Determination of Deflections of the Vertical Using the Global Positioning System

摘要

Modern astrogeodetic methods, although accurate, are inefficient and too complex to rapidly determine deflections of the vertical. This problem is the impetus for finding a more useful technique that can yield results much more quickly. The Global Positioning System (GPS), with its ability to provide coordinate differences in interferometric modes, can be used to determine these deflections. Using highly accurate coordinate differences in conjunction with orthometric height differences, one can develop a surface of the geoidal undulations as a function of latitude and longitude. Given three GPS stations, a local surface can only be approximated by a plane. With more points, however, the modeled surface will more accurately resemble the true undulation differences. From this modeled surface, one uses least squares fitting of polynomials to interpolate the 'average' partial of N with respect to phi and partial of N with respect to lambda in the survey area. Finally, the deflections zeta and eta are computed and a study of propagation of both absolute and relative errors is made. (r.h.)