2004 tsunami spurred development of NOAA warning system

When a tsunami killed more than 200,000 people in the Indian Ocean on Dec. 26, 2004, the National Oceanic and Atmospheric Administration’s warning system was in its infancy. In the five years since then it has matured into an international network of nearly 50 sensors feeding near-real-time data to sophisticated computer models to produce detailed forecasts and warnings.

NOAA’s Deep-ocean Assessment and Reporting of Tsunamis program (DART) has deployed 39 second-generation sensors in three oceans communicating with warning centers via IP satellite links. Data also is gathered from sensors deployed by four other coastal nations.

“We took an extremely challenging problem — the ocean is a brutal place to work — and have detected tsunamis and made forecasts that have proven to be accurate,” said Christian Meinig, director of engineering at NOAA’s Pacific Marine Environmental Laboratory in Seattle, where DART is based. “The American people are safer because of that.”

Responding to demands for more and more timely tsunami information in the wake of the 2004 disaster, PMEL transitioned from a small research facility to an operational laboratory. A technology transfer program has commercialized sensor technology developed by the lab to encourage its adoption by other countries. The nations of Australia, Chile, Indonesia and Thailand have deployed commercial DART sensors and supply data to the NOAA network, and China and India are in the process of deploying them.

In 2004, NOAA’s two tsunami warning centers were staffed 40 hours a week, with on-call coverage. Today, the Pacific Warning Center in Hawaii and the West Coast and Alaska Warning Center in Palmer, Alaska, are staffed 24-by-7 throughout the year.

In addition to the advancements made in hardware and communications, computer modeling for tsunami forecasting also has taken a leap forward. In 2004, NOAA had no high-resolution modeling programs for forecasting tsunami impact on U.S. coastlines. Today the warning centers have 43 models for producing real-time inundation forecasts.

“Over the last four years, that’s where the enormous strides have been made,” Meinig said. “Today we are on the cusp of providing detailed and accurate site-specific forecasts.”

The heart of the DART system is a network of ocean buoys that report sea level changes as measured by water pressure on the ocean floor, as far as 4,000 meters below the surface. This data is transmitted over an IP link through the Iridium satellite network to NOAA tsunami warning centers.

“The buoy is a gateway relay device,” Meinig said. “The brains are really at the sea floor.”

These “brains” constantly measure pressure and predict what that pressure should be in the next 15 minutes based on tides. If actual pressure varies from the predictions beyond a preset threshold an alert is sent. Data is relayed from the sensor to the surface buoy by acoustic modem.

“It operates at a whopping 600 baud,” Meinig said of the acoustic modem. The link from the buoy to the satellite operates at 2400 baud. “We’re still in the stone age” of low power global communications, he said. “We are an extremely low power system, operating at very low data rates. We don’t need more. The messages are small.”

When no tsunami events have been detected the sensors report four times a day with hourly readings, so data points can be compared with tides to confirm that systems are working accurately. When an alert is sent, more frequent reporting, up to once a minute, is triggered. Data is sent via satellite to a network operations center at NASA’s John C. Stennis Space Center in Mississippi, and from there over ground networks to the tsunami warning centers in Hawaii and Alaska. Real time data from DART sensors is available online at http://www.ndbc.noaa.gov/dart.shtml.

NOAA began prototype development of the DART system in 1995 and the first four stations were in place by August 2000. The 2004 Indian Ocean tsunami spurred further deployment and commercial development of the technology. The U.S. deployed stations developed by the DART project are operated and maintained by NOAA’s National Data Buoy Center.

DART II, the current generation of technology, has two-way communications to enable on-demand data transmission from the stations. This can allow the identification of tsunamis below the automatic reporting threshold of the sensors, which can provide valuable data. In the four years since DART has been in production, deployment of about a dozen micro-tsunamis have been detected. These have been too small to do damage, but can validate the accuracy of the data being reported and the forecasts being generated, Meinig said.

The next generation of sensors, DART EDT, or Easy to Deploy, now is under development by PMEL.

Accurate data does not always mean adequate warnings are available. The location of the event generating a tsunami and the placement of the sensors also are factors. A tsunami was triggered in September by a quake about 125 miles south of American Samoa. The wave was detected by two DART sensors within the hour and real-time forecasts were generated. Unfortunately, the wave hit Pago Pago in American Samoa about 20 minutes after the quake.

“We did get warnings out to the rest of the Pacific basin,” Meinig said.

That is why commercialization of the technology is valuable. The ability for other nations to buy and deploy off-the-shelf systems expands the sensor network and the amount of data available.

“It’s all plugged into the same network, with the same data formatting and detection schema,” Meinig said. These means all the data can be used by forecasters at warning centers and shared at decision support centers.

The formatting and reporting of tsunami data have not yet been formalized into technical standards. But, “we are heading that way,” through the International Tsunametor Partnership, Meinig said. This group of coastal countries is standardizing detection tools.