Integrated Processing of GPS and Gravity Data

Abstract

Using phase observations of the Global Positioning System (GPS) we are able to determine relative geometric three‐dimensional coordinates in the 0.1–1 ppm level. Most surveying needs, however, require orthometric heights, or more generally expressed to answer the question where water flows. This can be achieved by determining a high‐precision geoid in the area under investigation, a lengthy task which often is beyond the knowledge of a surveyor. On the other hand, geoid precision equivalent to that of the GPS baseline components is still a challenge for physical geodesy. With OPERA 2.4 (Operational Adjustment) and OPUS (Opera Utilization System) an interactive software system is developed which handles all adjustment problems in one, two, or three dimensions. Besides the densification of existing horizontal networks by GPS baseline components it can process in one integrated approach gravity and height information from a data base in order to come up with horizontal ellipsoidal coordinates and orthometric heights replacing the traditional time consuming and expensive spirit leveling. OPERA 2.4 is able to work purely geometrically or can also be used solely for high‐precision local geoid determination. Various pre‐ and postprocessing capabilities like graphical output are built in. As a practical example the GPS subsidence network in Maine is processed and results are compared to other adjustment techniques.