7.1 Overview

Conceptually, for a given AOT the derivation of Standard Processed Data (SPD) can be divided into three main stages:

• ramp processing: Readouts of an integration ramp in V are reduced to a signal in V/s.
• signal processing: Signals are corrected for instrumental effects and averaged over a given period in time.
• in-band power calibration:
  • For PHT-P and PHT-C, one or more FCS measurements that were collected according to the AOT logic are processed to determine photometric calibration factors. These factors are used to convert the signals from the sky measurements to an in-band power (in W) on the detector for the selected filter band. In case FCS measurements cannot be applied, the conversion is based on a default detector responsivity.
  • In the case of PHT-S the signals per pixel are converted to Jy/pixel by comparison with similar signals obtained from standard stars.

SPD processing derives a record for each consecutive period in the sky measurement for which the power on the detector is expected to be constant:

• a staring measurement yields one SPD record;
• a raster yields one SPD record per raster position;
• a chopped measurement yields two SPD records: one and one mean record;
• a PHT32 sky measurement contains one SPD record for each chopper plateau.

Apart from the mean in-band power, each record contains additional information such as the power uncertainty, median value, etc. (see Section 13.3).

The above description of SPD records applies to all AOTs except AOT PHT40 (PHT-S spectro-photometry). SPD for PHT40 contains flux densities (in Jy) instead of in-band powers (in W). In the processing level following SPD (see Chapter 8) the PHT-S flux densities are converted into flux densities per wavelength interval (in ) and surface brightness units (in ).

Besides the SPD products that yield the processed data for the sky measurements, a number of other products are derived based on non-sky internal measurements. The products refer to the following type of measurements (see Section 2.5):

• FCS measurement: The resulting product is also referred to as a Calibration-A (`Cal-A') file.
• Dark instrument configuration measurement: This measurement type is obtained with AOTs PHT05, PHT25, and PHT40 and is used to subtract dark signals (in case of PHT05 and PHT25) or to identify possible detector memory artifacts from a preceding measurement of a bright source in case of PHT40.
• Cold FCS measurement: This type of measurement occurs in the absolute photometry AOTs PHT05 and PHT25 to correct for straylight affecting the heated FCS measurement.