!===============================================================================
!
! README for OMSO2G (OMI Daily L2G for OMSO2)
!
! Peter J.T. Leonard (ADNET) - 04/03/08
!
! OML2G High Level Overview:
!   This is the main program for the OML2G Product Generation Executive (PGE).
!
!   The OML2G PGE creates an Ozone Monitoring Instrument (OMI) daily Level 2G
!   (L2G) gridded data product file from (as many as) 16 OMI orbital Level 2
!   (L2) swath data product files.
!
!   Each OMI L2G product file contains 24 UTC hours of OMI L2 data from a single
!   OMI L2 product subsetted onto a longitude-latitude grid.
!
!   An OMI L2G day is defined to be the 24 hours that lie between UTC times of
!   0 hours, 0 minutes, 0 seconds and 23 hours, 59 minutes, 59.999999 seconds.
!
!   The OMI L2G product currently excludes L2 data collected in spatial and
!   spectral zoom modes.
!
!   The format of the OMI L2G product files is consistent with the document
!   entitled "HDF-EOS Aura File Format Guidelines" by C. Craig et al.
!
! OML2G Algorithm:
!   The OML2G PGE populates each cell in the L2G grid with data for all L2
!   "scenes" that
!   1) have observation times that lie within the L2G day in question,
!   2) have centers that lie within the L2G grid cell in question, and
!   3) are "good".
!
!   The OML2G PGE makes use of different definitions of "good" to populate
!   the L2G grids that correspond to different L2 products.
!
!   In the case of the OMI L2G product named OMSO2G, which is L2G for the L2
!   product named OMSO2, the definition of a "good" scene is one that has
!   i)  a solar zenith angle that is less than or equal to 88.0 degrees, and
!   ii) a STL column amount SO2 that is not equal to the missing value.
!
!   The OMI L2 data that are reproduced in the OMI L2G product are not averaged
!   or weighted in any way by the OML2G PGE.
!
! Adopted L2G Grid:
!   The adopted L2G grid is a 0.125-degree by 0.125-degree grid in longitude and
!   latitude.  The dimensions of this grid are 2880 by 1440.  The origin of the
!   grid is at lower left.  That is, the grid cell at coordinates (1, 1)
!   is centered at (longitude = -179.9375 , latitude = -89.9375),
!   and the grid cell at coordinates (2880, 1440)
!   is centered at (longitude =  179.9375 , latitude =  89.9375).
!
!   Each "good" L2 scene is mapped onto only one L2G grid cell.
!
!   The number of L2 scenes that are mapped onto a given L2G grid cell can range
!   from 0 to 8.  These data are stored in an additional dimension of the grid.
!
!   The adopted L2G grid is consistent with the document entitled "Definition
!   of OMI Grids for Level 3 and Level 4 Data Products" by J.P. Veefkind et al.
!
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