NASA - National Aeronautics and Space Administration

Who Are NASA's Earth Explorers? The student thinking about El Niño. The scientist studying climate. And the farmer looking at satellite images. All of these people are Earth Explorers. They're all curious about how Earth works. This is a story about a NASA Earth Explorer. Nominate an Earth Explorer! Tell us about the Earth Explorers you know. We're looking for students, teachers, scientists and others who are working with NASA Earth science data and imagery to better understand our home planet. Send your nominations to Dan Stillman: dan_stillman@strategies.org.

Image above: Scientist Lee-Lueng Fu studies the ocean's surface to find out what's going on down below. Credit: NASA

It's not so easy to explore the ocean. First of all, it's HUGE. More than half of the Earth is covered by ocean. And it's hard to see what's going on in the ocean. The water is deep and dark.

The ocean is even harder to study than air. Look up on a clear day and you can see all the way to the sun. But stare as long as you want at the ocean. You still can't see much past the surface.

Lucky for us, you can tell a lot about the ocean from its surface. That's one way NASA uses satellites. They watch the ocean from space. They collect all kinds of facts about the ocean.

Lee-Lueng Fu has learned a lot about the ocean from satellites. Fu is a NASA scientist. He leads a team of scientists from across the globe. They study the ocean and how it changes the weather.

What facts are most important to Fu and his team? Facts about the sea level. The sea level rises when water heats up. And it drops when water cools down. So, they can tell how much heat is in the ocean if they know its height. Ocean heat affects hurricanes and other weather.

Sea level data is also used to make maps of ocean currents. These maps help fishermen fish. And ship captains use the maps to set their course.

Image above: Satellites measure sea level with unseen signals. Credit: NASA

How does a satellite measure sea level? It sends out an unseen signal. The signal bounces off the ocean. Then it comes back to space. The satellite times how long it takes the signal to go and come back. The longer it takes, the lower the ocean is. The shorter it takes, the higher the ocean is.

We didn't used to know so much about the ocean. At least not before 1978. That's when the first satellite made for looking at the ocean was launched. Before then, there was no quick way to scan the whole 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.

There's another reason we know more about the ocean. It's because people have been working together. Fu likes to work with scientists in other countries. He says that science connects people from all over the world.

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Dan Stillman, Institute for Global Environmental Strategies