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North Carolina State University researchers have developed a wireless system that uses radio transmitters and receivers to estimate soil moisture in agricultural fields at multiple depths in real time, improving on existing technologies that can be used to inform practices of irrigation that both improve crop yield and reduce. water consumption

“Estimating soil moisture is important because growers can use it to irrigate their fields more efficiently, only irrigating fields when and where water is needed,” says Usman Mahmood Khan, first author of ‘an article about the work and Ph.D. . student at NC State. “This conserves water resources and supports things like smart farming technologies, such as automated irrigation systems. In addition, conserving water resources can also help reduce carbon emissions, because less is used energy to pump water through the irrigation system.”

The new technology, called Contactless Moisture Estimation (CoMEt), does not require any sensors on the ground. Instead, CoMEt assesses soil moisture using something called “phase,” which is a characteristic of radio waves that is affected by both the wavelength of the radio waves and the distance between the transmitter and the the radio wave and the receiver of the wave.

Wireless signals are radio waves, and the medium these signals travel through affects the wavelength of those radio waves. When the signal travels through a medium such as air, it will have a specific wavelength. But when the signal travels through a different medium, such as the ground, its wavelength changes.

“We know that these phase changes are also influenced by the amount of water in the soil. If we know how far the signal has traveled and measure how the wavelength of a wireless signal has changed, we can determine the change of signal phase,” says Khan. “This, in turn, allows us to estimate the amount of water in the soil.”

CoMEt is based on a ground-based wireless device that transmits radio waves to the ground. Some of the radio waves pass through the ground before being reflected back into the air, where the wireless device can receive the signal and measure the phase shift. The system allows users to assess soil moisture at multiple depths by increasing the power of the transmitted signal: the stronger the signal, the deeper the assessment.

“This process allows us to assess soil moisture at multiple depths using a single signal, without using any sensors in the soil or in contact with the soil surface,” says Muhammad Shahzad, co-author of the paper and associate professor of computer science. at NC State. “For example, we have shown in experimental tests that if we use a signal powerful enough to penetrate 38 centimeters into the ground, we can evaluate how the phase of the signal changed at the surface level of the soil, 38 centimeters below the surface and at an intermediate level between these two.”

This is possible because the CoMEt device contains multiple antennas, allowing it to capture a significant amount of data from the radio waves that “bounce” off the ground. The measurements collected by the device’s array of antennas are connected to an algorithm that can determine both changes in signal wavelength and how deep the signal traveled into the ground. This allows the CoMEt device to accurately assess the phase shift of the signal, which in turn provides users with an estimate of soil moisture for relevant depths.

“It’s important to estimate soil moisture at multiple depths, because farmers often need to maintain certain moisture levels at different depths depending on the crop and where they are in the crop cycle,” explains Khan.

“We think CoMEt could be used in multiple ways,” says Shahzad. “Growers could manually move the CoMEt device to measure soil moisture at various points in the field; they could use CoMEt in conjunction with a manually operated drone to assess soil moisture; or they could use CoMEt with an automated drone that flies over a defined pattern . the countryside.”

Technologies currently used by growers to measure soil moisture are based on ground sensors. However, this approach requires farmers to place multiple sensors around the field in order to capture moisture levels, as moisture levels vary due to differences in drainage, proximity to irrigation lines , etc. For large fields, growers need a lot of sensors, and that gets expensive.

“We think it would be possible to make CoMEt devices for about the same amount of money as an accurate sensor on the ground,” says Khan. “But when a grower would only need one CoMEt device, they would have to buy quite a few sensors on the ground to collect the same amount of soil moisture information. In short, we think CoMEt would be significantly more cost-effective.

“Also, installing and maintaining sensors on the ground is time-consuming and inconvenient. And CoMEt requires neither.”

“Right now, we’re looking for industry partners to explore how we can get this technology into the hands of growers who will be able to make use of it,” says Shahzad.

The paper, “Estimating Soil Moisture using RF Signals,” will be presented at the 28th Annual International Conference on Mobile Computing And Networking (ACM MobiCom), which will be held October 17-21 in Sydney, Australia.