Comparative analysis of new hourly ERP series derived from GNSS data and the high resolution VLBI series based on complex demodulation

We analyze here the Earth rotation parameters (ERP) time series with hourly resolution, based on GPS and GPS+GLONASS observations. The two series cover 8 month in 2008 and 4 month in 2014; see the associated presentation by Nastula et al. for details about those high resolution GNSS series. Our purpose here is to assess the reliability of the GNSS-based ERP series at short periods, down to few hours, by comparing it with the independent alternative estimate based on VLBI data. The last series comprises diurnal and subdiurnal components of polar motion x, y and dUT1=UT1-UTC, estimated from the routine VLBI observations by Böhm et al. (2012, J. Geodynamics, Vol.62, pp.56-68). This estimation was based on the complex demodulation (CD) scheme incorporated into the Vienna VLBI Software VieVS. What is important here, the reliability of the VLBI ERP series based on CD VieVS has been successfully verified at diurnal and semidiurnal periods by comparing it with both the conventional model of ocean tide influences and the alternative VLBI solutions.