Estimation of the near surface soil water content during evaporation using air‐launched ground‐penetrating radar

Abstract

Evaporation is an important process in the global water cycle and its variation affects the near surface soil water content, which is crucial for surface hydrology and climate modelling. Soil evaporation rate is often characterized by two distinct phases, namely, the energy limited phase (stage‐I) and the soil hydraulic limited period (stage‐II). In this paper, a laboratory experiment was conducted using a sand box filled with fine sand, which was subject to evaporation for a period of twenty three days. The setup was equipped with a weighting system to record automatically the weight of the sand box with a constant time‐step. Furthermore, time‐lapse air‐launched ground penetrating radar (GPR) measurements were performed to monitor the evaporation process. The GPR model involves a full‐waveform frequency‐domain solution of Maxwell’s equations for wave propagation in three‐dimensional multilayered media. The accuracy of the full‐waveform GPR forward modelling with respect to three different petrophysical models was investigated. Moreover, full‐waveform inversion of the GPR data was used to estimate the quantitative information, such as near surface soil water content. The two stages of evaporation can be clearly observed in the radargram, which indicates qualitatively that enough information is contained in the GPR data. The full‐waveform GPR inversion allows for accurate estimation of the near surface soil water content during extended evaporation phases, when a wide frequency range of GPR (0.8–5.0 GHz) is taken into account. In addition, the results indicate that the CRIM model may constitute a relevant alternative in solving the frequency‐dependency issue for full waveform GPR modelling.

State-of-the-Art Review of Ground Penetrating Radar (GPR) Applications for Railway Ballast Inspection

“…The researchers also analysed the common surface reflection and full-wave inversion methods to retrieve the soil surface dielectric permittivity and correlated water content from air-launched ground-penetrating radar (GPR) measurements [ 120 ]. A later study showed that the full-waveform GPR allowed accurate estimation of the near-surface water content; thus, it was able to monitor the evaporation process [ 121 ]. Some researchers may argue that the high moisture may come from the high ballast fouling, but this is not always the case.…”

Spatiotemporal monitoring of soil water content profiles in an irrigated field using probabilistic inversion of time-lapse EMI data

“…There are numerous empirical and conceptual petrophysical models to relate soil electrical conductivity and water content according to relationship with soil type and salinity (Rhoades et al, 1976(Rhoades et al, , 1989Shutko and Reutov, 1982;Wang and Schmugge, 1980;Wagner et al, 2011). Moghadas et al (2014) showed that for high EM frequencies (MHz or GHz), the models of Shutko and Reutov (1982) and Wang and Schmugge (1980) should be taken into account because of the dispersion phenomenon (ECa increases with frequency). Due to the low operating frequency of the EMI, frequency-dependent petrophysical models are not relevant for our case.…”

Step-Frequency Ground Penetrating Radar for Agricultural Soil Morphology Characterisation

“…Ground Penetrating Radar is a non-invasive geophysical technique [21], which has proven to be very useful in characterising the subsurface properties, such as lithology, porosity, water content, water conductivity, soil moisture, and clay content [22][23][24]. One of the most interesting aspects of the application of GPR technology in agriculture is the estimation of the size, inclination, and spatial pattern of lithological subsurface layers to reveal textural discontinuities.…”