Out in the open ocean across the Pacific there are devices called DART, or Deep Ocean Assessment and Reporting of Tsunamis, buoys. If you saw one, it wouldn't look like much, just a round device painted orange and white with a short mast bearing a wind gauge and a couple of satellite antennas.
On the side is painted the word "Tsunami." Yet, despite their unassuming looks, these buoys are the critical reporting terminals for a worldwide data network linked to computers in Hawaii and elsewhere. This is the visible evidence of the Pacific Tsunami Warning Center.
When the massive earthquake struck Japan on March 11, it triggered shock waves that became a Pacific-wide tsunami. The DART buoys dutifully reported the passing of the wave, and that allowed the National Weather Service staff at the Pacific Tsunami Warning Center to accurately predict the arrival time of the waves that would strike Hawaii and the U.S. West Coast in a matter of hours.
The DART buoys are the visible half of a two-part system. Resting on the ocean floor below them are pressure sensors that transmit acoustic data to the buoy on the surface, which then combines it with its own observations of weather and wave action before instantly transmitting that data to a GOES (Geostationary Operational Environmental Satellite) satellite. Then the satellite forwards the information to the tsunami-warning center.
Each of these buoys, located mostly around the highly seismically active Pacific Rim (also known as the "Ring of Fire"), reports the signs of a tsunami as it passes. Once this data is gathered and processed at the tsunami-warning centers in Hawaii and elsewhere, it delivers a nearly instantaneous, real-time picture of the speed, direction and severity of a tsunami.
As the waves arrive, they trigger a device called a tide station. These perform a similar function to the DART buoys, but they are attached to piers and other coastal structures, and measure the actual severity of the tsunamis as they arrive from the open ocean. Again, these devices send their observations to the Pacific Tsunami Warning Center. When a 36-foot-high wave came ashore at speeds estimated at 600 miles per hour in Japan, this information was reported, and used by the center to estimate the seriousness of the threat as it struck other land in the Pacific.
Although the Pacific Tsunami Warning Center occupies an unassuming building in Ewa Beach, it is run by NOAA (the National Oceanic and Atmospheric Administration) and its impact is global. The PTWC is also the headquarters for the new tsunami-monitoring efforts in the Indian Ocean and in the Caribbean, which were put into place after the deadly 2004 tsunami triggered by an earthquake in the Indian Ocean off the west coast of Sumatra, Indonesia, that killed about 230,000 people in the region.