Articles
Evaluation of the METRIC EEFlux platform to estimate water use of moringa
Article number
1409_8
Pages
51 – 58
Language
English
Abstract
The Earth Engine Evaporation Flux (EEFlux) application is one of the most recent remote sensing tools developed by Google to automate the processing of spatial data via cloud computing.
The EEFlux application uses the Mapping Evapotranspiration at High Spatial Resolution with Internalized Calibration (METRIC) model to process imagery acquired by Landsat 7, 8 and 9 data sets at a 30 m spatial resolution, and a simultaneous 8-day temporal resolution.
The METRIC EEFlux system has the potential to be a cost-effective and pragmatic approach to acquire accurate spatially explicit crop evapotranspiration (ETa) information, which could be useful for various applications in data-scarce environments.
In this study, we aimed to evaluate the potential of EEFlux to estimate ETa at field-scale through comparisons with in-situ ETa measured by an eddy covariance flux tower in a homogeneous, 9-year-old, drip-irrigated moringa (Moringa oleifera) field situated in Tooseng, Limpopo Province of South Africa.
The results of these investigations indicated that EEFlux generally overestimated ETa with a mean absolute percentage error (MAPE) of 22%. This estimation error may be attributed to the global forcing meteorological data used within the model, and cloud cover that impacts the surface reflectivity values within some of the satellite imagery.
The estimates were improved by using fractional reference evapotranspiration (ETrF) provided by the METRIC EEFlux product and in-situ reference evapotranspiration (ETr) (MAPE of 8%). Further research is required on the analysis of low cloud cover images which affected ETa estimates in this study.
The low cloud cover effect requires evaluation in different seasons, for determining the appropriate correction factors to calibrate the ETrF and incorporating in-situ ETr in determining ETa.
The EEFlux application uses the Mapping Evapotranspiration at High Spatial Resolution with Internalized Calibration (METRIC) model to process imagery acquired by Landsat 7, 8 and 9 data sets at a 30 m spatial resolution, and a simultaneous 8-day temporal resolution.
The METRIC EEFlux system has the potential to be a cost-effective and pragmatic approach to acquire accurate spatially explicit crop evapotranspiration (ETa) information, which could be useful for various applications in data-scarce environments.
In this study, we aimed to evaluate the potential of EEFlux to estimate ETa at field-scale through comparisons with in-situ ETa measured by an eddy covariance flux tower in a homogeneous, 9-year-old, drip-irrigated moringa (Moringa oleifera) field situated in Tooseng, Limpopo Province of South Africa.
The results of these investigations indicated that EEFlux generally overestimated ETa with a mean absolute percentage error (MAPE) of 22%. This estimation error may be attributed to the global forcing meteorological data used within the model, and cloud cover that impacts the surface reflectivity values within some of the satellite imagery.
The estimates were improved by using fractional reference evapotranspiration (ETrF) provided by the METRIC EEFlux product and in-situ reference evapotranspiration (ETr) (MAPE of 8%). Further research is required on the analysis of low cloud cover images which affected ETa estimates in this study.
The low cloud cover effect requires evaluation in different seasons, for determining the appropriate correction factors to calibrate the ETrF and incorporating in-situ ETr in determining ETa.
Authors
K. Muchaonyerwa, S. Gokool, A. Clulow, N.A. Araya
Keywords
eddy covariance, evapotranspiration, fractional reference, Landsat, satellite remote sensing
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