Chris Hughes (University of Liverpool, United Kingdom)

The greatest direct impact of sea level is at the coast, but measurements of dynamic topography precisely at the coast are difficult to make, and are presently limited to the relatively small number of tide gauges for which precise GPS vertical coordinates are known. We show here that, using recent geoid estimates, these dynamic topography estimates are consistent with ocean model analyses at the 5-8 cm level. In order to expand the available dataset, we investigate a new method which does not require a tide gauge. Several recent papers have demonstrated the use of a single geodetic-quality Global Navigation Satellite System (GNSS) receiver to directly measure local sea level variations. This method uses recorded Signal-to-Noise Ratio (SNR) data and is based on interferometric interactions between the direct signal and reflected signals from the sea-surface. The sea level measurements are therefore naturally in a modern vertical reference frame that can be used to study mean dynamic topography, validate geoid models and help to define a world height system. We show the results from various GNSS sites with varying environments and including some with over 10 years of data. We find that in order to get an accuracy of around 5 cm requires the application of both the wet and dry tropospheric correction to the data.