Estimating Plant Transpiration and Soil Evaporation Using Remote Sensing.

Multispectral remote sensing can be used to estimate the components of crop evapotranspiration (ET).  In this study, we used remote sensing imagery of agricultural fields to estimate the daily plant transpiration and soil evaporation components of ET.  To estimate plant transpiration, image data in the near-infrared (NIR) spectral band was plotted versus corresponding image data in the red spectral band.  Crop ground cover (GC) was then estimated for the crop from the Perpendicular Vegetation Index (PVI).  Crop potential ET (PET) was calculated assuming a uniform, non-stressed plant canopy with 100% GC using the Penman-Monteith (P-M) Equation.  Plant transpiration for the crop was then estimated as the product of GC and crop PET.  Soil evaporation was estimated based on soil surface wetness (SSW).  SSW was determined from where the PVI intersected the bare soil line in the scatterplot of NIR and red image data.  Soil PET was calculated using P-M assuming a uniform wet soil surface.  Soil evaporation was then estimated from soil PET and a drying function based on SSW.