Geodetic and Geophysical Observations in Antarctica

Abstract

Ocean tide models around the coastline of Antarctica are often poorly constrained, due to sparse data input and poorly known bathymetry in the ice-shelf regions. Land-based measurements of Ocean Tide Loading Displacements (OTLD), such as those made by GPS, provide a means of assessment of ocean tide models in such regions. Up to 11 years of daily GPS data from 18 stations on the Antarctic continent were processed using an up-to date estimation strategy based upon a precise point positioning analysis. Carrier-phase ambiguities were fixed, and parameters representing harmonic ground displacements at 4 diurnal frequencies (M2, S2, N2 and K2) and 4 semi-diurnal frequencies (K1, O1, P1 and Q1) were estimated on a daily basis, and then combined to form the GPS estimates of OTLD. These were compared with estimates of OTLD computed by means of a convolution process with a Green’s function from seven global ocean tide models: CSR4, FES99, FES2004, GOT00.2, NAO.99b, TPXO6.2, TPXO7.0, and four regional ocean tide models: CATS02.01, CADA00.10, MTOs.05, AntPen04.01. Fixing of carrier phase ambiguities was, unexpectedly, found to result in a poorer agreement between GPS estimates and models. For Antarctica as a whole, the TPXO6.2 and TPXO7.0 global models offer very good agreement with the GPS estimates of OTLD in all regions, with CADA00.10, MToS.05, CATS02.01 also generally being in good agreement. In East Antarctica, where the models are well constrained and in good agreement, the GPS estimates offer good agreement with the models – often to a sub-millimetre level – particularly for the lunar N2 and Q1 constituents. In West Antarctica, there is greater divergence amongst the modelled estimates of OTLD due to the complex coastline and less well modelled ice sheet regions. Here, the TPXO6.2, TPXO7.0 and CADA00.10 models offer equally good agreement. In summary, GPS measurements of OTLD are of sufficient accuracy to distinguish between the models in certain regions of Antarctica, although some systematic biases remain at solar frequencies.