We used a global positioning system (GPS), levelling, and Sentinel-1 data to evaluate the stability of the Darbandikhan dam in northeast Iraq after the 2017 Mw 7.3 Sarpol-e Zahab earthquake. GPS and levelling datasets collected in March and November 2017 were used to compute the co-seismic surface displacements of the dam. Sentinel-1 synthetic aperture radar (SAR) images collected between October 2014 and March 2018 were employed to recover the displacement time series of the dam. The large-magnitude displacement gradient on the dam crest hindered the estimation of the co-seismic displacement using this medium-resolution SAR data. However, Sentinel-1 images are sufficient to examine the stability of the dam displacement before and after the earthquake. The results show that the dam was stable between October 2014 and November 2017, but after the earthquake, Sentinel-1 data shows a continuous subsidence of the dam crest between November 2017 and March 2018. To the best knowledge of the authors, this study is the first that utilises InSAR to investigate the behaviour of a dam after a large earthquake.

TerraSAR-X add-on for Digital Elevation Measurements (TanDEM-X) mission is designed to generate three-dimensional images of the Earth as the first bistatic synthetic aperture radar (SAR). However, few quantitative studies of TanDEM-X DEM quality validation have been conducted specifically in China. This article presents an iterative method to generate high-resolution TanDEM-X DEMs and assesses the vertical accuracy with high-accuracy GPS observations, 1 arc second global DEMs available (AW3D30 v2.2, ASTER GDEM v3, SRTM v3.1, NASADEM, and X-band SRTM), and TanDEM-X 90m DEM. The results demonstrate remarkable elevation quality and consistency in coastal areas with root mean square error (RMSE) of 1.7m and 90% linear error (LE90) of 0.4m, whereas 3-4 times weaker accuracies in steep mountainous areas. A positive bias of 1-2m for an overall LE90 measure exists in the dense vegetation and steep-slope mountainous areas. TanDEM-X DEM-based InSAR deformation uncertainty simulation indicates a low or even negligible topographic error contribution of 2-4mm in mountainous areas and less than 1mm in coastal areas. It indicates that the TanDEM-X DEM performs better than other global DEMs overall and show a better elevation consistence with SRTM C-band DEM in the coastal area. As an excellent source of up-to-date information, the TanDEM-X DEM are expected be an advantage for understanding dynamic land use changes and improving identification and delineation of coastal lands, mountainous landslides, and earthquakes disasters.