Atmospheric profile

The atmospheric profile is computed from a combination of input parameters and physical laws. The shape of the atmosphere density and pressure are defined by the physical laws (hydrostatic equilibrium + mixture of ideal gas). The shape of the temperature profile is defined by the following two parameters.

Troposperic lapse rate,

which is used to fix the temperature gradient up to the tropopause. Its recommanded value is -5.6 K/km.

Atmospheric type,

which is used to reproduce the shape of the temperature profile above the tropopause. For Pico Veleta and Plateau de Bure, it should be the well defined mid-latitude averaged profiles for summer and winter. Continuity of the temperature atmospheric profile is enforced at the tropopause.

The atmospheric model is computed assuming a plane-parallel geometry defined by the following three parameters.

Atmospheric upper boundary,

which is the maximum altitude of the modeled atmosphere, typically 48 km.

Primary pressure step,

which is the pressure step used to define the height of the first atmospheric layer, typically 10 mb.

Pressure step factor,

which is the multiplicative factor used to define the next pressure step from the current one, typically 1.2.

The atmospheric profile of the minor components is defined by the following two parameters.

Water vapor scale height,

which is used to define the exponential distribution of water, typically 2 km (could be between 1.5 and 3 km).

Atmospheric type,

which is also used to define the profile repartition of the other minor components (e.g. ozone) of the atmosphere.

For our applications (calibrating radio-astronomy data), most of these parameters should have a minor impact (still to be checked). The 3 remaining parameters, i.e. the ground temperature and pressure at the telescope as well as the amount of precipitable water vapor at zenith, are used to hook the atmospheric profile defined above to the current conditions at the telescope site. These three parameters thus have a major impact on the modeled results.