Ghost Position Model Product

$SetSchemaPath vis/euc-vis-GhostModel.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

Ghost Position Model - VIS Processfield and Ghost pipelines

Processing function using the data product

VIS

Proposed for inclusion in EAS/SAS

Yes

Data product elements

$PrintDataProductElements

Detailed description of the data product

Optical ghosts are artefacts created in VIS images by very bright sources (saturated stars). They are caused by internal reflections of light inside the dichroic plate which separates light between the VIS and NISP instruments. Infrared wavelengths are transmitted through the dichroic plate, while visible light is reflected by the front face of the dichroic plate. But visible light reflection is not perfect and about 1e-6 of it penetrates in the dichroic plate and is reflected by the back face of the dichroic, creating a defocused second light path which produces a ghost image of the primary mirror obscured by the three secondary mirror spider arms, on the VIS detector.

The output product of the Optical Ghosts Calibration pipeline is a JSON file containing a dictionary. This dictionary contains a ‘header’, with some metadata like the production date and the reference frames used, and a ‘data’ section which contains the actual ghost position model.

In the most complete model built from optical model ray tracing, the ‘data’ section contains a list of wavelength in nanometre, and for each wavelength, either “1” or “2”, correcponding to the ghost order (respectively 1 reflection on the dichroic plate back side, or 2 reflections). Each combination of wavelength/order in turn contains a dictionary of two 4x4 matrices, “A” and “B”, used to compute the ghost offset from its star, along the X and Y axes respectively.

Details on how to compute and to use the A and B matrices can be found in Samuel Ronayette’s note: https://euclid.roe.ac.uk/dmsf/files/4270/view

Detailed Tech Note can be found: https://euclid.roe.ac.uk/dmsf/files/17192/view