The utility and applicability of vegetation index based models for the spatial disaggregation of evapotranspiration

Authors: MUNUSAMY, S - Indian Institute Of Technology; RAJASEKJARAN, E - Indian Institute Of Technology; SARASWAT, D - Purdue University; Kustas, William - Bill; BAMBACH, N - University Of California, Davis; MCELRONE, A - US Department Of Agriculture (USDA); CASTRO, S - University Of California, Davis; PRUEGER, J - US Department Of Agriculture (USDA); Alfieri, Joseph; ALSINA, M - E & J Gallo Winery

Submitted to: Irrigation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/12/2024
Publication Date: 8/8/2024
Citation: Munusamy, S., Rajasekjaran, E., Saraswat, D., Kustas, W.P., Bambach, N., Mcelrone, A., Castro, S.J., Prueger, J.H., Alfieri, J.G., Alsina, M.M. (2024) The utility and applicability of vegetation index based models for the spatial disaggregation of evapotranspiration. Irrigation Science. https://doi.org/10.1007/s00271-024-00963-1.
DOI: https://doi.org/10.1007/s00271-024-00963-1

Interpretive Summary: Estimating evapotranspiration (ET) at finer spatial resolution is key for agricultural water management of individual fields and therefore spatial disaggregation is often used to improve the resolution of ET estimated from satellite data. Two vegetation index-based ET disaggregation models, the Disaggregation of Solar Radiation factor (DiSoRa) and the Multi-Sensor data fusion-ET (MSDF-ET) method are applied to disaggregate Landsat 30 m to 3 m resolution using images from PlanetScope to vineyards in California, USA and the other in Maharashtra, India. The DiSoRa disaggregation model estimated ET performed more consistently throughout the growing season when compared to ground truth measurements from both sites. This relatively simple model when combined with other modelling approaches can potentially provide near-continuous field scale ET especially during the main crop growth stages and therefore has potential to provide very useful information for precision irrigation scheduling.

Technical Abstract: Estimating evapotranspiration (ET) at finer spatial resolution is key for agricultural water management. Spatial disaggregation is often used to improve the resolution ET estimated from satellite data and we aim to test two vegetation index-based ET disaggregation models; Disaggregation of solar radiation factor (DiSoRa) and Multi-Sensor data fusion-ET (MSDF-ET) for disaggregating ET estimated from Landsat at 30 m to 3 m resolution using images from PlanetScope constellation of satellites. Two vineyards, one in California, USA and the other in Maharashtra, India were chosen for the study. ET at 30 m was estimated using the two-source Soil Plant Atmosphere and Remote Sensing Evapotranspiration (SPARSE) model and the validation was carried out using eddy covariance observations. The sensitivity of the disaggregation models to NDVI was tested and using NDVI from different sensors during the disaggregation process significantly affected the accuracy of disaggregation. The MSDF-ET model, which is based on a simple linear relationship between ET and NDVI, performed better under non-water stress conditions and during active crop growth stages of the crop. During the crop maturity stage, the errors in disaggregated ET from the MSDF-ET model increased significantly. The DiSoRa model performed more consistently exhibiting similar performance during all stages of crop growth. These simpler models when combined with other modelling approaches can potentially provide near-continuous field scale ET especially during the main crop growth stages.