A remotely sensed approach on waterline extraction of silty tidal flat for DEM construction, a case study in Jiuduansha shoal of Yangtze River

Tidal flat as geographically terrestrial and oceanic transition area is generally not mapped, also called "mapping blank area". However, it has paramount significance due to containing rich land and biological resources. For this reason, this paper discussed an approach that was how digital elevation model (DEM) of tidal flat was established by a series of waterlines extracted from multi-temporal Landsat Thermal Mapper (TM) data. It was found that each TM spectral band has distinct sensitivity to waterline extraction, and short-wave infrared band is optimistic for waterline extraction based on sand-flat type, but not on silty-flat type. The attribute of sets of waterline from multi-temporal satellite data were assigned into tidal level value by the estimation from tidal station record while the satellite was passing through the studied area. Then, DEM from waterline extraction was built with GIS. Compared with the results of in situ mapping, relative error was less than 0.5 m in most regions, and mean error was 0.18 m.