A 16-element autonomous receiving array

An autonomous receiving array system has been designed, fabricated, and deployed at-sea for the collection of broadband underwater acoustic data. The system consists of a 16-element hydrophone array, a pressure case containing the data acquisition and disk storage hardware, and a mooring which includes floats for buoyancy, a RF-beacon and flasher, deep-sea batteries, and an acoustic release. The array cable consists of 16 twisted-pairs with a polyurethane outer jacket and a Kevlar strength member. In the current configuration, the array cable is 75 m in aperture with take-outs spaced every 5 m. Hydrophone-preamplifier packages (HTI-94-SSQ) are attached at each take-out and essentially have a flat frequency response from 20 Hz through 20 kHz. The multi-channel data acquisition system consists of a compact PCI chassis with CPU, signal conditioning electronics, and A/D. The data is recorded on four IDE, 60 GB, 2.5" disk drives. All data acquisition functions are carried out in LabVIEW. The CPU includes a 100BaseT Ethernet interface which is made available through a bulkhead connector on the pressure case. Thus, high-speed access to the data on the internal disks is available without the need to open the pressure case. Power is supplied externally by two 24 volt, Deep Sea Power & Light batteries which provide approximately 48 hours of underwater data collection. An alternative mooring configuration currently being developed will enable power and Ethernet connectivity to be provided by a surface buoy which then can facilitate access to the data over a RF-telemetry link from shore or a nearby ship. (e.g. an 802.11b wireless LAN).