Since its first introduction into GILDAS in 1985, the ATM modelling
program completely changed. With the advent of large bandwidth receivers
and submillimeter receivers, it is time to upgrade the version of ATM
used in GILDAS to calibrate IRAM instruments. This memo tries to assess
the impact of changing the atmospheric model on the calibration of IRAM
instruments.
After a short description 1) of the single-dish calibration, 2) of ATM
2009 and 3) the GILDAS interface to ATM 1985 and ATM 2009, an in-depth
comparison of the results obtained with ATM 1985 and ATM 2009 is
described. From this study, we expect slight variations of the
calibration results when swapping from ATM 1985 to ATM 2009.