GLOWS L2: Apply cps-to-Rayleigh calibration factor using ancillary calibration file

[maxinelasp]

Summary

Overview

GLOWS L2 currently computes photon flux as raw counts / exposure time but does not apply the cps-to-Rayleigh calibration factor. The reference implementation in glows_example_code applies this conversion using imap_glows_l2-calibration_*.dat, a time-indexed file providing a calibration constant (cps/R) per observational day. This factor must be applied to both photon_flux and flux_uncertainties at L2.

Requirements

• Using the dataset passed into HistogramL2, look up the cps/R value for the observation date (most recent entry ≤ observation date) and divide photon_flux and flux_uncertainties by this factor.
  • The calibration is assumed constant for an entire observational day.
• Add a unit test covering the calibration lookup and application.

Related tickets

Reference implementation: toolkit/utils.py::calibration_factor() and toolkit/l2_data_histogram.py in glows_example_code.

Relates to #2880

[maxinelasp]

Steps:

• Find middle timestamp of epoch
• Go to calibration_dataset in glows_l2
• Look at calibration_dataset to confirm the format is correct, and update GlowsAncillaryCombiner if necessary
• Find the nearest timestamp before your middle timestamp
• This will correspond to the value for the observational day you are in
• Apply that value to flux and possibly flux uncertainties