Electromagnetic determination of soil water content: Measurements in coaxial transmission lines

Abstract

The dependence of the dielectric constant, at frequencies between 1 MHz and 1 GHz, on the volumetric water content is determined empirically in the laboratory. The effect of varying the texture, bulk density, temperature, and soluble salt content on this relationship was also determined. Time‐domain reflectometry (TDR) was used to measure the dielectric constant of a wide range of granular specimens placed in a coaxial transmission line. The water or salt solution was cycled continuously to or from the specimen, with minimal disturbance, through porous disks placed along the sides of the coaxial tube. Four mineral soils with a range of texture from sandy loam to clay were tested. An empirical relationship between the apparent dielectric constant Ka and the volumetric water content θv, which is independent of soil type, soil density, soil temperature, and soluble salt content, can be used to determine θv, from air dry to water saturated, with an error of estimate of 0.013. Precision of θv to within ±0.01 from Ka can be obtained with a calibration for the particular granular material of interest. An organic soil, vermiculite, and two sizes of glass beads were also tested successfully. The empirical relationship determined here agrees very well with other experimenters' results, which use a wide range of electrical techniques over the frequency range of 20 MHz and 1 GHz and widely varying soil types. The results of applying the TDR technique on parallel transmission lines in the field to measure θv versus depth are encouraging.

Variabilidade de atributos físicos do solo determinados por métodos diversos

“…A técnica de reflectometria de domínio do tempo (TDR) foi utilizada para se determinar a umidade volmétrica do solo com duas repetições (U-TDR09 e U-TDR11), por meio da relação entre a umidade e capacidade dielétrica de um solo mineral conforme equação empírica descrita por TOPP et al (1980) (Equação 1).…”

GPR Estimation of the Geometrical Features of Buried Metallic Targets in Testing Conditions

“…The electromagnetic features of this material, which is nonmagnetic and with negligible losses, were investigated independently through a Time Domain Reflectometry (TDR) analysis [48][49][50]. Such an analysis allowed us to fix the relative dielectric permittivity of the glass beads equal to 3.2 [20,50].…”

Survey and research frame for ground sediment

“…The following researches are based on the equation (Guerif et al 2001). References (Topp et al 1980) obtained the permeability coefficient by fitting and taking moisture as a variable. In the paper (Van Genuchten 1980), the water pressure and moisture can be taken to build a function to determine the relative hydraulic conductivity.…”