OMI Solar Spectral Irradiance Data
                        ##################################

Authors:  Sergey Marchenko and Matthew DeLand

Contact:  sergey.marchenko@ssaihq.com

Last revision:  20 January 2020


Data Product
************

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., in 
  press, doi:10.1029/2019EA000624.

Please note that this data set has been revised in three areas, as described in
our 2019 paper:

   1. We have improved the separation of pixels flagged as noise-affected, which
      provides more data in the later part of the OMI record.
   2. We now use an exponential time dependence for our degradation model, 
      replacing the previous linear function.
   3. We now require consistent absolute irradiance levels at the minimum of 
      Cycle 23 and Cycle 24 as a constraint for item (2).

Since Cycle 24 may not have reached its full minimum yet, we believe that 
item (3) currently leads to an underestimate of ~0.1% for solar cycle 
variability in the UV region (wv < 350 nm), and < 0.05% in the visible region.

The revised degradation model now enables us to extrapolate the correction 
function back to July 2006.

This update replaces some samples between 355-380 nm in mid-2006 that were 
accidentally omitted.  No other data have been changed.

Data Location
*************

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

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


File Contents
*************

The OMI irradiance data, corrected for long-term degradation, are provided in a 
single HDF file named 'omi_ssi_irradiance_20191125.h5'.  All data are originally 
measured in three spectral channels:

   UV1 channel, wavelength range = 265.0-309.5 nm
   UV2 channel, wavelength range = 310.0-355.5 nm
   VIS channel, wavelength range = 356.0-500.0 nm

The datasets presented here combine these data into a single spectral dimension.  

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 22 November 2019.  The HDF 
file contains the following variables:

   JulianDateAdj          Observation date in adjusted Julian day format 
                            [JD-2450000.0]
   Year                   Year of measurement
   DayofYear              Day of year of measurement
   Month                  Month of measurement
   Day                    Day of month of measurement
   Hour                   Hour of measurement
   Minute                 Minutes of measurement
   Second                 Seconds of measurement
   WavelengthScale        Wavelength scale [nm], sample interval = 0.5 nm
   IrradianceReference    Reference irradiance spectrum created by averaging data 
                            between April 2007 and September 2009 [mW/m^2/nm]
   IrradianceDaily        Daily spectra [mW/m^2/nm]
   IrradianceStDev        Standard deviation within each spectral and daily bin