Soil Moisture Assessment with a Waveguide Spectrometer

This paper describes a system for soil moisture measurement based on a waveguide spectrometer that acquires “gain” and “phase” spectra, with a frequency range of 1.5 – 2.7 GHz. The fundamental components of the system are a waveguide, containing TX and RX antennas, and an electronic circuit, generating the electromagnetic waves and elaborating data, driven by a microcontroller (MCU). This system was previously tested on samples created in laboratory, but a study of system behavior in environmental conditions was missing. Therefore, acquisition of measurements and samples were conducted on real soil, and these data were used to obtain a good calibration model between spectra and soil moisture values. Calibration coefficients were used to implement the moisture calculation directly in the MCU, obtaining a non-invasive and stand-alone system. The architecture shows promising results and prove the capability of electromagnetic waves to perform accurate and fast silty clay loam moisture assessments on a real environment.