Abstract:

This paper describes array element localization (AEL) for two vertical line arrays (VLA's) of hydrophones, which comprise part of the Spinnaker Array, a 3-D sensor array in the Arctic Ocean. The AEL system associated with each VLA monitors the location of three high-frequency acoustic receivers, positioned at intervals along the array cable, by measuring travel times from five seafloor transponders. The transponders are comprised of a controller unit at the base of the array and four remote units at ranges of approximately 500 m. The accuracy to which the AEL receivers can be located depends directly on the knowledge of transponder positions. Two steps were used to accurately determine the transponder positions. First, travel-time measurements were made to an independent set of acoustic sensors suspended just below the ice. Second, use was made of the AEL travel-time data themselves. Both data sets were inverted using an iterative regularized inversion that applied a priori information to overcome the nonuniqueness/instability of the inverse problem. Monte Carlo simulation of the inversion procedure indicates that the transponders and AEL receivers are localized to an accuracy of less than 1 m.