Previous abstract Next abstract

Session 11 - VLBI & Radio Instrumentation.
Display session, Wednesday, January 07
Exhibit Hall,

[11.03] VLBA Atmospheric Statistics

S. Redfield (Tufts University), A. J. Beasley, J. Herrnstein, M. Holdaway (NRAO)

Phase referencing is a technique designed to observe sources that are too weak to be self calibrated due to phase fluctuations incurred by water vapor in the troposphere. The use of periodic observations of a nearby calibrator source allow measurement of the tropospheric phase fluctuation, which can then be removed from the target source data. The two most significant parameters for phase referencing are the length of the switching times, and the angular distance between the calibrator and the source. We calculate the temporal structure function for VLBA baselines, in order to make conclusions on the limits of the switching time to insure phase connection with the VLBA. We develop a decomposition technique to obtain single antenna based structure functions, and fit them to a power law. The data consists of 17 experiments, including 11 sources, taken over a period of two years, observed at 15 GHz, and with a switching time of 3 minutes. We discuss single antenna switching time limitations, seasonal variation, and the applications to other frequencies.

Program listing for Wednesday