Submitted to: Remote Sensing of Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/16/2016
Publication Date: 7/30/2016
Citation: Kustas, W.P., Anderson, M.C., Alfieri, J.G., Hipps, L. 2016. Using radiometric surface temperature for surface energy flux estimation in Mediterranean drylands from a two-source perspective. Remote Sensing of Environment. doi: 10.1016/j.rse.2016.07.024.
Interpretive Summary: A recent analysis by an international group of researchers of the two-source energy balance (TSEB) model using land surface temperature (LST) developed by ARS scientists over a semiarid Mediterranean grassland indicated that TSEB produced large errors in estimating evapotranspiration (ET). However, an in-depth analysis of the micrometeorological and LST measurements indicated that the site did not have similar energy exchange characteristics observed at many other semi-arid and arid environments evaluating surface energy balance models with LST. This suggests that the results from this study must be treated as unique and with some degree of caution. Consequently, the utility of the TSEB model using LST observations for estimating ET in semi-arid and arid environments is likely still robust and provide reliable ET estimates at watershed and regional scales using satellite data. This is critical information for U.S. and international agricultural and water resource agencies monitoring conditions particularly in water-limited environments where relatively small changes in water resources can have a profound effect on food production.
Technical Abstract: The recent paper by Morillas et al. [Morillas, L. et al. Using radiometric surface temperature for surface energy flux estimation in Mediterranean drylands from a two-source perspective, Remote Sens. Environ. 136, 234-246, 2013] evaluates the two-source model (TSM) of Norman et al. (1995) with revisions by Kustas and Norman (1999) over an semiarid tussock grassland site in southeastern Spain. The TSM - in its current incarnation, the two-source energy balance model (TSEB) - was applied to this landscape using ground-based infrared radiometer sensors to estimate both the composite surface radiometric temperature and component soil and canopy temperatures. Morillas et al. found the TSEB model substantially overestimated the latent heat flux with errors on the order of ~90%. Using the same data set used by Morillas et al., we were able to confirm their results. However, we also found unusual energy transport and exchange behavior required by the observations themselves. This suggests either the environmental conditions of this site or, more likely, the measurements themselves are not consistent with those from previous studies evaluating flux-gradient relationships in semi-arid and arid environments. This suggests the results from Morillas et al. must be treated as unique and with some degree of caution.