GPS Satellite Surveys and Vertical Control

Abstract

Analysis of Global Positioning System (GPS) survey data has shown that GPS can be used to establish precise relative positioning in a three‐dimensional system. The results of many tests and operational projects have clearly shown that GPS survey methods can replace classical horizontal terrestrial survey methods. Comparable accuracies have also been achieved for GPS‐derived ellipsoid height differences. The problem of converting these ellipsoid height differences to orthometric height differences remains to be resolved. Can the accuracies achieved for these orthometric height differences provide a viable alternative to classical geodetic leveling techniques? Some results of analyses performed by the authors in estimating orthometric heights from GPS surveys indicate that with appropriate planning, consideration of GPS survey specifications for connection to bench marks, proper field observing procedures, and proper strategy for estimating geoid heights and final orthometric height values, it is possible to use GPS survey methods to estimate orthometric heights to meet a wide range of engineering requirements for vertical control. Therefore, another question needs to be addressed. What are the accuracy requirements of most engineering and mapping applications? This is best answered by users of the data and will influence how much effort should be directed toward determining more accurate geoid heights.