Methodology Development For Satellite Soil Moisture Retrieval From Optical/thermal Infrared Data

As a key parameter in surface energy budget and water cycle,timely accurate information of surface soil moisture(SSM)can help to better understand the energy and water exchange between the interface of the Earth’s surface and the atmosphere.Based on the state of the art of optical/thermal infrared remote sensing for SSM retrieval,the following investigations have been implemented in present study:First,a satellite temporal information-based SSM retrieval algorithm has been improved.A major disadvantage of the previous algorithm is that the coefficients are difficult to determine,depending on the meteorological conditions.In this improvement,the coefficients are divided into time-invariable and time-variable ones.The main achievement is that explicit relationships between coefficients and meteorological variables are developed.Hence,the time-invariable and time-variable coefficients can be determined by historical meteorological records,decreasing the dependence of the model coefficients on meteorological measurements when applying the algorithm.In addition,considering that the microwave-based coarse spatial resolution SSM products reveal different levels of data gaps,and obviously cannot well meet the requirement by various practical applications where SSM at finer spatial resolution is required,algorithm for the determination of the dry/wet edges of the land surface temperature(LST)-vegetation index(VI)trapezoidal feature space pixel to pixel and all-weather SSM at high spatial resolution,is investigated.On this basis,daily SSM product over mainland China is produced from the currently available optical/thermal infrared images.Following the algorithm for deriving all-weather daily SSM product,the method for deriving all-weather evapotranspiration is finally investigated.Moreover,based on the currently available satellite optical/thermal infrared data,instantaneous evapotranspiration product at a daily temporal resolution over mainland China is generated.