Hawaiʻi Station Key in Monitoring Sounds of the Pacific

University of Hawaiʻi
Milton Garces, Ph.D.
Scientific Director
Posted: Dec 5, 2001

KAILUA-KONA, Hawaiʻi — The Infrasound Laboratory (ISLA) of the University of Hawaiʻi at Manoa has installed a sensitive listening post that is slated to become part of the International Monitoring System (IMS), a worldwide system designed to detect nuclear explosions. The KONA listening post, located on the mountain slopes of Kailua-Kona on the island of Hawaiʻi, routinely detects severe weather systems, and has observed various meteor impacts in the Pacific, with two of them having an equivalent explosive strength of thousands of tons of TNT.

"In July 2000, we heard Hurricane Daniel approaching Hawaiʻi even before it was designated a hurricane. In August 2000, we detected a giant meteor that burst off the coast of Mexico, and we detected another giant meteor this past April that exploded between California and Alaska. When events like these occur, we drop everything we are doing and concentrate on interpreting the data," said ISLA Director Dr. Milton Garces.

Volcanoes, meteors, storms, and clandestine nuclear tests generate low-frequency sound waves that can be observed thousands of kilometers away. Even the slap of surf on a steep lava cliff will launch small but measurable sound pulses that are routinely recorded by the KONA station.

Operational since May 2000, KONA station passively records low-frequency sound waves, or infrasonic waves, that are below the hearing threshold of the human ear. KONA is scheduled to be the first U.S. infrasound station to be certified into the IMS. It is one of 60 stations in the global infrasound network of the IMS, which will provide unprecedented coverage of the sound field around the globe.

The KONA station consists of a four-microphone configuration, or array, that acts like an antenna to provide more information and amplification than a single microphone. The KONA array is exceptionally receptive because of its unique location. Infrasonic noise increases with wind speed. Trees and geographical barriers are used to break down and dissipate the wind. KONA is leeward of three massive volcanoes and in a dense tropical forest, so it has some of the lowest background noise levels encountered anywhere in the Earth. Because these conditions are difficult to duplicate in oceanic islands, the KONA array is particularly important in the acoustic monitoring of the Pacific basin.

Acoustic data recorded in the forest is sent by a radio link to ISLA, which is responsible for operating the station. At ISLA, the data is encrypted and sent via satellite to the International Data Center in Vienna, Austria, and via the Internet to the Center for Monitoring Research in Arlington, Va.
"As a scientist, it is satisfying to work with extremely sensitive equipment in a field of research that is bursting with new information. On a personal level, it is gratifying to work with competent colleagues in a technology that can be used to avert natural disasters and enhance national and international security. There is never a dull moment," said Garces. "The KONA station routinely detects severe weather systems across the Pacific, from Antarctica to Alaska, and has observed various meteor impacts. Because of its proximity to active Mauna Loa and Kilauea volcanoes, we can also monitor explosive eruptive activity if it occurs."

Under the direction of Dr. Henry Bass of the University of Mississippi, scientists from the University of Hawaiʻi, University of California, University of Alaska, Southern Methodist University, Los Alamos National Laboratories, and Sandia National Laboratories collaborate to form the core of a Global Infrasound Network Consortium. In the United States, stations that will be part of the IMS are presently operating in Hawaiʻi, California, and Alaska.

Additional points of contact:

Dr. Ralph Alewine
Deputy Assistant to the Secretary of Defense
Nuclear Treaty Programs
(703) 588-1983

Dr. Henry Bass
National Center for Physical Acoustics
University of Mississippi
(662) 915-5840

Dr. Klaus Keil
Hawaiʻi Institute of Geophysics and Planetology
School of Ocean and Earth Science and Technology
University of Hawaiʻi at Manoa
(808) 956-3184

* Photos available upon request by calling (808) 956-5039 or e-mail cabralkr@hawaii.edu.