CN112986994B - SAR chromatographic reference network rapid generation method - Google Patents
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- G—PHYSICS
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
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- G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
- G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
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Abstract
The invention provides a method for quickly generating a reference network based on a segmented search block networking. The technical scheme is that the SAR image is uniformly divided into a plurality of sub-blocks; generating a sub-block communication network in each sub-block by adopting a searching mode based on segmented ant colony; establishing a connecting edge between adjacent sub-blocks; and generating the SAR chromatographic reference network by using the information. The method has high calculation efficiency, and the generated SAR chromatographic reference network has strong full-scene coverage capability.
Description
Technical Field
The invention belongs to the technical field of remote sensing imaging, and relates to a reference model which is needed to be utilized for eliminating atmospheric influence when a plurality of satellite-borne SAR (Synthetic Aperture Radar ) images are utilized for high-dimensional imaging.
Background
The space-borne SAR three-dimensional imaging is also commonly called space-borne SAR tomography, namely, by utilizing multi-angle coherent observation on the same target, a synthetic aperture is formed in the height direction, the space-borne SAR three-dimensional imaging has high-directional resolution, and true three-dimensional imaging on the observed target can be realized. The main data source of SAR chromatography comes from a satellite-borne multi-navigation system, and APS (Atmospheric Phase Screen, atmospheric phase error) of each navigation SAR image obtained by the system changes randomly along with the observation time, so that the SAR chromatography can be seriously influenced. In order to eliminate the atmospheric influence, the SAR chromatographic processing mainly uses a reference network technology to realize the full-scene atmospheric phase correction, see document one: robust Detection of Single and Double Persistent Scatterers in Urban Built Environments, p.f.ma et al. The basic idea of the technology is as follows: based on the spatial ramp characteristic of the APS, the APS approximation of the adjacent pixels in the SAR image can be considered, and the APS error can be largely counteracted through the phase difference of the adjacent pixels. By utilizing the basic idea, the reference network technology is to connect single PS (Persistent Scatterer, permanent scattering points) covering the whole scene into a network (i.e. a reference network) covering the whole scene, and the rest pixels take the single PS point nearest to the reference network as a reference to perform phase difference so as to realize the APS correction and PS point detection of the whole scene. For reference network technology, the quality of the reference network will directly determine whether full scene APS valid correction can be achieved. Theoretically, it is desirable that the generated reference network can uniformly cover the full scene.
The reference network provided in reference one is the maximum connected network after the Delaunay triangulation network formed based on Delaunay triangulation is optimized. However, due to low network redundancy of the Delaunay triangle network, the problems of PS isolated points and isolated islands are easy to form after network optimization, so that the reference network does not have full scene coverage capability, and full scene APS correction cannot be realized based on the reference network. In addition, the maximum connected network search process is extremely time consuming, which can result in inefficient reference network generation.
Disclosure of Invention
The invention provides a rapid generation method of a reference network based on segmented search and block networking, the generated reference network has full scene coverage capability, and the generation efficiency of the reference network is very high.
The technical scheme of the invention is as follows: a rapid generation method of a reference network based on segmented search and block networking is characterized in that SAR images are uniformly divided into a plurality of sub-blocks; generating a sub-block communication network in each sub-block; establishing a connecting edge between adjacent sub-blocks; and generating the SAR chromatographic reference network by using the information.
Further, a sub-block communication network is generated in each sub-block in a mode based on segmented ant colony search.
The invention has the technical effects that: the rapid generation method of the reference network does not need to carry out the maximum connected network search, reduces the calculation time waste caused by directly carrying out single PS search in the whole search space through the segmentation search, can rapidly connect all the sub-blocks to form a large connected network through a block networking mode, and can greatly accelerate the generation efficiency of the large scene reference network in two modes, namely, the calculation efficiency of the method is very high. In addition, an ant colony network uniformly covering each sub-block is generated in each sub-block in an ant colony searching mode, and then the sub-block communication networks can be communicated into a maximum reference network uniformly covering the whole scene by establishing high-quality edges among the sub-block communication networks, namely, the SAR chromatographic reference network obtained based on the method has the full scene coverage capability.
Drawings
FIG. 1 is a schematic diagram of a SAR chromatographic reference network rapid generation method based on segmented search and block networking provided by the invention;
FIG. 2 is a flowchart of a method for rapidly generating SAR chromatographic reference network based on segmented search and block networking provided by the invention;
fig. 3 to 7 show results of actual measurement data processing according to the embodiment of the present invention.
Detailed Description
The SAR chromatography reference network generation method based on ant colony search provided by the invention is described in detail below with reference to the accompanying drawings.
The whole process is divided into three steps. Step1, region segmentation; step2, quickly generating a sub-block communication network; step3: the sub-block communication net is communicated. The specific description is as follows:
step1: region partitioning
And uniformly dividing the whole scene, namely the whole SAR image, into a plurality of sub-blocks. Suppose the SAR image size is: x is X a ×X r (Unit: pixel), the sub-block size set in the partitioning process is x a ×x r . The size of the sub-block is determined according to the actual situation. Through laboratory experiments, it was found that the selection is generallyPreferably, wherein: />Representing a rounding operator.
Step2: fast generation of sub-block communication network
A sub-block communication network is generated within each sub-block. Typically, the generation of the sub-block communication network may be formed using existing Delaunay triangulation-based techniques. The invention recommends to use a segmented ant colony search mode to generate a subblock communication network, and the process is as follows:
step (1): threshold distance D thres Divided into L subsections, and search space D corresponding to the ith subsection (i is more than or equal to 1 and less than or equal to L) i The definition is as follows: with a distance d from the picture element as the center i In the region of all picture elements in whichDistance threshold D thres The value of (2) is determined according to the actual situation, and is usually in the order of hundreds of meters. Experiments prove that the optimal selection range of the segmentation number is more than or equal to 5 and less than or equal to 20.
Step (2): let i=1, choose any pixel in the sub-block as the initial ant, in the search space corresponding to the 1 st sub-segment, adopt patent number: 202011621544.1 the method provides for the generation and screening of satisfactory P around the starting ant i A high-quality single PS side is formed, and the end point of the screened single PS side is used as a new starting ant;
step (3): let i=i+1, in the search space corresponding to the ith (1. Ltoreq.i.ltoreq.L) sub-segment, patent number: 202011621544.1 the method comprises the steps of generating and screening out high-quality single PS edges meeting the requirements around each initial ant, and taking the end point of the screened single PS edge as a new initial ant;
step (4): if the total number of the high-quality single PS sides screened in the first i sections of search space meets the cycle ending condition: i.e. p=p 1 +…+P i If not less than F (F represents a network redundancy threshold), ending the cycle; otherwiseAnd (3) returning to the step (3) to continue to search for the high-quality single PS side in the search space corresponding to the next sub-segment, and taking the end point of the screened single PS side as a new starting ant until the cycle end condition is met or all the sub-segments (i.e. i=L) are searched.
By searching in a sectional expansion range in the constraint space around each ant, the network construction time required by the sub-block connected network can be greatly reduced on the premise of not influencing the quality of the reference network edge construction. In the processing process of the step, all the sub-blocks are mutually independent, and the establishing process of the sub-block communication network is not affected, so that the processing can be performed in a parallel mode.
Step3: sub-block communication net communication
And establishing a connecting edge between the sub-block communication networks to form an SAR chromatographic reference network which uniformly covers the whole scene. I.e. between adjacent sub-block communication networks, using reference two: the method provided by New Approaches For Robust and Efficient Detection of Persistent Scatterers in SAR Tomography, X.X.Zhu et al establishes the connecting edges.
Fig. 3 to 7 show the results of actual measurement data processing.
FIG. 3 is a terraSAR-X average SAR intensity map. The horizontal direction represents the azimuth direction, the vertical direction represents the distance direction, and the resolutions of the azimuth direction and the distance direction are respectively 0.24m and 0.6m. The image is obtained by averaging the amplitude images of the SAR images of the 26-scene terra SAR-X satellite staring spotlight mode.
Fig. 4 is a reference mesh generated using the prior art method provided in reference one, which can only cover a portion of the viewing area. As can be seen from the figure, neither area 1 nor area 2 is effectively covered, and the line-shaped road object in area 3 is not covered.
Fig. 5 is a reference network established using the proposed method of the present invention. Distance-azimuth size X of SAR image a ×X r Size x of subblock 1370×3826 a ×x r For 688×1913, the whole SAR image is divided into 2×2 blocks, distance threshold D thres The number of segments is set to l=10, =300 meters. Compared with the reference network generated by the prior method, the reference network generated based on the method provided by the invention can cover the whole scene and has the whole sceneScene coverage capability.
Fig. 6 is a reference grid PS-point elevation map generated based on the prior art method provided in reference one. The horizontal direction represents the azimuth direction, the vertical direction represents the distance direction, the gray scale represents the height, and the hexagon in the figure represents the gray scale value of the zero elevation reference point. Since the reference network generated by the existing method cannot cover the current road targets in the area 1, the area 2 and the area 3, the PS point heights of the areas cannot be effectively inverted.
Fig. 7 is a reference network PS point elevation map generated based on the proposed method of the present invention. The horizontal direction represents the azimuth direction, the vertical direction represents the distance direction, the gray scale represents the height, and the hexagon in the figure represents the gray scale value of the zero elevation reference point. The reference network generated based on the method provided by the invention can cover the full scene, and the PS point heights of the full scene can be effectively inverted, so that the effectiveness of the method provided by the invention is proved.
The calculation time of fig. 4 is 832.8 seconds by using the existing reference network generation method provided by the reference document one, the calculation time of fig. 5 is 131.6 seconds by using the reference network generation method provided by the invention, the calculation efficiency of the reference network generation method provided by the invention is improved by about 6.3 times, and the high efficiency of the method provided by the invention is proved.
Claims (5)
1. A rapid generation method of a reference network based on segmented search and block networking is characterized in that SAR images are uniformly divided into a plurality of sub-blocks; generating a sub-block communication network in each sub-block; establishing a connecting edge between adjacent sub-blocks; generating a chromatographic reference network of the SAR image by utilizing the information; wherein SAR refers to synthetic aperture radar;
the process of generating the sub-block communication network in each sub-block is as follows:
step (1): threshold distance D thres Divided into L subsections, search space D corresponding to the ith subsection i The definition is as follows: with a distance d from the picture element as the center i In the region of all picture elements in which
Step (2): let i=1, select any one of the pixels in the sub-block as the initial ant, generate and screen out the P meeting the requirement around the initial ant in the search space corresponding to the 1 st sub-segment i The end point of the single PS side is used as a new starting ant, and PS refers to a permanent scattering point;
step (3): generating and screening out high-quality single PS edges meeting the requirements around each initial ant in a search space corresponding to the ith subsection, and taking the end point of the screened single PS edge as a new initial ant;
step (4): if the total number of the high-quality single PS sides screened in the first i sections of search space meets the cycle ending condition: i.e. p=p 1 +…+P i F represents a network redundancy threshold when the value is not less than F, and the cycle is ended; otherwise, returning to the step (3), continuing to search the high-quality single PS side in the search space corresponding to the next sub-section, and taking the end point of the screened single PS side as a new starting ant until the cycle ending condition is met or all the sub-sections are searched.
2. The method for quickly generating the reference network based on the segmented search and block networking according to claim 1, wherein the following process is adopted to uniformly divide the image into a plurality of sub-blocks:
suppose the SAR image size is: x is X a ×X r ，X a And X r The sub-block size is x a ×x r Representing the number of pixels in two directions of the sub-block,wherein: />Representing a rounding operator.
3. The method for quickly generating the reference network based on the segmented search and block networking according to claim 2, wherein the selection range of the number of segments of the sub-segments is 5-20.
4. A method for high-dimensional imaging using a plurality of spaceborne SAR images, wherein a chromatographic reference network of SAR images is established using the method of any of claims 1 to 3.
5. A system for high-dimensional imaging using a plurality of satellite-borne SAR images, wherein a chromatographic reference network of SAR images is established using the method of any of claims 1 to 3.
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