The dielectric properties of soil‐water mixtures at microwave frequencies

Abstract

Recent measurements of the dielectric constants of soil‐water mixtures have shown the existence of two frequency regions in which the dielectric behavior of these mixtures was quite different. At the frequencies of 1.4–5 GHz there was strong evidence that the variation of the dielectric constant ε with water content W depended on soil type. While the real part of ε, ε′, for sandy soils rose rapidly with the increase in W, ε′, for the high clay content soils rose only slowly with W. As a consequence, ε′ was generally higher for the sandy soils than for the high clay content soils at a given W. On the other hand, most of the measurements at frequencies < 1 GHz indicated the increase of ε with W to be independent of soil types. At a given W, ε′ (sandy soil) ≅ ε′ (high clay content soil) within the precision of the measurements. These observational features could be satisfactorily interpreted in terms of a simple dielectric relaxation model suggested by Schwarz (1962), with an appropriate choice of the mean relaxation frequency ƒm and the range of the activation energy β. It was found that smaller ƒm and larger β were required for the high clay content soils than for the sandy soils in order to be consistent with the measured data. These requirements on ƒm and β were strongly supported by the observed dependence of the soil surface area per unit weight on the soil types.

Synergetic Use of Sentinel-1 and Sentinel-2 Data for Soil Moisture Mapping at Plot Scale

“…It can be seen in Table 3 that the optimal values for the shape and compactness parameters have less variation than the scale parameter for the studied areas. The variation intervals are [0-0.2], [0.4-0.6], and [2][3][4][5][6][7][8][9][10][11][12][13][14][15] for the shape, compactness, and scale parameters, respectively. Object size and consequently the scale parameter appears to have wider variations than those of the shape parameters in the five study areas.…”

“…This capacity is due to the fact that microwave signals are influenced by dielectric properties (and thus the water content) of the soils [2]. It should be noted that other variables (roughness and vegetation) also affect microwave signals and this effect must be disentangled in the retrieval process of SMC from remotely sensed data.…”

Balanço de água por aquisição automática de dados em cultura de trigo (Triticum aestivum L.)

“…A água e o ar no solo determinam as propriedades dielétricas do meio, que é uma resposta dos meios à polarização em campos eletromagnéticos. A água tem constante dielétrica de aproximadamente 81; as partículas minerais, cerca de 4; e o ar, de 1 (Wang, 1980). Se as propriedades dielétricas do solo são diferentes da emitida, alguns sinais refletem e uma parte deles combina-se com os sinais aplicados para formarem uma onda-padrão.…”

Numerical Simulation of the Full-Polarimetric Emissivity of Vines and Comparison with Experimental Data

“…If the soil surface had a certain slope or l x ≠ l y , then e U ≠ 0, but e V = 0. The effect of the volumetric soil moisture (W) is introduced in the model through the simple Wang soil dielectric permittivity model [14], or [15], or more complete models that take into account the soil texture and porosity [16].…”