GARRETSON, S.D. - The millions of satellite images collected at a federal repository north of Sioux Falls help document forest fires, droughts, hurricanes, tsunamis and other calamities.

Scientists and engineers at the U.S. Geological Survey's EROS Data Center often focus on the data found in images' varying spectral bands, but sometimes they enjoy stepping back and simply admiring an image for its beauty.

The centre north of Sioux Falls has selected 40 of these standouts for its latest "Earth As Art" exhibit, now in its third incarnation. Prints of the images arrived in Washington, D.C, recently to begin a one-year stint at the Library of Congress.

Jon Christopherson, a contractor working at the EROS Data Center, said human eyes peering down on the Earth would miss out on the many spectral bands a satellite can capture.

"In other parts of the spectrum, there's a lot of variation," Christopherson said. "And that's what these satellites allow us to tease out of there, a lot of information that isn't otherwise available to us.

"And sometimes it just makes a pretty picture, too."

To create those pretty pictures, the scientists and engineers prepping the images might adjust or enhance settings such as saturation or contrast, but the prints still accurately depict the landforms and waterways below.

One of Pat Scaramuzza's favourites in the collection is "Ice Waves," a May 21, 2001, image snapped by Landsat 7 showing Greenland's intricate network of fjords funnelling glacial ice to the Atlantic Ocean.

During the summer melting season, newly calved icebergs join slabs of sea ice and older icebergs, swirled into interesting shapes.

"This is not land mass. This is ice," said Scaramuzza, a contractor working at the centre. "It's just floating around off the coast of Greenland. And if you look at this again, that won't be there."

The USGS Center for Earth Resources Observations and Science is the main federal repository for satellite images. Many of the land images gathered at EROS are beamed down by the Landsats, a pair of workhorse satellites operating long past their prime.

Landsat 5, launched in 1984, continues to transmit detailed images of the ground surface more than two decades past its scheduled mission end, while younger sibling Landsat 7 was launched in 1999 and is still putting in overtime.

In "Rocky Mountain Trench," an image snapped by the Landsat 5 satellite on Feb. 1, 2004, admirers see what appears to be a stroke of thick red paint, but it's actually interplay of light and cloud in the Canadian Rockies. Without the infrared band in the image, the clouds would be hardly visible.

"These are mountain valleys, actually, that the clouds filled in," said Linda Jonescheit, a project tech specialist. "They followed the valleys."

All of the Earth As Art images are free to download for personal or commercial use and some previous selections have made it into German coffee table magazines or neck ties.

As one copy of Earth As Art 3 continues its time in Washington, another will be on display at Augustana College's Center for Western Studies from May 31 through Sept. 3. The exhibit is also slated to travel to the University of North Dakota and California State University-Chico.