Towards the re-definition of the gravity network in Mexico
21/09/2016 | 16:45 | Session 4: Global gravity field modelling
Author(s): David Avalos, Spiros Pagiatakis, Peter Vanicek, Marcelo Santos and Apolo Alvarado
David Avalos, Spiros Pagiatakis, Peter Vanicek, Marcelo Santos and Apolo Alvarado
Relative gravity surveys remain to be the main source for gravity field modeling in Mexico. The reference g value for every survey corresponds to one or two of the 660 existing base stations, which are systematically linked to the IGSN71. Due to the instability of the base stations or to errors in the original measurements, recent gravity surveys made between two or more base stations measure the lack of consistency among several of those reference g values up to milligal level.
This work presents the progress made so far in the re-definition of reference gravity values of the base stations with respect to a reference epoch (which one?) by processing all observations, recent and historic, simultaneously. The scheme of processing implemented is a least squares adjustment with a time-variable g value associated with each station as an unknown. After a lengthy effort to collect and clean databases from different sources, a national map of the estimated time-varying gravity (g-dot) has been compiled and it is released as preliminary result. On one hand, the g-dot pattern shown in this map is considered as a quality control to the overall work on data cleaning and on the other hand it is now taken to study its relation to the actual geophysical processes of the Mexico’s territory.