Great Britain쳌s GPS Height Corrector Surface

M. Ziebart, J. Iliffe, P. Cross, R. Forsberg, G. Strykowski and C. Tscherning

Abstract:	Great Britain uses a traditional heighting datum (Ordnance Datum Newlyn) based on a series of tide gauge measurements made from 1915 to 1921. This datum is realised through the measured heights of a series of fundamental benchmarks established along geologically stable lines across the country. The establishment of the heighting network suffered from various systematic errors and, having been tied to the sea level measurements at a single point in space and a single epoch in time, does not model height above a physical surface such as the geoid. The reference surface is in fact numerical rather than physical deriving from the published height values of the monuments from which it is realised. However, as GPS has matured as a precision surveying and positioning technology it is used increasingly to establish both position and elevation. As most heighting data in Great Britain is still referenced to the traditional datum Britain’s national mapping agency, the Ordnance Survey, needed a way to exploit the precision and availability of GPS, whilst at the same time enabling users to determine height either above the WGS84 reference ellipsoid (GRS80) or with respect to the Newlyn datum, which is nominally orthometric, despite its contamination with systematic biases. This paper describes the solution to this problem. The process leading to the solution consisted of the computation of a rigorous physical reference surface (a gravimetric geoid model) that was subsequently warped to fit the differences between the datum surface (Newlyn) and the WGS84 ellipsoid. This ‘corrector surface’ is then used to convert GPS derived ellipsoidal heights into the Newlyn datum. The fitting process, its quality control and quality assessment are described. The post-fit residuals of this surface to the fundamental benchmark network had a standard deviation of 4mm, with maximum and minimum height residuals of +18 and -11mm respectively. The quality of these results is largely attributed to the excellence of the geoid model and the GPS data collected at the benchmark locations. This means that, given high precision GPS positioning, users in the UK can now determine their height with respect to the country’s fundamental benchmark network with a precision of 1-2 cm. This gives an unprecedented level of heighting consistency across a country of approximate extents 950 km (north-south) and 550 km (east-west). The derived corrector surface has also been adopted as the national standard for transforming height between Newlyn and the European Terrestrial Reference Frame (ETRF). The study was carried out under contract to the Ordnance Surveys of Great Britain, the Republic of Ireland and Northern Ireland.
Published in:	Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004) September 21 - 24, 2004 Long Beach Convention Center Long Beach, CA
Pages:	203 - 210
Cite this article:	Ziebart, M., Iliffe, J., Cross, P., Forsberg, R., Strykowski, G., Tscherning, C., "Great Britain쳌s GPS Height Corrector Surface," Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), Long Beach, CA, September 2004, pp. 203-210.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In