.. index:: Noise Bias Calibration Fields

.. _calobs-block-f-deep-fields:

**CALBLOCK-F-002:** Noise Bias Fields (Euclid deep fields)
==========================================================

.. include:: definitions.rst

Observation configuration file
------------------------------
Not applicable

Scheduling
----------

Planning and replanning by EC-SURV.

**Grism ratio and completion:** The final blue:red grism ratio is 25:15. A single pass shall always use the same grism. As a goal, a strong imbalance between blue and red data should be avoided toward the data releases. However, technical constraints and space weather may interfere with this goal.

**Zodi corrections:** The total number of passes, and the exposure-time ratio of 25:15, may require smaller corrections because of the actual zodiacal background at these fields. Corrections are at the discretion of EC-SURV.

**Data sharing between EDFs and CPCs:** The EDF-N, EDF-S, CPC-N, and CPC-S share the same sky areas, and the same blue:red exposure-time ratio. A deep observation therefore contributes toward completing the CPC, and vice versa.

Time-critical
-------------
No.

Objective
---------

A sample of 200000 galaxies shall be obtained with a S/N 6 times that of the wide survey area, obtained from a 40 square degree area constituted by the `Euclid Deep Fields <http://sci.esa.int/euclid/61408-the-euclid-deep-fields/>`_ (EDF-North, EDF-South, and EDF-Fornax). 

The primary drivers of this calibration are VIS and the WL experiment to quantify the noise bias in the wide survey.

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

Observe the deep field areas using the ROS, until at least 40 square degrees are covered to 6 times the average S/N of the wide survey area.

**Blue grism:** The exposure time ratio is blue:red = 25:15, to account for different zodi background, and the reduced number of photons per flux per wavelength interval in the blue grism compared to the red grism.

**Dithering:** Each pass of a Deep Field consists of a regular grid. The regular grid is offset at every visit. The offsets lie along a spiral, producing a non-regular, yet fairly uniform distribution. In polar coordinates :math:`(\rho, \theta)`, and for a total of :math:`n` points, the position of point :math:`k` is given by: 

:math:`(\rho, \theta) = (scale * \sqrt{k} / 60, k* GoldenAngle)`, with

:math:`scale = width / (2 \sqrt{n})`
	
:math:`GoldenAngle = (3 - \sqrt{5}) * 180\;{\rm deg}`
	
:math:`3' < width < 6'` (chosen by EC-SURV according to their constraints)

This produces  :math:`n` points inside a circle of diameter :math:`width` (in arcmin). The division by 60 converts arcmin to degree. The circle size increases with the number of points.

**VIS Cycling:** The VIS ROS-inline calibrations follow the nominal wide-survey cycling, as described in :ref:`ros-inline-vis-calibrations-and-cadence`.

Fulfilling
----------

:ref:`calobs-vis-noise-bias-fields`
     
:ref:`calobs-nisp-spec-cpc` (partially)

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

:command:`Pointing`: Straylight suppression as per MOCDA-SYS-003. 

.. csv-table:: **Noise bias fields.** :download:`CSV file <tables/targets-noise-bias-fields.dat>`
   :file: tables/targets-noise-bias-fields.dat

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

Instrument: Wide survey; including blue-grism observations

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

:command:`Commanding Method`: 

:command:`Dither Sequence`: Within a single pass, execute the ROS at each grid point. Passes are offset along a spiral, see `Observations`.

Inter-operability constraints
-----------------------------
None

In-orbit duration
-----------------
:command:`In-orbit Duration`:
	 
Processing input
----------------
:command:`Ground Processing Input Data`:

:command:`Data Description`:

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

Contact person
--------------
Calibration Lead  

.. raw:: latex

   \clearpage