The direct effect on geoid computations (ESP)


  • Juan G. Serpas Escuela de Topografía, Catastro y Geodesia, Universidad Nacional., Costa Rica


Helmert´s condensation method, geoid, direct effect


The most popular technique for the reduction of gravity to the geoid is the Helmert´s condensation method. Two different ways to apply this reduction are studied: the classical approach (Wang and Rapp, 1990 , Heiskanen and Moritz, 1967) and the one by Vanicek and Kleusberg (1987) extended by Martinec et al. (1993 ). The classical approach (Wang and Rapp, 1990 , Heiskanen and Morits , 1967 ) argues that the effect of the condensed layer has to be evaluated at geoid level and not at the terrain level as stated by Vanicek and Kleusberg , 1987. Jekeli and Serpas (2003 ) conclude that both methods are correct from a theoretical point of view ,and the difference is in the order of application of the remove, restore, and downward continuation procedure. The computation of the geoid is analyzed under the two mentioned approaches and the result are compared to geoid undulations coming from GPS and orthometric heights in three different regions in the USA. Numerical assessments of the different approaches shows that both yield similar results in relatively flat areas, and that the classical approach provides better results in mountainous areas with rough topography.




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