ERS_fails_000321 PARIS, France - A European satellite that revolutionized the science of monitoring events on Earth from space shut down last week.
Launched in 1991, the first European Remote Sensing (ERS 1) satellite was a pioneer in the sky, acquiring 1.5 million radar images in its nine years, more than triple its expected lifetime. ERS 1 monitored oceanic changes like El Nino, gave scientists startling views of the poles and provided the most precise measurements of topographical changes resulting from earthquakes ever recorded.
ERS 2, the satellite's successor, launched in 1995, is still functioning.
"When ERS 1 was conceived in the late 80s nobody knew all the applications and the breakthroughs that this new kind of satellite would bring," said Stefano Bruzzi, Earth observation program manager at the European Space Agency (ESA), in an exclusive interview to SPACE.com. "In 1995, ERS 2 -- an identical 2.5 metric ton satellite -- was launched to ensure a continuity of this series of Earth observation missions."
The most exciting results from the ERS 1 mission have been in the field of radar interferometry -- providing, for the first time, precise topographic and seismologic information on a routine basis from space.
In the rapidly developing region of Las Vegas, for example, "it was possible to observe a land subsidence over a large area," said Guy Duchossois, ERS mission manager. "Taking very accurate elevation measurements over a period of two years, the ERS SAR (Synthetic Aperture Radar) was able to measure about 4-inch (10-centimeter) land subsidence in this desert. This is due to water extraction from the underground in this arid region."
Using the two satellites -- ERS 1 and ERS 2 -- in tandem obtained these results. This technique, called interferometry, requires several passes by the two satellites over the same point. R. Goldstein and his team developed it at the Jet Propulsion Laboratory (JPL) in the 1980s. They used radar data of SEASAT, the U.S. precursor to ERS. But the U.S. satellite, launched in 1978, failed after only three months.
ERS 1's total mission cost, including the launch on Ariane, was $800 million.
Observation, innovation
Working in darkness or with bad weather conditions, the two ERS radar satellites were able to measure accurately the overall displacement of the ground after an earthquake over large areas, with a 60-mile-by-60-mile (100-square-kilometer) footprint.
The ground displacement from the 1992 Landers earthquake in California was detected with the use of ERS 1 and 2 radar by D. Massonet and his team from the French space agency -- CNES. The precision of the ERS approach may one day give seismologists the ability to accurately forecast an earthquake.
Like its predecessor ERS 1, the ERS 2 satellite is monitoring Earth by using its powerful, cloud-piercing radars.
"For the first time in history, oil tanker's captains have been jailed by Singapore court for causing oil spills" with prosecutors using ERS sea-surveillance data," Duchossois said. "The satellite's SAR radar was able to detect in real time illegal discharge of ships, even at night."
From its 485-mile (785-kilometer) high polar orbit, the ERS radar altimeters were able to "see" through the polar ice cap, producing the first "gravity map" of the seafloor. This "map" shows how the surface of the earth is divided into a dozen or so large plates near the surface, plus several smaller ones. By mapping the fracture zones of the South Pole, it was possible to prove the existence of the Bellinghausen plate, formerly only a theoretical concept, which is hidden under the South Polar icecap.
"The mapping of the seafloor worldwide was so accurate with the data provided by ERS satellites that it made the Pentagon decide to declassify -- a few years ago -- its underwater cartography," Duchossois said.
Recently, the last shuttle mission, the Shuttle Radar Topography Mission, used very similar interferometry technology with SAR radar. The only differences were the length and the orbital Earth coverage of the mission.
"With the shuttle, the Earth terrain [at] 57 degrees north and south latitudes -- like Canada, Scandinavia and the poles -- was left unmapped. Instead, the ERS missions did cover, over years, the entire Earth more than a dozen times," Bruzzi said.
Now with the loss of ERS 1, scientists must wait until 2001 to use the interferometry technique with another two-satellite combination. That is when ESA will launch the Envisat (Environment) satellite, which should also be able to work together with ERS 2.
The ERS 1 and ERS 2 tandem operations paved the way for the definition of the Envisat mission.
Envisat, which is an ESA civilian program, is a much larger satellite that will adopt ERS technology. Four of its 10 instruments will be the same as ERS. Envisat will have twice the mass and the scientific capability of ERS, while costing $2.2 billion, including launch and five years of operations.
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