Calibration of TanDEM-X DEM Scenes Using Icesat-2 Altimetry Data for Global Dem Change Maps

Abstract

The operational calibration of TanDEM-X Digital Elevation Model (DEM) raw scenes generated from 2017 onwards, using an interferometric delta-phase approach, achieves high vertical absolute accuracy for 90% of the acquired data. The remaining DEM scenes with calibration offsets affect the accuracy of subsequent products such as the TanDEM-X DEM Change Maps (DCM). This study aims to improve the calibration of DEM scenes by using Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) altimetry data as absolute height reference and the method is demonstrated with DEM scenes at two sites: Tangkeng, China with known calibration issues, and the city of Mthatha, South Africa, with good quality data covering. We filter ICESat-2 data to get reliable reference elevation points and perform plane fitting to estimate calibration offsets. An RMSE of 0.59 m and mean of 0.41 m are found on DEM scenes taken around Mthatha city. For the data taken at Tangkeng city, the RMSE is 0.4 m with mean offset of -3.26 m. These calibration results support the goal of the TanDEM-X 4D mission to monitor changes in surface elevation using time-series products.