.. index:: Wide survey

.. _calobs-block-pv-zodimodel:

**CALBLOCK-PV-006:** Background model
=====================================

.. include:: definitions.rst

Observation configuration file
------------------------------
| :download:`ocf_CALBLOCK-PV-006_ELAT-100.csv <tables/OCFs/ocf_CALBLOCK-PV-006_ELAT-100.csv>`
| :download:`ocf_CALBLOCK-PV-006_ELAT-90.csv <tables/OCFs/ocf_CALBLOCK-PV-006_ELAT-90.csv>`
| :download:`ocf_CALBLOCK-PV-006_GLAT.csv <tables/OCFs/ocf_CALBLOCK-PV-006_GLAT.csv>`

Scheduling
----------

Once, during PV phase.

In case of failure, repeat at next possible opportunity.

Time-critical
-------------

No.

Dependencies
------------

None.

Objective
---------

Validate and - if necessary update - the zodiacal and galactic background models. The overall background signal seen by Euclid is mainly comprised of the zodiacal background, out-of-field and in-field stray light, and galactic cirrus. In the NISP Y, J and H passbands, the zodi background constitutes about 85\% of the total background signal, the remainder coming from straylight. While the actual composition of the background signal is irrelevant to Euclid's primary science objectives, the legacy science and a thorough understanding of Euclid's telescope, instruments and S/N considerations require an accurate background model.

While the background model can in principle be obtained from every exposure in the nominal survey over time, we need to validate the model at the beginning of the mission. This also validates the premise upon which the Euclid Wide Survey footprint is constructed (galactic and ecliptic exclusion zones).

Observations
------------

Execute the ROS_D1 at the following ecliptic sky positions, sampling the typical range (and a bit beyond) of ecliptic latitudes and longitudes encountered during the survey:

.. code-block:: python
		
   for SAA in [90,100]:
       if SAA == 90:
           for ELAT in [90,...,-80] in steps of 10:
	       "execute ROS_D1"
       if SAA == 100:
           for ELAT in [80,...,20,0,-20,...,-80] in steps of 15:
	       "execute ROS_D1"

   for GLAT in [90,80,...,20]:
       if visible within SAA/AA constraints:
            "execute ROS_D1"   

**The ROS_D1 VIS variants** are mostly NominalScience+ShortScience [NS+SS], with [NS+Bias] at the beginning, middle and the end of the CALBLOCK.  The biases provide instrumental reference; the Short Science exposures are not mandatory.


**Remarks:**

1. The SAA=90, ELAT=-90 pointing is located in the Large Magellanic Cloud and should be skipped

2. For SAA=100, ELAT=90 cannot be reached.

3. The forward- or backward looking arc in orbit should be chosen, avoiding a crossing through the galactic plane if possible. Pointings at ``|GLAT|<=20`` are not useful and should be skipped.

4. **The final pointings will be provided by EC-SURV, depending on constraints from launch date, galactic plane, and bright stars.**
	    
       
Fulfilling
----------

:ref:`char-survey-zodimodel`

Targets and pointing constraints
--------------------------------

:command:`Pointing`: These observations require specific SAA angles - as indicated in the table below - to reach the requested pointing in ecliptic coordinates. Straylight suppression: :math:`{\rm AA}<=-3.5`. 

.. csv-table:: **Zodi background sampling points (tentative).** :download:`CSV file <tables/targets-zodiscan.dat>`
   :file: tables/targets-zodiscan.dat


Instrument configuration
------------------------

Instrument: Wide survey

Methodology / Uplink procedure
------------------------------
:command:`Entity`: VIS and NISP

:command:`Commanding Method`: 

:command:`Dither Sequence`: ROS_D1

Inter-operability constraints
-----------------------------

None.

In-orbit duration
-----------------
:command:`In-orbit Duration`: 14.4 h

Assuming 0.3 h per dither and 300 s slew time for a total of 38 fields 37 large slews.
	 
Data volume
-----------

``38*ROSD1 = 49514 MB``

Processing input
----------------
:command:`Ground Processing Input Data`:

:command:`Data Description`:

Processing output
-----------------

Mean background value per exposure, corrected for the straylight contributions, as a function of filter, ecliptic latitude and longitude

Validation
----------

Extract the background signal, correct for straylight contributions, and check against the current zodi model.

Recovery
--------

Update the zodi model.

Quality control parameters
--------------------------
DataModel:
`<https://gitlab.euclid-sgs.uk/>`_

Contact person
--------------
Survey Scientist (Roberto Scaramella)

.. raw:: latex

   \clearpage