Impact of the spatial resolution on the energy balance components on an open-canopy olive orchard

• Published in: International journal of applied earth observation and geoinformation 2019-02, Vol.74, p.88-102
• Main Authors: Ramírez-Cuesta, J.M., Allen, R.G., Zarco-Tejada, P.J., Kilic, A., Santos, C., Lorite, I.J.
• Format: Article
• Language: English
• Subjects: Energy balance; Evapotranspiration; METRIC model; Spatial resolution
• ISSN: 1569-8432; 1872-826X
• DOI: 10.1016/j.jag.2018.09.001

•First time that METRIC model has been run using very-high spatial resolution images.•Spatial resolution affects evapotranspiration estimation in heterogeneous systems.•Sensible and latent heat fluxes are the most scale-sensitive energy balance components. The recent technical improvements in the sensors used to acquire images from land surfaces has made possible to assess the performance of the energy balance models using unprecedented spatial resolutions. Thus, the objective of this work is to evaluate the response of the different energy balance components obtained from METRIC model as a function of the input pixel size. Very high spatial resolution airborne images (≈50 cm) on three dates over olive orchards were used to aggregate different spatial resolutions, ranging from 5 m to 1 km. This study represents the first time that METRIC model has been run with such high spatial resolution imagery in heterogeneous agricultural systems, evaluating the effects caused by its aggregation into coarser pixel sizes. Net radiation and soil heat flux showed a near insensitive behavior to spatial resolution changes, reflecting that the emissivity and albedo respond linearly to pixel aggregation. However, greater discrepancies were obtained for sensible (up to 17%) and latent (up to 23%) heat fluxes at spatial resolutions coarser than 30 × 30 m due to the aggregation of non-linear components, and to the inclusion of non-agricultural areas in such aggregation. Results obtained confirm the good performance of METRIC model when used with high spatial resolution imagery, whereas they warn of some major errors in crop evapotranspiration estimation when medium or large scales are used.