The Channel class

>>> from gwpy.detector import Channel

What is a ‘channel’?

Each of the laser-interferometer gravitational-wave detectors record thousands of different data streams capturing a single instrumental error or control signal, or the output of an environmental sensor. These data streams are known as ‘channels’, and are named according to a convention that describes its source in the instrument, and the signal it records, for example:

L1:PSS-ISS_PDB_OUT_DQ

describes the output signal (OUT) from photodiode-B (PDB) inside the Intensity Stabilisation System (ISS) of the Pre-Stabilised Laser (PSL) powering the L1 instrument, hosted at the LIGO Livingston Observatory. The DQ suffix indicates that this channel was recorded in data files for offline study (many more ‘test point’ channels are used only in real-time, and are never recorded).

A simple representation of this physical signal is provided by the Channel object:

>>> from gwpy.detector import Channel
>>> signal = Channel('L1:PSL-ISS_PDB_OUT_DQ')

This new Channel has a number of attributes that describe its source, derived from its name:

>>> print(hoft.ifo)
'L1'
>>> print(hoft.system)
'PSL'
>>> print(hoft.subsystem)
'ISS'

and so on.

Alongside nomnitive attributes, each Channel has the following attributes:

name

Name of this channel.

sample_rate

Rate of samples (Hertz) for this channel.

unit

Data unit for this channel.

dtype

Numeric type for data in this channel.

url

CIS browser url for this channel.

model

Name of the SIMULINK front-end model that defines this channel.

Each of these can be manually passed to the Channel constructor, or downloaded directly from the LIGO Channel Information System.

The LIGO Channel Information System (https://cis.ligo.org)

All of the LIGO interferometer data channels are recorded in the Channel Information System (https://cis.ligo.org), a queryable database containing the details of each channel recorded to disk from the observatories. The Channel.query() classmethod allows you to query the database as follows:

>>> from gwpy.detector import Channel
>>> chan = Channel.query('L1:IMC-F_OUT_DQ')
>>> print(chan.sample_rate)
16384.0 Hz
>>> print(chan.url)
https://cis.ligo.org/channel/282666
>>> print(chan.model)
l1lsc

In this example we have accessed the information for the frequency noise output signal (F_OUT) from the Input Mode Cleaner (IMC) of the L1 instrument.

The ChannelList

Groups of channels may be collected together in a ChannelList, a simple extension of the built-in list with functionality for finding and sieveing for specific Channel names, sample-rates, or types.

Class reference

This reference contains the following class entries:

Channel

Representation of a laser-interferometer data channel.

ChannelList

A list of channels, with parsing utilities.
class gwpy.detector.Channel(name, **params)[source]

Representation of a laser-interferometer data channel.

Parameters

name : str, Channel

name of this Channel (or another Channel itself). If a Channel is given, all other parameters not set explicitly will be copied over.

sample_rate : float, Quantity, optional

number of samples per second

unit : Unit, str, optional

name of the unit for the data of this channel

frequency_range : tuple of float

[low, high) spectral frequency range of interest for this channel

safe : bool, optional

is this channel ‘safe’ to use as a witness of non-gravitational-wave noise in the interferometer

dtype : numpy.dtype, optional

numeric type of data for this channel

frametype : str, optional

LDAS name for frames that contain this channel

model : str, optional

name of the SIMULINK front-end model that produces this channel

Notes

The Channel structure implemented here is designed to match the data recorded in the LIGO Channel Information System (https://cis.ligo.org) for which a query interface is provided.

class gwpy.detector.ChannelList(iterable=(), /)[source]

A list of channels, with parsing utilities.