OCEAN TIDE LOADING AND RELATIVE GNSS IN THE BRITISH ISLES

P J Clarke,N T Penna

doi:10.1179/003962610x12572516251844

Abstract

Ocean tide loading (OTL) affects all parts of the British Isles to varying degree, causing peak-to-peak vertical displacements of up to 13 cm in South-West England over semi-diurnal and diurnal timescales. Lateral displacements are typically around one-third of the magnitude of vertical displacements at a point, so are also considerable for carrier phase GNSS surveying. Using a recent numerical ocean tide model, we predict that widespread residual displacements up to ∼1 cm remain in kinematic or short-occupation static relative GNSS positions computed with respect to the nearest continuously operating reference station. Even if OTL is not modelled explicitly, these errors will be mitigated by network GNSS to an extent dependent on the number and location of reference stations used, and the adjustment or error interpolation scheme adopted in the processing. For a selection of error interpolation algorithms, we predict that throughout most inland regions of Great Britain and Ireland, network processing reduces the residual OTL error to within the expected kinematic GNSS system noise. However, pockets of OTL error exceeding 1 cm may remain, especially in coastal locations and in South-West Ireland, South Wales, South-West England, and the islands off the west coast of Scotland. Residual OTL error at semi-diurnal periods dominates that at diurnal periods. We derive a simple heuristic for estimating the magnitude of this error from a sample of observations at a locality, valid within a short window of the spring/neap tidal cycle, and show how the residual error may, if necessary, be mitigated by a suitable averaging scheme.

Highlights

Ocean tide loading (OTL) causes the periodic displacement of the Earth’s surface as a result of the tidal redistribution of the oceans’ weight that acts upon the seafloor
The frequencies of OTL displacement follow those of the solid Earth and ocean tides: the vast majority of tidal power is dissipated at four semi-diurnal periods close to 12 hours and four diurnal periods close to 24 hours, with lesser but still potentially significant amounts at approximately fortnightly, monthly, and semi-annual periods (Table 1)
We demonstrate the level of residual OTL-related error that could be experienced by a user in the British Isles using national or commercial geodetic infrastructure to adopt relative Global Navigation Satellite System (GNSS), whether kinematic or short-occupation static, and whether real-time or post-processed

Summary

Introduction

Ocean tide loading (OTL) causes the periodic displacement of the Earth’s surface as a result of the tidal redistribution of the oceans’ weight that acts upon the seafloor. The residual ocean tide loading error in a relative GNSS solution, whether instantaneous or averaged over a period very much shorter than the tidal timescale, will depend on the mapping of OTL displacements into the differenced carrier phase observations.

Results

Conclusion