We introduce a method to calculate evapotranspiration (ET) for individual plots in agricultural fields using the TSEB (Two-Source Energy Balance) model for high resolution thermal data from a UAS (unmanned aerial system). The model was developed for satellite remote sensing which has coarser spatial and temporal resolution. With the emergence of UAS remote sensing, this model needs to be adapted to be applied to the significantly higher resolution imagery. The average resolution of our thermal dataset is about 5 cm, which means we have multiple temperature measurements for a single plant, as opposed to satellite imagery which often views entire fields. The image resolution also means that soil contributes to overall temperature for certain pixels as well. A new algorithm is developed to classify pixels into 3 categories: soil, plant and mixture of soil and plant. Temperature distributions of plants are established and with other inputs like solar radiation, wind speed, plant height, we estimate ET distributions. Distributions of ET are acquired for the targeted plots in multiple images, and are evaluated versus stomatal conductance measurements from a steady state porometer.
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