Quantification du mouvement vertical de la croûte terrestre et de sa contribution au changement du niveau de la mer : le cas de la Côte Est du Canada, golfe du Saint-Laurent
Sea level changes are one of the indicators of climate change that has affected the world in recent decades. In coastal areas, this phenomenon has caused coastal erosion, saltwater intrusion into the groundwater and floods. These environmental changes can also be seen in Canada's coasts. Indeed, the sea level in these regions is currently increasing and follows the global trends. Among these coastal areas, those of the Gulf of St. Lawrence interested us. This area is characterized by specific physical properties such as relative isolation from the Atlantic Ocean, winter ice cover and spring freshwater flow that confer particular behavior in terms of sea level changes. Sea level changes can be determined by integrating the tide gauge and satellite altimetry data that the result of this procedure leads to a relative determination of mean sea level. However, because the measurement structures of these data are different, some corrections should be applied. One of the most essential corrections is the length of the Vertical Land Motion (VLM) which must be taken into account in tide gauge data, as these are connected directly to the Earth crust. Different phenomena can cause VLM. In the local scale, tectonics, subsidence and sedimentation are the factors that create vertical movement and in global scale, melting of ice sheets, which leads to change the mass loading of the earth's surface, cause the land motion. There are various global and local VLM correction models and methods such as, Glacial Isostatic Adjustment (GIA), Global Navigation Satellite Systems (GNSS), Interferometry Synthetic Aperture Radar (InSAR), Gravity Recovery and Climate Experiment (GRACE) and calculation of difference between satellite altimetry and tide gauge data. Between these methods, using the vertical velocity of GPS data is the most accurate one. However, due to the low number of GPS stations in or near the tide gauge stations, using a more comprehensive approach is inevitable. By applying this correction, the absolute mean sea level will be obtained. In this study, VLM is examined by one algorithm of InSAR which is called Persistent Scatterer InSAR (PSInSAR). The Sentinel-1 single-look SAR images are used for PSInSAR analysis. In order to accuracy assessment of this approach, the results of PSInSAR (obtained from Stanford Method for Persistent Scatterers software (StaMPS)) for two regions in east of Canada (Halifax and St. John's) are compared with GPS vertical velocity by analyzing their time series data. Equally, by using the same method, vertical land movement in 24 tide gauge station in Gulf of St. Lawrence will be corrected. Investigation of mean sea level is implemented by using the spectral analysis (Harmonic analysis and Least Square Spectral Analysis) in order to remove the long-term effects of tidal constituent (annual and semiannual constituents). Also, to assess the Absolute Mean Sea Level (AMSL) in considered region, calculated mean sea level is corrected based on the results of VLM. In conclusion, comparing of the results of PSInSAR technique with GPS data indicate the similar behavior of trends during the period of study. In other words, PSInSAR method measures vertical land motion in millimeter precision in study region (except of one station) and it can be applied for regions that they do not connect on continuous GPS positioning of tide gauges. In the case of sea level change, incompatibility between tide gauge and altimetry data in terms of time makes the conclusion harder. However, based on continues observations in time series of altimetry data, we obtained more homogeneous sea level trend (mean sea level) in all stations, but to evaluate the long-term sea level change and because of exact location of tide gauge station, this latter data must be considered (both in calculation of mean sea level and tidal constituents). Finally, because of small values of VLM, absolute mean sea level values are very close to relative one which indicate that, we can evaluate the sea level changes in Gulf of Saint Lawrence by using only the tide gauge and altimetry data. In addition to making corrections, the maps of sea level trend and phase differences between tide gauge stations will be represented. The quality of the tide gauge and satellite altimetry records will be discussed and reported over the drawn results of the study.
GPS Sea level Gulf of St-Lawrence Tide-gauge Satellite altimetry Vertical land motion GNSS PSInSAR Time series analysis