TESTS ON THE GEOPOTENTIAL MODEL EGM96 IN SÃO PAULO STATE REGION
Sérgio F. Souza1,2 and Nelsi C. de Sá1
1Departamento de Geofísica, Instituto Astronômico e Geofísico, Universidade de São Paulo.
2Departamento de Geodésia, Instituto de Geociências, Universidade Federal do Rio Grande do Sul.
The geopotential models defined by sets of coefficients which represent the anomalous gravitational potential expanded in spherical harmonics, are computed by combining data of different kind and accuracy. Today, the geopotential models have become part of the geodesic reference systems, and are being widely used as reference field of the terrestrial and oceanic gravity data for local and regional representations of the Earth's gravity field. However the geographic distribution of the available gravity data for the computation of high degree coefficients is still very irregular in global terms, and the gravity field computed from these models reflects this deficiency. Therefore, in representing the anomalous gravity field in regions with lack of gravity data, the spatial resolution corresponding to the higher degree of the geopotential model must be tested in order to select the best degree to be used. The Earth Gravitational Model 1996 (EGM96), available since 1998, was computed from a joint work by National Imagery and Mapping Agency (NIMA), NASA through the Goddard Space Flight Center (GSFC) and the Ohio State University (OSU), with the colaboration of many other international institutions. The EGM96 is a geopotential model complete up to degree and order 360, which means a spatial resolution of 30 arc minutes. As the effective resolution provided by the geopotential models changes from one region to another, the use of EGM96 model in representing the deterministic component of the anomalous gravity field in São Paulo state (latitude: 17º to 27ºS; longitude: 42º to 55º), raise up the following question: What is the best degree of the model to represent this component? To answer this question, two digital gravimetric models with resolutions of 30 arc minutes (MGD30) and 60 arc minutes (MGD60) have been used. The methodology consists in computing the differences between the models MGD30 and MGD60 with the values obtained from the model EGM96 up to degree 360 (EGM30) and 180 (EGM60), respectivelly, and to compute the statistics of the differences. The results of the statistical analysis show that, in the studied region, the effective spatial resolution provided by the model EGM96 corresponds to degree 180, which means 60 arc minutes.
( November 19, 1999 ) .
Publication Dates
-
Publication in this collection
07 Aug 2000 -
Date of issue
June 2000
