IRAM Memo 2009-5 Comparison of ATM versions: Impact on the calibration of IRAM instruments

# IRAM Memo 2009-5
Comparison of ATM versions:
Impact on the calibration of IRAM instruments

J. Pety, S. Bardeau & E. Reynier
1. IRAM (Grenoble)
2. Observatoire de Paris

Dec, 4th 2009
Version 1.0

### Abstract:

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.

- Contents
- Rayleigh-Jeans or not Rayleigh-Jeans?
- Single-dish calibration in a nutshell
  - Description of the received signal
  - Description of the calibration scheme
    - Skydips and determination of the forward efficiency
    - Load calibration and determination of the zenith opacity
    - Data calibration
- Description of ATM 2009
  - Atmospheric profile
  - (Sub-)mm radiative transfer
    - Line
    - Continuum
  - GILDAS interface
    - FORTRAN interface
    - ASTRO interface
- Comparison of ATM 1985 and ATM 2009
  - Comparison of the implementation
  - Comparison at constant amount of water vapor
  - Comparison of the full calibration scheme
- Recommendations
- Acknowledgement
- Bibliography
- GILDAS fortran interfaces to ATM
- Comparison at constant amount of water vapor as a function of the frequency
- Effect of Earth curvature
- About this document ...