A novel spectroscopy-based method using monopole antenna for measuring soil water content

• Soil water content can be determined by simply measuring resonant frequency. • Only monopole antenna to frequency scan soil, emitting and receiving EM waves. • Easy operation and high accuracy; air gap has little effect on measurement results. • Pick 2.4–2.5 GHz frequency range to tradeoff penetration depth and energy efficiency. • Potential to implement measuring soil particle size and material. Soil water content measurement is indispensable to precision agriculture. A novel soil water content measuring method based on frequency scanning is proposed in this research. The measuring system consists of a monopole antenna to emit and receive electromagnetic waves as well as a network analyzer. The soil equivalent circuit model is presented and its spectroscopy is obtained by comparing incident and reflected waves. The results indicate that the resonance frequency shifts towards the low frequency region as soil moisture increases, therefore soil water content can be obtained simply by detecting resonance frequency. The linear fitting curve has a determination coefficient of 0.9834 and a root mean square error of 1.4%. The measuring range from 5.0% to 37.4% is wide enough for actual agricultural production. The method offers a productive solution for soil water content measurement and provides an idea to sense other soil characteristics.