Soil-moisture Research From the Air – Don't Rain on My Parade!

The NASA Gulfstream III aircraft is currently in Saskatoon, Saskatchewan, Canada participating in an 18-day science campaign studying soil moisture.  The campaign, known as Canadian Experiment for Soil Moisture in 2010, is a partnership between NASA and multiple Canadian government agencies and universities.

The NASA G-III carries an active L-band synthetic aperture radar, or UAVSAR, that is capable of measuring soil moisture up to 50 mm beneath the surface while flying at approximately 40,000 feet altitude.    Environment Canada, which is responsible for renewable resources, weather  forecasting, and other functions, is our host while in Canada and they are flying a Twin Otter at about 10,000 feet altitude carrying a passive L-band radiometer.

Multiple teams of scientists and graduate students are doing field sampling in the test regions.      In addition to the ground-based and airborne assets, the work is being coordinated with overpasses from a number of internationally operated satellites.   Airborne remote sensing obtains much better resolution data than the satellites, although over a much smaller region.    For example, science flights are scheduled to coincide with the European Space Agency developed Soil Moisture and Ocean Salinity satellite. The CanEx test region, which covers an area of 33 km x 71 km on the ground, covers only two pixels of the SMOS image, while the G-III pixel resolution is 3 m x 3 m.

Hydrologists use accurate knowledge of soil moisture for modeling weather, predicting flooding and estimating crop yields. Accurate models can be very beneficial to nations and farmers in decision making, such as in deciding which crops to plant and when to irrigate or apply fertilizers.  It can also be useful for fighting diseases such as malaria.

The Soil Moisture Active Passive web site ( is an excellent site for learning more about the applications of soil-moisture research. NASA plans to launch the SMAP satellite in 2014.  NASA’s participation in the CanEx campaign is funded by the SMAP project because the combination of the two aircraft (active and passive sensing) will provide critical information for the purpose of developing algorithms for the SMAP mission.

Saskatoon is known as the “city of bridges” in Saskatchewan which has the state motto “Land of the Living Skies”. It is actually quite pretty along the banks of the Saskatchewan River where our hotel is located. The region is very flat and primarily farmland.

It turns out that years of drought are being broken during this science campaign – they have more soil moisture than they bargained for. The Land of Living Skies has lived up to its name also – not only has it been a problem for the science objectives, but it is a real problem for the local farmers, who have a shorter growing season than in the U.S. and have been unable to plant the majority of their crops due to multiple lakes and mud sitting on their fields. Uncharacteristically,  the G-II has been grounded multiple times due to the weather.  

The G-III is an all-weather aircraft and the UAVSAR sensor that it carries can see through clouds and rain. Typically, weather does not stop us. However, this is a soil moisture science campaign and observations must be coordinated with concurrent ground-truth. It is extremely difficult to instantaneously characterize the ground condition, or to have people plodding through mud, when it is raining.

The ideal soil moisture study would be a strong rain followed by remote sensing flights on multiple days without rain to observe the drying cycle. So far, we haven’t been so lucky.     We have completed four science missions since our arrival here on June 1, squeezed in between days of rain. It is looking promising for a two- or three-day drying cycle starting this weekend and we are ready to support. We’re expecting to complete four more science flights before we head back to California on June 18, and are hoping that the weather will cooperate to enable us to obtain the data needed to support soil-moisture research and its broad-ranging applications for the benefit of all.

By Tim Moes

G-III UAVSAR project manager