Every 15 minutes, 685 kilometres out in space, the National Aeronautics and Space Administration (NASA) satellite known as SMAP (Soil Moisture Active Passive) records the earth’s soil moisture and temperature. NASA then uses that data to produce the most accurate maps of global soil moisture, temperature and freeze-thaw states ever created with data from space. Agriculture and Agri-Food Canada (AAFC), Environment Canada and university scientists are assisting NASA in validating SMAP soil maps. AAFC is also producing higher resolution soil moisture maps from the Canadian RADARSAT-2 satellite.
The maps from SMAP and RADARSAT-2 are valuable tools that help improve people’s understanding of the processes affecting weather and climate. This, in turn, can help agricultural production.
“Soil moisture is an important variable in the development of extreme events,” says Heather McNairn, the AAFC team lead and a research scientist for geomatics and remote sensing in Ottawa. “If we don’t have enough water in the soil, drought can develop; if we have extended periods of wet soils, it puts us at risk of flooding.”
This is where the information from SMAP and RADARSAT-2 comes in. It reveals how much moisture is in the soil so scientists – and producers – can understand the risks for drought or flooding.
“Knowing how much water is available in the soil can help us understand drought risk, where drought might be developing and how severe the drought might be,” McNairn says. “If we can measure how much water is in the soil, we can determine if the soils have enough reserve space to absorb spring snow melt and rainfall. If the soils are saturated, they are unable to accommodate additional water and this tells us the risk of flooding is high.”
From an agricultural perspective, monitoring soil moisture will enable the sector to better mitigate agricultural risks regionally and nationally. It will also help Canadian producers make informed decisions for their farm operations based on changing weather, water and climate conditions. For example, producers could use the data to determine their variable rate irrigation needs.
Environment Canada will use data from SMAP for improved weather forecasting since the amount of water in the soil significantly affects temperature and rainfall forecasts. “We don’t currently have good data on soil moisture across Canada,” McNairn says.
The data will also help researchers outside of Canada, such as in Chile where agronomists are looking at variable rate irrigation. “Producers don’t know how to variably apply water because they don’t know where the moisture is in their fields,” McNairn says. She is assisting researchers in Chile to integrate soil moisture maps from SMAP and RADARSAT-2 into their variable rate irrigation practices.
While NASA launched SMAP in January 2015, AAFC began working with the space agency three years earlier. That’s when an AAFC team from Ottawa and Winnipeg took part in SMAPVEX12, a six-week field-testing campaign that involved government and university scientists collecting soil and plant measurements in southern Manitoba while NASA flew two aircraft equipped with the same sensors as the SMAP satellite. The measurements from that mission were then used to calibrate and validate the processing models NASA was planning to use with SMAP.
During the SMAP mission, which is expected to run at least three years, AAFC will provide NASA with data from its network of 12 soil monitoring stations in Manitoba and five in Ontario, all installed at private farm sites. The SMAP team will use this data to assess the accuracy of SMAP’s soil moisture products.
The 2012 SMAPVEX experiment used data from NASA aircraft to simulate what soil moisture maps from SMAP would look like. Now that SMAP is launched, NASA is returning to Manitoba this year for a second experiment. SMAPVEX16 will validate actual data from the satellite, and NASA will use what is learned during SMAPVEX16 to improve its models and SMAP’s global soil moisture maps.
Canada also collects data from its own satellite, RADARSAT-2, to produce soil moisture maps at resolutions higher than those produced by SMAP. These methods will be carried forward and used with Canada’s next generation of satellites, the RADARSAT-Constellation scheduled to launch in 2018. With this Constellation, data for use in soil moisture mapping would be available from three satellites.
“SMAP and RADARSAT-2 can work together to provide a range of soil moisture products,” McNairn says. The SMAP sensor provides very coarse resolution images covering approximately 1,000 kilometres, which are very good for large scale forecasting of weather and floods, but not detailed enough for field scale mapping. This is where higher resolution data from RADARSAT-2 can help.
Scientists are validating the maps from SMAP and also tackling how to downscale SMAP data to improve the resolution of soil moisture maps from this NASA satellite. Downscaled SMAP soil moisture products would provide producers with better data for use in variable rate irrigation and determining the disease risk at the field level. For example, “the risk of some crop diseases increases if the soil is wet for many days,” she explains. “The temporal persistence of wetness tells about risks and if we can determine this risk, this information will help producers make decisions in managing this risk.”
For now, it’s exciting that NASA is providing soil moisture maps for the whole world every three days, McNairn says. “We couldn’t do that without satellites.”