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How satellite images from space are used to monitor our soil

How satellite images from space are used to monitor our soil

Rumia Basu, PhD student at Teagasc, tells us about the connection between soil, rain and the climate is especially important for a grass-based economy like Ireland's

When I first landed in Dublin, three years ago, I was greeted with rain, a downpour rather, and this has remained constant through the time that I have been here. I used to get upset during the rainy season in India and could never romanticise rain as against what is shown in movies around the world.

Now here I am in Ireland, where it rains, and gorgeously so. The one thing, however, that made me fall in love with the rains here is the rainbow that appears after. I have probably seen more rainbows in the past three years than in my entire life. But, when it rains, how many of us care to look at the soil beneath?

We love the smell of the damp earth, the wild flowers and the lush grass. But what about soil? Did you know that soil is regarded as one of the essential climate variables that can provide information about our past and future climate? The connection between soils and rains is especially important for a grass-based economy like Ireland's.

Depending on the amount of rain and the specific characteristics of soil, like its texture, porosity etc., the moisture content of soil changes and this can directly affect the health of a crop, grass in our case. Information on soil moisture is crucial for crop management and overall planning. This is not just true for Ireland but anywhere around the world, since soil moisture drives the need for interventions like irrigation scheduling.

Information on soil moisture can be obtained through various ways. Traditionally, soil moisture would be measured by collecting samples from the field and then taking measurements in the lab. Such methods are time consuming and makes sampling of large geographic areas extremely difficult. This is where remote sensing technology has proved to be very handy and effective.

Satellites that revolve around the earth can provide us with information that would otherwise be very difficult to acquire. Imagine a field on a hill slope and having to sample the field on a very wet day in Ireland or on a very humid day in the tropics. Satellites help cover large geographic areas simultaneously and are also cost-effective. Free satellite imagery helps PhD students like me carry out research seamlessly, bringing to the forefront important issues and their possible solutions.

Soil moisture is one such variable that can be studied through remote sensing. The Sentinel suite of sensors launched by the European Space Agency (ESA) have been very instrumental in this regard. The Sentinel suite of Sensors provide optical and radar imagery in high spatial and temporal resolutions. This means you can look at your field every three to five days and notice any changes in soil moisture taking place from the comfort of your living room. Remote sensing data can help measure changes in soil moisture over time and this, when combined with in situ data and other meteorological data such as rainfall, can help us in knowing about its past and future trends. These trends provide important insights about changes in local and global climate.

Since cloud cover is a major problem in Ireland, it limits the use of optical imagery at times, since optical sensors, like Sentinel 2, cannot penetrate through clouds. However, radar data, like Sentinel 1, can be very useful in such situations since it can see through clouds and can operate even at night. There are numerous such optical and radar satellites that make imagery available free of cost for research purposes and have since been instrumental in answering important questions about our surroundings.

Soil moisture can be monitored effectively using both optical and radar data or a combination of the two. Predictions about soil moisture can help farmers take effective decisions about farm management strategies and achieve higher productivity.

So, the next time it rains, apart from appreciating the lovely flowers around or that bumble bee on your lavender bush, take a moment to bend down, pick up a handful of soil, take in the smell of damp earth, and know what you are holding carries secrets from the past, present and future.

Rumia Basu is a PhD student at Teagasc (VistaMilk) and NUI Galway

This article first appeared on RTÉ Brainstorm. https://www.rte.ie/brainstorm/2022/0915/1323524-satellite-images-soil-monitoring/ 

Read more: The dark mysteries of the soil beneath our feet