## 3 Results and Discussion
### Algorithm Tuning and Validation
#### 3.2.2 Algorithm Validation
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Algorithm** & **Waveband** & **N** & \(\mathbf{r^{2}}\) & _RMSE_ & _MAPD_ & \%_Bias_ \\ \hline  & [nm] & & & [nm\({}^{-1}\)] & [\%] & [\%] \\ \hline  & & \multicolumn{4}{c}{**MODIS-Aqua**} \\ \hline
**MLR** & **275-295** & **187** & **0.62** & **0.0034** & **11** & **6** \\
**MLR** & **300-600** & **213** & **0.15** & **0.0023** & **10** & **8** \\
**MLR** & **412-555** & **7825** & **0.06** & **0.0040** & **32** & **23** \\ RFTB & 275-295 & 214 & 0.58 & 0.0033 & 8 & \(-1\) \\ RFTB & 300–600 & 244 & 0.20 & 0.0019 & 8 & 4 \\ Shan11 & 350–600 & 188 & 0.01 & 0.2750 & 427 & 366 \\ TS11 & 412–555 & 6223 & 0.02 & 0.0290 & 217 & \(-209\) \\ \hline  & & \multicolumn{4}{c}{**MODIS-Terra**} \\ \hline
**MLR** & **275-295** & **284** & **0.41** & **0.0039** & **12** & **3** \\
**MLR** & **300-600** & **318** & **0.16** & **0.0024** & **10** & **9** \\
**MLR** & **412-555** & **10719** & **0.06** & **0.0036** & **27** & **20** \\ RFTB & 275-295 & 242 & 0.43 & 0.0000 & 10 & \(-3\) \\ RFTB & 300–600 & 271 & 0.11 & 0.0000 & 8 & 5 \\ Shan11 & 350–600 & 297 & 0.03 & 0.1250 & 255 & 176 \\ TS11 & 412–555 & 8078 & 0.00 & 0.0280 & 208 & \(-203\) \\ \hline  & & \multicolumn{4}{c}{**SeaWiFS**} \\ \hline
**MLR** & **275-295** & **350** & **0.44** & **0.0047** & **14** & **6** \\
**MLR** & **300–600** & **417** & **0.11** & **0.0021** & **8** & **4** \\
**MLR** & **412–555** & **10883** & **0.03** & **0.0029** & **17** & \(\mathbf{-12}\) \\ RFTB & 275-295 & 350 & 0.37 & 0.0053 & 11 & \(-7\) \\ RFTB & 300–600 & 418 & 0.09 & 0.0022 & 9 & 5 \\ Shan11 & 350–600 & 372 & 0.01 & 0.1320 & 202 & 140 \\ TS11 & 412–555 & 4716 & 0.03 & 0.0290 & 203 & \(-198\) \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Validation of algorithms for retrieving CDOM spectral slope (\(S_{g}\)). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Algorithm** & **N** & \(\mathbf{r^{2}}\) & _RMSE_ & _MAPD_ & \%_Bias_ \\ \hline  & & \multicolumn{4}{c}{**[umol} & **[\%]** & **[\%]** \\  & & \multicolumn{4}{c}{**L\({}^{-1}\)]**} & **[\%]** & **[\%]** \\ \hline  & \multicolumn{4}{c}{**MODIS-Aqua**} \\ \hline MLR1 & 164 & 0.23 & 40.8 & 41 & 24.7 \\
**MLR2** & **382** & **0.89** & **27.8** & **16** & \(\mathbf{-13.0}\) \\ RFTB & 161 & 0.57 & 27.3 & 26 & 13.8 \\ \hline  & \multicolumn{4}{c}{**MODIS-Terra**} \\ \hline MLR1 & 158 & 0.23 & 40.2 & 32 & 13.9 \\
**MLR2** & **369** & **0.90** & **26.7** & **15** & \(\mathbf{-12.3}\) \\ RFTB & 114 & 0.47 & 29.4 & 27 & 12.1 \\ \hline  & \multicolumn{4}{c}{**SeaWiFS**} \\ \hline MLR1 & 274 & 0.29 & 34.2 & 34 & 4.5 \\
**MLR2** & **339** & **0.89** & **28.9** & **15** & \(\mathbf{-14.2}\) \\ RFTB & 182 & 0.30 & 25.3 & 23 & 6.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Validation of algorithms for retrieving DOC. As anticipated, MLR retrievals of DOC using ocean color alone were only weakly correlated with field data (i.e., \(\mathrm{r}^{2}<0.3\), Table 8). RFTB performed considerably better, but was unable to match the performance of MLR2 (i.e., regression with retrievals of \(a_{g}\)(355) and known salinity; highlighted in bold in Table 8). Due to the newness of the Aquarius mission, there were too few retrievals available for incorporation in these validation results, and further validation of this approach is encouraged based on these results. We speculated above (Section 3.1) that small differences between the optimization and validation records may bias algorithm performance to favor oceanic waters. To test this hypothesis, a sensitivity analysis was evaluated for CDOM absorption retrieval by MLR to test correlations between algorithm error (percent error between retrievals and field data) and salinity, water column depth, and \(a_{g}\)(412) measured in the field.