Our work on low-cost, high accuracy in-situ soil moisture sensing has been accepted for publication at ACM COMPASS 2021. The paper is titled Low-cost In-ground Soil Moisture Sensing with Radar Backscatter Tags. ACM COMPASS aims to be the forum for the presentation and publication of original research from a broad array of disciplines, including computer and information sciences, social sciences, environmental sciences and engineering, that support the growth of sustainable societies worldwide.
Abstract: Despite decades of research confirming the benefits, most farms do not incorporate soil moisture sensing into their irrigation practices. Soil moisture sensing can be broken into two broad approaches, both of which have drawbacks. In situ sensors are installed in the ground, tend to be difficult to deploy and maintain, and have high costs. Remote-sensing based approaches use radars to infer soil moisture from surface reflection properties. While completely wireless, remote sensing suffers from lower resolution and accuracy compared to in situ sensing.
We propose a hybrid approach that combines the advantages of both. This paper introduces the idea of using inexpensive in situ backscatter tags with above-ground radars, which enables completely wireless soil moisture measurements at low cost and with high-accuracy and high-resolution. Our key idea is introducing a simple, power efficient modulation scheme that enables commodity radars to easily detect and range the underground tag. We have benchmarked our approach against oven-based ground-truth measurements and demonstrated that, at a realistic depth and across several types of soil, we achieve a 90th percentile error of 4%, which is the same accuracy as state-of-the-art in situ sensors. We also demonstrate that our approach works with similar accuracy at a real farm.
Our short paper titled Time-of-Flight Soil Moisture Estimation Using RF Backscatter Tags has been accepted to IGARSS 2020, the IEEE International Geoscience and Remote Sensing Symposium. It was virtually presented in October 2020.
Agricultural soil moisture measurement is usually done with extensive in situ sensor deployments. These sensor networks are often difficult to install and maintain. Ground penetrating radars have also been used to do fine-grained moisture measurements in farm fields, but usually require the radar to be in or near contact with the soil. In this paper we propose a hybrid approach that combines an in situ backscatter reflector with an ultra-wideband radar that is small enough to be handheld or mounted to a drone. The underground backscatter reflector allows for accurate time-of-flight measurements. The time-of-flight is determined by the permittivity of the soil, which is influenced primarily by the soil water content for non-saline soils. We performed both laboratory and in situ measurements, achieving an average accuracy within 0.013 cm3/cm3 of the ground truth with a 90th percentile of 0.034 cm3/cm3. This demonstrates the feasibility of our approach.
We were to present a live demo of our soil moisture sensing work at IPSN ‘20 in Sydney, Australia during April 21-24. Here’s a video for those who can’t make it to Australia: Note: due to the pandemic, IPSN 2020 was virtual, so nobody got to see this in-person.