טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentLavrov Dimitri
SubjectSpatial Time Dependent Sea Surface Mapping with GNSS
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Professor Gilad Even-Tzur
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

Sea surface height is constantly changing and the fact that a large portion of global population is concentrated in coastal areas only adds to the importance of monitoring it. Now days, monitoring of the sea level is carried out using several methods such as tide gauges, satellite altimetry and GNSS buoys.

This study presents an alternative method for sea surface height measurements, which incorporates the advantages of today's commonly used measuring methods. This method has spatial capabilities with high resolution and it produces high quality results in coastal areas as in open waters. Based on the measuring results a spatial sea surface can be calculated.

The presented method is based on ship borne GNSS measurements. Raw measuring data must undergo several correction processes before it could be used to create a time independent sea surface. Several factors such as ships dynamics, tide and atmospheric changes introduce errors to the measuring data. One of the innovations in this study is the ability to extract the correction ships dynamics based only on the raw measuring data collected during sailing.

This study offers an alternative method for tidal correction. The method is based on a classic analysis of tidal data collected from various tide gauges and the interpolation of several tidal (amplitude, phase) and non-tidal (residuals, datum offset) components.

The atmospheric changes correction refers to the short and long-term pressure changes cause by increase and decrease in the atmospheric pressure and wind forcing. They were obtained using a two dimensional nonlinear barotropic model.

The second part of the study focuses on the extraction of geoid heights based on the ship borne GNSS sea surface measurements. The novelty lies within the ability to extract geoid height without the use of any local nor global undulation models. It allows the examination of the local geoid model in coastal areas and in land lakes or alternatively creating one in areas where it does not exist. The realization ability of this method was examined in the Weser River in northern Germany, where we carried out a feasibility experiment. The estimated accuracy of the fitted geoid surface based on the sea surface measurements was better than 2 centimeters.

Following the successful feasibility experiment it was decided to implement the method for the Israeli coastal area. Several surveys have been performed along the coast of Herzelia. It was expected to create a spatial sea surface by combining the various sailing profiles and to calculate the approximate geoid based on it. The inner accuracy of the fitted surface was better than 3 centimeters.

By implementing the new method for the Israeli coastal area, we seek to expend the official geoid model by adding new points with geoid heights from the coastal area. The comparison results between the expanded model and the official model were very encouraging and proved that this method can improve and expand local geoid models for countries that are lacking the ability to create a precis marine geoid by means of gravimetric measurements.