  A new technique has been developed to remove the ionosphere's distorting
effects from low frequency VLBI data. By fitting dispersive and non-dispersive
components to the phases of multi-frequency data, the ionosphere can be
effectively removed from the data without the use of {\em a priori} calibration
information. This technique, along with the new gating capability of the VLBA
correlator, was used to perform accurate astrometry on pulsar B0950+08,
resulting in a much improved measurement of this pulsar's proper motion
($\mu_{\alpha} = -1.6 \pm 0.4$ mas/yr, $\mu_{\delta} = 29.5 \pm 0.5$ mas/yr)
and parallax ($\pi = 3.6 \pm 0.3$ mas). This puts the pulsar at a distance of
$280 \pm 25$ parsecs, about twice as far as previous estimates, but in good
agreement with models of the electron density in the local bubble.
