April 2, 2005
HPWREN Team Experiments with Real-Time Data from Automated Wildlife Acoustics Sensors
Originally instigated more than a year ago by the desire to capture wolf howls at the California Wolf Center (http://hpwren.ucsd.edu/news/040107.html and http://hpwren.ucsd.edu/news/050205.html), it became desirable to add an automated acoustics capability to HPWREN sensors. In addition, the work by Stuart Gage of Michigan State University (http://hpwren.ucsd.edu/news/050210.html) at the SDSU Santa Margarita Ecological Reserve has shown that this is a realistic and affordable application, as have discussions with Deborah Estrin and her research group about their work at UCLA (http://cens.ucla.edu).
To evaluate the feasibility of a system for an automated and
inexpensive capability to capture sounds from wolves and birds, HPWREN
utilized a small embedded XScale-based Linux platform and other
off-the-shelf components. The prototype uses a single board
Arcom Viper computer.
and compared various
microphones for the sound input. The platform
consumes fairly little electric current and is easily deployable in
the field in a solar-powered or Power-over-Ethernet (using a cable
For an initial use, the system was placed into a cooler box, with
electric current and network connectivity provided via a
Power-over-Ethernet setting. The microphone was mounted outside of the
box, which allowed for some interesting experiments to provide wind
shielding and to limit damage caused by rain and wildlife.
The objective was to automate the process of the sound-data collection, distribution to a central server, and to make the results available on a web site, which is similar to the motion-detect images shown at the HPWREN cameras web site.
The audio software in the XScale system uses the "listener" software by Folkert van Heusden, who has been instrumental with the success of this activity, including his modifications to the software so that it is more compatible with this particular application. "Listener" allows certain parameterization, such as sound threshold, sound filter, file format, and file disposition. For the disposition, a shell script is executed for a transfer to a central server and subsequent local file deletion. A program on the central server regularly looks for new files, processes them, and makes them available on a web site. http://grizzly.hpwren.ucsd.edu/Acoustics/Data/MCR/ shows some examples.
Of particular use to this application are audio spectrum analyzers, including Erik Olson's "baudline," and Dave Andruczyk's "eXtace." Both Erik Olson and Dave Andruczyk have been very helpful as well, and provided valuable information.
"Listener," "baudline," and "eXtace" are all freely available software,
and run on both Linux and FreeBSD systems.
The images below show graphing capabilities of the "eXtace" audio spectrum analyzer, including in 3-D. The original images were provided by Dave Andruczyk.
Some issues that need to be addressed prior to broader use is microphone survival under adversarial weather and wildlife conditions, and an automated pre-analysis of the collected data. A lower noise floor in the audio hardware and higher microphone sensitivity are also desirable, especially for fairly quiet wildlife monitoring environments.
Some additional analysis using baudline, with the images and quoted comments provided by Erik Olson
Note, the images are clickable for full-resolution versions.
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