# Modelling High-Resolution Actual Evapotranspiration through Sentinel-2 and Sentinel-3 Data Fusion
## 4 Discussion  
### ET Model Intercomparison  
Overall results listed in Table 3 show that TSEB models produced more robust estimates of both sensible and latent heat fluxes, with lower errors around 80 to 90 W m\({}^{-2}\) and larger correlation coefficient, while at the same time returning more valid cases than the other two models, METRIC and ESVEP. Those errors are within the expected and reported errors in literature, e.g., [PERSON] et al. [2] showed errors in \(\lambda\)\(\varepsilon\) ranging between 24 and 105 W m\({}^{-2}\) for a wide range of models, [PERSON] et al. [58] reported errors for TSEB \(>\) 100 W m\({}^{-2}\) in a semi-arid area of Mexico, and 50 W m\({}^{-2}\) errors are reported in [PERSON] et al. [35]. [PERSON] et al. [91] found TSEB-PT and METRIC produced similar errors of 54 W m\({}^{-2}\) in a watershed in Iowa, US. However it is worth noting that most of the reported errors in these studies [35; 58; 91; 92] used actual surface temperature at high spatial resolution (e.g., Landsat or ASTER), whereas in this study we used low resolution temperature sharpened to high spatial resolution, which provides an additional input uncertainty to the models. For that reason, Section 4.2 is dedicated to this issue in depth. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Variable** & **Climate** & **Model** & **N** & **Obs.** & **Bias** & **MAE** & **RMSE** & **rRMSE** & **r** \\ \hline \multirow{6}{*}{H} & \multirow{4}{*}{semi arid} & METRIC & 354 & 190 & 28 & 95 & 149 & 0.780 & 0.270 \\  & & TSEB-PT & 365 & 191 & \(-\)51 & 69 & 84 & 0.438 & 0.676 \\  & & disTSEB & 350 & 191 & \(-\)41 & 64 & 78 & 0.411 & 0.670 \\  & & ESVEP & 296 & 177 & 87 & 155 & 242 & 1.370 & 0.337 \\ \cline{2-10}  & \multirow{4}{*}{temperate} & METRIC & 96 & 126 & 126 & 133 & 182 & 1.441 & 0.356 \\  & & TSEB-PT & 102 & 134 & \(-\)32 & 53 & 71 & 0.530 & 0.635 \\  & & disTSEB & 102 & 134 & \(-\)26 & 52 & 69 & 0.513 & 0.637 \\  & & ESVEP & 90 & 132 & 62 & 92 & 122 & 0.927 & 0.586 \\ \hline \multirow{6}{*}{\(\lambda\)\(\varepsilon\)} & \multirow{4}{*}{semi arid} & METRIC & 335 & 178 & -6 & 90 & 114 & 0.641 & 0.534 \\  & & TSEB-PT & 366 & 170 & 32 & 71 & 86 & 0.504 & 0.763 \\  & & disTSEB & 349 & 171 & 33 & 70 & 85 & 0.498 & 0.776 \\  & & ESVEP & 245 & 202 & \(-\)30 & 103 & 134 & 0.665 & 0.391 \\ \cline{2-10}  & \multirow{4}{*}{temperate} & METRIC & 82 & 295 & \(-\)123 & 140 & 174 & 0.589 & 0.419 \\  & & TSEB-PT & 93 & 289 & \(-\)19 & 79 & 99 & 0.343 & 0.739 \\  & & disTSEB & 93 & 289 & \(-\)10 & 79 & 98 & 0.341 & 0.750 \\  & & ESVEP & 81 & 278 & \(-\)115 & 135 & 157 & 0.564 & 0.646 \\ \hline \multirow{6}{*}{Rn} & \multirow{4}{*}{semi arid} & METRIC & 401 & 442 & \(-\)9 & 42 & 53 & 0.121 & 0.893 \\  & & TSEB-PT & 401 & 442 & \(-\)11 & 47 & 59 & 0.133 & 0.877 \\  & & disTSEB & 376 & 446 & \(-\)8 & 42 & 52 & 0.116 & 0.902 \\  & & ESVEP & 398 & 444 & \(-\)23 & 48 & 62 & 0.140 & 0.876 \\ \cline{2-10}  & \multirow{4}{*}{temperate} & METRIC & 104 & 462 & \(-\)13 & 29 & 38 & 0.082 & 0.976 \\  & & TSEB-PT & 104 & 462 & \(-\)23 & 35 & 43 & 0.093 & 0.975 \\  & & disTSEB & 104 & 462 & \(-\)17 & 31 & 40 & 0.086 & 0.976 \\  & & ESVEP & 98 & 453 & \(-\)26 & 35 & 43 & 0.094 & 0.977 \\ \hline \multirow{6}{*}{G} & \multirow{4}{*}{semi arid} & METRIC & 401 & 84 & \(-\)3 & 41 & 52 & 0.616 & 0.431 \\  & & TSEB-PT & 401 & 84 & 11 & 44 & 54 & 0.643 & 0.398 \\ \cline{1-1}  & & disTSEB & 376 & 86 & 0 & 41 & 50 & 0.582 & 0.467 \\ \cline{1-1}  & & ESVEP & 398 & 84 & 21 & 49 & 61 & 0.727 & 0.316 \\ \cline{1-1} \cline{2-10}  & \multirow{4}{*}{temperate} & METRIC & 97 & 40 & 7 & 36 & 45 & 1.104 & 0.480 \\ \cline{1-1}  & & TSEB-PT & 97 & 40 & 26 & 43 & 55 & 1.362 & 0.399 \\ \cline{1-1}  & & disTSEB & 97 & 40 & 16 & 38 & 51 & 1.272 & 0.358 \\ \cline{1-1}  & & ESVEP & 93 & 39 & 29 & 42 & 53 & 1.355 & 0.477 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Climate dependence of errors for METRIC, TSEB and ESVEP modelled fluxes using Decision Trees sharpened temperatures. N, number of valid cases; \(\overline{\text{Obs.