Abstract
Measurement techniques to monitor the atmospheric transmission at millimeter and submillimeter wavelengths are necessary for the operation of instruments such as the Atacama Large Millimeter Array (ALMA). Our previous Fourier transform spectroscopy (FTS) work at the Caltech Submillimeter Observatory (CSO) has shown that the atmospheric transmission spectrum can be accurately measured by this technique up to ∼1100 GHz with a time resolution of a few minutes. An alternative technique is water vapor radiometry, generally using a few channels around the 183 GHz H2O line that can provide much finer time resolution but relies upon models to translate the derived water vapor columns into spectrum predictions over the required frequency ranges. Time resolutions of the order of 1 s are necessary to carry out phase correction in ground-based mm/submm interferometry that can easily be reached by water vapor radiometers but not by FTS. Water vapor radiometry has the added advantages of being easier to operate and having lower costs than an FTS.
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