Sovremennye problemy distantsionnogo zondirovaniya Zemli iz kosmosa, 2025, Vol. 22, No. 2, pp. 42-52
Methodology for refining parameters of the strict SAR model using data from automatic keypoint matching between optical and radar images
1 Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region, Russia
2 JSC Racurs, Moscow, Russia
Accepted: 13.03.2025
DOI: 10.21046/2070-7401-2025-22-2-42-52
Modern synthetic aperture radar (SAR) systems are crucial in various fields, including environmental monitoring, military surveillance and civil applications. However, despite significant advances in technology and data processing, many of these systems still face problems with the precision of determining the spacecraft position at the time of imaging, as well as determining the time and slant range to individual elements of the radar image (RI). These parameters are key when performing geometric transformation of RIs to form Level 2 processed information products. Hardware errors in determining these parameters lead to errors in calculating the ground coordinates of image elements. Obtaining refined information about the platform ephemeris often takes several days. In such conditions, a relevant task is to develop a methodology for automatic refinement of SAR rigorous model parameters using reference images obtained in the optical range. This paper describes a methodology for automatic refinement of SAR rigorous model parameters using reference optical data. A rationale is provided for transforming the optical reference image into a slant range projection (SRP) using the SAR rigorous model from the RI metadata. An algorithm for converting the image from a cartographic projection to SRP is presented. For keypoint detection, the use of SIFT (Scale-Invariant Feature Transform) and RANSAC (Random Sample Consensus) algorithms is proposed. A modification in the decision rule for selecting candidate points depending on the imaging mode is proposed. A method for analyzing pairs of matching keypoints to determine the error in time and range is described. The resulting error values allow for correction of the SAR rigorous model parameters. The methodology proposed in this paper is implemented as a software package. The package was tested on real data. The experimental results demonstrate a significant improvement in the quality of georeferencing of the final RIs processed to Level 2B1, obtained by orthorectification of the refined RI of Level 1A performed via the automatic method.
Keywords: synthetic aperture radar, georeference correction, Kondor-FKA, Kondor-E
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