Wireless system gives growers access to soil moisture data

The advance from North Carolina State University is claimed to improve on existing technologies that can be used to inform irrigation practices that improve crop yield and reduce water consumption.

“Estimating soil moisture is important because it can be used by growers to irrigate their fields more efficiently – only irrigating fields when and where the water is needed,” said Usman Mahmood Khan, first author of a paper on the work and a Ph.D. student at NC State. “This conserves water resources and supports things like smart agriculture technologies, such as automated irrigation systems. What’s more, conserving water resources can also help reduce carbon emissions, because less energy is used to pump water through the irrigation system.”

According to NC State, CoMEt does not require any in-ground sensors because it assesses soil moisture using ‘phase,’ which is a characteristic of radio waves that is affected by the wavelength of the radio waves and the distance between the radio wave’s transmitter and the wave’s receiver.

When the signal travels through a medium like air, it will have a specific wavelength but the wavelength changes when the signal travels through a different medium such as soil.

“We know that these phase shifts are also influenced by the amount of water in the soil. If we know how far the signal has travelled, and we measure how a wireless signal’s wavelength has changed, we can determine the phase shift of the signal,” Khan said in a statement. “This, in turn, allows us to estimate the amount of water in the soil.”

CoMEt is said to relay on an above-ground wireless device that transmits radio waves into the soil. Some portion of the radio waves passes through the soil 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.

“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 ground surface,” said Muhammad Shahzad, co-author of the paper and an associate professor of computer science at NC State. “For example, we’ve demonstrated in experimental testing that if we use a signal that is powerful enough to penetrate 38cm into the soil, we are able to assess how the phase of the signal changed at the surface level of soil, 38cm beneath the surface, and at an intermediate level between those two.”

This is possible because the CoMEt device contains multiple antennas, allowing it to capture data from the radio waves that ‘bounce’ out of the soil. The measurements collected by the device’s suite of antennas are then plugged into an algorithm that can determine changes in the signal’s wavelength and how deep the signal travelled into the soil. The team said that this allows the CoMEt device to accurately assess the phase change of the signal, which gives users a soil moisture estimate for the relevant depths.

The team will present their findings at ACM MobiCom in October.

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