Block adjustment with airbrone SAR very high-resolution images using trajectory constraints

ABSTRACT For mapping a large area with airbrone synthetic aperture radar (SAR), very high-resolution (VHR) images using radargrammtry, block adjustment, where strips and blocks of images are processed together, is a preferred method for geometric processing with the advantage of reducing the needed number of ground control points (GCPs). However, the weak intersection geometry between adjacent images from the same strip conflicts with the solvability of the iterative least squares adjustment. In order to overcome this challenge, this article focuses on block adjustment with airbrone SAR VHR images using r-D model combined with trajectory constraints from azimuth tie points (ATPs). Initially, r-D model is briefly introduced. Then, the trajectory constraint equations are proposed and formulated with ATPs. Finally, an improved solution method is applied to increase the computational efficiency of the least squares process. Experiments are carried out using Chinese airbrone SAR VHR images over Shanxi Yanliang, China. The results show that the proposed method can effectively improve the accuracy of block adjustment in both range and elevation direction, with the root mean square error reduced from 0.440 to 0.253 m in range direction and from 0.501 to 0.256 m in elevation direction, respectively. The effects of the distribution and number of GCPs are also investigated, based on which some rules-of-thumb are derived.