## 3 UWOC Channel Modeling  
UWOC offers numerous advantages such as high data rates, larger bandwidth, lower time delay, low latency, and reduced power consumption when compared to acoustic and RF technologies. However, the establishment of a wireless optical link underwater poses significant challenges. The main challenge arises from the fact that the optical signal is heavily impacted by the optical characteristics of the medium and disturbances caused by turbulence [30]. The optical properties of water that significantly impact the propagation of optical signals underwater are absorption and scattering. These properties are associated with absorption and scattering coefficients, represented as \(a(\lambda)\) and \(b(\lambda)\), respectively, and depend on the wavelength of the signal. The combined effect of absorption and scattering coefficients is referred to as the beam extinction coefficient, denoted as \(c(\lambda)\). This coefficient, \(c(\lambda)\), quantifies the overall attenuation experienced by the optical signal in water, encompassing both absorption and scattering phenomena as in Equation (1) [31]:  
\[c(\lambda)=a(\lambda)+b(\lambda) \tag{1}\]  
Absorption coefficient \(a(\lambda)\) measures light absorption in water, influenced by water properties and signal wavelength. Scattering coefficient \(b(\lambda)\) indicates light scattering by particles in water, occurring when the particle size is comparable to the light's wavelength. The beam extinction coefficient, represented by \(c(\lambda)\), accounts for both the absorption and scattering coefficients, providing a comprehensive measure of the overall attenuation experienced by optical signals in underwater conditions. The overall absorption \(a(\lambda)\) in underwater optical communication is influenced by several factors given as in Equation (2) [32]:  
\[a(\lambda)=C_{w}a_{w}(\lambda)+C_{phy}a_{phy}(\lambda)+C_{S}a_{S}(\lambda)+C_{ n}a_{n}(\lambda) \tag{2}\]  
where \(a_{w}\) is the absorption due to pure water, \(a_{phy}\) is the absorption due to phytoplankton, \(a_{g}\) is the absorption due to dissolved organic matter, and \(a_{n}\) is the absorption due to non-algal suspended particles. Each of these components contributes to the overall attenuation of optical signals in underwater environments. \(C_{w}\), \(C_{phy}\), \(C_{g}\), and \(C_{n}\) are the absorption coefficients of pure water, phytoplankton, dissolved organic matter, and non-algal suspended particles, respectively. Scattering primarily relies on the dimensions of the particles suspended within a water channel. When the suspended particles are smaller than the wavelength of the optical wave employed for propagation, Rayleigh scattering is observed. Conversely, Mie scattering occurs when the particle size surpasses the wavelength of the optical wave. Various regions of ocean water encompass suspended particles of distinct sizes. In the case of pure ocean water, the predominant presence consists of salts and ions, which possess a size on the same scale as the wavelength of the optical wave used. Consequently, Rayleigh scattering aptly describes the scattering phenomenon in this scenario [33]. The mathematical equation for the Rayleigh scattering coefficient for pure ocean water is given by [31]:  
\[b_{w}(\lambda)=0.005826\,\left(\frac{400}{\lambda}\right)^{4.322} \tag{3}\]  
The equation provided calculates the Rayleigh scattering coefficient based on the wavelength in nm. While scattering has a significant impact on shorter wavelengths, the overall attenuation in pure ocean water primarily occurs through absorption. When ocean water is located near land, it contains particulate and organic matter, leading to scattering as the primary cause of attenuation for optical waves. The scattering phenomenon in ocean water is significantly influenced by the presence of both organic and inorganic particles.