Friday, June 20, 2008

Sharper Satellite Images

A new satellite could produce color images of objects half the size of those visible to its predecessors.

By Lissa Harris

Preparing for takeoff: A photo of GeoEye’s new imaging satellite in May 2008 at General Dynamics’ facility in Gilbert, AZ, where the satellite underwent environmental testing. Credit: GeoEye

Next month, a commercial satellite company is scheduled to launch an Earth-orbiting satellite that will be able to produce color images so detailed that the U.S. government doesn't permit their public release. The new satellite, dubbed GeoEye-1, will provide images at its highest resolution for classified military and intelligence uses. Slightly lower-resolution versions will be available for commercial and research purposes, as well as through online services like Google Earth.

On August 22, Virginia-based GeoEye will launch the satellite, from Vandenburg Air Force Base in California. The satellite will be able to distinguish objects that measure 0.17 square meters. The best color satellite images now commercially available, from GeoEye competitor DigitalGlobe, can resolve objects that measure 0.36 square meters.

"We can see a beach ball 16 inches across," says GeoEye CEO Matt O'Connell. According to O'Connell, the satellite data will be accurate to within three meters of "ground truth"--a measure of how well the satellite imagery matches up to GPS data taken from the ground. DigitalGlobe's QuickBird satellite is accurate to 27 meters.

GeoEye-1 owes its improved accuracy to its star trackers--sensing devices that allow it to calculate its exact position based on the stars. Its star trackers were initially developed by Ball Aerospace for military applications and only recently cleared for commercial use.

Although federal regulations prohibit satellite companies from selling images with resolutions of less than 0.25 square meters, O'Connell says the images taken by GeoEye-1 will still be the highest-resolution color images available on the market--able to spot a person on the ground or distinguish between a tank and a truck.

GeoEye-1 will record color in four wavelengths: blue, green, red, and near-infrared. It is capable of imaging up to about 700,000 square kilometers a day--an area roughly the size of Texas. The company expects the satellite to last for at least seven years.

The fledgling industry of commercial satellite imagery has grown rapidly since its inception in the 1990s. Fifteen years ago, almost all satellite imagery worldwide was produced by governments and was highly classified. But since 1994, when President Bill Clinton signed a directive broadly declassifying commercially produced satellite data, military and intelligence agencies have increasingly relied on commercially acquired data, and U.S. government restrictions on that data have been steadily loosening.

The increasing quality of commercial satellite data is a tremendous boon to researchers, says James Garvin, chief scientist at NASA's sciences and exploration directorate at the Goddard Space Flight Center in Greenbelt, MD. Since 2006, NASA researchers have been using high-resolution color images of Mars from the HiRISE satellite to research the planet's climate, geology, and history. It's only recently, Garvin says, that earth scientists have begun to turn this kind of attention to our own planet.

"It's ironic that we implemented it on Mars before Earth," he says. "I'm particularly excited about its capabilities for helping train us to understand some of the unknown unknowns about climate change."