Abstract
This paper will show the electronic architecture of a portable and non-invasive soil moisture system based on an open rectangular waveguide. The spectral information, measured in the range of 1.5–2.7 GHz, is elaborated on by an embedded predictive model, based on a partial least squares (PLS) regression tool, for the estimation of the soil moisture (%) in a real environment. The proposed system is composed of a waveguide, containing Tx and Rx antennas, and an electronic circuit driven by a microcontroller (MCU). It will be shown how the system provides a useful and fast estimation of moisture on a silty clay loam soil characterized by a moisture range of about 9% to 32% and a soil temperature ranging from about 8 °C and 18 °C. Using the PLS approach, the moisture content can be predicted with an R2 value of 0.892, a root mean square error (RMSE) of 1.0%, and a residual prediction deviation (RPD) of 4.3. The results prove that it is possible to make accurate and rapid moisture assessments without the use of invasive electrodes, as currently employed by state-of-the-art approaches.
Highlights
In the last decade, the indirect techniques for soil moisture assessment have become increasingly important as alternative tools to the standard time-consuming thermo-gravimetric method [1].These techniques are based on the assessment of physical and chemical soil properties and are crucial in the new “precision agriculture” application field
A considerable part of literature is focused on the inference of moisture on soil dielectric properties [2], variables that describe the electric polarization of the matter when subject to an external electric field
In a previous work [4], we explored the potentiality of a non-invasive technique based on an open-ended waveguide for the prediction of the soil moisture content, starting from “gain” and “phase” spectral data acquired on samples of different types of soils in controlled lab conditions
Summary
The indirect techniques for soil moisture assessment have become increasingly important as alternative tools to the standard time-consuming thermo-gravimetric method [1]. These techniques are based on the assessment of physical and chemical soil properties and are crucial in the new “precision agriculture” application field. A considerable part of literature is focused on the inference of moisture on soil dielectric properties [2], variables that describe the electric polarization of the matter when subject to an external electric field. The complex (or apparent) relative dielectric permittivity is defined by real and imaginary components.
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