## 7 Results and Discussion
### Simulation Results with Sunlight  
For D-LOS horizontal links approaching the DCM, there seems to be a surprising preference for the yellow-amber spectrum for O-SNR (Figure 12a-p) in short-range horizontal links at an average of 25 m or less, in all profiles S1-8, in the upper depth layers. The color preference then alters to green and then blue (with increasing depth) in accordance with the attenuation curves. In P2P-LOS horizontal links (Figure 12q-x), although this yellow preference exists for more coastal profiles, the link lengths are very short and mostly at the level of the DCM. However, for the P2P-LOS clear profiles S1-S4, it is seen that the green wavelengths are preferred more for the depths above the DCM for the sunlit condition than for the night condition. Note that, in the coastal S5, the profile with a 1 W emitter shows an increasing preference for yellow wavelengths closer to its DCM, but this is minimized to a small elliptical region in the 10 W profile, suggesting that the choice of transmission power has a role to play. This is justified when observing that all 120\({}^{\circ}\) D-LOS profiles have greater yellow-amber regions than their 60\({}^{\circ}\) counterparts. This is due to the high geometric losses which have highlighted the yellow-amber spectrum for short link lengths due to being at a higher energy than sunlight's yellow-amber spectrum at these distances. However, due to experiencing higher attenuation, it is then succeeded by the green spectrum with increasing Tx-Rx distance. The greater penetration and availability of sunlight could be the possible reasoning behind why the clear profile S1 shows a greater yellow-amber region than S4: because even though the attenuation distributions for both are the lowest in the blue-green spectrum, the ambient blue-green spectrum in S1 experiences lesser degradation than S4 due to the deeper positioning of the DCM and the lower Chl-\(a\) concentration overall, and therefore is more abundant in the S1 profile. The explicit behavior of the S8 horizontal profiles which consistently showed a yellow-amber layer above the DCM, but below it gradually shifted to green and blue wavelengths, could be explained by referring to its attenuation profile (Figure 7b) that shows a big dip in the attenuation distribution in the amber spectrum at shallower depths but shifting to the blue-green region progressively below the DCM. Due to this, although the transmission parameters may have had some causality, the observations have been overshadowed by the effect from the attenuation profile, and thus may not display a preference based on horizontal link distance. This characteristic is also visible in other coastal profiles, but to a lesser effect due to a less comparable dip in the attenuation coefficient in the yellow-amber spectrum compared with S8. However, as a general trend, the depth of the yellow-amber preferred region is shifted vertically up and extended horizontally for all profiles with an increasing level of turbidity. The lateral observations could be due to the compounded effects of the relatively lesser abundance of the yellow-amber spectrum in downwelling sunlight compared to the blue-green spectrum, the preference of the yellow-amber region in the attenuation curves with increasing turbidity in the shallower regions, and the greater responsivity of the photodetector to these wavelengths, thus achieving longer link lengths there. The preference for shorter wavelengths overall with increasing depth can be explained by considering that the ambient sunlight gets attenuated and filtered in the upper layers, especially in the coastal profiles, where the DCM is closer to the ocean surface, thus promoting the blue-green spectrum for transmission in the lower layers for a higher O-SNR.