Correcting for instrument degradation

This example demonstrates the degradation of the filters on AIA over time.

import matplotlib.pyplot as plt

import astropy.time
import astropy.units as u
from astropy.visualization import quantity_support, time_support
from sunpy.net import Fido
from sunpy.net import attrs as a

from aiapy.calibrate import degradation

# These are needed to allow the use of quantities and astropy
# time objects in the plot.
time_support(format="jyear")
quantity_support()

The performance of the AIA telescope is unfortunately degrading over time, leading to the resulting images becoming increasingly dim. We can correct for this by modeling the degradation over time and then dividing the image intensity by this correction.

First, let’s fetch some metadata for the 335 Å channel of AIA between 2010 and 2018 at a cadence of 30 days. We choose the 335 Å channel because it has experienced significant degradation compared to the other EUV channels.

results = Fido.search(
    a.Time("2010-06-01T00:00:00", "2021-06-01T00:00:00"),
    a.Sample(30 * u.day),
    a.jsoc.Series.aia_lev1_euv_12s,
    a.jsoc.Wavelength(335 * u.angstrom),
)

We only need the date and mean intensity columns from the metadata that was returned. We select those and nothing else.

table = results["jsoc"].show("DATE__OBS", "DATAMEAN")
table["DATAMEAN"].unit = u.ct
table["DATE_OBS"] = astropy.time.Time(table["DATE__OBS"], scale="utc")
del table["DATE__OBS"]

print(table)

Next, we pass the date column to the aiapy.calibrate.correct_degradation function. This function calculates the time-dependent correction factor based on the time and wavelength of the observation. We then divide the mean intensity by the correction factor to get the corrected intensity. For more details on how the correction factor is calculated, see the documentation for the aiapy.calibrate.degradation function.

correction_factor = degradation(335 * u.angstrom, table["DATE_OBS"])
# This correction can be applied to a sunpy Map as well.
table["DATAMEAN_DEG"] = table["DATAMEAN"] / correction_factor

To understand the effect of the degradation and the correction factor, we plot the corrected and uncorrected mean intensity as a function of time. Note that the uncorrected intensity decreases monotonically over time while the corrected intensity recovers to pre-2011 values in 2020.

plt.plot(table["DATE_OBS"], table["DATAMEAN"], label="mean", marker="o")
plt.plot(table["DATE_OBS"], table["DATAMEAN_DEG"], label="mean, corrected", marker="o")
plt.title(f'{(335*u.angstrom).to_string(format="latex")} Channel Degradation')
plt.legend(frameon=False)

plt.show()