Friday, May 23, 2014

Science graphic of the week: Monitoring ocean waves from space

Image credit: ESA/DLR (Animation: WIRED)
Ships, oil platforms and offshore wind farms are threatened by rough seas.
Information provided by radar satellites can support the detection and forecast of extreme wave heights.

From Wired by Betsy Mason

The radar instruments on some satellites can be used to gather all sorts of interesting information.
The animation above (see video) illustrates wave heights in the North Sea that were derived from satellite radar measurements.

Wave height and frequency in a large body of water are largely dependent on the speed of the wind moving across the surface.
Satellites with specialized radar sensors can measure wind speed by looking at the ocean surface from several angles as it passes over.
The radar detects the reflectivity of the water, which is determined by the roughness of the surface.
Higher reflectivity means rougher water, which is caused by stronger winds.
Wind direction can be estimated by looking at wind streaks in radar images of the water’s surface.

In response to threats from extreme waves to ships, oil platforms and wind farms in the North Sea, the European Space Agency is using its satellites to monitor the roughness of the sea surface to help spot big waves and feed computer models that try to forecast dangerous waves.

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