GPS World, January 2017
WATCH MARKET MAPPING 2 Sinking Towers Shifting Lands T he European Space Agencys Sentinel 1 satellites show that the Millennium Tower skyscraper in San Francisco is sinking by a few centimeters a year Completed in 2009 the 58 storey tower has been showing signs of sinking and tilting possibly because the supporting piles arent firmly resting on bedrock Studying the city is helping scientists improve monitoring of urban ground movements particularly for subsidence hotspots in Europe Scientists combined multiple radar scans from the Copernicus Sentinel 1 twin satellites to detect subtle surface changes down to millimeters The technique works well with buildings because they better reflect the radar beam It is also useful for pinpointing displacement hotspots over large areas thanks to Sentinel 1 s broad coverage and frequent visits Working with the European Space Agency the team from Norut PPO labs and Geological Survey of Norway have also mapped areas in the wider San Francisco Bay Area that are moving European cities experience similar subsidence to the Bay Area For example the area around Oslos train station in Norway is reclaimed land Newer buildings such as the nearby opera house have proper foundation into bedrock but the older parts of the station experience severe subsidence The open data policy and regular coverage plan of Copernicus promise cost efficient and reliable deformation data The Copernicus Sentinel 1 mission is for the first time making it possible to launch operational national deformation mapping services said Dag Anders Moldestad Norwegian Space Centre The Sentinel 1 twins provide radar vision for Europes Copernicus environment monitoring program In addition to watching land movements they feed numerous other services for monitoring Arctic sea ice routine sea ice mapping surveillance of the marine environment mapping for forest water and soil management and mapping to support humanitarian aid and crisis situations Sinking Station Parts of the Oslo train station are sinking by 12 18 mm a year Staying in Place The new opera house has not moved Millennium Tower Data from the Sentinel 1 satellites show the Bay Area tower sinking by almost 50 mm a year The colored dots represent targets observed by radar The color scale ranges from 40 mm a year away from radar red to 40 mm a year towards radar blue Green represents stable targets 50 GPS WORLD WWW GPSWORLD COM JANUARY 2017
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