The phase variation from a 300-m baseline 11.2 GHz interferometer was cross-correlated with the phase variation estimated from the PWV measurements using two radiometers operating near the water vapour line at 183 GHz at the ALMA site of Llano de Chajnantor in Northern Chile at an altitude of 5,000 m. Care has been taken to have the radiometers observing the same path of atmosphere as the interferometers, with both beams matched as close as possible.
The result indicates that the cross-correlation varies during the day and thus the phase correction possible to achieve using the radiometric method at Chajnantor.
The results are discussed and comparisons are done with other variables, specially the height of the turbulence layer. The later is determined using two different methods: the first one is direct measurements from radiosonde data, and the second method involves the calculation of the time lag between the turbulence structures seen by the two interferometers deployed at Chajnantor. A relation is proposed between the height of the turbulence layer and the success of the cross-correlation, with a better cross-correlation when the turbulence layer is higher than about 300-400 m.
View a pdf version of ALMA Memo 361.
Download a ps version of ALMA Memo 361.
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