Using InSAR to monitor vertical ground motions in coastal cities

International audienceBefore the altimetry era, tide gauge are a unique source of information to evaluate past sea-level changes. However, they can be affected by vertical ground motions acting at different space scales. We use synthetic aperture radar techniques to assess these ground motions and their consequences for geodetic instruments such as Tide Gauge, GPS, Doris stations. Summarizing results obtained at Alexandria (Egypt; Woppelmann et al., 2013), Manila (Philippines; Raucoules et al., 2013) and Dakar (Senegal; Le Cozannet et al., subm.), we identify different situations in terms of data availability and ground motion context: - when strong ground motions affect the tide gauge, the technique can easily help rejecting tide gauges records from the database of reliable datasets (case of Manila) - however, when no ground motions can be observed using InSAR in the vicinity of geodetic instruments (Case of Alexandria and Dakar), it remains challenging to reach the accuracy required to confirm that tide gauge records are indeed suitable for monitoring sea level changes. To reach the required accuracy of this InSAR application, a large set of SAR data must have been acquired over the area. For future science application of Sentinel 1 in the field of geodesy underpinning sea level science, it will be necessary to define appropriate background missions covering coastal sites where key records have been aquired