Sandbar is a foot print of river into the sea. Sandbar can shield the current flow of ocean to reduce the coast erosion by ocean. Because of the shielding, the area between sandbar and coast always provide an excellent place for sea-farming. Monitoring the change of sandbar is a very important thing for the ecosystem and fishery economic of Taiwan. [1] Traditional remote sensing can't analyze the boundary of sandbar very well. Fully polarimetric SAR system has the capability to classify different structures based on their own scattering mechanism.[2] General propose four-component scattering decomposition (G4U), a model based decomposition method[3][4][5], provide a very good costal classification and analysis results. In this paper, 6 Radarsat-2 data sets were collected to analysis the changes of sandbar, oyster farm and the wave front of ocean along the sandbank with different ocean conditions using four decomposition scattering decomposition model.[6]