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"The heart of the newly developed underwater dolphin recorder is ADLINK's 4-channel multifunction DAQ card, DAQ-2010. The superb performance of this data acquisition card has absolutely been the key to the success of this new system in recording wild dolphin sounds", said Michiel Schotten, a Ph.D. candidate at the Dept. of Marine Biology at Groningen University, "By recording the sounds with 4 underwater microphones and then digitizing them on 4 separate channels, the sounds can be accurately localized in 3-D space".
Application Background
Dolphins live in a world of sound. Accordingly, to better understand wild dolphin behavior and their environment, attempts are made to accurately record and analyze the sounds they produce. However, this has proven very difficult in the past because of the ultrasonic dolphin sounds, which make the conventional audio recording systems miss the major part of these signals. Today, a special 4-channel Underwater Dolphin Data Acquisition System (UDDAS) had been developed, with ADLINK Technology. The UDDAS can gather, digitize and even accurately localize the dolphin sound in 3-D space. The digitizer of the system is ADLINK's DAQ-2010.
System Requirements
The 4-channel UDDAS can be taken under water by a diver to record the entire frequency bandwidth of dolphin signals. There are two major challenges in recording dolphin sound signals. The first challenge comes from the ultrasonic signal properties and determining signal orientation. Dolphin sounds have frequencies of at least 250 kHz, which can not be accurately recorded with conventional recorders. A 4-hydrophone array is necessary for determining the signal orientation in 3-D space, thus simultaneous sampling is essential to digitize the signals from the array. The second challenge is to modify the current on-boat recording system to be operational underwater with batteries, thus, the whole system must consume less power.
To sum up the above requirements, a very small low-power ultra-fast simultaneous-sampling DAQ card is necessary, and it has to digitize the signals at a sampling rate of 667 kHz (333 kHz Nyquist frequency) on 4 channels, upon a specific trigger event.
System Implementation
ADLINK's DAQ-2010 card is chosen as the digitizer in the UDDAS system. Positions of sound emitted by dolphins are determined with the 4-hydrophone array localization technique. Incoming dolphin signals on the 4 channels are amplified and filtered. After signal conditioning, the signals are fed into the DAQ-2010, and then digitized at a sampling rate of 667 kHz (333 kHz Nyquist frequency) on 4 channels. The DAQ-2010 starts to digitize the signals on a special trigger condition, and data are transferred through the scatter-gather DMA function to the onboard memory of single-board computer.
Conclusion
The modular design of the DAQ-2010 separates the digital circuitry and analog device into two-board piggy-back configurations. The configuration not only reduces the size of the board, but also minimizes the noise induced from the digital circuitry, which is of crucial importance for the UDDAS. In this application, the simultaneous sampling characteristic of the DAQ-2010 also meets the requirements of recording signals from multiple sensors.
ADLINK DAQ-2010 card features compact size, high immunity to noise, low power requirement, auto-calibration, and the scatter-gather DMA technique, which makes it ideal for the UDDAS. With the newly-developed UDDAS, scientists now can move forward with research on wild dolphin behavior and ecology.
For more information, please go to http://www.oceanwidescience.org/docs/4ch-UDDAS.html
User's information
Michiel Schotten, Ph.D. candidate at the Dept. of Marine Biology at Groningen University (The Netherlands) and affiliated with the Marine Mammal Research Program (Hawaii Institute of Marine Biology, University of Hawaii) on Coconut Island, Oahu, Hawaii. The research advisors are Prof. Whitlow W.L. Au (author of "The Sonar of Dolphins", 1993) at the University of Hawaii, and Prof. Wim J. Wolff and Prof. John J. Videler at Groningen University.
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