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Session 54 - Ground and Instrumentation Techniques and Catalogs.
Display session, Wednesday, June 12
Tripp Commons,

[54.15] Measurement of Wind Velocity using VLA Phase Data

J. P. Basart, J. W. Dixon (Iowa State U.)

Path delays due to atmospheric fluctuations over the VLA create errors in the phase data leading to errors in images. Determination of a phase reference allows direct estimates of atmospheric fluctuation patterns from the phase data. Such atmospheric patterns have traditionally been analyzed using full correlation analysis, but non-stationarity of the phase data prohibits accurate measurements. A new method has been developed that directly compares portions of time series data. By transforming the phase data from a time series to a spatial pattern, we can directly compare two overlapping sections of the sky pattern on the VLA arms. However, unlike full correlation methods, the new method does not provide any information about the blobs themselves. The difficulty in the method is in the visual interpretation of the comparison. Simulation results show that the method is far superior to correlation methods for data that contains few (0-3) blobs. The new method provides more consistent results when applied to VLA phase data than do full correlation techniques. The results obtained show a correlation between surface wind direction and phase-measured wind direction. Additionally, the new method straight- forwardly provides an ‘image’ of irregularities.

Program listing for Wednesday