# Evaluation of Water and Carbon Estimation Models in the Caatinga Biome Based on Remote Sensing
## 3 Results and Discussion
### Instantaneous Net Radiation Validation  
Table 1 shows the validation of the instantaneous Rn estimated using the two methodologies (Rn 1 and Rn 2) in relation to the observed values. Although the applied methodologies overestimated the field measurements on most days in DC, it is interesting to emphasize the role of the MOD05 product in the results, which caused attenuation in the Rn values. The methodology's performance corroborates other studies, such as those by the authors of [57], who found RMSE values ranging from 61.10 to 82.83 W\(\cdot\)m\({}^{-2}\) when estimating net radiation exclusively from MODIS at eight different locations over the continental United States. The data showed higher values for the SC than for the DC when considering the observed Rn. Observing other values found in the literature leads us to believe that the measurements performed in SC must have had some interference that caused an increase in the observed Rn, making it greater than that in DC. We note that the expected behavior was that higher values of Rn would occur in the dense area in comparison to the sparse area. The land covered by dense vegetation is expected to retain a greater amount of energy. It reflects less incoming radiation (lower albedo), indicating greater energy available to be converted into sensible and latent heat than the sparse area [1]. This can be observed in the results obtained via orbital data, with higher Rn values in DC than in SC. The authors of [1] showed that, in the SC area, the incidence of solar radiation was higher. These results indicate that the high solar radiation in this site may be a crucial contributing factor to the higher values of Rn. These results corroborate those of [24] in the municipality of Petrolina, state of Pernambuco based on simulations of land cover change with the Integrated Biosphere Simulator \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**DC**} \\ \hline \multicolumn{6}{c}{**Average \(\pm\) SD**} \\ \hline  & **Observed** & **Estimated** & **R\({}^{2}\)** & **MAE** & **MPE** & **RMSE** \\ \hline WP & 29.5 \(\pm\) 5.1 & 29.8 \(\pm\) 5.5 & 0.05 & 4.79 & 0.15 & 6.47 \\ \hline Tar & 28.1 \(\pm\) 1.9 & 25.9 \(\pm\) 2.6 & 0.54 & 2.62 & 0.09 & 2.94 \\ \hline R\({}_{n}\) 1 & 614 \(\pm\) 57.8 & 663.1 \(\pm\) 63.2 & 0.02 & 67.47 & 0.11 & 82.63 \\ \hline R\({}_{n}\) 2 & & 647.7 \(\pm\) 67.7 & 0.03 & 61.37 & 0.10 & 76.75 \\ \hline R\({}_{n}\)24 A & & 164.6 \(\pm\) 21.4 & 0.93 & 24.11 & 0.13 & 24.89 \\ \hline R\({}_{n}\)24 B & & 157.5 \(\pm\) 21.1 & 0.93 & 31.18 & 0.17 & 31.72 \\ \hline \multicolumn{6}{c}{**SC**} \\ \hline  & \multicolumn{6}{c}{**Average \(\pm\) SD**} \\ \hline  & **Observed** & **Estimated** & **R\({}^{2}\)** & **MAE** & **MPE** & **RMSE** \\ \hline Tar & 27.2 \(\pm\) 1.9 & 25.9 \(\pm\) 2.7 & 0.61 & 2.13 & 0.08 & 2.34 \\ \hline R\({}_{n}\) 1 & & 589.4 \(\pm\) 63.8 & 0.14 & 74.17 & 0.11 & 86.51 \\ \hline R\({}_{n}\) 2 & & 575.1 \(\pm\) 65.2 & 0.12 & 82.78 & 0.13 & 97.66 \\ \hline R\({}_{n}\)24 A & & 149.2 \(\pm\) 20.4 & 0.73 & 42.76 & 0.23 & 44.01 \\ \hline R\({}_{n}\)24 B & & 142.1 \(\pm\) 20 & 0.76 & 49.82 & 0.27 & 50.78 \\ \hline \end{tabular}
\end{table} 
Table 1: Statistical analyzes for Precipitable Water (WP) in mm, Air Temperature (Tar), in \({}^{\circ}\)C, Instantaneous Net Radiation (R\({}_{n}\) 1 and R\({}_{n}\) 2), in W\(\cdot\)m\({}^{-2}\), and Daily Net Radiation (R\({}_{n}\)24 A and R\({}_{n}\)24 B), in W\(\cdot\)m\({}^{-2}\), for the year 2013 in the DC and SC areas. (IBIS) model. The authors found a decrease in Rn of 35% as a result of the conversion of natural vegetation from Caatinga to Caatinga sparse in relation to the annual average of Rn for the preserved Caatinga. The authors of [58], using Landsat images in a region occupied by dense savanna in the Sao Francisco River Basin, found Rn values of 680.0 to 732.0 W\(\cdot\)m\({}^{-2}\). The areas with open steppe savanna, on the other hand, presented Rn values predominantly between 622.0 and 680.0 W\(\cdot\)m\({}^{-2}\).