VLBI and GNSS Frequency Link Instabilities during CONT Campaigns

We present frequency link instabilities derived from the analysis of VLBI and GNSS data observed during the CONT08 and CONT11 campaigns. The majority of the stations involved in these two CONT campaigns did connect their VLBI and GNSS equipment to the same hydrogen masers used as the common local frequency standard. This allows comparison of the frequency instability on individual baselines from both VLBI and GNSS data analysis. This was done by analyzing the relative clock parameters. For VLBI the relative clock parameters with respect to a reference clock in the VLBI networks were derived from standard VLBI data analysis. For GNSS the relative clock parameters were calculated by dierencing station clock parameters derived from GNSS precise point positioning analyses. The Overlapping Allan Deviation analysis was then applied to determine the frequency instability between pairs of stations. The most stable baseline for both CONT08 and CONT11 is the baseline between Onsala and Wettzell with instabilities of about 1.6e-15 at time intervals of one day. Frequency estimates from VLBI and GNSS analysis agree to a level of better than 5e-16 for the two week long data set with an RMS of less than 100 ps.