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Judging the Ocean by Its Cover

Who Are NASA's Earth Explorers?

The elementary school student wondering how El Niño will affect tomorrow's weather. The scientist studying connections between ozone and climate change. And the farmer using satellite pictures to keep track of crops. All of these people are Earth Explorers -- they are all curious about the Earth system. This series will introduce you to NASA Earth Explorers, young and old, with many backgrounds and interests.

Exploring the ocean is easier said than done. First of all, it's huge. The ocean's deep, dark waters cover about 70 percent of Earth. And it's hard to see what's going on in the ocean, especially compared to the atmosphere. Look up on a clear day and you can see all the way to the sun. But stare as long and hard as you want at the ocean and you still can't see much past the water's surface.

It turns out, though, that you can learn a lot about the ocean from its surface alone. That's why NASA has satellites in space that are always watching the ocean from above. Scientists use the data gathered from space to reveal many of the ocean's secrets.

NASA scientist Lee-Lueng Fu smiles while sitting at his computer desk studying satellite images of the ocean's surface
NASA's Lee-Lueng Fu leads a team of scientists from all over the world. Their goal is to better understand the ocean's role in our changing climate. Most of their data come from two satellites, named TOPEX/Poseidon and Jason-1. Both spacecraft carry "radar altimeters." These are instruments that measure the height of the ocean's surface.

Image to left: NASA's Lee-Lueng Fu is studying the ocean's surface to uncover what is happening below. Credit: NASA

Sea surface height can tell you more about the ocean than you might think. It can be used to calculate the amount of heat stored in the ocean. How? Water expands when it heats up. That causes sea level to rise. Conversely, water contracts as it cools. That causes sea level to fall. Sea surface height is also used to figure out the speed and direction of ocean currents.

Ocean heat and ocean currents affect our weather and climate in many ways. The more scientists know about them, the better they can predict things like hurricanes, global warming and El Niño. Also, maps of ocean currents help fishermen fish and ship captains set their course.

Fu's team is learning more about tsunamis, too. TOPEX/Poseidon and Jason-1 happened to be looking right at the Indian Ocean on December 26, 2004. You might remember that's where and when a deadly tsunami was born. The satellites were able to measure the heights of the tsunami waves.

"It's hoped that these data will help with the prediction of tsunamis and revealing more details of the earthquakes that cause them," Fu said.

Satellite measuring sea level
Image to right: NASA's TOPEX/Poseidon and Jason-1 satellites have radar altimeters onboard. These instruments measure the height of the ocean's surface by how long it takes a pulse of energy to travel from the satellite, to the Earth's water surface, and back. Credit: NASA

It wasn't so long ago that we knew a lot less about the ocean. NASA's Seasat was the first satellite designed to observe the ocean. It was launched in 1978. Before then, there was no quick way to collect data over the entire ocean.

"It takes a ship weeks to cross the Pacific. It takes only tens of minutes for a spacecraft to do the same," Fu said. "From space, we can watch the change in the ocean as it happens."

International cooperation has also advanced ocean research. The United States and France work together on TOPEX/Poseidon and Jason-1. And Fu works with scientists from Japan, the United Kingdom and other nations. Working with people in different countries is what Fu says he enjoys most about his work.

"Science has been among the best bridges connecting people from all over the world." Fu said.

Where Are They Now?

You might just be able to see TOPEX/Poseidon or Jason-1 yourself. Follow the directions at the Where Are They Now? site to find out where the satellites are located and when they can be viewed from your area.

See previous Earth Explorers articles:
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Related Resources
Ocean Surface Topography From Space
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Dan Stillman, Institute for Global Environmental Strategies