GRAVIMETRICALLY DETERMINED GEOID IN THE 

 WESTERN NORTH ATLANTIC 



Manik Talwani, Herbert R. Poppe, and Philip D. Rabinowitz 

 Lamont-Doherty Geological Observatory of 

 Columbia University 

 Palisades, N. Y. 10964 



1. INTRODUCTION 



We describe in this paper a detailed gravimetric geoid for the western 

 North Atlantic. In the past it has not been possible to obtain a gravimetric 

 geoid in ocean areas because of scarcity of gravity data. However, since the 

 nineteen sixties, the development of surface ship gravimeters has led to the 

 accumulation of considerable amounts of sea gravity data, and it is now possible 

 to make the first detailed determination of a gravimetric geoid over an extended 

 oceanic area. 



The success in the determination of the Earth's gravitational field from data 

 based on satellite observations has been so spectacular that one must enquire whether 

 sea gravity data can provide any additional useful information. Gaposchkin and 

 Lambeck (1970, 1971) describe the Earth's gravitational field to the sixteenth 

 order and degree from satellite and terrestrial data (1969 Smithsonian Standard 

 Earth) . A solution to the sixteenth order and degree represents wavelengths longer 

 than about 2500 km. Gaposchkin and Lambeck state that "comparison with surface 

 gravity indicates that up to 10,10 the satellite solution is about as good as can 

 be expected but that some of the higher order terms are poorly determined. The 

 terms between degrees 11 and 16 are determined largely from the surface-gravity data." 

 A solution to the tenth order and degree represents wavelengths larger than about 

 4000 km. Hence it is clear that in order to provide information for wavelengths 

 smaller than a few thousand kilometers it is necessary to use surface gravity data. 



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