In September, I participated in a field campaign for the SMAP (soil moisture active passive) satellite in Yanco, Australia. My team and I sampled the soil moisture every 250m across farmlands to validate both the satellite measurements as well as sensors on board an aircraft. Farmlands were picked because measurements were notoriously bad and they are important for society. The location was also selected because there are long term ground observations, which can supplement the measurements taken on land, air, and space.
We used a GETAC system to find the points via GPS and log the measured values. The GETAC was connected to a long pole, at the base of which was a soil moisture probe. The probe has several prongs, which send an electrical signal through the soil; the resistance is used to determine water content. The analytical term for determining soil moisture is referred to as gravimetrics. The probe also collected soil temperature and soil salinity. We took measurements three times at each point to try to get a representative sample. It’s amazing how much variability there is just a few inches apart.
Of my 14 days days in Yanco, about half were spent taking soil moisture measurements. On the other days, we did intensive vegetation sampling. We would pick a square meter of space and harvest all the plants. These were carefully weighed, dried for two days in an oven, and then weighed again. The difference was used to measure the water content. A “representative specimen” was selected, and the stalk length, thickness, as well as the leaf count, thickness, length, and angle were measured. We also noted the overall characteristics of the field, such as row orientation and irrigation. This information could be used to improve model parameters or to find what types of crops introduce errors to soil moisture estimates.
As someone who spends most of their time sciencing indoors, it was really cool to see where my data comes from. It’s an enormous effort to organize these projects, and things didn’t always go as planned. Some teams had equipment break or parts were missing and we had to improvise with lots of rubber bands. We got a very good laugh at one of the ground stations, which was overgrown with vegetation while being surrounded by a completely mowed field. You better believe there is bias on those measurements!
Lastly, this was hard work! According to my fitness tracker, I walked approximately 6-10 miles over some rough terrain. Mornings were pretty chilly and the the dew that collected on the wheat in the morning made its way into my boots and walking became squishy. It was quite empowering to be alone working around for hours. My team and I got to know each other really well, and we helped each other to get the job done. I also became protective of my equipment, wanting to keep it clean and the prongs straight (my precious!!!).
We also had fun too. I saw kangaroos hop by. There was little light pollution, which made for amazing stargazing. There was a koala preserve nearby which I visited twice and a local derigidoo artisan who asked if I wanted to sample wiggly grubs (no thanks!). Driving on the left side of the road turned a mundane task into a thrill. It was an amazing experience that I think all scientists should do at least once!