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The Science of Surfing
on top, Satellite data shows waves developing in Pacific; on bottom left, two days later, a surfer at Half Moon Bay, Calif. rides those waves; at bottom right, Radarsat shows the swell one day after the surfer rode them
Top: Topex data shows waves developing in Pacific. Bottom left: Two days later, a surfer at Half Moon Bay, Calif. rides those waves. Bottom right: Radarsat shows the swell one day after the surfer rode them
Surfer images courtesy Frank Quirarte, Mavsurfer.com

Topex image -- browse
Browse image -- surfer
Browse image -- data
Ocean surface topography from space
QuikScat data
Dude, keep missing those killer waves? Maybe 'rocket' science can help.

Surf forecasters are now using near real-time meteorological data from satellites to find big waves. With a click of a mouse, they can use the Internet to link to satellite sources like NASA's QuikScat satellite with its JPL SeaWinds Scatterometer, which provides data used for studying ocean circulation, forecasting weather and understanding air-sea interactions that control global climate.

"We are using satellite data to study the global and coastal oceans in many different ways. Surfers are now using it too, including to figure out where to ride gigantic waves," said JPL oceanographer Ben Holt. "The skill and nerve needed to ride big waves is awe-inspiring."

Space technology allows surf forecasters to access extensive information about the ocean, enabling them to pinpoint the exact location and time for an ideal surfing experience. For example, there is a well-known big wave site called Mavericks, based in Half Moon Bay, San Francisco, Calif. A group of surfers uses QuikScat data to help locate areas around the world where big waves will reach when they develop from growing weather systems like storms and hurricanes. Big weather systems mean big waves-some taller than 60 feet (18 meters)-that move so fast, surfers need to be towed in with jet skis just to catch them. Some surfers will do whatever is necessary to ride those waves, whether that means driving to another beach or packing up for a transatlantic journey.

What exactly is a good wave? The best and biggest waves are products of intense, distant storms that generate heavy winds. At first these winds cause water to displace in a rippling effect. Blowing a powerful fan on a tub of water creates a similar effect. Winds that blow continuously for many days create many waves that eventually slam into one another and create what's known as "chop." With enough energy, these waves can accumulate and develop a large swell that travels faster and farther than smaller waves, away from the storm itself, and eventually makes it all the way to distant shores. A large, long swell is the driving force behind a large, sweet wave, built up by winds pushing several waves together. It's like a power surge of water-the wave true surfers dream about.

Surfer at Half Moon Bay, Calif
Surfer at Half Moon Bay, Calif.
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"My ideal wave would be something at the Dungeons at Capetown, South Africa," said Megan Curry, a surfer who works at the Green Room Surf Shop in Newport Beach, Calif. "(It would be) very heavy with very thick water, a dark gorgeous blue color, perfect barrels and long rides...like 50 feet (15 meters) tall."

Finding and tracking these waves is a matter of comparing data and observations from multiple sources, like satellites, wave charts and buoys. The first thing to do is to locate a potential swell-producing storm. Geo-synchronous satellites are good for this because they show atmospheric conditions by the hour while positioned about 35,800 kilometers (22,300 miles) above Earth. There are five key geo-synchronous satellites currently positioned above the equator and orbiting at the same speed as Earth, so they seem stationary over Europe and the Atlantic, Pacific and Indian oceans. The instruments on these satellites produce detailed images of clouds and weather patterns. From space, a storm basically looks like a large, swirling mass of clouds. As the storm gets stronger, it starts to resemble a spinning top with a tail or two swirling out of it.

Radarsat data of Point Reyes, Calif.
Radarsat data of
Point Reyes, Calif.

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Only through analyzing its surface pressure can a forecaster confirm whether the storm is at the ocean's surface. Surface wind analyses also confirm whether wind speeds are strong enough to produce a swell. Polar orbiting satellites, like the Topex/Poseidon spacecraft, a joint project between NASA and the Centre National d'Études Spatiales, come in handy for this. Orbiting 1336 kilometers (830 miles) away from Earth, Topex/Poseidon measures the height of the ocean's surface. Data obtained from the satellite can help determine ocean wave heights. The European Space Agency's second European Remote Sensing satellite and the Defense Meteorological Satellite Program's Special Sensor Microwave Imager sensors help confirm sea heights and near-surface wind speed and direction inside a storm. The data from these and other satellites are not only crucial to surfers. They are also particularly important for monitoring events on the ocean's surface inside large storms, where the view is obstructed by clouds and where neither buoys nor ships can reach. Fine resolution radar imagery from synthetic aperture radar including from the Canadian Space Agency's Radarsat as well as the European Space Agency's second European Remote Sensing satellite, produce detailed imagery of ocean swell useful for measuring wave direction and wave height. From such imagery, you can visualize waves forming within storms and changing their structure and direction as they approach the shore.

Perhaps the best support yet for forecasters comes from the SeaWinds Scatterometer, launched in 1999 aboard the QuikScat satellite and managed for NASA's Earth Science Enterprise by JPL. The scatterometer provides extreme detail with a specialized microwave radar capable of measuring near-surface wind speed and direction under almost all weather and cloud conditions. It also tracks almost 100 percent of the global ocean's surface in a 24-hour period, combining the abilities of both the Special Sensor Microwave Imager sensors and the second European Remote Sensing satellite. The quality and strength of its signal enables the QuikScat satellite to provide more detail and accuracy than previous technology could, making it the standard for viewing surface wind direction and speed inside ocean storms.

Overwhelmed by all this technology? Never fear. One basic formula-big storms equal big surf-is all surfers need to grab a board and hit the waves. The right technology is up there in space to help dedicated and determined surfers find out where and when these storms occur. Internet links to satellite data and storm forecasts can be found with little effort, making it fairly simple for anyone to learn how to forecast future surf. A word of caution, though; old-time surfer and JPL oceanographer Bill Patzert advises novice surfers to "be careful out there. Your forecast might be better than your ability to cut those curls." That said, nothing quite substitutes for experience in the water.

Charli Schuler
Jet Propulsion Laboratory