Application of High-Resolution Thermal Imaging and Novel Heat Pulse Technology to Quantify Soil Evaporation.

Soil-water evaporation is a key process coupling heat and energy exchange between land and atmosphere. It is therefore a critical component of both the surface energy balance and the hydrologic cycle, especially in arid and semi-arid regions of the world. It is a process, which if unmanaged, can lead to considerable loss of water in both irrigated agriculture and urban landscaping. Prevention of evaporative loss of water demands advanced management strategies that rely on better predictive capabilities of evaporation rates. Prediction of evaporation rates from porous media suffers from a lack of detailed knowledge regarding underlying physical processes. It thus becomes imperative to contribute to a more comprehensive understanding of underlying processes to provide better capabilities for prediction of evaporation rates. Evaporation is jointly controlled by atmospheric demand and soil properties. The shift in the control causes a transition in evaporation rate from a high and constant rate (first stage) to a falling rate (second stage). We conducted preliminary laboratory experiments with differently textured soils to measure evaporation rates from soil columns under various atmospheric evaporative demands. This enabled prediction of the first stage of evaporation duration, exhibiting the highest water losses. In addition, small lysimeters were used under laboratory conditions to conduct an evaporation study from fully saturated soils with textural contrast employing high resolution thermal imaging and a recently developed array of penta-needle heat pulse probes (PHPP). Insights gained from application of thermal imaging in conjunction with PHPP measurements coupled with physically based modeling provide a novel approach to precision evaporation determination. When scaled to field and landscape scale these approaches can be used to predict large-scale evapotranspiration based on thermal satellite images that are available in relatively high resolution. Both novel methods, though in an early stage of development, showed remarkable potential for measurement and prediction of soil evaporation.