Acoustic communication performance of the WHOI Micro-Modem in sea trials of the Nereus vehicle to 11,000 m depth

The new, unmanned, deep-diving Nereus hybrid vehicle can be configured as a tethered remotely operated vehicle (ROV) using a fiber-optic cable, and it can operate un-tethered as an autonomous underwater vehicle (AUV). During planned autonomous operations and un-tethered ascents, or if the fiber breaks, the vehicle uses an acoustic communication system to allow engineers and scientists at the surface to monitor its systems and control its operation. The Woods Hole Oceanographic Institution (WHOI) Micro-Modem, programmable for different data rates, bandwidths and carrier frequencies, uses directional transducers on both the ship and the vehicle, operating in the band from 7 to 14 kHz, to provide the communications link. During recent sea trials of Nereus in the Mariana Trench to 10,903 m depth, ten different combinations of rates, bandwidths, and carrier frequencies were tested to establish the performance of each with respect to acoustic range. 5000 bps was possible to 6000 m range, and at 11000 m range, 200 bits per second was reliable.