## 3 Types of Underwater Communication Systems
### Underwater Wireless Communication
[10] highlighted the successful implementation of underwater radio systems by Wireless Fibre System (WFS) Technologies in 2007, with further developments between 2008 and 2011 in various regions around the world, demonstrating notable progress. Collaborative efforts by companies such as WFS Technologies, Fugro Subsea Technologies, and Viper Subsea Ltd have led to the creation of reliable underwater radio communication systems, overcoming many of the common barriers associated with underwater communication [10]. These radio communication systems enable remote connectivity and management of subsea equipment [10]. Sound travels 4.5 times faster in water than in air [17; 59], which contributes to the longer historical application of underwater acoustic communication (UWAC) compared to underwater optical communication (UWOC). For instance, the transmission between nodes and the buoyant gateways in a USWN system UWAC is used due to its long-range transmission capability despite its low bandwidth and high latency [5; 21]. The communication advantage is primarily attributed to the extended propagation range and low attenuation associated with UWAC [61]. UWAC, also known as hydroacoustics, is an established system used in both military and civilian applications, including sensor networks, gaining traction since the 1980s using the same single-sideband terrestrial radio approach [91]. For example, the a US military underwater communication system that consists of a control station, a remote control station, a receiver-transmitter, as well as low- and high-frequency transducers (AN/WQC-2A) system is a set of sonar communication that submarine crews use to maintain communication over several nautical miles [91]. The Atlantic Undersea Test and Evaluation Center (AUTEC) in the Bahamas also employs the AN/WQC-2A system to coordinate submarine operations, which include testing, exercises, and \"torpedo firing evolutions\" [91]. In the 1980s, the US Navy funded the Baggeroer and Cattipovic projects at the Massachusetts Institute of Technology (MIT) to advance underwater digital communication and acoustic telemetry [91]. SONAR can be categorised into two main types: passive and active [11; 12; 28; 92; 93]. Passive sonar, also known as passive acoustics, involves the direct recording of acoustic signals produced by various sources in air, water, or other media [11; 12; 28; 93]. Passive SONAR, also known as passive acoustics, involves detecting targets by listening to their acoustic emissions without actively transmitting signals [2]. The non-intrusive method is widely employed to detect target signals [5; 21] while minimising the impact on marine life, as it does not introduce additional acoustic emissions into the environment [1; 3]. Essentially, passive SONAR has a low acoustic footprint [3]. Target signals originate directly from sources such as fish, marine mammals, and other organisms. Training and classification of passive target signals for effective detection of sound sources have become standard practices among researchers and commercial ventures [2; 5]. Two forms of passive acoustic monitoring SONAR detection are recognised: the direct approach employs purely algorithmic methods, processing the detected signal of interest using techniques such as signal processing and filtering and comparative analysis of previous data while implementing adaptive and predictive approaches [5]. The second method involves more sophisticated data processing algorithms, such as Machine Learning (ML) and Deep Learning (DL) while also employing adaptive and predictive approaches [5]. Both ML and DL are subsets of Artificial Intelligence (AI). Although often used interchangeably, they have distinct characteristics and applications. ML is a broad discipline that leverages a diverse array of algorithms and techniques to empower computers to learn patterns from data and generate predictions or decisions autonomously [2; 5].