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Session 107 - Radio Astronomy and VLBI Instruments.
Display session, Thursday, January 16
Metropolitan Ballroom,
We have conducted an experiment to evaluate the usefulness of GPS data for estimating the 333 MHz ionospheric Faraday rotation and interferometer phase shifts at the VLA. Four GPS receivers were installed at the VLA site, one at the end of each arm, and one at the array center. Each receiver provides information concerning the total electron content (TEC) in the direction of each of the visible GPS satellites. In order to estimate the TEC in the direction of the radio source under observation, a simple ionospheric model was developed and fitted to the GPS data from each station. This model allows a prediction of both the TEC and the rotation measure (RM) along any direction to a radio source. In addition, the GPS receiver and transmitter biases were determined. Combining the data from the four receivers allows a measurement of the phase gradient along each arm of the VLA. We have made 333MHz observations of polarized sources to permit comparison of the predictions to real data.
