الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 239 |  |  |
| | | from | 239 | | |
Abstract
Abstract
New Global Geopotential Models (GGMs) have now been released into the public domain, these models include data from the CHAMP, GREACE and GOCE dedicated satellite gravimetric mission. Those satellite tracking data have resolved the global long wave length component of the Earth’s gravity fieldwith very high accuracy [Ellmann and Jurgenso, 2008]; therefore, it is important to evaluate those new models over Egypt to determine which of them is the most appropriate GGM there. In this study, a comparison of the performance of three of the GGM released between 1996 tell now (EGM96, EGM2008 and EIGEN-6C 2011) over Egypt is made. The gravity anomalies have beencomputed from these models and compared with a point of free air gravity anomalies on ground. The results show that, EGM2008 is the best global geopotential model over Egypt in terms of root mean square (R.M.S).
The results of GGMs evaluation over the whole area of Egypt have indicated that the smallest root mean square error is (19.94 mgal), referred to EGM2008, this model is the best than other compared models EGM96 and EIGEN6C -2011 that have indicated (24.81 mgal) and (57.50mgal) respectively.
As regarding EGM2008 when applied over the three elected regions noticed that The previously mentioned value (19.94 mgal), is larger than the others obtained values(18.87mgal), (14.35mgal) and (11.38 mgal) this is logically, where the (ST.DEV). is larger there and amounts to (28.27mgal) because of the existence of several gap areas; empty of terrestrial data in the whole territory of Egypt.
Consequently, we can notice that the best model of the three is EGM2008, since it gives the lowest root mean square (R.M.S) compared with the other two models when applied over the three regions (1),(2) and (3). The graduation in the values of the obtained (R.M.S) i.e. (18.870), (14.953) and (11.38)mgalof three regions respectively, seems to be reasonable and was logically expected since the standard deviation (ST.DEV.). of the terrestrial data used in their computation were (20.25mgal), (16.79mgal) and (12.58mgal) respectively .
EGM2008 has thus 1.20 times better statistics than the EGM96 and 2.63 than EGM2011-EIGEN6C in terms of (R.M.S) therefore; this model makes a significant improvement over all other models and thus is advised to be used in computation of the geoid in Egypt.