Background

All GBT scan Calibration FITS files should conform to the standards specified in the GBT Software Project Note 4.0, ``Device and Log FITS Files for the GBT.'' All receiver calibration data from bench tests are stored in a relational data base. These data will in general be stored in raw form, in sanitized form (obvious spurious values rejected) and in a smooth or interpolated form. The Measurements Manager, given the receiver to be used in a scan, extracts from the data base the most recent smoothed results for that receiver and generates a FITS file containing the calibration data. If no smoothed values are available, no FITS file will be produced.

In addition to the calibration temperatures, the most recent values for the atmospheric zenith optical depth $\tau_{o}$, rear spillover efficiency $\eta_{l}$, aperture efficiency $\eta_{A}$ and beam efficiency $\eta_{M}$ will be read from the database, and written to the primary HDU. In version 1.1 of the Calibration FITS files, simple scalar values for each of these quantities will be provided. Subsequent versions of the FITS file may contain a more complex parameterisation of these quantities (for example tables of gain dependence on azimuth, elevation and frequency).

The FITS file is regenerated if new results are available or a new project or receiver is selected. The number of receiver calibration binary tables in a FITS file is wholly dependent on the number of independent tests run by the engineers.