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Paper: APHID: A Wideband, Multichannel Radiometer for Phase Delay Correction
Volume: 217, Imaging at Radio Through Submillimeter Wavelengths
Page: 336
Authors: Staguhn, J.; Harris, A. I.; Munday, L. G.; Woody, D. P.
Abstract: Atmospheric phase fluctuations of mm and sub-mm signals are predominantly caused by line of sight fluctuations in the amount of water vapor. Measurements of the line emission from tropospheric water vapor can be used to track and correct these fluctuations. We present model calculations which led to the design of a multichannel water vapor radiometer for phase correction of millimeter arrays. Our particular emphasis is on designing a phase correction scheme for mid-latitude sites (BIMA, OVRO), and for high-altitude sites. The instrument being implemented at OVRO and BIMA is a cooled double-sideband heterodyne receiver centered on the 22.2GHz water vapor line with a 0.5 - 4.0GHz IF. The back end is a 16 channel analog lag correlator similar to the WASP spectrometer (Harris et al 1998). We present two applications for the multichannel radiometer. A line fit to the observed spectra is expected to provide sufficient accuracy for mm phase correction with the 22 GHZ line. The radiometer can also be used for the determination of the vertical water vapor distribution from the observed line shape. We discuss how this information can be used to improve the accuracy of water vapor radiometers which have too few channels to observe the line shape, and for phase correction schemes which are based on a 183 GHz water line radiometer.
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