We processed the GPS data in daily batches. Each point position
was based on the ionosphere-free combination of the zerodifferenced
GPS carrier phase and pseudorange observations at 5-
minute intervals, with a cut-off elevation angle of 15°. Tropospheric
delays and gradients were stochastically estimated at each time
interval. Ocean loading effects were modelled with the GOT00.2
model (Scherneck and Bos, 2009). To account for different GPS
antennas, relative antenna phase center corrections from the U.S.
National Geodetic Survey (NGS) were applied (NGS, 2009).