Surface energy fluxes in the Northeast Asia ecosystem: SEBS and METRIC models using Landsat satellite images

• Published in: Agricultural and forest meteorology 2015-12, Vol.214-215, p.60-79
• Main Authors: Liaqat, Umar Waqas, Choi, Minha
• Format: Article
• Language: English
• Subjects: Balances (scales); Bias; Calibration; Eddy covariance; Errors; Evapotranspiration; Fluxes; Intercomparison; Mathematical models; Regional; Remote sensing; Surface energy; Surface energy budget
• ISSN: 0168-1923; 1873-2240
• DOI: 10.1016/j.agrformet.2015.08.245

•SEBS and METRIC modeled fluxes were validated with closed and un-closed EC measurements.•Both the models were verified with relatively identical error ranges for estimating ET.•They showed fully contrasted outputs of G and H at both tower and spatial scale.•An albedo-based method performed best than fractional vegetation cover method for estimating G.•A sensitivity analysis described the influence of major parameters on performance of two models. The reliable assessment of turbulent heat fluxes and evapotranspiration (ET) from the field to regional scales is fundamental to comprehending land-atmosphere interactions and water balance dynamics. In this study, we evaluated two single-source operational methodologies, the Surface Energy Balance System (SEBS) and Mapping Evapotranspiration at high Resolution with Internalized Calibration (METRIC), to scrutinize the surface energy balance components using Landsat TM/ETM+ images collected between 2002 and 2013. Estimations from the models were compared with ground observations from two grassland and two cropland AsiaFlux tower sites. To examine model behaviors adequately, both SEBS and METRIC were parameterized using the same predictions of instantaneous and daily net radiation (RN). The RN estimations were quite promising; the ensemble averaged (from all sites) bias and root mean square error (RMSE) were within 39Wm−2. In terms of the soil heat flux (G) and sensible heat flux (H), both models showed various contrasted outputs at the tower and spatial scales, yielding a maximum difference of 77Wm−2. The estimated G from the albedo-based method (METRIC) had low bias and RMSE within 46Wm−2, whereas that obtained from the fractional vegetation cover based method (SEBS) exceeded 125Wm−2. However, the SEBS model performed better for H estimations, yielded less bias and an RMSE (averaged) within 82Wm−2, compared with errors of 102Wm−2 obtained from METRIC. The slightly higher errors in METRIC were caused by its original design based on internal calibration, which lumped the maximum biases from other variables into the estimated H. The errors in G (SEBS) were almost equal to the errors in H (METRIC) but of the opposite sign. Because the latent heat flux is calculated as a rest-term, the errors in G and H compensate for each other. Therefore, both models performed similarly in consistently overestimating the latent heat flux (LE) and corresponding daily ET because of energy balance misclosure in the eddy covariance flux