First Results for the GPS Survey of South Africa Tide Gauges

Abstract

Tide gauge measurements are used for a variety of scientific purposes, not least of which are the definition of vertical data and the detection of long-term variations in mean sea level. GPS measurements at tide gauge sites provide a means of separating local verticl motions from sea level rise, and a means of unifying vertical data in a single reference system. This paper describes a GPS survey to determine the positions and heights of reference stations at South African tide gauge sites. The data were processed in baseline mode using a commercial software package. The heights of the tide gauge stations relative to the fixed ITRF reference station HRAO were determined at a precision of around 3 cm – better than 0.1 ppm. Analysis of the error sources showes that use of the precise ephemeris contributed to a substantial improvement in accuracy, as did the use of ionosphere-free fixed integer baseline solutions. Variations in the antenna phase centers also contributed significant changes in height. © 2001 John Wiley & Sons, Inc.