Combined Block Adjustment for Optical Satellite Stereo Imagery Assisted by Spaceborne SAR and Laser Altimetry Data

Abstract

To ensure the accuracy of large-scale optical stereo image bundle block adjustment, it is necessary to provide well-distributed ground control points (GCPs) with high accuracy. However, it is difficult to acquire control points through field measurements outside the country. Considering the high planimetric accuracy of spaceborne synthetic aperture radar (SAR) images and the high elevation accuracy of satellite-based laser altimetry data, this paper proposes an adjustment method that combines both as control sources, which can be independent from GCPs. Firstly, the SAR digital orthophoto map (DOM)-based planar control points (PCPs) acquisition is realized by multimodal matching, then the laser altimetry data are filtered to obtain laser altimetry points (LAPs), and finally the optical stereo images’ combined adjustment is conducted. The experimental results of Ziyuan-3 (ZY-3) images prove that this method can achieve an accuracy of 7 m in plane and 3 m in elevation after adjustment without relying on GCPs, which lays the technical foundation for a global-scale satellite image process.

Combined Adjustment Pipeline for Improved Global Geopositioning Accuracy of Optical Satellite Imagery With the Aid of SAR and GLAS

“…In the last iteration, the errors converged to approximately 3 m (close to the GF-3 nominal accuracy), which is less than the error caused by the SRTM as the elevation reference. In conclusion, the overall accuracy of this algorithm is better than that of SRTM-assisted optics, SAR, and GLAS [13], [15]. In summary, the proposed pipeline compares favorably with existing methods, permitting better accuracy and wider applicability.…”

“…The final horizontal and vertical geo-positioning accuracies of each area (Method VII) were 3.16 and 1.45 m (for area A), 3.36 and 1.17 m (for area B), and 3.17 and 1.28 m (for area C), respectively, close to the nominal accuracy of multi-source reference data. This accuracy is better than that of Method VI (combination of SRTM-assisted optics and SAR) [13], [15]. This demonstrates that the information of multi-source data is fully utilized.…”

“…Method V introduced SAR and GLAS data, but SRTM was still used as the SAR elevation reference according to existing methods [13], [15]. The results show that the accuracy improved by 7.87-6.43 m for area A and 9.28-7.34 m for area B in the horizontal direction; thus, the improvement was less than that for methods VI and VII.…”

“…Fan et al [13] obtained the elevation value of SAR imagery points, and then used corresponding Shuttle Radar Topography Mission (SRTM) [14] data to calculate their geographical coordinates and generate VCPs of optical imagery. With the help of SRTM, Zhang et al [15] produced a SAR orthophoto of the Hubei region of China, and obtained plane control points through cross-modal matching [16]. These control points were used to improve the geo-positioning accuracy of the optical images.…”

Exploiting High Geopositioning Accuracy of SAR Data to Obtain Accurate Geometric Orientation of Optical Satellite Images

“…Based on HOG, Ye et al [78] proposed the histogram of oriented phase congruency (HOPC) feature descriptor by replacing the gradient feature with a phase congruency feature, obtaining good performance on the matching of SAR and optical satellite images. Zhang et al [79] applied HOPC to a combined block adjustment framework for optical satellite stereo imagery which is assisted by spaceborne SAR images and laser altimetry data. Ye et al [80] further proposed a similarity metric, DLSC, using the NCC of a novel dense local selfsimilarity (DLSS) descriptor which is based on shape properties.…”