January 15, 2000

The "CTBTs" (Left to Right), Kay Lawson, Charles "Buck" Wilson, and Dan Osborne. (The infrasonic microphone is in the centre).

One of the many intriguing science projects taking place at Palmer Station is not involved with Antarctic ecology, per se. Rather, it is a facet of the monitoring protocol of the Comprehensive Nuclear-Test-Ban Treaty, or CTBT, for short. Charles "Buck" Wilson, Kay Lawson and Dan Osborne from the Geophysical Institute at the University of Alaska in Fairbanks are on Station to install and test an array of infrasonic microphones. These listening devices are designed to pick up very low frequency acoustic signatures of underground nuclear tests, from anywhere in the world. Infrasound is generally understood to be the part of the audio spectrum that lies below the range of human hearing, i.e., less than about 16Hz, or cycles per second. When a nuclear device is detonated, the explosion produces an extremely low, and powerful, sound which travels all around the planet. The array in the Palmer Station area is one of several strategically placed listening posts around the globe: part of an international effort to verify treaty compliance.

Rob Edwards navigates a zodiac through brash ice around Janus Island.

Since their arrival last week the "CTBTs" have been busy troubleshooting their gear, putting pieces together and positioning the microphones at different locations in the area. Three rigs have been deployed: at Old Palmer (identified as "Brit"), Torgersen Island and behind Station in "the backyard." The tripartite arrangement of the array is an essential aspect in localizing a sound. By measuring the difference in signal arrival times to the microphones, in a process known as triangulation, the scientists can accurately identify a point of origin. This information can be extremely accurate, particularly when correlated with recordings from arrays elsewhere. Buck and his crew brought an extra unit, as a backup. With all the equipment working, they decided to place this last component of the array at Janus Island--thereby extending the triangular configuration (see diagram).

Buck Wilson's map of the infrasonic microphone array. Distances are in kilometres from one location to another. The Janus site is at the lower left, Torgersen Island in the centre, Old Palmer (Brit) at the top and Palmer Station to the right.

While the application of the CTBT technology serves an important role in maintaining world peace, there are also "sidebands" of acoustic activity from the natural world that may be perceived through this lens. When not keeping watch on the state of nuclear weaponery, Dan Osborne is following natural infrasound. From sonic booms issuing from the aurora to "sprites" associated with lightning strikes, there is a world of sound that lies out of our range of hearing. One of the interesting "tests" of the CTBT arrays has been the lower frequency booms associated with glacial calving. At Loudwater and Arthur Harbor Coves, I experienced a physical sensation, or impact, from a couple of large-scale events. On the one hand, my ears tuned in to the vibrations that I could hear, while I could also feel the ice fracture--a pulse that slammed against my body like a sudden gust of wind. It is this range that shows up as a trace, a coherent infrasonic wave, on the special data recorders that Buck, Dan and Kay use.

Spectrograph of ice calving. Time is shown on the horizontal axis, while amplitude (relative loudness) is shown on the vertical. This time slice shows a 1.25 second event, recorded from the microphone at Torgersen Island. An identical trace was recorded a few seconds later at Palmer Station, as the sound wave propagated across the area.

Steve and I decided to tag along, lend a hand and learn a bit more about a different dimension of the soundscape--infrasound. Rob Edwards took the CTBTs and their gear in one boat, accompanied by wildlife photographer and environmentalist, Gary Braasch. U.S. News and World reporter, Charlie Petit, joined us in our zodiac. Together, we worked our way through the brash in the approach to Janus Island. A light, beaded snow fell and visibility was limited. The swell around Janus was several feet. The landing and offloading of equipment proved to be a challenge and we found ourselves working a surge to jump ashore--only to try and gain footing on slippery rocks, covered in an emerald green seaweed. The batteries for the microphone and data collection unit weighed 70 pounds each! A few brown skuas circled and displayed when we approached their nests. It was warm and we soon broke into a good sweat.

Deploying the infrasonic microphone on Janus Island. (Note the hoses that extend out from the small white unit by Kay's knee).

The microphone itself is a modest size--less than 20 cm in diameter. One of the interesting problems in gathering low frequency sounds is that ambient noise from wind can mask and obscure what you are seeking. In order to work around this problem--which is perennial for all sound recordists--the solution involved running out lengths of porous, soak hoses. Low frequencies can be detected through this material and there is a certain noise reducing quality that makes them especially useful for this application. For all the high end technology, this was a garden-grade, hardware store item: albeit a particular brand and qualified to treaty specifications. The hoses radiated, like tendrils, from the hub of the microphone, in a cruciform plan along the rocks. The total extent, or footprint, is nearly 30 metres. We helped Buck and his team secure the hoses, while Dan tested the data flow and Kay took detailed Global Positioning System (GPS) readings. Within an hour, it was all working well.

Steve, Charlie and I then split off to have a listen underwater on the far side of DeLacca Island. It was pretty quiet--no seals, whales or even any iceberg activity, just the din of the sea state...

"The CTBTs"

Charles "Buck" Wilson logs notes on site.

Dan Osborne checks his data.

Kay Lawson takes GPS readings.

For more information about this project and other aspects of low frequency research, be sure to visit the Infrasonics Program website.