The evaluation of the accuracy of GNSS-derived path
delays is a difficult task. In the absence of independent
external information, a way to evaluate the precision of
estimates is by comparing tropospheric delays obtained
using different software and processing strategies.
To this end, the U.Porto solutions were compared with
the corresponding IGS or EPN ZTD, by performing a statistical
analysis of the differences between the two groups of
tropospheric parameters for the 51 stations mentioned
above and for the period from 2002 to 2009. Since the three
data sets provide measurements at different epochs, they
were compared by using linear interpolation.