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| Honey, I Shrunk The Data! |
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Spacecraft that study Earth have a lot to keep an eye on! Every second they may pass over a different location. Every second they take pictures of Earth or measurements of the atmosphere. All this information adds up quickly!
If you were downloading this information from the Internet to your computer, it might take hours for you to receive just a few minutes-worth of data collected by a spacecraft.
 Receiving the data down here on Earth from the spacecraft may not be much faster than downloading data to your computer over a phone line. But what if the spacecraft is watching a fast-moving hurricane in the Atlantic Ocean? It's important to rush the images down to the weather forecasters on Earth so they can warn ships in the area and people who live where the hurricane might hit land.
The Earth Observing 3 mission will study Earth's atmosphere to help scientists better understand weather. It will also test some new and better methods to compress--or shrink--the data before it is sent down to Earth. These methods are . . .
 Keep them all and make them small:
Just re-package the data. For example, 100 pennies weighs a lot more than a 1-dollar bill. But they are worth the same! Space engineers call this method "lossless compression," meaning no data get lost.
Squeeze them more and open the door:
Some data that are not very important or useful may escape. But the important data can then be squeezed into an even smaller package. Space engineers call this method "lossy compression," meaning some data get lost.
Save the best and scrap the rest:
Special data are selected for a special reason. For example, scientists might want to know how fast the clouds are moving 5 miles above Earth's surface. These data are separated from the rest, and the rest are thrown out. Space engineers call this method "superchannel data compression," since only one kind of data is saved.
Suppose the data were music on a CD. Normally the CD would hold 12 songs (about 1 hour of music).
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If the music were compressed using lossless compression, the CD could hold 32 songs. This one CD could play for about two hours and 45 minutes, and you would hear the full orchestra.
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If the music were compressed using lossy compression, the CD could hold 240 songs. This music would play for 20 hours! However, the music might sound a little thin, missing some of the backup instruments, like percussion (drums) or bass or flute.
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If the music were compressed using superchannel compression, the CD could hold 12,000 songs! It would take well over a month to play all these songs. However, you might hear only the bare melody, as if played by a solo instrument with no other instruments to accompany it. But, this part of the music might still be all you would need to dance to!
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All this data shrinking is done with computer software and math. Earth Observing 3 is one of the missions of NASA's New Millennium Program. The main job of these missions is to test new technologies in space. If these data compression methods work well on Earth Observing 3, future spacecraft can use this software to allow better studies of the weather.
Some of the most useful technologies invented involved nothing more than doing clever things with bits of data. After all, these are the kinds of technologies that allow you to be reading this over the Internet right now!
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