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Paper: Amplitude Calibration in Interferometry
Volume: 217, Imaging at Radio Through Submillimeter Wavelengths
Page: 309
Authors: Welch, W. J.; Bock, D. C.-J.; Fleming, M. C.; Thornton, D. D.
Abstract: Amplitude calibration is as important for interferometry as it is for single dish observing. When self-calibration is not possible, it is valuable to be able to have reliable and accurate radiometer scales on all of the array antennas. Good dynamic range in the final maps depends on it. The problem arises especially in the combination of data sets from different instruments or in the comparison of maps made with different instruments. In particular, it is difficult to get the same scales in the combination of interferometer and single dish data for large scale imaging. We have devised a novel two temperature scheme for amplitude calibration of the BIMA antennas. Each of two temperature regulated loads can be weakly coupled to the radiometer through a small hole in the antenna secondary mirror. This amounts to a stable, but small, broadband signal that can be injected into the radiometer input. The switching is done with a small mirror which can be moved rapidly. We have built and tested a prototype, which gives a calibration accuracy of better than one percent. This will also be useful for the calibration of the planned water-vapor phase monitors.
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