Soil surface moisture estimation over a semi-arid region using ENVISAT ASAR radar data for soil evaporation evaluation

摘要

The present paper proposes a method for the evaluation of soil evaporation,using soil moisture estimations based on radar satellite measurements. Wepresent firstly an approach for the estimation and monitoring of soilmoisture in a semi-arid region in North Africa, using ENVISAT ASAR images,over two types of vegetation covers. The first mapping process is dedicatedsolely to the monitoring of moisture variability related to rainfall events,over areas in the "non-irrigated olive tree" class of land use. Thedeveloped approach is based on a simple linear relationship between soilmoisture and the backscattered radar signal normalised at a referenceincidence angle. The second process is proposed over wheat fields, using ananalysis of moisture variability due to both rainfall and irrigation. Asemi-empirical model, based on the water-cloud model for vegetationcorrection, is used to retrieve soil moisture from the radar signal.Moisture mapping is carried out over wheat fields, showing high variabilitybetween irrigated and non-irrigated wheat covers. This analysis is based ona large database, including both ENVISAT ASAR and simultaneously acquiredground-truth measurements (moisture, vegetation, roughness), during the2008–2009 vegetation cycle. Finally, a semi-empirical approach is proposedin order to relate surface moisture to the difference between soilevaporation and the climate demand, as defined by the potential evaporation.Mapping of the soil evaporation is proposed.