Abstract: Retrieval of offshore bathymetry has important significance in shallow topographic survey, coastal protection and development. In this study, Dongluodao waters in South China Sea was taken as a typical study area, using the SPOT-6 6 m high resolution data, six band ratio model such as blue-green and blue-red were set up respectively based on SPOT-6 multi-spectral data and depth measured values. The results show that green-red band ratio model has the highest accuracy and the R² value reaches 0.706 4. This has certain reference significance for retrieval of offshore bathymetry in tropical oceans. Comparing with the average relative error of the different depths range based on the above model, the conclusion is that the depth range from 0 to 5 m has the higher average relative error, mainly because the conditions are complex. The depth range from 5 to 10 m has a minimum average relative error of 13.62%. Accretion of the average relative error with the increasing of the depth, while SPM, CDOM and chlorophyll concentration are the main causes of this phenomenon.

Key words: bathymetry retrieval, band ratio model, error analysis, South China Sea