Remote Sensing is a key tool for hydrological modelling given that it allows assessing some of the state variables that play a role in hydrological processes.
Several satellites have been launched for Earth observation covering a wide range of the electromagnetic spectrum, from optical to microwaves. Data from these sensors can be used for the assessment of near surface soil moisture content, using microwave remote sensing, and evapotranspiration with thermal infrared remote sensing. In addition, optical sensors are valuable to characterize the surface properties such as albedo or leaf area index.
The European microwave SMOS mission (Soil Moisture and Ocean Salinity) will e.g. provide images with a temporal resolution of 3 days and with a coarse spatial resolution of microwave brightness temperature that will allow the operational retrieval of soil moisture. Also, multiangular thermal remote sensing, provided by the Advanced Along Track Scanning Radiometer (AATSR), is used to retrieve soil and leaf temperatures. These component temperatures are crucial for the estimation of soil evaporation and canopy transpiration.
Furthermore, the future Sentinel missions from European Space Agency (ESA) will allow the continuity of some of this data, in order to provide an operational assessment of hydrological processes in a long time series.