Order Original Unfiltered Subsetted Daily Level 2G Data
Clicking on this button will launch a new window containing instructions for
downloading spatial and/or parameter subsetted daily Level 2G data that meet
the user's criteria.
Characteristics of downloaded data files:
Subsetted files are available in either HDF-EOS5
or ASCII table-like format.
The subsetted files are from the original Level 2G OMI data (one file per day).
The subsetting criteria are based on the user inputs (Parameter and/or
Spatial Selections) from the Giovanni OMI interface.
The total number of subset files will equal the number of days in the
user selected time period.
Note: Only spatial and/or parameter, as well as
temporal input selections are
used for subsetting. Subsets include a set of default parameters (Time,
SecondsInDay, Latitude, Longitude, SolarZenithAngle, ViewingZenithAngle,
SceneNumber, LineNumber, QualityFlags, GroundPixelQualityFlags), so as to
allow the user to apply their own filtering on the original data.
Subset files in HDF-EOS5 format
HDF-EOS5 format preserves all of the attributes and
metadata that were supplied in the original data files. These can be utilized
by software that support HDF-EOS5.
User will need to have software that can read and manipulate objects
inside the HDF-EOS5 files. See http://acdisc.gsfc.nasa.gov/tools.shtml for a
list of software for reading and displaying HDF-EOS5 data files.
The subset files contain the selected parameter(s) only over the
spatial region of interest.
Subset files in ASCII format
The ASCII format includes a short header with the original file attributes,
and number of data pixels (rows) within the subset spatial region. Each data
pixeel row includes a set of default parameters as well as the user selected
parameter(s) are arranged in columns which are delimeted by spaces. It is
fairly simple to import the ASCII file into a spreadsheet or mathematical
software. This section describes the OMI output in ASCII (text format), and
how to import it into a spreadsheet.
Header
Name of the original file
The following global attributes are displayed in the ASCII file header:
OrbitNumber (array listing orbit numbers used in the original file)
OrbitPeriod (array listing the period of each orbit)
InstrumentName (name of the instrument, always = OMI)
ProcessLevel (data processing level, always = 2G)
GranuleMonth (month of year of the original data file)
GranuleDay (day of month of the original data file)
GranuleYear (year of the original data file)
GranuleDayOfYear (day of year of the original data file)
TAI93At0zOfGranule (TAI93, or seconds since Jan. 1, 1993, at 00:00 UTC)
PGEVersion (Program Generated Executable Version number)
StartUTC (Start time in UTC of the original file)
EndUTC (End time in UTC of the original file)
Period (Time period for granule, always Daily)
QAPercentMissingData (QA Percent Missing Data for each orbit)
Spatial Subset Region (latitude and longitude)
Number of Pixels (Rows) found in spatial subset region
Data Table
Along with the user selected parameter(s), each row includes the following columns:
Time (in TAI93 foramt, seconds since Jan. 1, 1993)
SecondsInDay (seconds since start of day)
Latitude (geodetic latitude, in degrees -90 to +90)
Longitude (geodetic longitude, in degrees -180 to +180)
SolarZenithAngle (in degrees)
ViewingZenithAngle (in degrees)
SceneNumber (cross-track position of orbit, 1 to 60)
LineNumber (along-track position of orbit, 1 to 1300)
QualityFlags (see product description documentation)
GroundPixelQualityFlags (see product description documentation)
Import into spreadsheet
After downloading the file(s) to your desktop, select the spreadsheet
application of your choice.
Your spreadsheet application should have an IMPORT function, allowing
you to import external ASCII files into a spreadsheet. Select the IMPORT function.
In the IMPORT function set the "space" character as the delimiter,
and tell it to ignore duplicate delimiters.
Select OK, and you should now have the data in your spreadsheet.
