ESA satellite prepares for water watch

To a passing alien, Earth would appear as a water world, largely covered by oceans and clouds. Without this precious liquid, life on Earth would not exist. However, there is still a lot we don’t know about the planet’s water and its impact on weather and climate. ESA’s next Earth Explorer mission, known as SMOS, is expected to provide some answers.

Water is the only natural substance that can exist on Earth as a gas, liquid or solid. When it is warmed by the Sun, the water evaporates and turns into a gas (water vapour). This gas rises and cools, forming clouds and rain. The rain falls back to the surface to complete the water cycle.

Although most water vapour comes from the oceans, about one tenth is released by plants and evaporation from soil. However, if the ground gets too wet, it may result in floods and soil erosion. Too little moisture and the land turns into a desert. At present, there are few measurements of soil moisture, but this is about to change with the launch of SMOS.

The satellite will also measure the salinity (‘saltiness’) of the oceans, searching for areas that are much more salty, and therefore more dense. Such differences affect the ocean currents, which, in turn, influence weather and climate.

SMOS carries a special instrument to measure both soil moisture and ocean salinity. 69 receivers on Y-shaped arms will measure microwave radiation coming from the surface. They will be able to detect soil moisture of only 4% – equal to one teaspoonful of water in a handful of dry soil. During a three year mission, it will create the first global maps of soil moisture and ocean salinity made from space.