## 7 Results and Discussion
### Simulation Results with Sunlight
For example, conducting the analyses nearer to the equator may result in a greater preference for the yellow-amber spectrum due to greater availability of sunlight. This study, considering a wavelength resolution of 2.5 nm, further verifies that just the use of bandpass optical filters without any additional special discriminatory characteristics may not be an effective solution due to the downwelling solar spectra encompassing the full visible light spectrum used in UOWC. Instead, for example, a scheme such as differential signaling that incorporates two or more emission spectral bands could be more effective, where a choice of green and yellow wavelengths may benefit link length and the SNR. Where multiple links are to be established, such as for swarming, a depth- and distance-based wavelength division multiplexing scheme may be effective, where a separate wavelength is assigned for bands of distances from the transmitter. This study also provides preliminary insights beneficial for routing operations, where cooperative links would need to shift between carrier wavelengths for maximum performance based on the node depth and intermediate link distances. It also appears more favorable to route through paths beneath the DCM, where transmission distance is a priority or the number of intermediate nodes is limited. This could provide an alternative solution to the issues faced in cooperative UOWC faced by [PERSON] and [PERSON] [62], where their strategy for using shallow-water surface reflections were significantly affected by sunlight. It should further be noted that no modulation scheme was implemented in this analysis, which means that the maximum achievable link lengths as per the modulation scheme will depend on several factors, such as the modulation scheme itself and the bandwidth, dependent on the overall SNR and at which distance is often considered where the forward error correction rate is approximately \(3.8\times 10^{-3}\) on a bit error plot. This distance is expected to be less than that represented by the magenta-colored line for the horizontal profiles. Another limitation of this study is the non-inclusion of the transimpedance circuitry, due to it being an engineering choice, that would have introduced Johnson noise into the system from the gain resistance. However, given that the Johnson noise from an ideal preamplifier of infinite gain is a negligible value, we determine that our findings hold true for this scenario. Furthermore, the variation in salinity gradients and turbulence across the vertical channel have not been implemented in this study for the purpose of limiting the scope of this current work. This is due to its impacts mainly affecting the beam alignment due to refraction in P2P-LOS links with much smaller beam divergent angles with lasers than assessed here \(\left(\theta\ll\frac{\pi}{30}\right)\). Additionally, the perspective of this work was to highlight how choosing an optimal light wavelength could result in a higher SNR. To further limit its impacts, we only considered perfectly horizontal and vertical link establishments. Under the considered stratification model, the horizontal beam travels through the same medium composition and the vertical beams will have an AOI of \(0^{\circ}\) to the stratified layers, thus passing straight through without refraction. Furthermore, the key insights of this study are associated with D-LOS links, where link misalignments have little impact. In waters where salinity and turbulence effects may be prominent, modulation-based strategies, as demonstrated by [PERSON] et al., may be explored to mitigate the effects [63]. We adopted SPCTRL2 to model sunlight due to its relative simplicity for generating the solar spectrum based on location and atmospheric information easily available in the public domain. This is a matter of convenience for on-the-go engineering needs.