ALOS PALSAR Investigation of Coastal Geomorphologic Mapping

High precision DEM of a tidal-flat is valuable to coastal management as well as pure scientific interest including erosion and sedimentation rate study. Geomorphologic mapping in coastal zone is, however, complicated by the rapid and significant changes on many fluvial forms and poor topographic expression of the landform. Three space-borne SAR systems including ALOS PALSAR, TerrrSAR-X and ERS-ENVISAT tandem mode were examined for effectinves of interferometry at the west coast of Korean Peninsula. Tide level and tidal conditions such as ebb or flood tide play important role in coherence of radar interferogram. A long antenna baseline and a short temporal baseline are required for coastal applications. ALOS PALSAR with a 43 day repeat cycle produced coherent pairs over vegetated land but was not very effective at tidal flats. The coherence was ranging from 0.3 to 0.5. ALOS PALSAR DEM reflects the surface variation reasonably with a standard deviation of 7.4 m. The eleven day repeat cycle of TerraSAR-X may not be perfect for coastal observation but shorter than ALOS PALSAR. The high resolution capability with salt marsh sensitive X-band observation is also a great advantage for coastal area study. However, X-band was sensitive to moisture content in troposphere. The seasonal variation was very common in TerraSAR-X pairs and winter was better to observe at least in Korea according to vapor content. TerraSAR-X was also useful for salt marsh mapping with a strong backscattering by halophyte. In addition, the high resolution X-band is very good in discrimination of water and exposed tidal flat. The ERS-ENVISAT cross interferometry was most effective with a long baseline and only 30 minute temporal baseline for tidal flat DEM generation. Detailed topographic variation were well rendered by the ERS-ENVISAT cross interferometry. In summary, a cross interferometric system with a synchronized two or more would be an optimal spaceborne SAR system for coastal study.