ALMA Memo #373
Relative Pointing Sensitivity at 30 and 90 GHz for the ALMA Test Interferometer

M.A. Holdaway and Jeff Mangum
May 2001

We compare the relative sensitivity of conducting pointing measurements at 30 and 90 GHz with the ALMA Test Interferometer (TI) at the VLA site. If pointing is performed interferometrically, the 90 GHz system will actually be 2.3 times more sensitive than the 30 GHz system due to very similar system temperatures but a smaller beam at 90 GHz. If pointing is performed in single dish mode, the system will be subject to sky brightness fluctuations, which are worse at 90 GHz than at 30 GHz. Even so, the sky fluctuations will usually not dominate the system noise. There are no compelling reasons not to do the test interferometer pointing at 90 GHz.

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