[to complete] NIR Relative Photometric Calibration factors among exposures

$SetSchemaPath nir/euc-test-nir-RelPhotoExpCalibration.xsd

Data Product Name

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Data Product Custodian

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Name of the Schema File

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Data Product Elements

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Detailed Description of the Data Product

The DpdNirRelPhotoExpCalibration data product identify the photometric offset among different exposures of the same observation, 4 in case of wide survey.

Those factors are considered as quality parameter indexes to identify problems during the photometric images calibrations. The creation task is executed on sources relatively calibrated, but not absolutely. That is all photometric corrections are applied on images, save for the zeropoint offest.

Is therefore expected that the same source shows the same flux regardless of the exposure and detector where it is was observed. This data product contains a median value of sources fluxes differences for all exposures to check photometry. It is created and applied during the same pipeline.

This is a “pure” xml Data Product that contains a list of single exposures offsets.

A DpdNirRelPhotoExpCalibration data product for each Observation is foreseen.

Processing Element(s) creating/using the data product

The DpdNirRelPhotoExpCalibration is calculated for each Observation comparing photometry of sources extracted in subsequent exposures. The task responsible of its creation is NIR_calculate_relative_exposures task (under NIR_RelativePhotometry project) inside the NIR_ProcessField_Pipeline.

The catalog extracted from each exposure is compared with the ones of the others exposures. The magnitude difference is calculated for each source in common between two exposures. Then it is evaluated the median values of those differences, after a sigma clipping to keep out variables and contaminant.

At the end for each exposure is associated the median value among flux differences with all the others exposures.

In case of right photometric corrections (i.e. flats, detector offset factors) it is expected to have a value close to 1 for all exposures. Value that can move away from 1 in case of trouble in some specific exposure photo calibration.

Processing function using the data product

The DpdNirRelPhotoExpCalibration is applied by the NIR_apply_relative_calibrations task (under NIR_RelativePhotometry project) inside the NIR_ProcessField_Pipeline.

We do not expect any variation in photometry among exposures due to the short time interval among them. This value is therefore considered as a quality parameter and not a photometric correction factor. The task writes the keyword QPRELEX, and its corresponding error QPRELEXE, on the main exposure header, that traces a quality parameter, as described in NIR Calibrated Frame section.

Data Product structure description

The main elements inside the Data section are:

  • Filter: The filter name (e.g. NIR_Y, NIR_J, NIR_H)

  • ValidityRange: Calibration file validity period estimated

  • ObservationId: Observation Id

  • CorrectionFactorList: a list of single exposure photometric offset

    • Value: detector photometric correction factor

    • Error (optional): detector photometric correction factor error

    • Exposure: exposure number