Guangdong in south China has the largest area of mangrove wetlands in China.However

the mangrove wetlands have been rapidly diminishing because of the rapid urbanization.Remote sensing can be used to provide important information for the protection of the mangrove wetlands.Traditional optical remote sensing has difficulties in monitoring the wetlands in this region because of frequent cloud covers.The well-known NDVI index from optical remote sensing has drawbacks in obtaining the trunk information for mangrove forests.In this paper

comparisons were made between the NDVI models and backscatter models in estimating wetland biomass.Regression and analytical models were used to establish the relationships between remote sensing data and wetland biomass.The optimal parameter values for the analytical model were determined by using genetic algorithms.Experiments indicate that the models using radar remote sensing data have significant accuracy improvement in terms of Root Mean-Square Error（RMSE）.It is found that the use of the single NDVI index may produce serious errors in biomass estimation.The errors occur because some herbaceous species with dense canopy

such as Spartina anglica

may have much higher NDVI values than mangrove forests.