## 3 Results
### Benthic Cover  
Uncertainty in the retrieval of endmember benthic cover increased with sensor noise (decreasing _SNR_) and the reference bottom depth (Figure 5). As the bottom depth increased, the lower confidence bound for \(B_{c}^{\prime}\) decreased from the reference condition of 100% coral cover while \(B_{a}^{\prime}\) and \(B_{s}^{\prime}\) increased from the reference condition of 0% cover. Allowing water constituent concentrations and bottom depth to vary across the allowable range (\(S1\)), coral and benthic algae were indistinguishable for \(SNR\) = 100 and \(D_{o}\) > 1.1; \(-1\leq\Delta B_{c}\leq 0\) and 0.79 \(\geq\Delta B_{a}\geq 0\), where \(\Delta\) indicates the difference between the upper and lower bounds of the test conditions and the reference condition. Negative values indicate under estimation of reference benthic cover while positive values indicate overestimation. Increasing \(SNR\) to 500 decreased the underestimation of \(B_{c}^{\prime}\) to \(-0.28\) and the overestimation of \(B_{a}^{\prime}\) to 0.23. This trend continued as \(SNR\) increased to 1000, but the rate of change as a function of \(SNR\) was considerably less. Uncertainty in distinguishing between \(B_{c}^{\prime}\) (or \(B_{a}^{\prime}\)) and \(B_{s}^{\prime}\) was generally lower, due to a greater contrast between the vegetated and uncolonized substrates. The increase in uncertainty in benthic cover with increasing bottom depth is well understood and reported. The impact of \(SNR\) on benthic cover uncertainty was also reported by [PERSON] et al. (2016) and expressed as the statistical overlap between specific conditions with noise applied, but their analysis did not suggest a large impact of \(SNR\) compared with environmental noise. Constraining water constituent concentration to the reference condition (\(S2\)) resulted in a decrease in uncertainty in benthic cover detection regardless of \(SNR\). For example, when \(D_{o}\) = 1.1, underestimation of \(B_{c}^{\prime}\) decreased from the \(S1\) values to \(-0.78\) for \(SNR\) = 100, \(-0.18\) for \(SNR\) = 500, and \(-0.09\) for \(SNR\) = 1000. Detection uncertainty between coral and benthic algae and between vegetated and uncolonized substrates decreased similarly. Incorporating knowledge of bottom depth (\(S3\)) decreased uncertainty further; for \(D_{o}\) = 1.1, the underestimation of \(B_{c}^{\prime}\) decreased to \(-0.58\), \(-0.12\), and \(-0.06\) for \(SNR\) = 100, 500, and 1000, respectively. Figure 4: Uncertainty in water depth (\(\Delta D\)), expressed as the difference between the upper and lower bounds of the test conditions relative to the reference condition, plotted against optical depth (\(D_{o}\)) for variable water constituent concentration (\(S1\), upper figure) and constant constituent concentration (\(S2\), lower figure). Uncertainty in distinguishing between the average coral endmember and the coral species _Porites astroeides_ (\(B^{\prime}_{c,p}\)), scenario _S4_, was consistently greater than the uncertainty in distinguishing between coral and benthic algae because the coral reflectance spectra were more similar to each other than the average coral and algae spectra (Figure 6). At the shallowest depths considered, \(D^{\prime}\leq 3\) m (\(D_{o}\leq 1.3\)), uncertainty in \(B^{\prime}_{c,p}\) was between two and three times greater than the uncertainty in \(B^{\prime}_{a}\). Uncertainty increased with bottom depth and the difference in uncertainty between the coral covers and that of algae gradually diminished as the signatures from each benthic cover gradually became more similar, due to water attenuation. At the same time, detection uncertainty was significantly impacted by sensor noise. At \(D^{\prime}\) = 1 m (\(D_{o}\) = 0.41), uncertainty in coral cover, \(\Delta B^{\prime}_{c,p}\), for \(SNR\) = 100 was 0.29 relative to the reference condition \(B^{\prime}_{c}\) = 1 (100% average coral cover). In other words, a fractional cover of 29% _Porites a._ was confused with 100 % average coral cover.