## 6 Simulation and Parameters
### Simulation  
The simulation was conducted using MATLAB. First, the horizontal UOWC link configuration (Figure 8a) was simulated for a \"night\" condition, with no downwelling sunlight. This would show link behavior as such when only attenuation was the link determining factor. Possible lunar radiation was not applied due to reasons mentioned in Section 4.1. Thereafter, each water profile was simulated with sunlight for the configurations shown in Figure 8a,b. S1-S4 were modeled for a depth of 250 m, and S5-S8 up to 110 m, due to Chl-_a_ concentrations reaching near zero. Given these depths are below the DCM, they are sufficient for observing the nuanced characteristics of the profiles. The horizontal link distance was simulated up to about 100 m for D-LOS links and about 300 m for P2P-LOS links, seen in the results to be the sufficient upper limit for link lengths. S9 was not modeled due to its lack of completeness in parameterization with its Chl-_a_ concentration data from just 18 samples being limited to the near-surface water [34], but observations made for S8 as the next most coastal profile, may be extended for S9. Reflections at the air-water boundary were not included due to it being a non-line-of-sight path, which may contribute to both noise and gain depending on the delay spread, which is a consideration in modulation, not in the scope of this analysis. The sun was assumed to be at zenith, directly above the ocean surface. This negated the peaking of the underwater radiance at the solar azimuth at shallow depths, which would have caused the receiver to experience more light facing toward this direction and lesser light when turned away for the horizontal UOWC link configuration compared to the average value this model assumes. This was due to the lack of radiance data that corresponded to these water profiles to model otherwise. Despite it, this is a reasonable assumption, given that the underwater radiance reaches an \"asymptotic form\" with increasing depth, where the light field becomes increasingly diffuse and peaks at the zenith [48]. The 10 nm bandwidth resolution from SPCTRL2 was interpolated to a resolution of 2.5 nm, the minimum resolution to which coefficients in Section 5.1 were evaluated for. Results have been discussed for S1 (most clear ocean), S4 (least clear ocean), S5 (least coastal) and S8 (most coastal profile). Blackbody radiation was not included in this model because this radiation peaks in the IR spectrum for an ambient temperature of 300 K and spectral magnitudes less than 1% of the typical noise-equivalent power of the PD of 4 \(\times\) 10\({}^{-14}\) W/\(\surd\)Hz, suggesting an insignificant contribution as noise. We asked two questions. Firstly, how does changing emission parameters such as transmit power and beam divergence angle at each wavelength in the visible spectrum affect the overall O-SNR observed at the receiver under changing attenuation and sunlight conditions for horizontal and downlink orientations? Secondly, for a given set of transmission parameters, could altering the transmission wavelength help achieve longer link establishment distances in these environments, and if so, what is the observed trend?