Washington

Picture this: researchers rely on Landsat's images, such as this one of silt in the Gulf of Mexico. Credit: LANDSAT

Engineers are struggling to fix a problem with the Landsat 7 remote-sensing satellite that has left global-change researchers without their primary source of new large-scale images of the Earth.

Project managers for the US Geological Survey, who manage the satellite from NASA's Goddard Space Flight Center in Maryland, have yet to fully understand the situation. The fault, which first occurred late last month, lies with the Scan Line Corrector, a device that compensates for Landsat's motion and stops pictures becoming blurred. Without it, about 25% of each image is severely degraded.

Bruce Quirk, the Geological Survey's chief scientist for remote-sensing systems, says it may take two more weeks to find out whether the failure is electrical or mechanical. An electrical fault would be preferable, as the satellite carries back-up electrical systems.

But engineers could find new ways of creating useable images if the failure is mechanical, adds Quirk. Data near the centre of each image are less affected, and it should be possible to provide equivalent coverage by combining multiple images of a ground target — although the process would increase the time needed to create undistorted scenes.

Regular photography has been suspended, a blow to the remote-sensing researchers who used it. The satellite and its predecessors, each government-run, have been taking the same kind of image for 31 years, allowing users to track changes over time. Landsat 7 normally collects 250 large-scale images, of 183 × 170 kilometres each, every day.

The problem comes just as Landsat's privatization is being considered. Congress and the Bush administration would like to see the next satellite owned and run by the private sector, which would sell the data to scientists and other users (see Nature 419, 328; 200210.1038/419328a).

But one of two companies expected to bid for the contract — DigitalGlobe of Longmont, Colorado — withdrew earlier this year, saying the venture was too risky commercially. The government insists on keeping image prices low enough for researchers to afford, and the market — mainly federally funded scientists — is not large.

That left Resource21 of Denver, Colorado, as the only company known to be in the running. NASA officials won't say whether they have received other bids, but the contract award, planned for this month, has been delayed, probably until late summer.

Thomas Lillesand, director of the Environmental Remote Sensing Center at the University of Wisconsin at Madison, says that trying to increase Landsat usage is a chicken-and-egg problem. The market for images should be growing as new image-analysis tools become available, but users won't commit themselves unless “we can get sufficient numbers of satellites up there that we can depend on”.