Off-Nadir Photogrammetry for Airborne SAR Motion Compensation: A First Step

Abstract

A photogrammetry system operated simultaneously with a synthetic aperture radar (SAR) from the same aerial platform provides strong sensor fusion possibilities that can improve the accuracy of repeat pass Interferometric SAR (InSAR) processing. Motion compensation is a key step in airborne SAR/InSAR processing, and the availability of accurate external digital elevation models (DEMs) is at the heart of many InSAR applications. Eventual research goals are (1) to produce high precision photogrammetric DEMs as reference for interferometric and tomographic applications, and (2) to use photogrammetric block adjustment parameters to fine-adjust the flight trajectory for enhanced motion compensation in repeat pass InSAR. To meet these goals; as SAR is oblique looking by design, an un-conventional off-nadir photogrammetric field-of-view coinciding with the SAR swath is required for our combined system. In this paper we focus on the accuracy implications of the derived photogrammetric DEMs from off-nadir vs nadir configuration as well as the potential for trajectory refinement from the derived photogrammetric block adjustment parameters. Additionally, we carry out an accuracy comparison of our photogrammetric system with established references (Fairbanks fodar™ and WorldDEM™). Vertical photogrammetric DEMs produced with our system over a test site near Silver City, Yukon Territory, Canada were found to be accurate with a mean height difference of 0.45 m and a corresponding standard deviation of 0.78 m from the reference fodar™ system; whereas produced nadir vs. off-nadir DEMs were found in accordance with each other with a mean difference of 0.29 m and standard deviation of 0.75 m. Furthermore, the estimated flight trajectory refinement for the test data had a mean value of 0.19 m with a standard deviation of 0.09 m.