping regions generated by spaceborne dual-antenna interferometric SAR in the study area; The study area mentioned above is the area that requires adjustment of the satellite-borne dual-antenna interferometric SAR DSM regional network; the unwrapped interferograms and additional data of the above multiple adjacent and overlapping regions can be obtained by observing the study area by the satellite-borne dual-antenna interferometric SAR satellite and processing the data through the InSAR DSM data process.

[0028] In some embodiments of the present invention, the specific implementation of the unwrapped interferogram and additional data of the spaceborne dual-antenna interferometric SAR within the production and research area can be as follows: (1.1) Perform echo imaging and standard slicing processing on the acquired echo data of the main and auxiliary antennas of the spaceborne dual-antenna interferometric SAR system; (1.2) Register and resample the master and slave SAR images after imaging; (1.3) Interferograms are obtained by interferometric processing of the registered and resampled master and slave SAR images; (1.4) Using an external reference DEM to simulate the flat terrain phase, the interferogram is differentially processed to obtain a differential interferogram, and lookup table data is generated; (1.5) The differential interferogram is filtered and phase-unwrapped, and then the removed flat terrain phase is added to obtain the radar coordinate system unwrapped interferogram. The radar coordinate system and radar coordinate system image are as follows: Figure 2 As shown.

[0029] The aforementioned additional data includes: baseline parameter files, master image parameter files, lookup table data, and master intensity images. Furthermore, the pixels and extents of different images in the radar coordinate system are in a one-to-one correspondence, as are the pixels and extents of different images in the geographic coordinate system. The unwrapped interferograms and additional data are explained in Table 1 below.

[0030] Table 1. Generated unwrapped interferograms and additional data descriptions

[0031] Step S2: Obtain the initial DSM of the radar coordinate system based on the interferometric baseline model of the spaceborne dual-antenna interferometric SAR and the phase elevation transformation, and obtain the initial DSM of the geographic coordinate system through geocoding; Step S2.1: Construct an interferometric baseline model based on the time-varying characteristics of the interferometric baseline of a spaceborne dual-antenna interferometric SAR. The imaging frequency of each row of pixels in a SAR image is much higher than the measurement frequency of the interferometric baseline vector. To obtain the 3D position of the ground target point corresponding to each pixel in the unwrapped interferogram using the look-vector decomposition method, it is necessary to calculate the interferometric baseline vector corresponding to each row of pixels in the unwrapped interferogram. Traditional linear interferometric baseline time-varying models only consider the baseline constant and the linear variation of the baseline, which is insufficient to effectively describe the change of the interferometric baseline of a spaceborne dual-antenna interferometric SAR over time. Therefore, this invention, based on the time-varying characteristics of the interferometric baseline of a spaceborne dual-antenna interferometric SAR, establishes a spaceborne dual-antenna interferometric SAR interferometric baseline model to calculate the interferometric baseline vector corresponding to each row of pixels in the unwrapped interferogram.

[0032] The interferometric baseline in the Earth-centered, Earth-fixed space rectangular coordinate system is: ; in, Let be the transformation matrix from the TCN coordinate system to the geocentric rectangular coordinate system. Let be the interferometric baseline vector represented in the TCN coordinate system. The three-dimensional position of the phase center of the main antenna in the Earth-centered, Earth-fixed space rectangular coordinate system. The velocity vector of the main antenna phase center in the Earth-centered, Earth-fixed space rectangular coordinate system. The unit vector along the C-axis of the TCN coordinate system. The unit vector along the N-axis of the TCN coordinate system; Based on the time-varying characteristics of the spaceborne dual-antenna interferometric SAR flexible antenna, the interferometric baseline vector in the TCN coordinate system is: ; in, , and The components of the interferometric baseline vector along the T-axis, C-axis, and N-axis in the TCN coordinate system. , and for , and The constant part in The view from the main antenna radar side. This refers to the change in the azimuth direction of the auxiliary antenna's phase center caused by the vibration of the antenna support arm. The change in the phase center of the auxiliary antenna in the slant range direction caused by the jitter of the antenna support arm, such as Figure 3 As shown, The main antenna arm roll bending amplitude. The damping coefficient of the main antenna arm. The main antenna arm jitter angular frequency. For direction and time, Main antenna arm rolls and bends reference phase. To measure the roll bending amplitude of the auxiliary antenna arm, The damping coefficient of the auxiliary antenna arm, To reduce the angular frequency of the auxiliary antenna arm jitter, The auxiliary antenna arm rolls and bends to reference the phase.

[0033] For cross-track interferometry, the baseline along the T-axis after SAR registration and resampling... It is 0, and The error has a negligible impact on InSAR altimetry measurements. Therefore, the interferometric baseline components along the T-axis can be set to constants that do not change with time; the specific value can be the average of all low-frequency interferometric baseline observations along the T-axis. For the C-axis and N-axis of the interferometric baseline, the parameters in the interferometric baseline model need to be adjusted using the low-frequency baseline vector measurement data from the baseline parameter file. Make an estimate, and then determine the time based on the azimuth. Calculate the C-axis and N-axis components of the interference baseline corresponding to each pixel. Let: ; Assuming the baseline parameter file contains For each low-frequency interferometric baseline measurement data point, there is an error equation: ; in, Indicates the first Interferometric baseline observation data, . , It represents the observation data error at points Bci and bni.

[0034] Expressed in matrix form as follows: ; in, ; ; ; , , The equation takes initial values ​​for the interferometric baseline parameters. The value of time, , For the first C-axis and N-axis components of low-frequency interferometric baseline observations; By iteratively solving for the corrections to the model parameters using the least squares criterion as the adjustment criterion, we obtain: ; The root mean square of the difference between the baseline vectors of the TCN coordinate system before and after each iteration is: ; In the formula, Indicates the first The measurement data is the first one. The interferometric baseline vector in the TCN coordinate system is calculated using the adjusted parameters in the next iteration. The iteration stops when the value is less than the set value. This yields the adjusted interferometric baseline model parameters. ; After obtaining the parameters of the interferometric baseline model, the azimuth time of each row of pixels in the unwrapped interferogram can be determined. Calculate the interferometric baseline vector corresponding to each row of pixels. .

[0035] Step S2.2: Based on the view vector decomposition method and the transformation relationship from spatial rectangular coordinate system to geodetic coordinate system, the unwrapped interferometric phase to elevation transformation is realized to obtain the initial DSM of radar coordinate system, and the initial DSM of geographic coordinate system is obtained through geocoding; According to the view vector decomposition method, the three-dimensional position vector of the ground target point corresponding to the pixel on the unwrapped interferogram is: ; in, This represents the three-dimensional position vector of the ground target point in the Earth-centered, Earth-fixed space rectangular coordinate system. The three-dimensional position vector of the main antenna phase center in the Earth-centered, Earth-fixed space rectangular coordinate system. The slant range from the phase center of the main antenna to the ground target point. This refers to the unit line-of-sight vector expressed in a geocentric Cartesian coordinate system, i.e., the unit vector from the phase center of the main antenna to the ground target point. The transformation matrix from the Madsen translation coordinate system to the Earth-centered, Earth-fixed Cartesian coordinate system is: , , ; The three-dimensional velocity vector of the main antenna phase center in the Earth-centered, Earth-fixed space rectangular coordinate system. The interference baseline vector of the main and auxiliary antenna phase centers in the geocentric Cartesian coordinate system is the phase center of the main antenna. This is the representation of the unit view vector in the Madsen translation coordinate system. For radar signal wavelength, The Doppler frequency at the phase center of the main antenna. The magnitude of the phase center velocity of the main antenna. For the magnitude of the interferometric baseline vector, Let be the magnitude of the component of the interferometric baseline vector in the direction of velocity at the phase center of the main antenna. The unit velocity vector at the phase center of the main antenna. Let be the magnitude of the component of the interferometric baseline vector in the direction perpendicular to the velocity of the main antenna phase center. For the absolute interferometric phase of the ground target point, For absolute phase shift, For the unwrapped interference phase, in the formula of The imaging time is determined by the satellite's flight direction, side-view imaging geometry, and the right-handed coordinate system relationship of the Madsen moving coordinate system.

[0036] To obtain the elevation of the ground target point corresponding to the pixel in the unwrapped interferogram It is necessary to obtain the three-dimensional location information of the ground target points. The way to express it in the geodetic coordinate system, that is : ; in, The latitude of the ground target point. The longitude of the ground target point. The elevation of the ground target point. Let be the three-dimensional coordinates of the ground target point in the Earth-centered Earth-fixed space rectangular coordinate system. The semi-major axis of the Earth's ellipsoid. The minor semi-axis of the Earth's ellipsoid. For the first eccentricity, , For the second eccentricity, , The radius of curvature of the Earth's ellipsoid is the geoid. The range of values ​​is , The range of values ​​is .

[0037] By using the phase elevation transformation method to obtain the elevation information of the ground point corresponding to each pixel in the unwrapped interferogram, the initial radar coordinate system (DSM) can be obtained. Then, the initial radar coordinate system DSM and the initial geographic coordinate system DSM are transformed by looking up the correspondence between the radar coordinate system image row and column number and the geographic coordinates in the lookup table data.

[0038] Step S3: Calculate the row and column numbers and elevation of the control points in the initial DSM of the radar coordinate system; Step S3.1: Obtain the row and column numbers of the control points in the initial DSM of the geographic coordinate system based on the geographic information of the control point data; Calculate the row and column numbers of the control point data in the initial DSM of the geographic coordinate system based on the six parameters of the affine transformation: ; in, To control the latitude, To control the longitude, The longitude of the top left pixel of the initial DSM. This is the initial DSM longitude resolution. The rotation coefficient is , The initial DSM top-left pixel dimension, This is the initial DSM latitude resolution. The rotation coefficient is , This refers to the column number of the control point on the initial DSM in the geographic coordinate system. This refers to the row number of the control point on the initial DSM in the geographic coordinate system.

[0039] Step S3.2: Use the lookup table data to obtain the row and column numbers of the control points on the initial DSM of the radar coordinate system. The initial DSM elevation of the radar coordinate system at the corresponding row and column number is calculated using the bilinear interpolation algorithm.

[0040] Step S4: Determine the adjacency relationship of each initial DSM, uniformly select the same points in the overlapping area of ​​adjacent initial DSMs as connection points, and determine the row and column number and elevation of the connection points in the corresponding radar coordinate system initial DSM. Specifically, based on the latitude and longitude range of the initial DSM in the geographic coordinate system, it is determined whether two DSM images overlap. If they overlap, with the assistance of the main intensity image in the geographic coordinate system, corresponding points within the overlapping area of ​​the initial DSM are uniformly selected as connection points. The row and column numbers of the connection points in the corresponding initial DSM in the geographic coordinate system, as well as their elevations, are then obtained. The specific steps include: Step S4.1: Determine whether two DSMs are adjacent and overlap based on the latitude and longitude range of the initial DSM; Let the longitude range of an initial DSM be... The latitude range is Another scene requires determination of the longitude range of the initial DSM. The latitude range is denoted as ; if or or or This indicates that there is no overlapping area between the two DSMs; otherwise, there is an overlapping area between the two DSMs. in, Indicates the degree of overlap along the longitude axis. Indicates the degree of overlap in the latitudinal direction.

[0041] Step S4.2: Uniformly select corresponding points in the overlapping areas of adjacent initial DSMs as connection points, and determine the row and column numbers and elevations of the connection points in the corresponding radar coordinate system initial DSM. The conversion between geographic coordinate system imagery and radar coordinate system imagery both rely on the same lookup table data. Furthermore, the main intensity imagery after radar coordinate system registration and resampling corresponds one-to-one with the initial DSM. Therefore, the row and column numbers of the tie points in the initial DSM of the geographic coordinate system can be determined based on the row and column numbers of the tie points in the main intensity imagery. For initial DSMs of the geographic coordinate system with overlapping areas, corresponding points are uniformly selected as tie points with the assistance of the main intensity imagery of the geographic coordinate system. Then, the row and column numbers of the tie points in the corresponding initial DSM of the radar coordinate system are obtained using the lookup table data. The initial DSM elevation value of the radar coordinate system at the connection point was calculated using the bilinear interpolation algorithm.

[0042] Step S5: Establish a regional network adjustment model based on the elevation constraints of control points and connection points, perform regional network adjustment correction on the initial radar coordinate system DSM, and obtain the adjusted geographic coordinate system DSM through geocoding. Step S5.1: Establish the initial DSM elevation regional network adjustment model of the radar coordinate system based on the elevation constraints at the control points and connection points; After generating the initial DSM based on the interferometric baseline model of spaceborne dual-antenna interferometric SAR and phase elevation transformation, the systematic error of the initial DSM elevation can be corrected using the following model: ; in, , , These are the coefficients of the initial DSM elevation system error correction model. Indicates the initial DSM column number of the radar coordinate system. Indicates the initial DSM row number of the radar coordinate system. For the initial DSM in Correction of elevation system errors at the location.

[0043] Under the constraint that the DSM elevation and the control point elevation are consistent, the elevation error equation at the initial DSM control point of the radar coordinate system can be expressed as: ; in, For the elevation residual at the control point, The initial DSM elevation of the radar coordinate system at the control point. Correction for the initial DSM elevation system error in the radar coordinate system at the control point. Elevation of the control point.

[0044] Under the constraint that the elevations of adjacent DSM image tie points are equal, the elevation error equation at the initial DSM tie points of the radar coordinate system can be expressed as: ; in, The elevation residual at the connection point, , These are the system errors of the initial DSM elevation system in adjacent radar coordinate systems. , These are the elevation values ​​corresponding to the connection points on the initial DSM images of adjacent radar coordinate systems; In summary, for One connection point, One control point, The matrix form of the error equation for the initial DSM elevation area network adjustment model can be written as: ; in, ; ; ; in, It is the elevation residual vector. The coefficient matrix, Let be the coefficient vector of the initial DSM elevation system error correction model for the radar coordinate system to be solved. Let be the elevation difference vector at the control point and the connection point. This refers to the column number of the control point or tie point on the initial DSM of the radar coordinate system. This refers to the row number of the control point or connection point on the initial DSM of the radar coordinate system. For the Kth initial DSM, the th The column number of each control point For the Kth initial DSM, the th The row number of each control point For the second initial DSM The column number of each connection point For the second initial DSM The row number of each connection point For the first initial DSM that is adjacent to the second initial DSM On the first initial DSM The column number of each connection point For the first initial DSM that is adjacent to the second initial DSM On the first initial DSM The row number of each connection point , , The coefficients of the initial DSM elevation system error correction model for the Kth radar coordinate system are: For the first scene of radar coordinate system initial DSM, the first The initial DSM elevation of each control point location. For the first scene of radar coordinate system initial DSM, the first Elevation of each control point For the first initial DSM The initial DSM elevation of each connection point. For the first initial DSM that is adjacent to the first initial DSM, the first initial DSM is the first initial DSM. Initial DSM elevation at each connection point.

[0045] Under the least squares criterion, the solution to the above error equation is: ; in, Represents the coefficient matrix Transpose The weight matrix is ​​the observation weight matrix. The initial weight matrix can be the identity matrix. This is the parameter vector for the error correction model of all initial DSM elevation systems.

[0046] To improve the stability and accuracy of model parameter estimation, an iterative reweighted least squares algorithm is used to solve the parameters. The solution of the error equation... Substitute into the error equation to calculate the elevation residual vector Then, the new weights are calculated using the following formula: ; in, For the first The second iteration The weights corresponding to each observation. For the first The second iteration The weights corresponding to each observation. For the first The second iteration The elevation residuals corresponding to each observation value For the first The unit weight mean square error at the next iteration.

[0047] The formula for calculating the unit weight error is: ; The newly calculated weights are combined into a weight matrix and re-introduced into the error equation to iteratively calculate the model parameters until the [number]th ...]. Second and third If the unit weight error difference is less than a certain threshold, the iteration stops, and the final initial DSM elevation system error correction model coefficient vector is obtained.

[0048] Step S5.2: Perform regional network adjustment correction on the initial radar coordinate system DSM, and obtain the adjusted geographic coordinate system DSM through geocoding; Specifically, the initial DSM elevation system error is corrected based on the calculated radar coordinate system initial DSM elevation system error correction model coefficients, and the corrected radar coordinate system initial DSM is converted to the geographic coordinate system through lookup table data to obtain the geographic coordinate system DSM, thereby completing the adjustment of the spaceborne dual-antenna interferometric SAR DSM regional network.

[0049] This invention enables a further improvement in the accuracy of the initial DSM products produced by a spaceborne dual-antenna X-band interferometric SAR system.

[0050] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for adjusting a spaceborne dual-antenna interferometric SAR regional network, characterized in that, include: Step S1: Obtain unwrapped interferograms and additional data for multiple adjacent and overlapping regions generated by spaceborne dual-antenna interferometric SAR in the study area; Step S2: Obtain the initial DSM of the radar coordinate system based on the interferometric baseline model of the spaceborne dual-antenna interferometric SAR and the phase elevation transformation, and obtain the initial DSM of the geographic coordinate system through geocoding; Step S3: Calculate the row and column numbers and elevation of the control points in the initial DSM of the radar coordinate system; Step S4: Determine the adjacency relationship of each initial DSM, uniformly select the same points in the overlapping area of ​​adjacent initial DSMs as connection points, and determine the row and column number and elevation of the connection points in the corresponding radar coordinate system initial DSM. Step S5: Establish a regional network adjustment model based on the elevation constraints of control points and connection points, perform regional network adjustment correction on the initial radar coordinate system DSM, and obtain the adjusted geographic coordinate system DSM through geocoding.

2. The method for adjusting a spaceborne dual-antenna interferometric SAR regional network according to claim 1, characterized in that: The study area refers to the area where satellite-borne dual-antenna interferometric SAR DSM regional network adjustment is required; the unwrapped interferograms and additional data of the multiple adjacent and overlapping regions are obtained by satellite-borne dual-antenna interferometric SAR satellites observing the study area and processing the data through the InSAR DSM data processing flow.

3. The method for adjusting a spaceborne dual-antenna interferometric SAR regional network according to claim 1, characterized in that: Step S2, which involves obtaining the initial radar coordinate system DSM based on the spaceborne dual-antenna interferometric SAR interferometric baseline model and phase elevation transformation, and obtaining the initial geographic coordinate system DSM through geocoding, specifically includes: Step S2.1: Construct an interferometric baseline model based on the time-varying characteristics of the interferometric baseline of a spaceborne dual-antenna interferometric SAR. Step S2.2: Based on the view vector decomposition method and the transformation relationship from spatial rectangular coordinate system to geodetic coordinate system, the unwrapped interferometric phase to elevation transformation is realized to obtain the initial DSM of radar coordinate system, and the initial DSM of geographic coordinate system is obtained through geocoding.

4. The method for adjusting a spaceborne dual-antenna interferometric SAR regional network according to claim 3, characterized in that: Step S2.1, which involves constructing an interferometric baseline model based on the time-varying characteristics of the interferometric baseline of a spaceborne dual-antenna interferometric SAR, includes: The interferometric baseline in the Earth-centered, Earth-fixed space rectangular coordinate system is: ； in, Let be the transformation matrix from the TCN coordinate system to the geocentric rectangular coordinate system. Let be the interferometric baseline vector represented in the TCN coordinate system. The three-dimensional position of the phase center of the main antenna in the Earth-centered, Earth-fixed space rectangular coordinate system. The velocity vector of the main antenna phase center in the Earth-centered, Earth-fixed space rectangular coordinate system. The unit vector along the C-axis of the TCN coordinate system. The unit vector along the N-axis of the TCN coordinate system; Based on the time-varying characteristics of the spaceborne dual-antenna interferometric SAR flexible antenna, the interferometric baseline vector in the TCN coordinate system is: ； in, , and The components of the interferometric baseline vector along the T-axis, C-axis, and N-axis in the TCN coordinate system. , and for , and The constant part in The view from the main antenna radar side. This refers to the change in the azimuth of the auxiliary antenna's phase center caused by the vibration of the antenna support arm. The change in the phase center of the auxiliary antenna in the slant range direction caused by the jitter of the antenna support arm. The main antenna arm roll bending amplitude. The damping coefficient of the main antenna arm. The main antenna arm jitter angular frequency. For direction and time, Main antenna arm rolls and bends reference phase. To measure the roll bending amplitude of the auxiliary antenna arm, The damping coefficient of the auxiliary antenna arm, To reduce the angular frequency of the auxiliary antenna arm jitter, Auxiliary antenna arm roll bending reference phase; For cross-track interferometry, the interferometric baseline components along the T-axis are set to constants that do not change with time; specifically, the value is the average of the low-frequency observations of the interferometric baselines along all T-axis directions. For the C-axis and N-axis of the interferometric baseline, the parameters in the interferometric baseline model need to be adjusted using the low-frequency baseline vector measurement data from the baseline parameter file. Make an estimate, and then determine the time based on the azimuth. Calculate the C-axis and N-axis components of the interference baseline corresponding to each pixel, and let: ； Assuming the baseline parameter file contains For each low-frequency interferometric baseline measurement data point, there is an error equation: ； Among them, subscript Indicates the first Interferometric baseline observation data, , , The error is the observation data at points Bci and bni; Expressed in matrix form as follows: ； in, ; ； ； , , The equation takes initial values ​​for the interferometric baseline parameters. The value of time, , For the first C-axis and N-axis components of low-frequency interferometric baseline observations; By iteratively solving for the corrections to the model parameters using the least squares criterion as the adjustment criterion, we obtain: ； The root mean square of the difference between the baseline vectors of the TCN coordinate system before and after each iteration is: ； In the formula, Indicates the first The measurement data is the first one. The interferometric baseline vector in the TCN coordinate system is calculated using the adjusted parameters in the next iteration; when The iteration stops when the values ​​are less than the set value; thus, the parameters of the adjusted interferometric baseline model are obtained. ; After obtaining the parameters of the interferometric baseline model, the azimuth time of each row of pixels in the unwrapped interferogram can be determined. Calculate the interferometric baseline vector corresponding to each row of pixels. .

5. The method for adjusting a spaceborne dual-antenna interferometric SAR regional network according to claim 1, characterized in that: Step S3, which calculates the row and column numbers and elevation of the control points in the initial DSM radar coordinate system, specifically includes: Step S3.1: Obtain the row and column numbers of the control points in the initial DSM of the geographic coordinate system based on the geographic information of the control point data; Step S3.2: Use the lookup table data to obtain the row and column numbers of the control points on the initial DSM of the radar coordinate system. The initial DSM elevation of the radar coordinate system at the corresponding row and column number is calculated using the bilinear interpolation algorithm.

6. The method for adjusting a spaceborne dual-antenna interferometric SAR regional network according to claim 1, characterized in that: Step S4 involves determining the adjacency relationships of each initial DSM, uniformly selecting corresponding points within the overlapping area of ​​adjacent initial DSMs as connection points, and determining the row and column numbers and elevations of the connection points in the corresponding radar coordinate system initial DSMs. Specifically, this includes: Step S4.1: Determine whether two DSMs are adjacent and overlap based on the latitude and longitude range of the initial DSM; Step S4.2: Uniformly select corresponding points within the overlapping area of ​​adjacent initial DSMs as connection points, and determine the row and column numbers and elevations of the connection points in the corresponding radar coordinate system initial DSM.

7. The method for adjusting a spaceborne dual-antenna interferometric SAR regional network according to claim 6, characterized in that: Step S4.1, determining whether two DSMs are adjacent and overlap based on the latitude and longitude range of the initial DSM, specifically involves: Let the longitude range of an initial DSM be... The latitude range is Another scene requires determination of the longitude range of the initial DSM. The latitude range is denoted as ; if or or or If the result is true, it means that there is no overlapping area between the two DSMs; otherwise, there is an overlapping area between the two DSMs. in, Indicates the degree of overlap along the longitude axis. Indicates the degree of overlap in the latitudinal direction.

8. The method for adjusting a spaceborne dual-antenna interferometric SAR regional network according to claim 1, characterized in that: Step S5 involves establishing a regional network adjustment model based on the elevation constraints of control points and connection points, performing regional network adjustment correction on the initial radar coordinate system (DSM), and obtaining the adjusted geographic coordinate system (DSM) through geocoding, including: Step S5.1: Establish the initial DSM elevation regional network adjustment model of the radar coordinate system based on the elevation constraints at the control points and connection points; Step S5.2: Perform regional network adjustment correction on the initial radar coordinate system DSM, and obtain the adjusted geographic coordinate system DSM through geocoding.

9. The method for adjusting a spaceborne dual-antenna interferometric SAR regional network according to claim 8, characterized in that: Step S5.1 involves establishing an initial DSM elevation regional network adjustment model for the radar coordinate system based on the elevation constraints at control points and connection points. Specifically: One connection point, One control point, The matrix form of the error equation for the initial DSM elevation area network adjustment model is as follows: ； in, ； ； in, It is the elevation residual vector. The coefficient matrix, Let be the coefficient vector of the initial DSM elevation system error correction model for the radar coordinate system to be solved. Let be the elevation difference vector at the control point and the connection point. This refers to the column number of the control point or tie point on the initial DSM of the radar coordinate system. This refers to the row number of the control point or connection point on the initial DSM of the radar coordinate system. For the Kth initial DSM, the th The column number of each control point For the Kth initial DSM, the th The row number of each control point For the second initial DSM The column number of each connection point For the second initial DSM The row number of each connection point For the first initial DSM that is adjacent to the second initial DSM On the first initial DSM The column number of each connection point For the first initial DSM that is adjacent to the second initial DSM On the first initial DSM The row number of each connection point , , The coefficients of the initial DSM elevation system error correction model for the Kth radar coordinate system are: For the first scene of radar coordinate system initial DSM, the first The initial DSM elevation of each control point location. For the first scene of radar coordinate system initial DSM, the first Elevation of each control point For the first initial DSM The initial DSM elevation of each connection point. For the first initial DSM that is adjacent to the first initial DSM, the first initial DSM is the first initial DSM. Initial DSM elevation at each connection point.

10. A method for adjusting a spaceborne dual-antenna interferometric SAR regional network according to claim 9, characterized in that: Under the least squares criterion, the solution to the error equation is: ； in, Represents the coefficient matrix Transpose The observation weight matrix is ​​initially taken as the identity matrix. For all initial DSM elevation system error correction model parameter vectors; The parameters are solved using an iterative reweighted least squares algorithm, which solves the error equation. Substitute into the error equation to calculate the elevation residual vector Then, the new weights are calculated using the following formula: ； in, For the first The second iteration The weights corresponding to each observation. For the first The second iteration The weights corresponding to each observation. For the first The second iteration The elevation residuals corresponding to each observation value For the first Unit weight error at the next iteration; The newly calculated weights are combined into a weight matrix and re-introduced into the error equation to iteratively calculate the model parameters until the [number]th ...]. Second and third If the unit weight error difference is less than a certain threshold, the iteration stops, and the final initial DSM elevation system error correction model coefficient vector is obtained.

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