Making a power spectrum from a TimeSeries

How to estimate the power spectrum of a TimeSeries.

import matplotlib.pyplot as plt
from scipy import signal
import astropy.units as u

import sunpy.timeseries
from sunpy.data.sample import RHESSI_TIMESERIES

Let’s first load a RHESSI TimeSeries from SunPy’s sample data. This data contains 9 columns, which are evenly sampled with a time step of 4 seconds.

ts = sunpy.timeseries.TimeSeries(RHESSI_TIMESERIES)

We now use SciPy’s periodogram to estimate the power spectra of the first column of the Timeseries. The first column contains X-Ray emmisions in the range of 3-6 keV. An alternative version is Astropy’s LombScargle periodogram.

x_ray = ts.columns[0]
# The suitable value for fs would be 0.25 Hz as the time step is 4 s.
freq, spectra = signal.periodogram(ts.data[x_ray], fs=0.25)

Out:

/home/docs/checkouts/readthedocs.org/user_builds/sunpy/conda/v1.1.4/lib/python3.8/site-packages/sunpy/timeseries/timeseriesbase.py:125: SunpyUserWarning: Using .data to access the dataframe is discouraged; use .to_dataframe() instead.
  warnings.warn("Using .data to access the dataframe is discouraged; "

Let’s plot the results

plt.semilogy(freq, spectra)
plt.title(f'Power Spectrum of {x_ray}')
plt.ylabel('Power Spectral Density [{:LaTeX}]'.format(ts.units[x_ray] ** 2 / u.Hz))
plt.xlabel('Frequency [Hz]')
plt.show()
Power Spectrum of 3 - 6 keV

Total running time of the script: ( 0 minutes 0.418 seconds)

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