Atacama Pathfinder EXperiment APEX
SHeFI Calibration
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SHeFI Re-Calibration Information

SHeFI Calibration Correction Factors

As a result of several hardware and software interventions to the SHeFI instrument, the antenna temperature scale TA applied to the data has been wrongly calibrated between 2014/02/01 and 2014/06/13. Consequently, all data observed until that date need to be rescaled. The scaling factors to apply are given in the following tables, as a function of LO frequency and observing date. They are also shown in the Fig. 1 below. These factors were derived from our calibration plan database (observations of spectral line calibrators).
Since it was impossible to properly measure the miscalibration at all the observed frequencies, data observed at frequencies other than the main CO(2-1) or CO(3-2) USB tunings have a calibration uncertainty of 15% (HET230) or 20% (HET345 and HET460), higher than the usual 10%. Due to the limited of amount of data available for the HET460 receiver, only a single factor measured at the CO(4–3) frequency is provided for the whole band.

The rescaling of the data can be easily carried out by using the command multiply in CLASS. For example, if you have data in CS(5-4), USB tuning, observed between February and April 23rd, the following procedure can be applied:

file in < input_file >.apex
find /all
file out < new_file >.apex single

for i 1 to found
   get n
   multiply 0.74

Figure 1: Calibration correction factors for the SHeFI receivers. Blue crosses represent the LO frequencies tuned while observing science projects. Green circles and Red triangles represent the calibration factors derived from our calibration plan observations.

In case of question, please contact to apexobs(at)