Gain-Elevation and Opacity Corrections

As higher frequencies (particularly $>$20 GHz) it is important to make corrections for atmospheric opacity and gain-elevation effects.

Note that currently the elevation is not written correctly into Tidbinbilla rpfits files. This means that gain-elevation and opacity corrections will not work unless these get recalculated.

  ASAP>scans.recalc_azel()                # recalculate az/el 
              							  # based on pointing

Gain-elevation curves for some telescopes and frequencies are known to ASAP (currently only for Tidbinbilla at 20 GHz and Parkes at K-band). In these cases making gain-corrections is simple. If the gain curve for your data is not known, the user can supply either a gain polynomial or text file tabulating gain factors at a range of elevations (see help scantable.gain_el).

Examples:

  ASAP>scans.gain_el()   # If gain table known
  ASAP>scans.gain_el(poly=[3.58788e-1,2.87243e-2,-3.219093e-4])

Opacity corrections can be made with the global function opacity. This should work on all telescopes as long as a measurement of the opacity factor was made during the observation.

  ASAP>scans.opacity(0.083)

Note that at 3 mm Mopra uses a paddle wheel for Tsys calibration, which takes opacity effects into account (to first order). ASAP opacity corrections should not be used for Mopra 3-mm data.

Malte Marquarding 2007-08-16