Note
Go to the end to download the full example code.
Plotting a spectrogram of all open data for many hours¶
In order to study interferometer performance, it is common in LIGO to plot all of the data for a day, in order to determine trends, and see data-quality issues.
This is done for the LIGO-Virgo detector network, with up-to-date plots available from GWOSC.
This example demonstrates how to download data segments from GWOSC, then use those to build a multi-hour spectrogram plot of LIGO-Livingston strain data.
Getting the segments¶
First, we need to fetch the Open Data timeline segments from GWOSC.
To do that we can call the DataQualityFlag.fetch_open_data()
method
using 'H1_DATA'
as the flag (for an explanation of what this means,
read up on The S6 Data Release).
from gwpy.segments import DataQualityFlag
l1segs = DataQualityFlag.fetch_open_data(
"L1_DATA",
"Aug 17 2017 08:00",
"Aug 17 2017 16:00",
)
For sanity, lets plot these segments:
splot = l1segs.plot(
figsize=[12, 3],
epoch="August 17 2017",
)
splot.show()
splot.close() # hide
We see that the LIGO Hanford Observatory detector was operating for the majority of the day, with a few outages of ~30 minutes or so.
We can use the abs()
function to display the total amount of time
spent taking data:
print(abs(l1segs.active))
25796
Working with strain data¶
Now, we can loop through the active segments of 'L1_DATA'
and fetch the
strain TimeSeries
for each segment, calculating a
Spectrogram
for each segment.
from gwpy.timeseries import TimeSeries
spectrograms = []
for start, end in l1segs.active:
l1strain = TimeSeries.fetch_open_data(
"L1",
start,
end,
verbose=True,
)
specgram = l1strain.spectrogram(30, fftlength=4) ** (1/2.)
spectrograms.append(specgram)
Fetched 4 URLs from gwosc.org for [1186992018 .. 1187001382))
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Finally, we can build a plot()
:
# Create an empty plot with a single set of Axes
from gwpy.plot import Plot
plot = Plot(figsize=(12, 6))
ax = plot.gca()
# add each spectrogram to the Axes
for specgram in spectrograms:
ax.imshow(specgram)
# finalise the plot metadata
ax.set_xscale("auto-gps", epoch="Aug 17 2017")
ax.set_ylim(20, 2000)
ax.set_yscale("log")
ax.set_ylabel("Frequency [Hz]")
ax.set_title("LIGO-Livingston strain data")
ax.colorbar(
cmap="viridis",
norm="log",
clim=(5e-24, 1e-21),
label=r"Strain noise [1/$\sqrt{\mathrm{Hz}}$]",
)
# add the segments as a 'state' indicator along the bottom
plot.add_segments_bar(l1segs)
plot.show()

Total running time of the script: (0 minutes 12.168 seconds)