Precise Global Positioning System (GPS) estimated positions are degraded by ocean tide induced periodic displacements of the land upon which the GPS antenna is sited. 

This ocean tide loading (OTL) displacement arises from the Earth’s response to the change in mass distribution of the water in the oceans as they move periodically due to the gravitational attractions of the Moon and Sun. 

The (predominantly vertical) OTL displacement is spatially very variable and not simply a function of distance from the coast. 

In some places, notably Cornwall, Great Britain, the land can move by up to about 14 cm in around 6 hours, which is amongst the largest in the world.

This work, which was supported with funding from the RICS Education Trust, assessed the effect of ocean tide loading on 24 hour GPS position estimates for sites in Great Britain, and the suitability of different ocean tide models for its mitigation.