Mapping Soil Moisture from Space

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Soil moisture might not be considered a critical factor to the health of our planet but a series of satellite missions are proving otherwise. Scientists recently created maps from NASA’s Aquarius satellite of soil moisture, or the amount of water contained within soil particles, across the globe. These maps have scientists and researchers excited about the possibilities. The data could have a positive impact on understanding the climate, predicting the weather, monitoring droughts, forecasting floods, predicting agricultural productivity, and informing decisions about water management.

The maps from Aquarius and its remote sensing equipment show not only the current amount of soil moisture across the globe but also how the wetness of the Earth’s has changed over time due to various weather phenomena. For example, the maps confirmed the change between the droughts that ravaged the U.S. Midwest in 2012 to the catastrophic flooding that occurred there in the spring of 2013. The maps also displayed the heavy rainfall that hit the eastern coast of Australia in early 2012 in the aftermath of Cyclone Jasmine. In addition, these soil moisture maps confirm the periodic changes as evidenced by a wide band of wet soil that follows the seasonal rains in Africa.

Map showing what the soil moisture conditions around the planet were like in August 2013: dry areas are represented in the brown scale, while wetter areas are in blue and green. Image Credit: NASA Goddard's Science Visualization Studio/T. Schindler
Map showing what the soil moisture conditions around the planet were like in August 2013: dry areas are represented in the brown scale, while wetter areas are in blue and green.
Image Credit: NASA Goddard’s Science Visualization Studio/T. Schindler

Remarkably, NASA’s Aquarius was not originally intended to track the moisture in the soil. The primary objective of the mission was to study the salt content of the ocean’s surface waters. The alternation came when a NASA team led by researchers from the U.S. Department of Agriculture (USDA) established a way to measure soil moisture from the satellite’s microwave radiometer. The radiometer can detect microwaves emitted from the top two inches, or 5 centimeters, of land. These signals shift when the moisture content of the soil does. The Aquarius takes global measurements of soil moisture every eight days.

Of course, there are some gaps in the coverage of the soil moisture maps. This is due to elements such as snow and ice, thick vegetation, and mountainous terrain. Aquarius also cannot gather data from small islands or pieces of land narrower than 62 miles like California’s Baja peninsula. This is because the instrument only has a 62-mile-wide footprint.

The Aquarius satellite is not the first to map soil moisture or the last. It builds on data already collected by the European Space Agency’s Soil Moisture and Ocean Salinity (SMOS) mission launched in 2009. There is also another upcoming mission to map soil moisture in the works from NASA called the Soil Moisture Active Passive (SMAP) set to launch in November of 2014. Whereas the measurements taken by Aquarius are courser in spatial resolution than those from SMAP, SMAP has been designed to provide the highest quality and greatest number of measurements.

Overall, everybody wins with three instruments in orbit that take measurements of soil moisture. It will allow scientists to compare data from the different sensors as well as track long-term changes. SMAP, in particular, is set to provide global soil moisture maps every three days with an improved spatial and temporal resolution. The maps could also enhance life on earth. Improved forecasts could help farmers and markets adjust their prices to production and help relief agencies better respond to food emergencies.


NASA’s Aquarius Returns Global Maps of Soil Moisture – July 7, 2014

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