Global fringe fitting for polarization VLBI.

Standard wide-band VLBI fringe-search procedures impose a signal-to-noise limit of about 7 on usable data. This is especially damaging for polarization-sensitive VLBI since the cross-polarized fringes are one to two orders of magnitude weaker than the parallel-hand fringes. Here, it is presented a method for recovering low-signal-to-noise cross-hand fringes that would otherwise be lost. The technique determines the station-based delay offsets between the two hands of circular polarization from strong parallel- and cross-hand fringes, and then predicts the delay location of weak cross-hand fringes from the parallel-hand fringes on the same baseline. This method is straightforward, and requires only modest amounts of additional data processing.