OMI Solar Spectral Irradiance Data
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Authors:  Sergey Marchenko and Matthew DeLand

Contact:  sergey.marchenko@ssaihq.com

Last revision:  3 November 2022


Data Product
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This file gives a basic description of the solar spectral irradiance data that 
we have produced from Aura OMI solar measurements.  Detailed discussion of the 
procedures used and validation steps can be found in the following papers:

S. V. Marchenko and M. T. DeLand (2014), "Solar spectral irradiance changes 
  during Cycle 24", Ap. J. 789:117, doi:10.1088/0004-637X/789/2/117.

S. V. Marchenko, M. T. DeLand, and J. L. Lean (2016), "Solar spectral irradiance 
  variability in Cycle 24:  Observations and models", J. Space Weather Space 
  Climate, 6, A40, doi:10.1051/swsc/2016036.

S. V. Marchenko, T. N. Woods, M. T. DeLand, S. Mauceri, P. Pilewskie, and M. 
  Haberreiter (2019), Improved Aura/OMI solar spectral irradiances: Comparisons
  with independent data sets and model predictions, Earth and Space Sci., 6, 
  2379-2396, doi:10.1029/2019EA000624.

We designate this dataset as Version 5 ('_v5') to recognize the use of 
the Collection 4 OMI L1B data, as described by Kleipool et al. [2022]. Other 
changes from the Version 3 OMI SSI product described in our 2019 paper were 
previously incorporated in our Version 4 product, and include the following 
items:

   1. The instrument degradation model is now based on data from all three OMI 
      channels (UV1, UV2, VIS) for better spectral consistency.
   2. The averaging period used to define our solar minimum reference spectrum 
      has been shifted to cover 1 July 2008 - 30 April 2009. This provides 
      symmetric coverage around the sunspot minimum at ~2008.9 shown in NOAA 
      NGDC (National Geophysical Data Center) data.
   3. The filtering process to remove instrument noise has been revised to 
      improve flexibility.
   4. The SSI data are provided on a 0.5 nm wavelength grid for consistency 
      with the OMI spectral resolution (~0.4-0.6 nm).

Kleipool, Q., et al. (2022). Ozone Monitoring Instrument (OMI) collection 4: 
  establishing a 17-year-long series of detrended level-1b data. Atmos. Meas. 
  Tech., 15, 3527-3533, doi:10.5194/amt-15-3527-2022.


Data Location
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The OMI data can be retrieved at the following web site:

   https://sbuv2.gsfc.nasa.gov/solar/omi/


File Contents
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The OMI irradiance data, corrected for long-term degradation, are provided in a 
single IDL save set named 'corrected_solar_flux_regular_diff_v5_nov2022.sav'.
All data are provided separately for each of three spectral channels, where the 
term 'CHN' in the variable name has the following definitions:

   'uv1'  =  UV1 channel, wavelength range = 265.0-309.5 nm
   'uv2'  =  UV2 channel, wavelength range = 310.0-364.5 nm
   'vis'  =  VIS channel, wavelength range = 365.0-500.0 nm

The save set contains the following variables, where 'CHN' is defined as above 
for each channel:

   JUL_DATE          Observation date in adjusted Julian day format 
                       [JD-2450000.0]
   chn_REFERENCE     Reference irradiance spectrum created by averaging data 
                       between July 2008 and April 2009 [photons/cm^2/sec/nm]
   chn_BIN           Daily spectra, expressed as normalized irradiance relative 
                       to the reference spectrum irradiance value at each 
                       wavelength
   chn_BIN_STD       Normalized standard deviation within each spectral and 
                       daily bin
   LA_chn            Wavelength scale [nm], sample interval = 0.5 nm

For users who prefer to use data in HDF format, the file 
'omi_ssi_update_v5_20221103.h5' is also available.  It contains the same 
information as the IDL save set, with the following mapping of variables:

   JUL_DATE       -->  JulianDateAdj
   chn_REFERENCE  -->  IrradianceReference{chn}
   chn_BIN        -->  IrradianceNormalized{chn}
   chn_BIN_STD    -->  IrradianceStDev{chn}
   LA_chn         -->  Wavelength{chn}

The first measurement date available in the OMI data product is 2 July 2006, 
and the last date included in the current data file is 24 July 2022.