1. Introduction

Prior to processing any OmegaCAM data, the frames need to be matched in terms of setup and in terms of dependencies. The Organization, Classification, and Association (OCA) of frames (raw calibrations and science, as well as pipeline processed products) occurs at several places within the VLT Data Flow.

Based on information available in the headers, raw frames are matched to the files (i.e. product frames) that they require in order to be processed, and in terms of association rules based on the keywords:
INS.FILT1.NAME (i.e. any of the current OmegaCAM filters:
u_SDSS / g_SDSS / r_SDSS / i_SDSS / z_SDSS / u_g_r_i_SDSS / B_JOHN / V_JOHN / v_STRM / H_ALPHA / NB_659 / NB_852 / opaque)
DET.WIN1.BINX (i.e. the x-axis binning used for the given exposure. Generally, 1)
DET.WIN1.BINY (i.e. the y-axis binning used for the given exposure. Generally, 1)
DET.READ.MODE (i.e. the detector read-out mode. Generally, normal)
DET.READ.SPEED (i.e. the detector read-out speed. Generally, normal)
OBS.PROG.ID (i.e. science data and specific calibrations matched to a given scientific program)

For example, matching rules could be as follows:

- match to the closest (in time) stack of raw twilight flat frames that have INS.FILT1.NAME=r_SDSS and DET.WIN1.BINX=1 and DET.WIN1.BINY=1 and DET.READ.MODE=normal and DET.READ.SPEED=normal, to the master bias frame, hot pixel map, master dome flat, and cold pixel map having the same matched keywords that are needed to process the raw twilight flats into a master flat and a master bad pixel map.
- match to all standard stars for the program OBS.PROG.ID=098.A-0987(B), that have INS.FILT1.NAME=i_SDSS and DET.WIN1.BINX=1 and DET.WIN1.BINY=1 and DET.READ.MODE=normal and DET.READ.SPEED=normal, within the same night, and with an airmass difference to the science data of no more than delta_airmass = +/- 0.2.

2. Basic and Static Calibrations

Static calibrations are only needed for processing standard stars and science frames. To do this, the OmegaCAM data reduction scheme requires:
a) a reference standard star catalogue (REFERENCE_STAR_CATALOG)
b) a reference USNO A2 catalogue (MASTER_USNOA2_CATALOGUE)
c) an input extinction curve (EXTINCTION_CURVE) and
d) a monitoring report (MONITOR_REPORT)

Raw frames generated by the bias, bias readnoise, detector gain and linearity, dark, and shutter test templates can be reduced by the pipeline without the need for any other calibration products.

3. Dependent Calibrations

The dome flat recipe (omega_mdome) requires, apart from the raw dome-flat frames, a master bias and a hot pixel map. The recipe output will be a master dome flat and a hot pixel map.

The twilight flat recipe (omega_mflat) requires, apart from the raw sky-flat frames, a master bias, a hot pixel map, a master dome flat, and a cold pixel map. The recipe output will be a master twilight flat, a master flat (a combination of the master dome and twilight flats), and a bad pixel map (a combination of the hot and cold pixel maps).

The standard star recipe (omega_standard_star) requires, apart from the raw standard star frame, a master bias, a master flat, and a master bad pixel map. The recipe output will be a fully reduced standard star field, a standard star field mask, a zeropoint fits table, and a photometric fits table.

4. Association Cascade

The calibration cascade is can be represented as:

Further details about the OmegaCAM calibration cascade can be found here.