In furtherance of its mission to “monitor Earth’s vital signs from space, air and land,” NASA will launch its Soil Moisture Active Passive (SMAP) satellite on January 29 to “measure the moisture lodged in Earth’s soils with an unprecedented accuracy and resolution.”
According to NASA:
The topsoil layer is the one in which the food we eat grows and where most other vegetation lives. Moisture in the soil indirectly affects us in a variety of ways. In the course of its observations, SMAP will also determine if the ground is frozen or thawed in colder areas of the world.SMAP is designed to measure soil moisture over a three-year period, every 2-3 days. This permits changes, around the world, to be observed over time scales ranging from major storms to repeated measurements of changes over the seasons.
Everywhere on Earth not covered with water or not frozen, SMAP measures how much water is in the top layer of soil. It also distinguishes between ground that is frozen or thawed. Where the ground is not frozen, SMAP measures the amount of water found between the minerals, rocky material, and organic particles found in soil everywhere in the world (SMAP measures liquid water in the top layer of ground but is not able to measure the ice.)
SMAP will produce global maps of soil moisture. Scientists will use these to help improve our understanding of how water and carbon (in its various forms) circulate. The water cycle involves more than evaporation from the oceans and land, forming clouds (condensation) that drop rain or snow on the ground (precipitation), where water flows across the land before returning to the sea.
For example, plants absorb water from the soil to grow but also “transpire” some of it straight back into the air. Animals drink water and eat plants, delivering water back to the ground where it may end up flowing to the ocean or be evaporated as the ground dries.
For more on the SMAP misssion follow this link.