Communication and Localisation using Underwater Acoustics

Abstract

The inspection and monitoring of underwater nuclear facilities such as Spent Fuel Ponds (SFPs) are crucial tasks in both modern as well as legacy nuclear installations. Such tasks have been typically conducted by tethered Remotely Operated Vehicles (ROVs). The use of tethered ROVs in legacy SFPs is a challenging task due to their cluttered inventory which increases the hazard of an entangled tether, that may result in the inability to retrieve the ROV. The typically turbid conditions of legacy SFPs also limit visibility and impede ROV control. The use of untethered ROVs has been proposed as a practical alternative to inspecting and monitoring these facilities. Untethered ROVs require a communication infrastructure to relay control signals and retrieve data from the ROV. In addition, a localisation infrastructure is required to determine the position of the ROV in the SFP. In an underwater environment, such an infrastructure is feasible only via the use of Underwater Acoustic (UWA) waves as optical technologies and radiofrequency waves are generally impractical. Nevertheless, Underwater Acoustic Communications (UWAC) have been studied almost exclusively in open-ocean scenarios with near-anechoic conditions. The reverberant characteristics of confined underwater environments such as SFPs pose additional challenges to achieving reliable communication and localisation. Consequently, the development of an UWA communication and localisation system requires the systematic study of the UWA channel of confined underwater environments to develop techniques that mitigate the challenges posed by reverberation. This thesis presents the systematic characterisation of the UWA channel and the performance evaluation of UWAC in an underwater environment measuring approximately 6.4 m long, 6.4 m wide, and 6 m deep. The design, development, and evaluation of a large-scale automated Measurement System capable of executing UWA channel sounding and UWAC measurements is presented. The Measurement System was used for the execution of a set of Preliminary, Systematic, and Supplementary UWA channel sounding and UWAC measurements, which led to the creation of a dataset of more than 6,000 measurements. The analysis of the UWA channel sounding measurements is presented, which enabled the quantitative characterisation of the levels of channel fading exhibited by a confined underwater environment due to multipath propagation. Furthermore, the analysis of the UWAC measurements is presented, which assessed UWAC performance in terms of bit-error ratio and data rate. Furthermore, this thesis presents the design, implementation, and evaluation of a Demonstration System, used for delivering practical demonstrations of UWAC and ranging in a confined underwater environment to industrial stakeholders.

Date of Award	9 Oct 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Peter Green (Main Supervisor) & Barry Lennox (Co Supervisor)