You are hereProjects/ 4-channel UDDAS/ Technical specs

Projects/ 4-channel UDDAS/ Technical specs

PREVIOUS: How the 4-channel UDDAS addresses these challenges

Technical specifications

The first-generation 4-channel UDDAS is a digital acoustic/video recording system that is battery powered and packaged in an underwater housing.  The housing, custom-made and partly donated by The Sexton Company LLC, holds a Sony digital camcorder with wide-angle lens, 2 sealed lead-acid 12V/ 8.5 AmpHr batteries, and a custom-developed 4-channel acoustic recording unit.

4-hydrophone localization techniqueAttached to the housing is an array of 4 omni-directional hydrophones in the shape of the letter Y, with 1 hydrophone in the middle (underneath the dome for the camcorder lens) and 3 hydrophones sticking out at the ends of 0.5 m long, hollow delrin pipes spaced 120º apart.  The spherical hydrophones (custom-built by Don Norris) have a sensitivity of –214 dB re 1V/μPa and a flat frequency response up to 300 kHz.  Positions of sound emitting dolphins are determined with the 4-hydrophone array localization technique.  Range, horizontal angle, and vertical angle are calculated from the differences in arrival time of the sound at each of the 4 hydrophones, which gives the 3-D position of the dolphin (see Schotten et al. 2004, PDF = 4.2 MB, for further technical details on this localization technique).  Localizations are accurate up to a range of at least 15 meters away.

Incoming dolphin signals on the 4 channels are amplified and filtered by programmable ispPAC80 filter chips (donated by Lattice Semiconductor) on a custom-made signal conditioning unit.  The amount of amplification is user controlled, with a choice of 20, 40, or 52 dB re 1 μPa through a switch outside the housing.  In the ispPAC80 chips, a 5th order low-pass filter with a programmed cut-off frequency of 220 kHz acts as an anti-aliasing filter.

4-channel UDDAS without hydrophone arrayAfter signal conditioning the signals are fed into the DAQ-2010, a small 4-channel simultaneous analog-to-digital conversion board from ADLINK Technology, which digitizes the signals at a sampling rate of 667 kHz (333 kHz Nyquist frequency) on 4 channels.  The PCI data acquisition board, which has been generously donated by Adlink, is stacked onto a PC/104-plus computer stack with a PCI-to-PC/104-plus adapter board (donated by Douglas Electronics).  PC/104-plus is the ideal format because of its small size and the compact way the computer modules stack together.  PC/104-plus was chosen over PC/104 because it conforms to the 33 MHz PCI data bandwidth, which is needed to run the DAQ-2010 and to handle the high data throughput of 5.4 MB/s (i.e. 4 channels simultaneously sampling at 667 kHz with 14-bit = 2-byte resolution).

After digitizing, data are transferred through the scatter-gather DMA function of ADLINK’s DAQ-2010 to the onboard memory of the MOPS/lcd7.  This is a PC/104-plus single-board computer, with a fanless 300 MHz Celeron processor and 512 MB of SDRAM memory, and has been donated to this project by Kontron America.  Subsequently, data are written from the onboard memory onto the Hitachi Travelstar, a 2.5” notebook hard disk of 60 GB and 7,200 rpm.

Fish shelterThe computer operates on Windows 2000 and a hand-written LabView program drives the data acquisition and data storage process.  The program waits for a TTL trigger to begin recording, which is user controlled from outside the housing.  The entire system runs off two 12V batteries, converted from +24V to +5V by a PC/104-plus power supply module, which has been custom-adapted and donated by Sanmina-SCI.  The PCI-to-PC/104-plus adapter, PC/104-plus power supply, and single-board computer are all stacked on top of each other and connected via the PC/104-plus bus.

Completion of the 4-channel UDDAS was possible because of the Oregon based Sexton Company, one of the very few manufacturers in the world building custom underwater housings for scientific research.  The scientific expertise and many years of experience of its director, Ken Sexton, as well as his top-of-the line 3-D designing software and manufacturing equipment, guaranteed the best possible housing for this project.

Spotted dolphin cruising alongKen came up with many great ideas for the final design of the 4-channel UDDAS:  all parts were mounted on a tray, which can be taken out of the housing entirely for easy access;  a semi-spherical dome in front of the housing accommodates the wide-angle lens of the video camcorder;  a Noren heat pipe transfers heat from the heat sink on the MOPS/lcd7 to a heat sink on the rear outside the housing, to cool the computer processor to the sea water;  a tv-monitor (model: Liliput) connected to the camcorder was mounted in the back of the housing, so that a diver is able to see what is being recorded.  There are controls for camcorder record, on/off, start acoustic recording, and amount of amplification. The system is slightly positively buoyant and easy to swim with.

NEXT: Fieldwork