Comparison of vegetation optical depth estimation methods using AMSR-E data

The vegetation optical depth (τ, tau), which describes microwave attenuation properties of vegetation, is a key parameter for vegetation biomass and soil moisture estimation. In this paper, we have implemented five semi-empirical/empirical methods for vegetation optical depth estimation. The Advanced Microwave Scanning Radiometer- Earth Observing System (AMSR-E) data and field experimental data provided by Climate Change Initiative (CCI) project were used to evaluate the estimated vegetation optical depth. Its dynamic ranges and time series trends were analyzed at one site located in USA. Correlations between optical depth estimated using the five methods and MVIs_B, MPDT, MDPI, and NDVI were calculated in order to explore the relationship between vegetation indices and optical depths. With exception of the Radiative Model (RT) method, the vegetation optical depths from other four methods exhibit a similar trend with time. The dynamic ranges and the correlation coefficients are significantly different from each other. This study would further help us to study the uncertainty of a variety of current soil moisture products.