9 May 2024

NASA will monitor soil moisture on Earth’s surface


Soil moisture monitoring is also among the goals of NASA’s latest missions. For the U.S. Space Agency, this is a new contribution to the study and protection of soil thanks to satellite data

by Matteo Cavallito


NASA recently launched two remote monitoring missions of the soil and atmosphere with the goal of detecting traces of water and signs of volcanic activity according to a statement. One receiver, called Signals of Opportunity P-Band Investigation (SNoOPI), specifically aims to measure soil moisture in the root zone by exploiting radio signals produced by commercial satellites. Another instrument, the Hyperspectral Thermal Imager (HyTI), on the other hand, measures traces of gas linked volcano activity.

Both detectors were launched March 21 from the Cape Canaveral Space Station aboard a spacecraft that subsequently released them into orbit more recently.

Measuring soil moisture from space

The idea, explained James Garrison, professor of aeronautics and astronautics at Purdue University and principal investigator for SNoOPI, is to collect radio signals produced by many commercial telecommunications satellites and reuse them for scientific applications.

“By looking at what happens when satellite signals reflect off the surface of the Earth and comparing that to the signal that has not reflected, we can extract important properties about the surface where the signal reflects,” Garrison said.

The radio signals analyzed by SNoOPI, in particular, are able to penetrate the Earth’s surface up to about 30 cm deep. This characteristic makes them ideal tools for studying soil moisture in the root zone. “By monitoring the amount of water in the soil, we get a good understanding of crop growth. We can also more intelligently monitor irrigation,” he adds.

The importance of low frequencies

The mission launched in recent weeks is not the only soil monitoring operation being conducted by NASA. For example, the Soil Moisture Active Passive initiative, or SMAP, is still collecting moisture data by employing a different radio frequency (the higher L-band) to map the presence of water in the top five centimeters of soil on Earth’s surface. SMAP, however, cannot detect moisture at root level and faces some difficulties in monitoring forested and mountainous areas.

The SNoOPI system makes use of lower frequencies, which allows it to take detections four times deeper into the soil or snowpack, Reusing existing telecommunication signals, it also does not need a transmitter or a large antenna. If the mechanism proves successful, the space agency says it could “fly as many as nine small satellites along a polar orbit to build root-zone maps needed by weather forecasters, water managers, farmers, and power-plant operators.”

With a little help from satellite data

The SMAP and SNoOPI initiatives, in turn, are not isolated cases. Already in the past, for example, NASA has been involved in accumulating data on the level of erosion of farmland in the Corn Belt, in the heart of the west-central US. Through a monitoring effort, specifically, the space agency‘s satellites have collected useful information to guide farmers in choosing the best restoration practices.

Also NASA has been a partner since 2021 in an initiative to curb deforestation launched by FAO and the World Resources Institute (WRI). This program is supported by the U.S. Agency for International Development (USAID) and several partners including Google. The operation is called the Forest Data Partnership and in based  on the NASA-USAID SEVIR program. The initiative, FAO explained, aims to create “a consistent geospatial data ecosystem related to forest-risk commodities and restoration.” With the goal of “understanding and preventing deforestation and restoring degraded lands.”