Soil water retention function hysteresis determined by ground-penetrating radar

Abstract:

Soil hydraulic properties, represented by the soil water retention
θ and hydraulic conductivity K(h) functions, dictate water
flow in the vadose zone, as well as partition between infiltration
and runoff. Those functions can be described by several mathematical
expressions, such as the Mualem-van Genuchten (M-vG) function. The
determination of the parameters defining the van Genuchten soil water
retention function is usually done using laboratory experiments, such
as the hanging water column method.

For a few decades Ground Penetrating Radar (GPR) has been known to be an
accurate geophysical method to measure water content variations in
soils. The work presented here is based on mono-offset detection of
hysteresis on the soil water retention curve with on-ground surface
GPR.

Soil surface GPR measurements were acquired above a large column of
sand (40 cm high and 60 cm diameter), using a 1600 MHz antenna, for
variable ground water table depths at hydraulic equilibrium. We
inverted the GPR data to obtain the M-vG parameters considering
hysteresis on the soil water retention curve, using the Shuffled
Complex Evolution (SCE-UA) algorithm. The method is presented on
synthetic examples and on laboratory experiments. Modeling of the
water dynamics were made using Hydrus-1D, GPR data were computed using
GprMax suite programs. The estimated parameters were compared to those
obtained from hanging water column experiments.