NASA’s newest, more technologically advanced radiometer instrument detects microwave energy from space, allowing scientists to study how much water is in the Earth's soil.

Soil moisture is an important measurement for weather forecasting, drought and flood predictions, and agriculture. All types of soil emit microwave radiation, but the amount of water changes how much of the energy is emitted. The drier the soil, the more microwave energy; the wetter the soil, the less energy. Radiometers measure the radiation, and scientists use the data to calculate water content.

The new radiometer launches into orbit aboard the Soil Moisture Active Passive (SMAP) satellite. SMAP carries two instruments to measure how much water is in the soil. In addition to the radiometer, which detects naturally emitted energy, a microwave radar will send a signal to the ground that will bounce back to the satellite with information after it encounters and interacts with the soil. To collect signals from the surface for both the radiometer and radar, SMAP has a 20-foot-wide mesh antenna that rotates 14 times per minute – the largest such spinning antenna in space. A receiver then interprets both sets of signals.

The two instruments complement each other: the radiometer provides an accurate measurement of a large block of land, while the radar provides finer detail of the soil moisture in smaller parcels.

"Combine the two together, use the best of both, and you come up with a pretty accurate soil moisture product at a spatial resolution of 6 miles," said Peggy O’Neill, SMAP deputy project scientist.

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Also: Learn about the Soil Moisture Active Passive (SMAP) mission.