On-irrigator moisture sensors for precision irrigation

Abstract

We are developing a method that allows remote soil moisture measurement from electromagnetic sensors that are mounted on irrigators. To do that, techniques from the impulse (ultra-wideband) radar are applied, which enables the measurement of soil reflection at resolutions smaller than the antenna beamwidths of the radar. We derive a relationship between the radar’s parameter (i.e. pulse-width, antenna parameters, radar location and sensing angle with respect to ground level) and the soil surface resolution that the radar is capable of achieving. In addition, we also propose a method to calculate the radar backscatter coefficient of the ground from the signals that are received by the radar. Using the proposed method, radar measurements are performed on pastureland to measure the radar backscatter coefficients of wet grassland at different elevation angles. Measured results show that radar backscatter coefficients can be reliably measured at the angles up to 60 degrees from nadir. This paper presents the progress in our ongoing work to develop a small and practical remote soil moisture measurement for smart irrigation.