A Microwave Sensor of Moisture Content and Salinity of Soil

Abstract

A new method dedicated to the measurement of the moisture content and salinity of soil is proposed in this paper. The method takes the advantage of the most accurate permittivity sensor available at microwave frequencies based on a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathrm {TE}}_{01\delta }$ </tex-math></inline-formula> mode dielectric resonator providing the effective complex permittivity of the measured mixture. The measurement has been undertaken mostly at 1 GHz due to the fact that conductive losses of liquids are substantially varying with salinity at low microwaves, thus, increasing measurement sensitivity. At first, intrinsic properties of the major components of the soil, such as sand, salt and saline water, are extracted from the effective parameters measured at microwave frequencies and compared with the Maxwell-Garnett mixing rule to extract their intrinsic properties. In case of the soil, the unknown moisture content and salinity are extracted from raw measurement results using an empirical permittivity model of a conductive mixture which, unlike to analytical dielectric mixing rules, accounts for a percolation threshold.