2 - Estimation of Soil Water Conditions Using Passive Microwave Remote Sensing

Abstract

The water content of soil, or soil moisture, is a key element in several fields, such as hydrology, meteorology, agriculture, and forestry. This statement is explained by the determining role of soil moisture in the processes (infiltration, runoff, evaporation, etc.) governing the water cycle and the global energy balance. This role has resulted in the recognition of soil moisture as an essential climate variable by the Global Climate Observing System (GCOS). However, as a result of its dependence on several factors, the spatial and temporal variability of soil moisture is very complex. In addition to precipitation and evapotranspiration, it is linked to surface characteristics such as the type of soil and vegetation, the topography, the surface roughness and so on. In order to analyze the variability of soil moisture, dense network stations for soil moisture observation have been temporarily installed during short field campaigns, among them the Cold Land Processes Field Experiment (CLPX) in northern Colorado, the Soil Moisture Experiment in 2002 (SMEX02) in Iowa, the Canadian Experiment for Soil Moisture in 2010 (CanEx-SM10) and the SMAP Validation Experiment in 2012 (SMAPVEX12) in the Canadian Prairies. For continuous soil moisture data, the installation of dense networks capable of providing historical series of soil moisture is ideal, but expensive. As a result, the International Soil Moisture Network has been developed through international cooperation in order to put together and archive in a database soil moisture measurements collected during field campaigns, and to make this database available to researchers. At the watershed or regional scale, hydrological models are used as an alternative for determining soil moisture. At the global scale, information about soil moisture can be obtained from passive or active microwave satellite measurements. In an effort to help soil moisture users, a database of soil moisture estimated at the global scale from passive and active microwave satellites has been developed as part of the Climate Change Initiative (CCI) program launched in 2010.