MEASUREMENT OF SOIL WATER DIFFUSIVITY OF AN UNDISTURBED FOREST SOIL USING DUAL-ENERGY GAMMA RADIATION TECHNIQUE

Abstract

A procedure is described to measure the soil water diffusivity of a heterogeneous porous medium, a clay-loam forest soil. A dual-energy gamma-ray apparatus was used to determine nondestructively water content variations in soil samples during infiltration. The general principles of the dual-source technique (in particular correction of the Compton effect caused by cesium photons in the americium window) are reviewed, and a calibration method to determine the mass attenuation coefficients of soil is described. Infiltration measurements on disturbed soil samples were obtained by dual-energy gamma-ray technique to validate the calibration procedure. Imbibition tests were done on undisturbed soil core samples, and the soil water diffusivity of soil was calculated with a classical Boltzmann method. An optimization technique was used to determine the parameters of the hydraulic diffusivity model.