.. DO NOT EDIT.
.. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY.
.. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE:
.. "examples/frequencyseries/coherence.py"
.. LINE NUMBERS ARE GIVEN BELOW.

.. only:: html

    .. note::
        :class: sphx-glr-download-link-note

        :ref:`Go to the end <sphx_glr_download_examples_frequencyseries_coherence.py>`
        to download the full example code.

.. rst-class:: sphx-glr-example-title

.. _sphx_glr_examples_frequencyseries_coherence.py:


.. currentmodule:: gwpy.timeseries
.. sectionauthor:: Duncan Macleod <duncan.macleod@ligo.org>

Calculate the coherence between two channels
############################################

The `coherence <http://en.wikipedia.org/wiki/Coherence_(physics)>`_ between
two channels is a measure of the frequency-domain correlation between their
time-series data.

In LIGO, the coherence is a crucial indicator of how noise sources couple into
the main differential arm-length readout.
Here we use use the :meth:`TimeSeries.coherence` method to highlight coupling
of motion of a beam periscope attached to the main laser table into the
strain output of the LIGO-Hanford interferometer.

These data are available as part of the |GWOSC_AUX_RELEASE|_.

.. GENERATED FROM PYTHON SOURCE LINES 40-43

Data access
-----------
First, we import the `TimeSeriesDict`

.. GENERATED FROM PYTHON SOURCE LINES 43-46

.. code-block:: Python


    from gwpy.timeseries import TimeSeriesDict








.. GENERATED FROM PYTHON SOURCE LINES 47-50

and then :meth:`~TimeSeriesDict.get` the data for the differential-arm
length servo control loop error signal (``H1:LSC-DARM_IN1_DQ``) and the
PSL periscope accelerometer (``H1:PEM-CS_ACC_PSL_PERISCOPE_X_DQ``):

.. GENERATED FROM PYTHON SOURCE LINES 50-60

.. code-block:: Python


    data = TimeSeriesDict.get(
        ["H1:LSC-DARM_IN1_DQ", "H1:PEM-CS_ACC_PSL_PERISCOPE_X_DQ"],
        1186741560,
        1186742160,
        host="nds.gwosc.org",
    )
    darm = data["H1:LSC-DARM_IN1_DQ"]
    acc = data["H1:PEM-CS_ACC_PSL_PERISCOPE_X_DQ"]





.. rst-class:: sphx-glr-script-out

 .. code-block:: none

    /home/duncan.macleod/gwpy-nightly-build/conda/envs/gwpy-nightly-3.11/lib/python3.11/site-packages/igwn_auth_utils/requests.py:46: DeprecationWarning: Support for identity-based X.509 credentials for LIGO.ORG is being dropped.
    Calls to this utility will stop working on/around 20 May 2025.

    For details on this change please see

    https://computing.docs.ligo.org/guide/compsoft/roadmap/LVK/x509_retirement/

    If you have questions about this message, or its implications, please
    consider opening an IGWN Computing Help Desk ticket:

    https://git.ligo.org/computing/helpdesk/-/issues/new
      return func(*args, **kwargs)




.. GENERATED FROM PYTHON SOURCE LINES 61-66

Calculating coherence
---------------------
We can then calculate the :meth:`~TimeSeries.coherence` of one
`TimeSeries` with respect to the other, using an 2-second Fourier
transform length, with a 1-second (50%) overlap:

.. GENERATED FROM PYTHON SOURCE LINES 66-69

.. code-block:: Python


    coh = darm.coherence(acc, fftlength=2, overlap=1)








.. GENERATED FROM PYTHON SOURCE LINES 70-74

Visualisation
-------------
Finally, we can :meth:`~gwpy.frequencyseries.FrequencySeries.plot` the
resulting data:

.. GENERATED FROM PYTHON SOURCE LINES 74-84

.. code-block:: Python


    plot = coh.plot(
        xlabel="Frequency [Hz]",
        xscale="log",
        ylabel="Coherence",
        yscale="linear",
        ylim=(0, 1),
    )
    plot.show()




.. image-sg:: /examples/frequencyseries/images/sphx_glr_coherence_001.png
   :alt: coherence
   :srcset: /examples/frequencyseries/images/sphx_glr_coherence_001.png
   :class: sphx-glr-single-img





.. GENERATED FROM PYTHON SOURCE LINES 85-90

We can clearly see the correlation between the periscope motion and the
differential-arm length servo control loop error signal between 100 Hz
and 1000 Hz. Such physical couplings can interfere, mask, or even mimic
a gravitational wave signal inferred from the differential arm
length motion.


.. rst-class:: sphx-glr-timing

   **Total running time of the script:** (0 minutes 4.332 seconds)


.. _sphx_glr_download_examples_frequencyseries_coherence.py:

.. only:: html

  .. container:: sphx-glr-footer sphx-glr-footer-example

    .. container:: sphx-glr-download sphx-glr-download-jupyter

      :download:`Download Jupyter notebook: coherence.ipynb <coherence.ipynb>`

    .. container:: sphx-glr-download sphx-glr-download-python

      :download:`Download Python source code: coherence.py <coherence.py>`

    .. container:: sphx-glr-download sphx-glr-download-zip

      :download:`Download zipped: coherence.zip <coherence.zip>`


.. only:: html

 .. rst-class:: sphx-glr-signature

    `Gallery generated by Sphinx-Gallery <https://sphinx-gallery.github.io>`_