A Channel Median Line–based Method for Detecting Spatiotemporal Change of Intertidal Shoals from TM Images: An Example from the Yellow Sea, East China

Detecting the morphologic change of intertidal shoals from satellite images is severely hampered by the requirement that they be acquired at the same tidal height. This limitation is circumvented with a new detection method proposed in this paper. It is based on the median line of tidal channels from which the stability of adjoining intertidal shoals is inferred. This method was applied to detect the changes of intertidal shoals in the vicinity of Jiangang Town in Jiangsu Province of East China from seven Thematic Mapper images recorded between 1988 and 2003. The delineated median lines of three tidal channels from the seven images were overlaid with each other in MapInfo. It is found that the net positional change of a channel varies with its section. The closer a section is to the shore, the larger change it underwent. On average, the magnitude of change in a section ranges from 25 to 134 m per annum. Temporarily, all three channels experienced more changes in early than in recent years of the study. The intertidal shoals have shifted their boundaries at a rate of about 110–150 m per annum, which would decrease further offshore. It is concluded that the intertidal shoals have shown some degree of stability over the study period.