Radar satellites of the European Space Agency Sentinel-1 showed that a skyscraper in downtown San Francisco called the Millennium Tower goes into the ground by several centimeters a year. The study of the region is helping scientists to improve monitoring of ground movement in cities, which is important for monitoring sinking points in Europe.
Built in 2009, the 58-story Millennium Tower has recently shown signs of tilting and sinking into the ground. Although the cause has not been precisely determined, it is believed to be due to the support piles that are not firmly embedded in the bedrock.
To investigate these subtle shifts, the scientists combined a large amount of radar scans from Copernicus' Sentinel-1 satellites to detect subtle surface changes down to the millimeter. The method is well suited for working with buildings, as they better reflect the radar beam, and can be used to accurately identify unstable areas over large areas thanks to the wide coverage of Sentinel-1 and frequent data updates.
San Francisco
In collaboration with ESA, a team from Norut, PPO.labs and the Norwegian Geological Survey also mapped other areas of displacement in the San Francisco Bay Area. These include areas with buildings located on them along the Hayward Fault and the subsidence of newly reclaimed land in San Rafael Bay. In the vicinity of Pleasanton, an uplift was detected, possibly due to rising water tables following a drought that lasted four years and ended in 2015.
European cities are experiencing similar subsidence, and San Francisco's research is helping to improve the way they do it. For example, the area around Oslo train station in Norway is reclaimed land. The nearby opera house and other new buildings have proper foundations, but older areas are seriously sagging.
Oslo
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“The experience and knowledge gained through ESA's Scientific Exploitation of Operational Missions (SEOM) program gives us firm confidence that Sentinel-1 will be a versatile and reliable platform for operational deformation monitoring in Norway and around the world,” said the employee Geological Survey of Norway John Dehls.
San Francisco and Oslo research is paving the way for a shift from local research to research on a national or even continental scale. The Sentinel-1 satellites provide “radar vision” for the European Copernicus environmental monitoring program. In addition to observing ground transformations, they provide many other services for monitoring Arctic sea ice, mapping the terrain to control forests, water bodies, soil and crisis situations.