OMI level2 products contain geophysical information at ground pixel resolution and derived from level 1B product.
Level 2G (L2G) datasets contain one day's worth of the Level 2 data (typically 14 orbits) ordered by ground position rather than by time.
What does it mean by ordered by ground position rather than by time?
OMI's Level 2 products are stored as two-dimensional arrays in the instrument's frame of reference. The first dimension of these arrays has 60 entries in across-track direction, which are obtained at the same time (push broom scanner). The second dimension has about 1600 entries in along-track direction. In along-track direction, entries are sorted by time from the first to the last measurement in an orbit. As there are about 14 orbits per day, you will find 14 files for each day.
The Level 2G product are also stored in a two-dimensional array, but with first and second dimension being longitude and latitude, respectively. Each entry of these arrays has a list of all measurements obtained at this longitude-latitude position. The Level 2G product contains all data of a single day in one file.
To summarize, the Level 2 product is using measurement time as array dimensions and the Level 2G product is using longitude-latitude ground position as array dimensions. Thus Level 2 data are ordered by time, while Level 2G is ordered by ground position.
I hope my explanations help to answer your questions.
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