الفهرس 
Fundamentals and Methods for Modeling Marine Geoid
The Area under Study and Used DataOnly 14 pages are availabe for public view
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Abstract
Modeling marine geoid contributes essentially to the main task of geodesy, i.e. determination of the figure of the earth and its gravity filed. Furthermore, the determination of marine geoid itself is essential for many researches and applications in marine areas. Hence, there are continuously trends for modeling marine geoid, and necessity to upgrade the existing models and to develop new ones globally and regionally.
This work aims to provide an optimal regional marine geoid model, in terms of accuracy and resolution, for the Eastern Mediterranean and with more interest with the area offshore Egypt. This had been performed taking the advantages of the new available data sources and models, along with the appropriate processing.
The satellite altimetry data of geodetic mission (GM) is considered the most important source for modeling marine geoid. The availability of new generations of satellite altimetry GM (i.e. CryoSat-2 and Jason-1) with increased range precision compared with the old missions for the first time since 1995, permit to develop a new marine geoid model with more accuracy and resolution.
However, the remaining errors in the official altimetry datasets will form the main challenge in linking the different altimetry datasets, along with the challenge in the accurate employment of the individual altimetry dataset itself, in the suited marine researches. Hence the new GM datasets have to be calibrated and validated before its employment in geodetic applications. This was one of the sub-objectives of this work.
Furthermore, the advent of new altimetric GM has been coincided with the release of new global geopotential models (GGMs) of high order and degree, i.e. EIGEN-6C2, EIGEN-6C3-stat and EIGEN-6C4, after the widely used one i.e. EGM2008. Actually, the availability of such ultra high resolution GGMs motivates to assess their employment through combination with altimetry data in regional scale.
On the other hand, the mean dynamic topography (MDT), the difference between the mean sea surface (MSS) and the geoid, plays an important role in marine geoid determination, since it is employed to reduce the sea surface height (SSH) to the geoid. However, in closed sea when no accurate regional MDT model existed and due to its small values, the MSS and marine geoid are assumed to be coincided. Actually, the most marine geoid models for the Eastern Mediterranean had been computed under this assumption. But now, the availability of new MDT models, globally and regionally, arises the need to investigate their employment.
Accordingly, the new altimetric GM datasets had been calibrated and validated. Results indicated that the official new altimetric GM datasets contain significant biases that must be taken into account before their employment in the geodetic applications. It was found that the derived SSH from CryoSat-2 LRM baseline-B product must be raised by 93.1 cm and the derived SSH from Jason-1 GM GDR-c product must be lowered by 10.7 cm as absolute biases w.r.t. stacked Jason-2 SSHs as a reference mission. Moreover, this work highlighted the possibility along with the efficiency and stability, of using a simple regional absolute calibration method if appropriate processing procedures had been performed.
Several solutions had been investigated to obtain a new regional marine geoid model for the Eastern Mediterranean basin, based on the combination of the new altimetric GM datasets with the new GGM and MDT models, along with appropriate processing. The stacked Jason-2 SSHs had been used as a reference mission and as control points for validation. Through this investigation, it was concluded that there are a preference of employing the new GGMs in general, compared to the widely used EGM2008. Additionally, the superiority of employing the EIGEN-6C4 in combination with the new altimetric GM datasets had been outlined. Moreover, results revealed that employing the MDT should be unavoidable in the Eastern Mediterranean. However, there is ineffectiveness of employing the new available regional MDT model (SMDT-MED-2014), but on other hand, some improvements can be obtained in the final model when employing the latest global MDT model (MDT-CNES-CLS13).
Finally, a new regional marine geoid model for the Eastern Mediterranean basin had been introduced in this work, accurate to about 3-4 cm (1σ), and with unprecedented accuracy in the Mediterranean Egyptian coasts to about 2-3 cm (1σ). Furthermore, the accuracy is relatively increased by the increasing distance from coasts and increasing depth.