ERS SAR Interferometry for tidal flat DEM

It is essential to construct a high precision digital elevation model (DEM) annually or seasonally in tidal flats to monitor coastal erosion. To monitor active coastal changes using the tidal flat DEM, a vertical accuracy of higher than 20 cm is required. We apply space-borne radar interferometry (InSAR) to the Korean tidal flats to test the feasibility of InSAR in tidal flats. We also investigate favorable conditions for the data acquisition of interferometric pair. We first carried out a simulation of radar backscattering using parameters of the r.m.s. height, correlation length, and moisture content measured in the test sites. The simulation results led us to a conclusion that C-band VV-polarization would be the most effective combination for InSAR applications in tidal flats, while L-band HV-polarization might be useful for discriminating surface conditions. Under favorable conditions, we successfully constructed tidal flat DEMs using ERS-1/2 tandem pairs. In that case, the tidal flat DEM construction from ERS-1/2 tandem pairs was as effective as a waterline method. However, it was not always successful to obtain coherent interferometric pairs in tidal flats even though the bottom surface was fully exposed to the air. The results indicate that tidal conditions are not the one and only parameter accounting for interferometric coherence. One interesting result was that the coherence of the ERS interferometric pairs generally agreed with the reflectance of Landsat TM bands 4 and 5. The correlation coefficient R was about 0.7. The correlation was higher in middle and upper tidal flats, while it was lower in lower tidal flats. The results imply that the tidal flat parameters controlling the optical reflectance of the near and mid infrared are closely related to the parameters governing radar backscattering. Using sophisticated future single-pass or near single-pass space-borne SAR systems, a high precision tidal flat DEM will possibly be constructed if data acquisition plans are properly designed. Tidal flat, DEM, InSAR, ERS SAR, Landsat TM.