distance range up to a few hundred meters [7; 8]. However, these networks must also consider harsh environments with limited bandwidth, high scattering, and absorption effects that cause temporal dispersion and inter-symbol interference (ISI) [9].  
Maintaining optical communication underwater is a crucial task, and it is not feasible to design a communication link with accurate pointing and required performance. That is because of the numerous constraints induced as a result of channel effects. Absorption and scattering are two diverse effects of the same phenomenon, i.e., interaction of light photons with particulate matter and water molecules, leading to path loss, deviation of photons, and degradation in received power [10]. These inherent optical properties of water (i.e., absorption and scattering) can severely contribute to time-varying multipath effects. These multipath effects can be categorized into spatial and temporal dispersion. Spatial dispersion is caused by the spreading of light beam as a result of multiple scattering, consequently reducing the number of photons at the receiver. If light is diffused by nature, spatial spreading may also occur due to initial transmitter beam distribution apart from channel effects [10; 11]. Temporal dispersion, on the other hand, causes the photons to take longer to reach the receiver, thus increasing time delays and path length differences.  
Effects such as absorption can be controlled by (i) operating in the black-green portion of the visible light region, (ii) by using efficient photon receivers, or (iii) by increasing the transmit power [12]. However, effects such as scattering that cause spatial and temporal dispersion can essentially limit the optical communication range and bandwidth. Since scattering is not directly controlled, its effects can be minimized by optimizing the essential system parameters such as FoV, link separation, and aperture. Therefore, it is of key importance to characterize the underwater optical channel and set the essential system parameters to enable high-quality communication. In this paper, we carry out a detailed study on the sources of temporal dispersion in harbor, coastal, and ocean water for underwater wearables operating in shallow waters where optical wireless communication is limited to a few centimeters. Our main contributions can be summarized as follows:  
* We designed a unified system model that accommodates channel loss due to multiple scattering and characterized its respective performances in terms of magnitude response for different system configurations (FoVs, apertures) and water types (clear ocean, coastal, and turbid harbor).  
Figure 1: A general Internet of Underwater Things (IoUTs) framework.  
* We proposed a Monte Carlo-based statistical model that utilizes a discrete histogram of the total received power to characterize temporal dispersion.
* Based on our model, the respective BER and magnitude responses resulting from the temporal dispersion under different FoVs, apertures, and water types are simulated and presented.  
The rest of the paper is organized as follows. In Section 2, we discuss the existing methods of temporal dispersion modeling underwater. In Section 3, we provide analytical details about the simulated underwater environment and our proposed method. Section 4 explains our findings on various system configurations and parameters, and Section 5 compares our methodology. Section 6 concludes our work and suggests future research directions.