USGS serves up fresh satellite views of Earth

USGS serves up fresh satellite views of Earth

The New York City area, including Long Island and Newark, N.J., was captured in a July Landsat7 image, left. Landsat7 also caught images of Supericeberg B10A, a chunk roughly the size of Rhode Island, drifting off the southern coast of Argentina.

By Patricia Daukantas

GCN Staff

Earth's newest eye is beaming down trillions of bytes in many colors.

Early this month, the Geological Survey began offering images from the Landsat 7 remote-sensing satellite that was launched into near-polar orbit on April 15 after four months of shakedown testing.

The spacecraft can see details as small as 15 meters in diameter, or 49 feet.

The sixth Landsat craft to reach orbit in 25 years, Landsat 7 is transmitting up to 125G of data each day'a staggering 4T per month. The Earth Resources Observation System Data Center in Sioux Falls, S.D., is capturing and offering the data to the public on the Web.

In 24 hours, Landsat 7 can send up to 250 scenes, said Tracy Zeiler, Landsat 7 mission management officer for USGS. The number of daily images depends on the cloud cover 445 miles below the satellite.

On average, a minimally processed image takes up 500M, Zeiler said. To handle so many bytes, the EROS Data Center is using robotic tape silos [GCN, Feb. 8, Page 34].

Where's it go?

Depending on its orbital position, Landsat 7 downloads data to one of three ground stations: the Sioux Falls center, the Poker Flat Research Range near Fairbanks, Alaska, or the Svalbard Ground Station in Norway.

At Sioux Falls, a RAID system temporarily holds the downloaded images until they are archived, Zeiler said. Data from the polar ground stations is captured on tape and forwarded to the EROS Data Center by mail.

'It's a high volume of data, so getting network connections in and out of Svalbard and Alaska is a very expensive deal,' Zeiler said.

This is the first Landsat mission for which the center has had its own antenna and its own data collection and archiving facility.

The image archiving process generates metadata and browse data, which are ar-chived separately from the images, Zeiler said. Metadata provides information about location and cloud cover; the browse data shows low-resolution versions of each scene.

The data is available to users within 24 hours of image acquisition. 'Obviously, we have to keep up,' Zeiler said. 'If we get behind, we'll have a never-ending queue growing. So yes, every day we have to keep up with that day's acquisition.'

From the Web gateway, at, users can browse the data holdings and order scenes. The Landsat program's current and historical images have many uses, such as crop monitoring, urban-sprawl determinations and detailed mapping, Zeiler said.

Landsat 7's detector takes images in three colors of visible light and three bands of near-infrared light, all at 30-meter resolution. The sensor also images in a thermal band of longer-wavelength infrared light at 60-meter resolution. In panchromatic mode, the camera picks up most of the visible-light spectrum with fine detail at 15-meter resolution.

Landsat 7 products cost $475 for a raw image and $600 for a minimally processed image. Images from earlier Landsats, as well as from space shuttle missions, non-Landsat satellites, weather balloons and aircraft observations, are available at various prices.

Landsat 7 images are stored in the Hierarchical Data Format developed by the National Center for Supercomputing Applications in Urbana, Ill., said Hilary Lewis, a spokeswoman for Fortner Software LLC of Sterling, Va. The company, which develops software for analyzing HDF data, helped fine-tune the Landsat 7 data archive formatting.

As Landsat 7's four-month testing and calibration period wound down, the Earth Observing System Data Gateway started taking orders in late August for the new images, said Ronald E. Beck, a spokesman for the EROS Data Center. USGS officially an-nounced the data's availability on Sept. 7.

Hot shots

The agency received more than 100 orders during the early offering, Zeiler said. Beck said he expects business to pick up as word gets out about the new satellite images.

NASA's Goddard Space Flight Center in Greenbelt, Md., which managed construction of the spacecraft and its detector, still operates Landsat 7. Plans call for NASA to transfer operations to USGS in late 2000.

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