Measurement of Tidal Flat Topography using Long-Baseline InSAR

Abstract

Tidal flats which are located between land and ocean are very vulnerable to the change of environment. These places are now facing many environmental challenges related to climate change and human-induced impacts. Topographic changes related to sedimentation or erosion in tidal flats are the most evident sign of the environmental changes. The tidal flats usually have small variations of topographies and experience ebb and flood tides every day. The conventional SAR interferometric techniques (such as repeat-pass InSAR) cannot be applied for generating digital elevation models (DEMs) in these tidal flats because of low coherence caused by ebb and flood tides. In this study, we developed a long-baseline single-pass airborne interferometric SAR (InSAR) system that has a small ambiguity height. We collected InSAR data in several tidal flats, the west coast of Korean peninsula, using our airborne InSAR system and TanDEM-X. The TanDEM-X is a space borne quasi-single pass interferometic SAR system. We also investigated the expected accuracy of DEM as function of baseline and coherence. In general, longer baseline is better for generating very sensitive and fine DEM that is absolutely needed for tidal flats, because longer baseline has smaller ambiguity height. But longer baseline can also cause low coherence due to baseline decorrelation. As the baseline increase, common spectral region is also decreased resulting in poorer coherence and poor vertical accuracy. Based on these investigations, we proposed optimal baselines for airborne InSAR system and space-borne SAR system. Finally, we compared the constructed topographies from our long-baseline airborne InSAR and TanDEM-X with GPS-RTK measurements.