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.