Underwater wireless optical communication unit and system

An underwater wireless optical communication (UWOC) unit for underwater deployment on or in a submerged earth layer or a submerged structure, wherein the UWOC unit is configured for wireless optical communication in an underwater environment and comprises:

• an optical transmitter, configured to transmit data by emitting an optical signal into the surroundings of the UWOC unit;
• an anidolic optical receiver including an optical detector, which is omnidirectionally sensitive and configured to receive a further optical signal approaching substantially along a first azimuthal plane that is orthogonal to a nominal axis extending through the UWOC unit, and
• a processor, communicatively coupled to the optical receiver, and configured to process received further optical signals,
• wherein the processor is configured to determine an indication of an inter-unit distance between the first UWOC unit and a second UWOC unit, on the basis of sending with the optical transmitter an optical interrogation signal to the second unit, and receiving with the optical receiver an optical response signal from the second unit.