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SMAP Mission

Image of satellite over earth. Text reads: SMAP: Soil Moisture Active Passive. Mapping soil moisture and freeze/thaw state from space."
The amount of water that evaporates from the land surface into the atmosphere depends on the soil moisture. Soil moisture information is key to understanding the flows of water and heat energy between the surface and atmosphere that impact weather and climate. NASA's Soil Moisture Active Passive Mission (SMAP) can measure this soil moisture from space at regional and global scales. 

SMAP also has applications in science, agriculture and environmental management, each of them vital to Earth's health and sustainability. From understanding Earth's interconnected climate processes to improving weather and climate prediction models, SMAP continues to advance environmental knowledge. 

Learn more about the SMAP Mission.


SMAP Benefits from the partnership with GLOBE through the collection of "ground truth" measurements by GLOBE students. These measurements contribute to the SMAP calibration and validation program. Additionally, SMAP receives feedback from students on how SMAP's soil moisture information can be useful to their communities. Through this partnership, the public can participate in, and become more aware of, SMAP's societal contributions and the availability of high-quality SMAP data products.

GLOBE benefits from this partnership through SMAP scientists providing guidance on GLOBE soil moisture protocols and measurement procedures, reviewing the data contributed and interacting with the GLOBE community. Students can also get involved with a NASA mission and learn how satellite information can improve the collective knowledge of Earth systems.

Two students at a table, working on a small device.
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How to Participate

You can participate in the SMAP mission by:

  1. Collecting data using the SMAP Block Pattern Soil Moisture Protocol
  2. Coordinating your measurements with the SMAP Overflight Tool

Gravimetric soil moisture measurement is the standard method for determining the amount of water in the soil. These observations provide point measurements in contrast to the SMAP radar and microwave radiometer instruments that measure volumetric soil moisture over large areas (roughly 30km x 30km). This area is called the "measurement footprint" and is analogous to the 30m x 30m pixels of LandSat images.

Soil moisture conditions can vary significantly within these pixels, so ground-truth measurements at several point locations can provide more detailed  information about the variation in soil moisture conditions within the SMAP measurement footprint. The more ground-truth measurements that are available, the better scientists can validate SMAP soil moisture observations and track soil moisture accurately in the Earth system.

Synchronizing your soil moisture measurement collections with the SMAP spacecraft is the best way to compare the two datasets. The SMAP satellite crosses the equator at approximately 6:00 AM and 6:00 PM, which means that the best time for soil moisture data collection might be in the morning or in the evening. To best determine which days and what collection times your data will have the most impact, you can use the NASA LaRC Satellite Overpass Predictor.

How to Use the Satellite Overpass Predictor

  1. Go to NASA LaRC Satellite Overpass Predictor.
  2. In the "Satellite Name" field, select "SMAP"
  3. Enter in your start date, latitude and longitude.
  4. Select "Submit."
  5. Take note of the date and corresponding times under the first "GMT" column. This is the GMT time the SMAP satellite will be overhead in your submitted coordinates on the given date. To determine what your local time is in GMT, you can use this online time conversion tool.
Note: You should collect your soil moisture data within a 6-hour window (3 hours before or after) of the overpass time.

SMAP Videos