CARMAN, Man. — A prairie sunrise is not easily rivalled, but Canadian astronaut Chris Hadfield once described the sight of daybreak from space, where sunrises occur every 92 minutes, as a breathtaking display in which the “secret patterns of our planet are revealed.”
These secret patterns are precisely what I am seeing after this July morning as the first colours of dawn appear on Winnipeg’s skyline.
I am a summer student in the University of Manitoba’s soil science department, preparing for another day of field work on the SMAPVEX16-MB project.
The project calibrates the Soil Moisture Active Passive (SMAP) satellite launched by NASA in January 2015. It orbits 685 kilometres above the Earth and produces maps every two to three days of the moisture in the top five centimetres of soil around the planet.
In Manitoba, the project is co-ordinated by Paul Bullock at the U of M.
“I have lots of big hopes,” Bullock said about how the soil moisture maps will be used in the future.
Soil moisture is linked closely to pest and disease prevalence.
“Knowing how those conditions are changing on a near real time basis can provide people with a heads up on these issues in larger areas,” he said.
“(SMAP will) pick up hot spots where there might be problems.”
Paul Bullock and Amy Unger take soil moisture readings using a POGO instrument at a SMAP site near Elm Creek, Man. | Krista Hanis photo
This morning, our moisture sampling day begins in Bullock’s lab. Ten teams of people file in to pick up their equipment and any special instructions about field conditions and logistics before loading up and driving to their assigned fields near Carman and Elm Creek, Man.
Our ground crews, each comprising two or three people, are made up of a diverse group of students and professionals from a variety of organizations:
- Manitoba, Guelph and Sherbrooke universities
- Agriculture Canada
- Environment Canada
- Canadian Space Agency
- Jet Propulsion Laboratory
- Goddard Space Flight Center
Over a four-week period this summer, we collected samples and monitored conditions in 50 representative fields located within one 36 km pixel of the satellite.
Co-ordination is the name of the game in this project. Measurements are taken simultaneously from space, air, ground level and below ground.
Radiometer and radar technology power many of our measurements. Radiometers detect the energy given off naturally by the Earth, while radar works by sending out a signal and measuring the back scatter that returns.
Wet and dry soil respond differently with both types of technology. When the equipment is calibrated properly, we can accurately document the amount of moisture present in the soil.
The SMAP satellite carries a radiometer and provides information on the community scale.
Overhead, our Second World War era DC3 carries the Passive/Active L-band Sensor (PALS), which is equipped with radiometer and radar. The DC3 flies grid patterns over the sampling sites at one and three km altitudes to provide information on a field scale.
SMAP soil moisture data comes from four sources: the NASA satellite, the DC3, the SMAP ground crews and this low-flying drone equipped with cameras that read five different wavelengths. | Amy Unger photo
We also fly a drone equipped with a special camera that measures five wavelengths to determine the vegetation biomass water content on each field at a 10 cm resolution.
On the ground, we have a network of permanent and temporary weather stations on the 50 sampling fields. The stations have surface and underground probes that constantly measure and record soil moisture.
There are also two ground based radiometers.
All the instruments and methods have one thing in common: they indirectly measure soil moisture.
However, it’s important to obtain a direct measurement of the amount of moisture in the soil if you expect all the other data to be of any value. The only way to do this is to physically collect a core of soil and compare the core’s wet weight to the oven dried weight.
This is where our 10 ground crews enter the picture. We’re in the field at 6 a.m. and navigate to our first sampling point using handheld GPS.
This early start allows us to beat the heat of the day. More importantly, it ensures that our data collection is synchronized with the satellite overpass and the flight of the DC3 so when all is said and done, the calibration of the satellite will be as precise as possible.
Armed with a backpack full of tools, we walk a mile loop through each field and stop at 16 points along the way to collect data.
“The key is everybody has to do the same thing, and they have to do it in a tight time window,” Bullock said.
“At the end of each day we have a pretty full data board.”
Ground crews collect three types of measurements on each field:
- Soil cores are taken from specified points on the field. Later in the day, the lab team will weigh the cores before putting them in the oven to dry for two days.
- Thermal infrared sensors and thermometers are used to find the temperatures of the sunlit and shaded soil and crop surfaces and the temperature at various depths in the soil.
- A portable moisture probe, the POGO, collects data and is connected to an iPod to record information. This instrument was designed for golf courses when making irrigation decisions, but it serves our purposes quite well.
By the time we finish one sampling day, the entire ground crew has walked 50 fields to collect 100 soil cores, 1,200 temperatures and 2,700 POGO readings.
Collecting information about soil moisture is not enough to properly calibrate the satellite because soil moisture is affected by “noise” from the overlying vegetation and the roughness of the soil surface.
This 1930s DC3 was flown by NASA over southern Manitoba fields as part of a project using satellites to document soil moisture levels on Earth. Members of the SMAP ground crew were invited to see the Second World War era airplane while it was in Winnipeg. | Amy Unger photo
We have to measure and subtract the effects of this noise to produce maps that show only soil moisture. Soil roughness stays the same throughout the growing season, so we measured roughness values only once after planting this spring.
However, vegetation is constantly growing and changing.
The days we aren’t sampling soil moisture are dedicated to measuring the moisture and structure of crops on our fields.
We stop at three points in each field to record average crop height, take fish-eye pictures of the crop rows for the Leaf Area Index, take portable Crop Scan radiometer readings and bag up samples of the vegetation.
A portable lab is set up in Elm Creek on these days to weigh the vegetation samples and determine the crops stages so we can begin the process of reducing the noise that SMAP receives.
“Something that is really key: SMAP by itself is not going to be a magic bullet,” said Bullock about the long-term goals of this project.
“It has to be combined with other data and information to build a useful picture of soil moisture in space and time.”
Our work is not done, even as the day draws to a close and we return to the university with our data sheets, soil cores and stories from the field. We look forward to another day of sampling and, some day, having a more complete understanding of global soil moisture.