Massive, continuous, and non-invasive surface measurement of degree of saturation by shortwave infrared images

Abstract

Short wave infrared (SWIR) image analysis provides an accurate procedure to measure the degree of saturation (Sr) of soils. Changes in Sr result in reflectance changes, which are recorded by a special digital camera optimized for a particular range of wavelengths that provides the maximum resolution of the method. This paper describes the developed methodology that relies on sample-determined calibration of soil reflectance for a few values of Sr covering the dry to fully saturated range of moistures. The accuracy of the method was checked by comparing equilibrated profiles of SWIR-determined Sr with other procedures (sensor readings and water retention information). It was found that the SWIR-based method correlates well with the degree of saturation of the soil but not with its water content, which may change for a given Sr when the soil deforms volumetrically. The transient variations of Sr are also well captured by the method. The recorded evolution of two-dimensional Sr maps of an initially unsaturated soil column compares satisfactorily with the results of a numerical model.