On Computation of Combined IVS EOP Series
  Three topics related to computation of the combined IVS EOP series are discussed. The first one is the consistency of the VLBI EOP series with the IERS reference frames ITRF and ICRF. Not all IVS analysis centers use ITRF/ICRF as reference system for EOP solutions. Some of them realize global solution for simultaneous determination of CRF, TRF and EOP with no-net-rotation constrains w.r.t. ITRF/ICRF. Analysis shows that such a method can hardly provide consistency of computed EOP series with the IERS reference frames with sufficient accuracy. Direct use of ITRF and ICRF for computation of EOP series submitted to the IERS seems preferable. Second problem is the long-time stability of the IVS EOP series. Analysis of yearly biases w.r.t. C04 and NEOS is presented. A possible ways are proposed to save long time stability of the combined IVS EOP series. At last, various strategies of computation of weighted mean value are considered. It's shown that usual methods used for this purpose do not provide satisfactory result for the error of the mean. A new method is proposed. 
Zinovy Malkin