|M.Sc Student||Rokhlin Elena|
|Subject||Monitoring Vertical Displacement of TGBM Using GNSS|
Measurements and Connect them to the Permanent
GNSS Stations in Israel
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Gilad Even-Tzur|
|Full Thesis text|
Nowadays assessment of sea level in Israel is done using sea level measurements produced by tide gauges located in protected sites along the coast. The measurements made by a tide gauge provide the relative movement of the sea level with respect to primary reference point TGBM (Tide Gauge Benchmark) located on the land near to the tide gauge. Recent studies have shown that neither the sea levels nor the land are constant over long periods of time and every point on Earth can move vertically. In order to obtain sea level changes properly, the different sea level and land signals have to be decoupled. Hence the main goal of the research is to monitor vertical displacements of TGBM.
Currently, the measurements of sea level in Israel are relative and each tide gauge is defined in a different datum. In this research, each tide gauges were connected to ellipsoidal reference frame based on the permanent GNSS stations in Israel. Three-dimensional geodetic network between tide gauges of Survey of Israel was established using GNSS measurements. In this way, the MSL (Mean Sea Level) measured by the tide gauge was defined in a national geocentric reference frame. This furnishes an absolute measure of mean sea level, rather than MSL relative to each local TGBM.
The research is based on static GNSS measurements of the TGBM points, the permanent GNSS stations of Israel and IGS (International GNSS Service) stations. TGBM points were measured simultaneously twice using dual-frequency GNSS receivers.
To monitor vertical movements and avoid the effects of horizontal displacement on the height component the 3D network was divided into two sub-networks, horizontal network and vertical network. Deformation analysis on horizontal and vertical networks is done using a two-step analysis. The first step is independent adjustment of the network of each campaign by using Bernese GPS Software Version 5.2. The solution of the network points’ position for each monitoring epoch and their variance-covariance matrix are used as pseudo-measurements for the solution of the second step, where in each solution different models can be tested to describe the position of the network points.
The deformation analysis of the vertical plane indicates no vertical movements of the TGBM points.
The research results show that TGBM points located near the tide gauges in sites: Acre, Ashdod, Ashkelon and Eilat were confirmed as stable in the horizontal plane, while TGBM point located in the Tel-Aviv site is unstable.