Featured Research

from universities, journals, and other organizations

Scientists Find Tsunami 'Shadow' Visible From Space

Date:
July 16, 2009
Source:
National Oceanic and Atmospheric Administration
Summary:
For the first time, scientists have demonstrated that tsunamis in the open ocean can change sea surface texture in a way that can be measured by satellite-borne radars. The finding could one day help save lives through improved detection and forecasting of tsunami intensity and direction at the ocean surface.

The ground track of the Jason-1 satellite is shown here as it crossed the Sumatra-Andaman tsunami at hourly intervals after the earthquake occurred. White stars show the location of the tsunami wave sources.
Credit: NOAA

For the first time, NOAA scientists have demonstrated that tsunamis in the open ocean can change sea surface texture in a way that can be measured by satellite-borne radars. The finding could one day help save lives through improved detection and forecasting of tsunami intensity and direction at the ocean surface.

“We’ve found that roughness of the surface water provides a good measure of the true strength of the tsunami along its entire leading edge. This is the first time that we can see tsunami propagation in this way across the open ocean,” said lead author Oleg Godin of NOAA’s Earth System Research Laboratory and the Cooperative Institute for Research in Environmental Sciences, in Boulder, Colo.

Large tsunamis crossing the open ocean stir up and darken the surface waters along the leading edge of the wave, according to the study. The rougher water forms a long, shadow-like strip parallel to the wave and proportional to the strength of the tsunami. That shadow can be measured by orbiting radars and may one day help scientists improve early warning systems. The research is published online this week in the journal, Natural Hazards and Earth System Sciences.

The new research challenges the traditional belief that tsunamis are too subtle in the open ocean to be seen at the surface. The findings confirm a theory, developed by Godin and published in 2002-05, that tsunamis in the deep ocean can be detected remotely through changes in surface roughness.

In 1994, a tsunami shadow was captured by video from shore moments before the wave struck Hawaii. That observation and earlier written documentation of a shadow that accompanied a deadly tsunami on April 1, 1946, inspired Godin to develop his theory. He tested the theory during the deadly December 26, 2004, Indian Ocean tsunami, the result of the Sumatra-Andaman earthquake.

Godin and colleagues analyzed altimeter measurements of the 2004 tsunami from NASA’s Jason-1 satellite. The data revealed clear evidence of an increased surface roughness along the leading edge of the tsunami as it passed across the Indian Ocean between two and six degrees south latitude.

Tsunamis can be detected in several ways. One detection method uses a buoy system that warns coastal communities in the United States of an approaching tsunami. NOAA’s Deep-ocean Assessment and Reporting of Tsunamis (DART) early warning system uses sensors on the ocean floor to measure changes in pressure at each location. The DART network of 39 stations extends around the perimeter of the Pacific Ocean and along the western edge of the North Atlantic Ocean and Gulf of Mexico. The technology provides accurate, real-time information on the amplitude, over time, of an approaching tsunami. NOAA's tsunami warning centers then use this information to forecast the tsunami's impact on coastlines.

A second method uses space-borne altimeters to detect tsunamis by measuring small changes in sea surface height. Only a handful of these instruments are in orbit and the observations are limited to points along a line.

The new study presents a third way to detect tsunamis — by changes in the texture of the surface water across a wide span of the open ocean.

Godin’s research confirmed his theory that a tsunami wave roughens the surface water through air-sea interaction. First the leading edge of the tsunami wave stirs up the surface winds. Those same winds, which become more chaotic than the wave itself, then churn the surface waters along the slope of the wave.

Because rough water is darker than smooth water, a contrast forms between the dark, rough water of the wave and the bright, smooth water on either side of it. Common scientific instruments, called microwave radars and radiometers, are able to detect this contrast, known as a tsunami shadow.

When orbiting the Earth, microwave radars and radiometers can observe a band of ocean surface hundreds of kilometers wide and thousands of kilometers long. If programmed correctly to observe sea surface roughness, they could potentially map an entire tsunami, said Godin.

The paper, “Variations in sea surface roughness induced by the 2004 Sumatra-Andaman tsunami,” by O. A. Godin, V. G. Irisov, R. R. Leben, B. D. Hamlington, and G. A. Wick, appears in Natural Hazards and Earth System Sciences, a journal of the European Geosciences Union.


Story Source:

The above story is based on materials provided by National Oceanic and Atmospheric Administration. Note: Materials may be edited for content and length.


Cite This Page:

National Oceanic and Atmospheric Administration. "Scientists Find Tsunami 'Shadow' Visible From Space." ScienceDaily. ScienceDaily, 16 July 2009. <www.sciencedaily.com/releases/2009/07/090716103849.htm>.
National Oceanic and Atmospheric Administration. (2009, July 16). Scientists Find Tsunami 'Shadow' Visible From Space. ScienceDaily. Retrieved April 21, 2014 from www.sciencedaily.com/releases/2009/07/090716103849.htm
National Oceanic and Atmospheric Administration. "Scientists Find Tsunami 'Shadow' Visible From Space." ScienceDaily. www.sciencedaily.com/releases/2009/07/090716103849.htm (accessed April 21, 2014).

Share This



More Earth & Climate News

Monday, April 21, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Drought Concerns May Hurt Lake Tourism

Drought Concerns May Hurt Lake Tourism

AP (Apr. 18, 2014) Operators of recreational businesses on western reservoirs worry that ongoing drought concerns will keep boaters and other visitors from flocking to the popular summer attractions. (April 18) Video provided by AP
Powered by NewsLook.com
Man Claims He Found Loch Ness Monster With... Apple Maps?

Man Claims He Found Loch Ness Monster With... Apple Maps?

Newsy (Apr. 18, 2014) Andy Dixon showed the Daily Mail a screenshot of what he believes to be the mythical beast swimming just below the lake's surface. Video provided by Newsy
Powered by NewsLook.com
First Ever 'Female Penis' Discovered In Animal Kingdom

First Ever 'Female Penis' Discovered In Animal Kingdom

Newsy (Apr. 18, 2014) Not only are these newly discovered bugs' sex organs reversed, but they also mate for up to 70 hours. Video provided by Newsy
Powered by NewsLook.com
Ark. Man Finds 6-Carat Diamond At State Park

Ark. Man Finds 6-Carat Diamond At State Park

Newsy (Apr. 18, 2014) An Arkansas man has found a nearly 6.2-carat diamond, which he dubbed "The Limitless Diamond," at the Crater of Diamonds State Park. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins