With the global warming of our planet, extreme meteorological events are going to occur more and more frequently. There will also be more episodes of drought. The American SMAP satellite (an acronym of Soil Moisture Active Passive), launched on Saturday 31st January, will have the very precise mission of monitoring the changes in soil moisture. Compared with other satellites capable of making these measurements, such as the European ERS and SMOS, SMAP will have the advantage of being able to make observations simultaneously of the radio frequency energy given off by the Earth and the echoes of the radio frequency pulses that bounce back off the surface (backscatter). Their combination will provide information on the presence of H2O molecules in the top five centimetres of the soil surface, being able to peer through moderate vegetation cover with a 9-km resolution. Its orbital trajectory enables it to scan the complete surface of the globe every two or three days, over a period of three years. SMAP does not merely monitor the occurrence of droughts. It can also provide information on the risks of flash flooding, which is quite common in the United States and aggravated by a soil that is too dry to absorb the rainstorms rapidly. Soil moisture also has an influence on agricultural productivity, the carbon cycle and also the weather, influenced by the phenomena of evaporation. These are the areas where SMAP data will be invaluable.
