.. _NIRRelPhotoExpCalibration:
  
[to complete] NIR Relative Photometric Calibration factors among exposures
==============================================================

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

Data Product Name
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.. DataProductNameStart

$PrintDataProductName

.. DataProductNameEnd

Data Product Custodian
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.. DataProductCustodianStart

$PrintDataProductCustodian

.. DataProductCustodianEnd

Name of the Schema File
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.. NameSchemaStart

$PrintSchemaFilename

.. NameSchemaEnd

Data Product Elements
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.. DataProductElementsStart

$PrintDataProductElements

.. DataProductElementsEnd


Detailed Description of the Data Product
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.. DetailedDescStart

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
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.. PECreatorStart

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.

.. PECreatorEnd


Processing function using the data product
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.. PFUsingStart

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 :ref:`NIRCalibratedFrame` section.

.. PFUsingEnd

Data Product structure description
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. DataProductDescrStart

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

.. DataProductDescrEnd

.. DetailedDescEnd