## 3 Results
### Validation
#### 3.2.2 In Situ Spectrometry Waters Quality Algorithms  
The best algorithms for the five water quality variables analyzed in this study are summarized in Table 5. The rest of the results can be consulted in Tables 2-7 (Appendix B). The following aspects were taken into account to choose the best algorithms: the validation statistics, the Rrs validation results, the number of available samples (quality flags and match-up exercise for C2-Nets), and the wide of used data range. The best result for SDD was obtained with the Blue/Green ratio (\(R492/R560\)) using 111 data points and the Polymer program; and used AC which obtained the best Rrs validation results for the bands (Table 5). However, observing all the results in Table 2, the lowest RMSE (1.38 m) was obtained with C2X using the R560/R704 ratio and 42 data points, but obtaining the same RRMSE (47%). Regarding the bias, the lowest value was obtained with C2 RCC (0.07 m) using R492/R704 ratio and 86 data points, but the RMSE (2.32 m) and RRMSE (59%) were higher (Table 2). Although overall CDOM results were not very good (Table 3), the best results for all the validation statistics except for bias were obtained with C2 XC using the \(R704/R492\) ratio and 46 data points (Tables 5 and 3). For the bias, the lowest value (0.08 \(\upmu\)g/L QSE) was recorded by applying the R560/R704 ratio to Polymer (Table 3). \begin{table}
\begin{tabular}{c c c c c c c c} \hline Variable & \(N\) & **Range** & **Bands Relation** & **AC** & **R\({}^{2}\)** & **RMSE** & **RRMSE** & **Bias** \\ \hline SDD (m) & 111 & 0.35-9.33 & \(R492/R560\) & Polymer & 0.636 & 1.59 & 47 & 0.47 \\ CDOM (\(\upmu\)g/L QSE) & 46 & 0.03-17.5 & \(R704/R492\) & C2 XC & 0.797 & 0.42 & 87 & 0.32 \\ TSS (mg/L) & \(>\)20 & 70 & 0.67-19.76 & \(R704\) & Polymer & 0.920 & 13.3 & 25 & 0.97 \\ CL\({}_{1}\)A & \(<\)5 & 44 & 0.59-49.46 & log\({}_{10}\) [max. (R443; R492)/R560] & C2 XC & 0.376 & 0.93 & 51 & 0.01 \\ (mg/m\({}^{3}\)) & \(>\)5 & 42 & 5.02-30.96 & \(R560/R665\) & Polymer & 0.927 & 28.1 & 50 & 1.35 \\ FC (mg/m\({}^{3}\)) & 45 & 0.751.1 & \(R704/R665\) & C2 XC & 0.968 & 38.9 & 39 & 5.45 \\ \hline \end{tabular}
\end{table} 
Table 5: Best validation results for in situ spectrometry waters quality algorithms and AC type. Considering all the mentioned aspects, TSS results demonstrate that R704 is the best band for suspended matter estimation because it was the one that obtained the best results for the two validated algorithms, for values below and above 20 mg/L (Tables 5 and A4). Applying the algorithm for values below 20 mg/L, the best AC was Polymer, with the best R\({}^{2}\) and RMSE. The lowest RRMSE of 29% (Table A4) was obtained with C2X for a range with a lower limit than Polymer. To validate the algorithm for data greater than 20 mg/L, there were very few data points available for the C2-nets, three or four, so Polymer, with 13 data points and its good validation statistics results, was considered the best result. The lower threshold of 0.015 sr\({}^{-1}\) to the R704 band was determined to facilitate the algorithm application for concentrations above 20 mg/L. With the Chl_a values, like TSS, different algorithms were validated for concentrations below and above 5 mg/m\({}^{3}\) of Chl_a. For lower values, only one algorithm was tested, and although all the coefficients of determination obtained were low (Table A5), the best results for the rest of the validation statistics were obtained with C2 XC (Tables 5 and A5). Considering the decision aspects, for values above 5 mg/m\({}^{3}\), the best result was obtained with the Green/Red ratio (R560/R665) using 42 data points and Polymer AC (Tables 5 and A6). With Polymer, the lowest RRMSE was obtained using the largest number and widest range of data, and although the other validation statistics were not the best, its values were very close to the other AC validation statistics. The lower threshold of 0.8 sr\({}^{-1}\) to the ratio \(R704/R665\) was determined by [PERSON] et al. [6] to facilitate the algorithm application for concentrations above 5 mg/L.