Wild dolphins live
in a world of sound. Of all forms of energy, sound is the
one form that propagates most effectively in water, much better
for example than light. Dolphins use this to their full advantage
and have excellent hearing and echolocation capabilities,
which they use to communicate with each other and to probe
their surroundings. Therefore, to better understand wild dolphin
behavior and ecology, an important first step is is to accurately
record and analyze the sounds they produce. However, this
has proven very difficult in the past.
One of the main
problems with recording their sounds is the high frequency
content of dolphin signals. Most dolphin species produce three
types of signals: echolocation clicks, the faster paced burst
pulse clicks, and whistles. Echolocation clicks are used by
dolphins to detect and recognize objects in the water from
the returning echoes, akin to a biological (and much superior)
version of man-made SONAR. Burst pulse clicks and whistles
on the other hand are thought to be used mainly for communication.
Click signals are extremely short (50 microseconds) and broadband
high frequency signals, ranging from 0 to over 200 kiloHertz.
Whistles are generally within human hearing range, but also
have ultrasonic components called harmonics which can go up
to over 100 kHz. However, conventional audio recording systems
only go up to about 20 kHz (also the upper limit of human
hearing), and therefore miss the majority of energy of these
signals.
Another major problem
is that it is usually impossible to tell which, or how many
dolphins produced the recorded sounds. This information is
essential, however, to associate acoustic features of the
sounds with behaviors of individual dolphins, or to find out
how communication signals are exchanged among them. Also,
the distance of the sound producing dolphin, needed to determine
the amplitude of the sound, is usually unknown, as well as
the orientation of its head with respect to the recording
device. The reason it is important to know head orientation
is because dolphins emit sounds from their foreheads in a
directional “beam” of sound, somewhat comparable
to the light on a miner’s helmet. Only recordings from
the beam axis represent the actual signals, while signals
recorded off-axis can be highly distorted. Since recording
systems are usually operated from boats, it is hard to control
for any of these factors.
The Underwater
Dolphin Data Aquisition System (UDDAS,
designed by Dr. Marc Lammers) and 4-channel
UDDAS (designed by Michiel Schotten) were developed at
OSI as tools to deal with each of these challenges. Their
main asset is that they are self-contained units and can be
taken under water by a diver to record the entire frequency
bandwidth of dolphin signals. With simultaneous video, behaviors
of the sound producing dolphins and their head orientations
can be recorded as well. Using the 4-channel UDDAS, one can
also localize recorded sounds to a 3-D position in the water.
This allows one to determine the amplitude of the sounds,
and to attribute them to individual dolphins on the video.
UDDAS
Specifications
Broadband
recording unit:
The heart of the
recording unit is a single-board computer by Aaeon electronics
(model: GENE 4310) with a low-power 233 MHz processor. It
conforms to a PC-104 format. Stacked onto the computer are
a PCMCIA module, a hard drive module and a power supply module,
all connected via the PC-104 bus. The PCMCIA module holds
an A/D board by Measurement Computing (model: DAS16/330) capable
of sampling up to 330 kHz. The hard drive module carries a
6 GB 2.5" Toshiba hard drive. The computer operates on
Windows 98 and the data acquisition software is written in
LabView. The acquisition program waits for a user "TTL-high"
trigger to begin recording. Typically, data is acquired at
a sampling rate of 220 kHz (110 kHz Nyquist) in 10-second
blocks.
A custom-built
directional transducer made of a piezocomposite material receives
incoming signals. It has a flat sensitivity of approximately
-180 dB re 1 uPa up to at least 150 kHz. A signal-conditioning
unit in the housing is mounted below the computer stack to
amplify and filter incoming sounds before recording. Signals
are amplified by 40 dB with a user option to amplify an additional
10 dB. A 5th order low-pass filter by Lattice Semiconductors
(model: ISPpac-80) is used as an anti-aliasing filter. It
is programmed to have a cutoff frequency of 100 kHz.
Video
camera unit:
A Sony digital
video camera (model: DCR-PC110) is used to record simultaneous
behavioral data. The camera is housed in a customized housing
manufactured by Ocean Images. A trigger switch near the left
handle connects via a cable to the electronics housing mounted
below the camera housing. An omnidirectional hydrophone (built
by Don Norris) with a sensitivity of - 205 dB provides acoustic
input for the video camera. Inside the camera housing, a custom-built
pre-amp provides 20 dB of gain before the signal is fed into
the camera.
4-channel
UDDAS
Specifications
The
4-channel UDDAS is a digital acoustic/video recording system
that is battery powered and packaged in an underwater housing.
The housing, custom-made by The
Sexton Company LLC, holds a Samsung digital camcorder
(model: SCD103) with wide-angle lens, 2 sealed lead-acid 12V/
8.5 AmpHr batteries, and a custom-developed 4-channel acoustic
recording unit. Attached 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/uPa 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.
Localizations are accurate up to a range of at least 15 m
(50 ft) 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 uPa 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. After 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 extremely 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. The 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. Ken 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 heatsink on the MOPS/lcd7 to a heatsink 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, zoom, on/off, start acoustic recording, and amount
of amplification. The system is slightly positively buoyant
and easy to swim with.
Fieldwork
The 4-channel UDDAS
is a welcome new tool to study the acoustic behavior of Hawaii’s
resident spinner dolphins (Stenella longirostris) in OSI’s
Nai'a Kuwili Project. Additionally, in an ongoing collaboration
with Dr. Denise Herzing of the Wild Dolphin Project, the 4-channel
UDDAS is also being used to study wild Atlantic spotted dolphins
(Stenella frontalis) and bottlenose dolphins (Tursiops truncatus)
in The Bahamas. Dr. Herzing has studied this pod of dolphins
since 1985 using underwater video, and has currently identified
over 200 individual dolphins which can be recognized from
their specific patterns of body spots. WDP’s knowledge
of the individual spotted and bottlenosed dolphins in its
catalog acquired over 20 years of fieldwork is unique in the
world, and present an ideal setting to employ a system as
the 4-channel UDDAS, which focuses on getting recordings from
individual dolphins. After all, if the life history and family
relationships of a dolphin are well known, it puts the high
frequency sounds recorded from that dolphin into a very meaningful
perspective.
The
first employment of the 4-channel UDDAS in The Bahamas was
during a fieldtrip with WDP in the summer of 2005. High frequency
sounds were successfully recorded from both spotted and bottlenosed
dolphins, engaged in a variety of different behaviors such
as crater feeding on the sand, night feeding, courtship, aggression,
and play. Analyzing these recordings, which involves localizing
the sounds and attributing them to specific individuals visible
on the simultaneous video, will take many months. It is our
hope that this information will shed new light on how communication
sounds are exchanged within a dolphin group, how echolocation
clicks might be adapted by dolphins, and whether specific
sounds are indicative of specific behaviors.
Documentation
The 4-channel UDDAS
has been documented in JASA
117(4):2552 (2005) and won the Readers’ Choice Award
as best Research Category entry of the 2005
PC/104 Design Contest (see bottom of their webpage).
Sponsors
and Acknowledgements
Development of
the 4-channel UDDAS has been made possible by a number of
sponsors, who willingly donated parts to support this research
project. The Sexton
Company LLC dba Sexton Photographics donated half of the
underwater housing and has been incredibly supportive of this
project. ADLINK Technology
America, Inc. made a major donation by providing the DAQ-2010,
a 4-channel data acquisition board. Because of the combined
small size and outstanding performance of this board, development
of the 4-channel UDDAS became possible in the first place.
Kontron America donated
the MOPS/lcd7, a passively cooled single-board computer with
enough processing power and memory to support the extremely
high data throughput of the 4-channel UDDAS. Sanmina-SCI
Corporation donated and specially adapted a PC/104-plus
power supply to this project, one of the very few existing
power supplies in the PC/104-plus format. Douglas
Electronics, Inc. donated its PCI-to-PC/104-plus adapter
which allowed connecting the PCI data acuisition board to
the PC/104-plus stack. Finally, Lattice
Semiconductor Corporation provided 30 ispPAC80 filter
chips, an ideal chip for the 4-channel UDDAS because of its
capability to output differential signals (which reduces system
noise significantly) and because its gain and filter settings
can be easily programmed.
Michiel Schotten
wishes to thank the Royal Netherlands Academy of Arts and
Sciences (KNAW, Schure-Beijerinck-Popping Foundation ) as
well as the Royal Dutch Society of Sciences (KHMW, Pieter
Langerhuizen Foundation) for providing personal research funding.
Also, a big Mahalo goes out to a number of people who were
of special assistance to this project. The support of Ken
and Adrienne Sexton in the last phase of this project was
greatly appreciated. Dr. Whitlow Au is acknowledged for his
on-going support of this research and excellent electronics
coaching. Hank Lin and Roy Wan of Adlink Technology have been
extremely helpful with programming the data acquisition card.
Don Norris is acknowledged for his time and useful advices.
Furthermore, Bruce McGrath, Chuck White, Dwight Webster, Jim
Krebs, and Chad Pennebaker are acknowledged for their personal
dedication in realizing sponsorships. Co-investigator Dr.
Denise Herzing and all crew members of RV Stenella have been
extremely supportive and encouraging of this research. Profs.
Wim Wolff and John Videler of Groningen University are thanked
for their on-going research feedback and logistics support.
John Schotten has always been very supportive. Natasja Baints
is thanked for her love and personal support.
Additional
sponsors needed!
All donations to
OSI (which is a 501(c)(3) nonprofit organization) are 100%
tax-deductible. Additionally, if you wish we will add your
company’s logo and/or weblink to this webpage as a contributing
sponsor, and will acknowledge your sponsorship in any publications
that will result from this research, i.e. both publications
in scientific journals and in the popular media. Furthermore,
if your company or organization wishes to use sponsorship
of this research for advertising purposes, that can also be
arranged..
If you would like
to make a donation to this project directly, please send your
check using our donations
form and indicate the amount under ‘UDDAS research’.
If you wish to contribute to any other OSI project, please
indicate this on the form as well. Thank you for your interest
and support!
Links:
Introduction
