High-resolution shortwave infrared imaging of water infiltration into dry soil

A novel proximal sensing framework for high-resolution soil water content profile retrieval under laboratory conditions has been developed. Constant-head upward-flow experiments were conducted for a number of soils that cover a wide textural range. The soils were packed into quartz Hele–Shaw cells, and the profile was imaged at high temporal frequency with a shortwave infrared (SWIR) camera in the 900- to 1700-nm electromagnetic domain during upward infiltration of water. The SWIR reflectance recorded for each spatial pixel was converted to soil water content with a recently developed linear physical model. Because of the linearity of the model, its parameters were assumed to be identical at both the pixel and column scales, and this allowed simple self-calibration during the experiment. The obtained water content profiles were in good agreement with soil water content data measured independently with a recently developed time domain reflectometry array with 1-cm depth resolution. In addition, the accuracy of the soil water content profiles was verified based on the water mass balance. The high-spatiotemporal-resolution SWIR reflectance-derived water content profiles allow calculation of water flux densities, which provides a potential new avenue for the rapid estimation of soil hydraulic properties and processes via inverse numerical or analytical modeling.