Cross-shore hydrographic transects obtained offshore of Barrow with the Remote Environmental Measuring UnitS

Use of an autonomous underwater vehicle (AUV) to obtain environmental observations beneath coastal sea ice offshore of Barrow, Alaska is described. The work is motivated by the desire to obtain cross-shore hydrographic transects (temperature, salinity and velocity vs. depth) that would provide estimates of the transport of relatively dense, salty water from the Chukchi Sea to the Arctic Ocean in winter. Although personportable AUVs are well suited to the task, it was recognized that achieving the science goals would require increasing the range of acoustic navigation and communication as well as developing a robust approach to through-ice deployment and recovery. These needs drove three modifications to the AUV: 1) Incorporation of a lower frequency (10 kHz) transponder and associated hardware for navigation and communication, 2) Addition of special-purpose sensors and hardware in a hull extension module, 3) Development of a homing algorithm utilizing Ultra-Short Base Line (USBL) acoustics. In March 2010, eight days of field work offshore of Barrow provided successful demonstration of the system. A total of 14 km of track lines beneath a coastal ice floe were obtained from four missions, each successfully terminated by net-capture recovery.