Vis Master Flat Frame Product

$SetSchemaPath vis/euc-vis-MasterFlatFrame.xsd

Data product name

$PrintDataProductName

Data product custodian

$PrintDataProductCustodian

Name of the Schema file

$PrintSchemaFilename

Last Edited for DPDD Version

1.1

Processing Element(s) creating/using the data product

Final data product of the Master Flat (PRNU) Calibration pipeline. Used by the PRNU Correction task in several pipelines: (ProcessField, LargeFlat, BrighterFatter).

Processing function using the data product

VIS

Proposed for inclusion in EAS/SAS

Yes

Data product elements

$PrintDataProductElements

Detailed description of the data product

The Master Flat Calibration Pipeline result is created from a series of flat-field calibration exposures. It contains a Master PRNU image which describes the Pixel Response Non-Uniformity (PRNU) of each pixel in each VIS CCD quadrant.

The product contains a Flagmap FITS file, the same size as the Master PRNU, in which each pixel is a standard bitfield. The Master PRNU will set the bits for flagging hot and cold pixels. The Flagmap data format is defined in the data model here and is described in VIS_Flags.pdf.

The product contains an LED Profile FITS file which quantifies the illumination of the quadrant by the calibration unit (CU) LED.

Each pixel in a CCD has slightly different levels of response to light, due to manufacturing irregularities. The PRNU of a pixel is defined here as the level of responsiveness relative to its near-by neighbours, where the local average is 1.0. The nearest neighbour pixels have the highest weighting in this average. This weighting is implicit in the use of surface fitting to remove larger scale variations. Those variations include sky background, calibration LED illumination and shutter effects.

The PRNU model is stored as a 2-D image, not including prescan or overscan areas. PRNU is calibrated using a set of PRNU exposures, illuminated by an LED in the Calibration Unit (CU) which sits in front of the VIS focal plane. Flat exposures have different fluence levels and are also used for other purposes in other pipelines.

When the PRNU product is used during Correction, is a multiplicative effect, so the application of a correction involves simply dividing an image by the PRNU model.

The final product has 144 image extensions, one per VIS CCD quadrant. Each is identified by the EXTNAME, and contains 2048x2066 pixels in ADU units.

Detailed Algorithm information can be viewed in tech note: https://euclid.roe.ac.uk/dmsf/files/16476/view

Primary Header:

$PrintPrimaryHeader fit/euc-vis.xml vis.masterFlat

Extension Header:

$PrintExtensionHeader fit/euc-vis.xml vis.masterFlat FRAME.n