Abstract
Soil morphology plays a fundamental role in the vertical and lateral movements of solutes and water transport, providing knowledge regarding spatial distribution of its textural properties and subsurface dynamics. In this framework, the measured values of electrical conductivity are able to reveal the heterogeneity of soil that is present in a particular agricultural field and they are affected by more than one important physical characteristic: soil texture, organic matter, moisture content, and the depth of the clay pan. In the microwave region, these dynamics are known to exhibit a frequency dependent behaviour. This study explores the application of a Step Frequency Continuous Wave Ground Penetrating Radar (SFCW GPR) to shed light on the practical impact that these dependencies have on the imaging results, not only regarding the electrical characterisation of the subsurface morphology, but also in its correct interpretation. This information is of notable importance for determining water-use efficiency and planning precision-agriculture programs. The results clearly show visible and significant fluctuations of the amplitude levels, depending on the considered central frequency, demonstrating that the frequency dependence of electromagnetic properties of heterogeneous soil are significant and cannot be ignored if the aim is to properly define the subsurface attributes. The measurements also suggest that correlating the delineated variations might help in the identification of extended features and the classification of areas that possess similar properties in order to increase the confidence in monitoring soil resources.
Highlights
The information that was obtained from monitoring soil properties at agricultural sites is critical for optimising crop quality, achieving high irrigation efficiencies, and minimising the potential environmental impacts of farming
This study explores the application of a Step Frequency Continuous Wave Ground Penetrating Radar (SFCW GPR) to shed light on the practical impact that these dependencies have on the imaging results, regarding the electrical characterisation of the subsurface morphology, and in its correct interpretation
It can be seen that, what has been described in Figure 8 reflects in its correspondent histogram, as the sharp shape of the distribution (y-axis) defines an image, in which there are a limited number of amplitude levels
Summary
The information that was obtained from monitoring soil properties at agricultural sites is critical for optimising crop quality, achieving high irrigation efficiencies, and minimising the potential environmental impacts of farming Characterising such properties can be difficult, as the governing physical and chemical parameters are often both spatially and temporally variable, and obtaining sufficient measurements to describe the heterogeneity can be prohibitively expensive [1,2,3,4]. Soil layer properties influence water percolation, causing a distinct layering of soil water above the impeding layer that can be formed by a clay layer, dense till, or sand lens All of these functional variables are closely related to the soil electromagnetic properties, which measures the ability of a material to conduct an electrical current. Because the spatial pattern for crop yield commonly exhibits a strong correlation with the electrical conductivity pattern, which is in turn governed by lateral changes in soil properties, it becomes apparent that conductivity maps have potential as a valuable precision agriculture tool [5]
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