Although the amount of moisture stored in soil is just a small fraction of Earth’s water, it plays a big role in the Earth system—affecting processes as diverse as plant growth and cloud formation, as well as influencing the occurrence of extreme events like floods and droughts. NASA’s Soil Moisture Active Passive (SMAP) satellite, launched into orbit this morning, will measure soil moisture worldwide every 2–3 days for the next three years.

“Active Passive” refers to the two measurement techniques that SMAP will use: a radar instrument will actively emit a signal and measure the backscatter from Earth’s surface, while a radiometer will passively record the microwave signal that Earth emits naturally. These combined measurements will determine the amount of moisture in the topsoil layer and will detect whether or not the soil is frozen.

The SMAP mission has a wide range of applications. Better information about soil moisture can improve the accuracy of weather forecasts over scales of days to weeks, for example, and can enhance crop yield forecasts and support irrigation planning to aid global food production. The amount of moisture present in soil determines the severity of drought conditions and the likelihood that heavy rains will cause flooding; thus, SMAP’s higher-resolution measurements will contribute to better monitoring and early-warning systems for these hydrologic extremes.

Last but certainly not least, detailed measurements of soil moisture can provide a better view of how the different components of the Earth system work together. Earth’s water, energy, and carbon cycles are linked through soil moisture, and future changes in global climate and the environment depend in part on how these cycles change and interact. SMAP will serve as an important new contribution to the array of Earth observing capabilities that form the foundation of climate and global change research. 

To learn more:

• Visit the SMAP mission site or NASA’s SMAP page
• Read the full SMAP fact sheet or download the infographic
• See all NASA Earth observing missions
• Learn more about observations of global change