Sub-metre height determination using a combination of satellite and zenith distance measurements

The Global Positioning System (GPS) has proven to be a tool suitable for determining coordinates of features to an accuracy suitable for mapping applications. The pseudorange observable is generally used in such applications due to its unambiguous nature, providing metre level position estimates in a few seconds. However, in periods of poor satellite geometry and in high multipath environments, position errors can increase to several metres. The height component is particularly vulnerable to an increase in error under such circumstances and errors greater than ten metres are commonly encountered. The accuracy and reliability of the height component can be improved by simultaneously integrating zenith distances with the satellite measurements. An abney level can be used to provide rapid zenith distance measurements without significantly increasing equipment costs.