Estimating absolute sea level variations by combining GNSS and Tide gauge data

摘要

Indian tide gauges can be used to estimate sea level rise. To separate relative sea level rise from vertical land motion at the tide gauges, various GNSS stations have been installed in the last years at, or nearby, tide gauges. Using the PSMSL database, we have computed new sea level rise estimates for seven Indian tide gauges with realistic error bars. These error bars should be combined with the uncertainty of the vertical land motion to obtain the error bar of the absolute sea level rise. Using the GNSS properties of two inland stations, Hyderabad and Bangalore, as a proxy of the noise observed at the coastal stations, we conclude that around 5 years of observations are required to estimate the vertical land motion with an accuracy of around 0.1 mm/yr. Since the error by which the relative sea level rise can be estimated at the Indian tide gauges is mostly larger than 0.2 mm/yr, with the exception of Mumbai, such a small error of the vertical land motion is sufficient to cause no noticeable effect on the accuracy of the estimated absolute sea level rise.