|M.Sc Student||Ronen Hagi|
|Subject||Scheme for a Dynamic Geodetic Datum for Israel|
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Gilad Even-Tzur|
|Full Thesis text - in Hebrew|
A Geodetic Datum is a reference surface defined by a set of monuments fixed to the earth's crust and a reference ellipsoid (e.g. GRS80) so coordinates can be given.
Today, thanks to the proliferation of continuous operating GNSS stations and the advance of technology, the modern Geodetic Datum is three dimensional and surpasses the classical datums.
The accuracy and precision of the Geodetic datum which is based on these stations enables, besides precise measurements, the monitoring of its defining parameters, namely the origin, orientation, scale and their variation in time, as well as the coordinates of the stations which move with the earth's crust.
In contrast to the above, most Geodetic Datums today are static, do not change through time, are referenced to one of the realizations of the International Terrestrial Reference System (e.g. ITRF08) in a particular moment in time and from that moment on depart from it.
A possible alternative to the static datum is to define a dynamic geodetic datum which like a static datum is a set of physical points attached to earth's surface, but that can span more than one tectonic plate and its defining points have fixed velocities and coordinates, in a stable International Terrestrial Reference System, that continuously change through time, primarily because of crustal movements.
In order to deal with such a datum two more definitions are needed:
1. A national deformation model which includes a velocity field that allows the estimation of the plate velocity at any point in the country and patches of modeled displacements to account for substantial ground movements.
2. A 14 parameter transformation from the datum into the geodetic projection system so the projected coordinates are fixed in time to a chosen date and are stable for a very long period within the accuracy of the measurement and transformation.
The realization of such a Datum was done with the help of long term time series of daily position solutions of the stations. The time series were modeled in order to calculate velocities, discontinuity, annual and semi-annual effects and blunder detection and removal which influence the calculation of station velocity.
After station velocities were calculated it was possible to calculate the velocity field, which is part of the national deformation model and the 14 transformation parameters the first was estimated using a spatial interpolation method and the second as an expansion of the well-known similarity transformation.