Earth-science researchers in the United States are clamouring for a satellite system dedicated to observing the Earth's surface. Such a tool, they say, will transform studies of earthquakes, volcanoes, ice sheets and global land cover.

When the Earth moved: radar interferometry tracked ground displacements during California's 1999 Hector Mine earthquake. Credit: NASA/SPL

Organizers of a workshop to discuss the issue in Oxnard, California, last month were forced to turn people away. Some 350 researchers wanted to attend, 300 more than expected. Yet despite this growing scientific support, the price-tag of US$450 million means that the project has so far failed to get off the ground.

The satellite-based technology that the researchers want is called InSAR, for interferometric synthetic aperture radar. These instruments bounce radar off the ground, creating a precise map of the surface, including information about the type of ground cover. Unlike global positioning systems, which can only take spot measurements of the location of receiver stations, InSAR-equipped satellites can image large continuous swaths of land.

“This is critical for studying natural hazards, polar ice sheets and large-scale land-cover changes resulting from climate change,” says Jean-Bernard Minster, a geophysicist at Scripps Institution of Oceanography in La Jolla, California.

The few InSAR satellites launched by Japan, Europe and Canada have made some eye-opening discoveries in the past decade. Volcanoes thought to be dormant have been shown to be active, for example, and active volcanoes have been shown to be inflating and deflating much more frequently than previously thought. Massive ice sheets in Antarctica and Greenland have also been mapped.

But researchers say they cannot continue to rely on these satellites for InSAR data, as many were not optimally designed for radar imaging. Some have imprecise orbits, and so do not pass over the same spot of land on each revolution, making it difficult to measure change. Others use radar wavelengths that are unable to penetrate vegetation to image the ground beneath.

The lack of suitable satellites means that many events important to Earth scientists were not imaged by InSAR equipment. The area struck by California's 1994 Northridge earthquake, for example, was only imaged two months before and two years after the event, says Andrea Donnellan, a geophysicist at NASA's Jet Propulsion Laboratory in Pasadena, California. And the recent Parkfield earthquake (see Nature 431, 618; 200410.1038/431618b) was not covered at all, she adds. “Missed opportunities are too many to mention,” says Minster.

After ten years of requests and failed grant applications, the US InSAR hopefuls still do not have a dedicated satellite. Donnellan, who convened last month's workshop, hopes this will soon change. The group is currently applying to the US space agency NASA for funding that could kick-start an InSAR programme. But the lengthy grant-approval process and the design and planning procedure mean that the earliest possible launch would be in 2010.

Donnellan says that a dedicated InSAR system would quickly prove its worth, in much the same way that satellites dedicated to the oceans and atmosphere have vastly improved our understanding of climate and allowed us, for example, to predict El Niño events. “Atmospheric scientists demonstrated the value of spaceborne observations a little over 20 years ago, oceanographers about a decade ago, and when we have an InSAR mission, the same thing will occur for our field,” she says.

In the meantime, other countries are continuing with their own InSAR projects. Japan plans to launch a ¥60-billion (US$600-million) satellite next year, and China may launch its own as early as 2006.