Throwing DART Buoys into the Ocean

The “new” tsunami-warning buoy network being proposed for the United States is actually an extension of a system that has been in the water for five years. The Pacific Marine Environmental Laboratory, a NOAA research laboratory based in Seattle, began development of the Deep Ocean Assessment and Reporting of Tsunamis (DART) project in the mid-1990s and installed its first buoy in 2000.

Each DART installation includes a seafloor bottom pressure-recording (BPR) instrument, an acoustic modem, and a surface buoy with satellite transmitters. The BPR records changes in the pressure of seawater on the ocean floor, detecting tsunami waves as small as 1 centimeter. The acoustic modem uses sound waves to transmit data from the BPR to the buoy, which is then relayed to shore through NOAA’s Geostationary Operational Environmental Satellites.

The six DART buoys, now operated by NOAA’s National Buoy Data Center, are arrayed along the Aleutian Islands and Cascadia (Pacific Northwest) seismic zones, with one other buoy in equatorial waters between Hawaii and California. Before the December 2004 tsunami, NOAA had plans to install 20 buoys by 2011.

According to NOAA, the tsunami-warning network for the Pacific was plagued by a 75 percent false alarm rate when it relied solely on seismic data—monitoring of earthquakes—to predict tsunamis. (The 8.7 earthquake near Nias, Indonesia, on March 28 highlighted the dangers of relying solely on seismic monitoring, as thousands of people panicked and evacuated coastal areas though no tsunami was generated.) Since DART was established, several false alarms and evacuations have been averted; in one case, officials estimate that $68 million was saved by DART data that prevented an unnecessary evacuation.

The technology behind DART’s underwater communications was born more than a decade ago at WHOI. Starting in 1989, Josko Catipovic, Steve Merriam, and Lee Freitag worked on the development of acoustic modems. The WHOI technology was eventually sold to Datasonics, Inc., now part of Benthos, Inc., of Falmouth, Mass. Benthos has since adapted and commercialized the acoustic modems, building the modems now used in the DART system. (See What Could a Tsunami Network Look Like in the Future?)