Determining the Optimum Conditions for Generating Fine Topography in Tidal Flats Using an In-SAR System

Abstract

Continuous monitoring of the topographic heights and changes in tidal flats has been important but extremely challenging. It is generally difficult to observe the change of tidal flat topography from only on-site measurements. In this regard, interferometric synthetic aperture radar (In-SAR) measurements can be an effective strategy to generate precise DEMs and detect large-scale topographic changes. Nevertheless, utilizing interferometric synthetic aperture radar to detect topographic change in tidal flats is not practical because the average slope of tidal flats is usually less than a degree and the overall spatial height variation is less than 5 m. Besides, the temporal height variation is small requiring long observation periods. Therefore, the accuracy of In-SAR DEMs must be especially high to detect meaningful topographic variation. In order to minimize the error of In-SAR DEMs, height of ambiguity (HoA) and random phase deviation of interferogram should be taken into account. These two factors are related to incidence angle as well as baseline. In this study, we investigate topographic error level in tidal flat when using single-pass In-SAR system. Phase deviation of interferogram is derived by conventional geometry and equations. SNR and geometric decorrelation is expressed by function of baseline as well as incidence angle. The result shows that height error of DEM is minimized to be less than 15 cm when baseline is 1500 m with an incidence angle of 29˚ in TanDEM-X system. Finally, validation of the model was carried out by comparing with TanDEM-X interferograms out which is the only single-pass interferometric satellite mission carrying on SAR sensor. Finally, deposition and erosion pattern of Gomso bay was analyzed from difference of TanDEM-X DEMs.