Repeat-pass SAR Interferometry Experiments with Gaofen-3: A Case Study of Ningbo and Nanjing Area

This paper illustrates the repeat-pass interferometric SAR (InSAR) results of Gaofen-3 (GF-3), a Chinese civil SAR satellite. The SAR images are acquired in November 2016 and March 2017 from Ningbo and Nanjing area, particularly, the images in Nanjing area are the first meter degree interferometric pair. With the spatial baseline about 600 m and time baseline 116 days, the coherence of the most urban areas still achieves good enough to generate the digital elevation model (DEM), whereas for the mountain areas, the decoherence phenomenon is serious. During the InSAR processing, we compared several baseline estimating methods and obtained a good flat-earth phase removed interferogram map. By using the latest SAR interferogram filter and phase unwrapping method we proposed, we improved the coherence up to 0.8 in urban area. To reduce the spread unwrapped phase errors coursed by low coherence area, we partitioned the unwrapped phase map and calibrated the baseline and phase offset parameters based on the partitioned image. Then the DEM of high coherence areas were retrieved in each block, and for low coherence areas, the existing DEM auxiliary method was used. In addition, after the orthorectification, we evaluated the elevation model by comparing with the elevation values extracted from SRTM and field measured GPS elevation. And the result shows that accuracy of the elevation map is about 10 m (RMSE) in most of the studied region.