Estimation of bell pepper evapotranspiration using two-source energy balance model based on high-resolution thermal and visible imagery from unmanned aerial vehicles

Authors: TUNCA, E. - Ondokuz Mayis University; KOKSAI, E. - Ondokuz Mayis University; TORRES, A. - Utah State University; Kustas, William - Bill; NIETO, H. - University Of Alcala

Submitted to: Journal of Applied Remote Sensing (JARS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/17/2022
Publication Date: 3/7/2022
Citation: Tunca, E., Koksai, E.S., Torres, A., Kustas, W.P., Nieto, H. 2022. Estimation of bell pepper evapotranspiration using two-source energy balance model based on high-resolution thermal and visible imagery from unmanned aerial vehicles. Journal of Applied Remote Sensing (JARS). 16(2):022204-1-16. https://doi.org/10.1117/1.JRS.16.022204.
DOI: https://doi.org/10.1117/1.JRS.16.022204

Interpretive Summary: Accurate determination of crop water use or evapotranspiration (ET) is vital for agriculture water management. Many satellite-based ET models have been developed to map ET at the field scales, but the spatial resolution of the satellite observations, particularly thermal infrared imagery, is insufficient to estimate ET for small agricultural fields. With the advancement of unmanned aerial vehicle (UAV) technology, high spatial and temporal images can be acquired with UAVs to monitor ET for small fields or even at the plant level. In this study, the Two-Source Energy Balance (TSEB) model to estimate daily and seasonal crop (bell pepper) ET using high-resolution visible and thermal UAV imagery is compared with ET values derived by using a soil water balance approach. The results of this study showed that there is a high correlation between TSEB model and water balance estimates of ET at daily and seasonal timescales with relatively minor differences for daily and seasonal estimates of 0.6 mm and 11 mm, respectively. The sensitivity of TSEB output to the spatial resolution indicated that different pixel resolutions do not significantly impact ET estimates. This study suggests that the TSEB model has potential for agricultural water management applications for small agricultural fields using high-resolution UAV multispectral and thermal imagery.

Technical Abstract: Crop evapotranspiration (ET) is a crucial component of energy and water budgets. The accurate determination of ET is vital for agriculture water management. Commonly, ET at the patch or local scale is estimated by using soil water content profile, lysimeters, and micrometeorological techniques using Eddy Covariance, Bowen ratio, surface renewal, and scintillometer instrumentation. Although these ET methods are widely used and can estimate ET reasonably accurately, they are local observations and do not represent the ET variation at the field, landscape, and regional scales. Thus, several satellite-based ET models have been developed to map ET at the field to regional scales. The spatial resolution of the satellite observations, particularly thermal-infrared imagery, is insufficient to estimate ET for small (<1 ha) agricultural fields. With the advancement of unmanned aerial vehicle (UAV) technology, high spatial and temporal images can be acquired with UAVs to monitor ET for small fields or even at a canopy scale. The aim of this study was the evaluation of the Two-Source Energy Balance (TSEB) model to estimate daily and seasonal crop (bell pepper) ET (ETTSEB) using high-resolution visible and thermal UAV imagery. Also, the impact of using different pixel resolutions (40, 50, 60, and 70 cm) with TSEB is compared with ET values derived by using a soil water budget approach (ETSWD) with a profile soil water content. The results of this study showed that there is a high correlation between ETTSEB and ETSWD values (R2=0.73 for daily, R2=0.98 for seasonal). The RMSE values for daily and seasonal ETTSEB are 0.62 mm day-1 and 11.46 mm season-1, respectively. The sensitivity of TSEB output to the spatial resolution indicated that different pixel resolutions do not significantly impact ET estimates. This study suggests that the TSEB model has a real potential for agricultural water management applications for small agricultural fields using high-resolution UAV multispectral and thermal images.