This paper describes the use and in-field evaluation of a Networked-Long Base Line system (Net-LBL) where a network of underwater nodes cooperate to support the localisation and navigation of mobile vehicles. To avoid the use of dedicated transponders, as for traditional long baseline systems, each node of the network makes use of its underwater acoustic modem to transmit both data and positioning information. The use of the proposed Net-LBL systems has been validated and evaluated during two at-sea campaigns. More specifically, this paper investigates how the use of different communication schemes to reserve the shared underwater channel (i.e. Time Division Multiple Access (TDMA) and Carrier Sensing Multiple Access (CSMA)) impact on the acquisition of range measurements and on the localisation results. The collected results show that CSMA, being more flexible and responsive, can obtain a reduction of the impact on the localisation error by 30% on average and up to 90% with respect to TDMA.
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