GPS Solution ULR6a

The ULR6 solution has taken part to the second reprocessing campaign of the International GNSS Service (IGS). It corresponds to 749 stations for which the entire dataset between 1995.0 and 2013.9 was reprocessed using the most up-to-date models and corrections available at that time. First, daily solutions are computed through the adjustment of positions of the global network of stations, Earth Orientation parameters, satellite orbits and zenith tropospheric delays. This process results in global daily solutions that are expressed in their own (daily) terrestrial frame. Then, the daily times series are obtained after the combination of these daily solutions. The velocities are estimated simultaneously of the mean station position, station position offsets and transformation parameters (translation, rotation and scale) for the alignment to a unique terrestrial reference frame (ITRF0). A minimum of three continuous years without an offset (e.g., due to an equipment change or an earthquake) in the time series were required to estimate a “robust” vertical velocity, leading to a fields of 498 vertical velocities, among which 322 are nearby a tide gauge (less than 15 km). The formal uncertainty of the estimated velocities has been computed taking into account the time-correlated noise in the residual time series to make them as realistic as possible. The median uncertainty on the estimated vertical velocities is about 0.36 mm/year.