We propose a method that takes advantage of the large variation of atmospheric transmission across the 8 GHz receiver bandpass of ALMA, at some sky frequencies, to cancel the time variations of atmospheric water emission that otherwise limit single dish continuum emission mapping of extended sources. This technique could be useful for on-the-fly maps of extended sources for which the use of a focal plane chopper or a nutating subreflector is not practical due to limited beam throw.
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Last modified: April 12, 2000
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