ALMA Memo # 495

Estimated Performance of the Water Vapour Radiometers

Richard Hills  (Cavendish Laboratory, Cambridge, UK)

Date(14/06/2004)

Keywords: Phase COrrection,  Water Vapour Radiometer 

Abstract

The sensitivity and accuracy to be expected from the ALMA water vapour radiometers is estimated.  Even with quite pessimistic assumptions about noise temperature and gain stability, it appears that the sensitivity of the present design is at least a factor of 2 better than the specifications.  It is more difficult to predict the medium term stability and accuracy that will be achieved, but the indications are that these will not be a limiting factor in using the data from the radiometers.  An estimate of the errors that would occur in correcting the single-dish pointing for the effects of water vapour gradients is also given.