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ESA Combats Ground Interference to Earth Observation Satellites

PRAGUE — The European Space Agency has modified the frequencies used by some of its radar Earth observation satellites to reduce the signal interference from ground-based wireless communications systems that are often operating illegally, ESA Earth Observation Director Volker Liebig said June 13.

Liebig said the interference is one reason the 20-nation ESA and other space agencies are joining operators of telecommunications satellites in fighting attempts by wireless broadband network operators to be granted use of spectrum now reserved for satellites.

Addressing a briefing at London’s Royal Society to discuss results from ESA satellites studying climate change, Liebig said many users of wireless communications are violating the regulatory terms of use for their devices — for example, operating them outside when only indoor use has been given regulatory approval.

ESA has protested against ground users, some of them military, of radars that should not be in the frequencies used by radar Earth observation spacecraft. The agency’s Soil Moisture and Ocean Salinity satellite regularly encounters signal interference.

A similar satellite being designed for NASA, the Soil Moisture Active Passive satellite to launch late this year, has been specifically designed to be able to separate environment signals from the interference it is certain to encounter from terrestrial networks.

Liebig said ESA will be active at the World Radiocommunications Conference organized by the International Telecommunication Union and scheduled for 2015, at which terrestrial wireless network operators are expected to seek additional bandwidth, some of it now reserved for satellite telecommunications and Earth observation systems.

Europe’s Sentinel satellites are among those whose frequencies have been modified to get around interference. The Sentinel spacecraft, with a variety of payloads and sensors including radar, are part of the European Commission-owned Copernicus Earth observation program.

The first of these spacecraft, the radar-equipped Sentinel-1A, was launched in April aboard a European version of Russia’s Soyuz rocket.

Liebig said the Soyuz rocket left Sentinel-1A in an orbit that was about 8 kilometers lower than planned — but still within the contracted orbital parameters agreed to with launch services provider Arianespace of Evry, France.

As a result, it will take ground controllers about four weeks longer than planned to raise the orbit and complete verifications before declaring it fully operational.

As Sentinel satellites are launched and begin adding to the Copernicus data bank they will increase the already huge volume of satellite data that need to be stored and analyzed.

To do this, ESA in 2009 persuaded its member governments to fund what then was considered an odd agency program called the Climate Change Initiative (CCI). The British government is paying about one-quarter of CCI’s 75 million euros ($100 million) in cost between 2009 and 2016.

British Science Minister David Willetts, who is responsible for space policy, said Britain is making further investments in computing power for the U.K. Met Office to aid it in producing data on climate change, and in climate-change analysis by the British National Physical Laboratory.

Liebig said that ESA’s CCI proposal met so much resistance from the agency’s governments that it was easier for him to win backing for a billion-euro satellite infrastructure than for the 75 million-euro CCI program.

Several governments at the time said ESA’s job as a research and development agency should not extend to taking responsibility for the long-term storage of environmental data, just as ESA will be transferring the Sentinel satellites to the European Commission for operations in Copernicus.

“I think this is one of the best investments ESA ever made,” Liebig said, referring to CCI. Whether ESA governments will agree when they will be asked to renew the program in 2016 is not clear, he said.

Especially through its Cryosat satellite, ESA has made monitoring of polar ice sheets one of its specialties among the 50 essential climate variables that have been identified by the Global Climate Observing System, part of the World Meteorological Organization, as important indicators.

ESA and NASA joined forces on the IceBridge program that has culled several decades of data from 10 satellites to examine polar ice. The data from the program, which is ongoing, show that the net amount of ice in the polar regions is reducing despite regional variations and is a contributor to the global rise in sea levels.