SAN FRANCISCO — In the wake of last month’s earthquake in Japan, the U.S. National Oceanic and Atmospheric Administration (NOAA) was able to provide more detailed information than ever before on the ensuing tsunami due, in part, to enhancements in the network that relays sea level data to warning centers by satellite.
NOAA’s tsunami warning network has improved dramatically since 2004 when an earthquake in the Indian Ocean triggered a series of tsunamis that killed more than 200,000 people in 11 countries. NOAA since then has expanded its network of ocean buoys from six to 39 and configured 164 sea-level stations in the U.S. and its territories to provide high-resolution tsunami data to warning centers. Data on wave height and movement also flows more quickly over NOAA’s satellite network because agency officials have equipped ocean buoys with powerful transmitters.
In 2004, NOAA tsunami warning centers received data on waves and ocean height every one to three hours. Now, NOAA receives those data approximately once per hour, said Kay Metcalf, program manager for NOAA’s Geostationary Orbiting Environmental Satellite (GOES) Data Collection System. “We have made a lot of progress in the last few years, but we have a long way to go,” Metcalf said.
NOAA’s tsunami warning system relies on buoys in the Pacific Ocean, Atlantic Ocean, Gulf of Mexico and Caribbean Sea to detect tsunamis with the potential to threaten the United States and its territories. The buoys, known as Deep-ocean Assessment and Reporting of Tsunamis (DART), feature a pressure sensor anchored to the sea floor. By measuring changes in pressure, those sensors provide information used to calculate ocean height at specific locations, said David Benner, chief of NOAA’s satellite services division. Once a wave passes several sensors, NOAA officials can determine a tsunami’s speed, he added.
The sensors on the sea floor are tied to floating buoys equipped with two antennas. One antenna uses the Global Positioning System to obtain precision location data while the other sends data on ocean levels to NOAA’s tsunami warning centers through Iridium Communications constellation of mobile communication satellites. Typically, the DART buoys gather ocean-pressure data once every 15 minutes. When triggered by a tsunami, however, the sensor begins taking readings every minute, said Natalia Donoho, user services coordinator for NOAA’s satellite products and services division.
NOAA relies on commercial Iridium satellites to carry the signals because the Iridium constellation offers the capability for two-way data transmission. Through Iridium, NOAA officials not only receive data from the DART buoys but can also send signals to the buoys to upgrade software, perform tests or reboot stations when equipment is not working properly, Donoho said.
In addition to the DART buoys, NOAA gathers data on wave height from 164 tide gauges stationed along the coastlines of U.S. states and its territories. Those observations are transmitted through a NOAA GOES satellite as often as every five minutes. Once the data reach the satellite, they can be relayed to NOAA stations on the ground in approximately five seconds, Metcalf said.
“The data is transmitted to the tsunami warning center and NOAA [headquarters] where we can use it to issue warning guidance, provide hazard assessment and coordinate emergency response,” Donoho said. Information drawn from the coastal gauges and DART buoys also feeds into NOAA’s high-resolution, digital elevation models, which are used to predict the impact of tsunamis on local communities. During the last five years, NOAA officials have created more than 100 digital elevation models showing the impact tsunamis would have on specific coastal areas, according to Barry Eakins, scientific leader for NOAA’s marine geology and geophysics division. Those models are used to predict areas likely to be inundated by flood waters and to assist community leaders in mitigating the impact of a tsunami, Donoho added.
During the last year, NOAA’s tsunami warning network was expanded to include data gathered from tide stations that belong to many coastal countries in Central and South America, Metcalf said. Those warning stations are operated by foreign governments, but rely on GOES to transmit their data, and are planned through Intergovernmental Coordinating Group for Tsunamis and Other Hazards, part of the United Nation’s Educational Scientific and Cultural Organization, Metcalf said.
NOAA officials also continue striving to make more efficient use of the communications bandwidth available on GOES satellites, which in addition to relaying information on waves are used to transmit many types of environmental data including river height measurements that are used to alert communities to the possibility of flooding. “We haven’t increased bandwidth but we have made improvements to transmitters,” Metcalf said. New tsunami detection stations are being equipped with transmitters capable of relaying data in half the bandwidth and at faster speeds than the components they replace. In addition, since GOES traffic moves according to a schedule that allots a certain amount of time for each station to transmit data, NOAA officials are using increasingly precise clocks to make the schedules tighter, she added.