March 10, 2005
UCSD Optical Fiber Infrasound Sensor Utilizes HPWREN for the Data Transport from the Piñon Flats Observatory
An Optical Fiber Infrasound Sensor (OFIS), a revolutionary new
instrument to record atmospheric acoustic waves at frequencies below
that which a human can hear, is a compliant tube wrapped with two
fiber-optic cables which are used to interferometrically measure
the integrated atmospheric pressure changes along the length of the
tube. In other words, it is a directional microphone tuned to
listen to the whispers in the atmosphere. Recording these whispers,
this instrument will facilitate the investigation and monitoring
of a wide variety of phenomena including meteors, thunderstorms,
atmospheric turbulence, volcanic processes, earthquakes, surf
conditions, and certain human activities.
A multi-arm OFIS is capable of measuring the direction from which an infrasound signal originates. Compared to traditional infrasound arrays that perform the same task, a multi-arm OFIS is comprised of cheaper materials, requires less space, and is installed in far less time. In addition, previous measurements suggest that in the frequency range between 1-10 Hz, the noise floor of the sensor is a few orders of magnitude below that which can be achieved with a typical pipe array.
Various geometric configurations are currently being tested to
determine the optimal configuration for signal characterization.
As in most equipment designing, this research is done both in the
lab and in the field. Our field site is the Piñon Flats Observatory
(PFO), which is located about 2 hours northeast of San Diego in the
high desert about 15 miles south of Palm Springs.
This has been an ongoing project since the late 1990's, and
consequently many people have been involved at one point or another.
The people currently involved with the OFIS at IGPP/SIO are Mark
Zumberge, Kris Walker, Petar Durdevic, Patrick Walsh, Jon Berger,
and Michael Hedlin.
In the above figure, using a real recorded signal, synthetic waveforms were created with an input back azimuth (BAZ). For each set of synthetic data, a grid search is employed (trial BAZ) to map out a characteristic objective function (color). Blues are lows, and indicate that the algorithm "thinks" it is determining the correct back azimuth. Perfect resolution would be one increasing blue line in a sea of red. The best multi-arm OFIS configuration of these three is a five-arm OFIS connected at one end, but with each of the arms separated by an angle of 72 deg (asterisk pattern; 5-72 configuration).
-- Kris Walker, IGPP/SIO/UCSD
More information can be found at http://sail.ucsd.edu/~ofis/.
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