Shortname: OMSO2e Longname: OMI/Aura Sulfur Dioxide (SO2) Total Column Daily L3 Best Pixel Global 0.25deg Lat/Lon Grid PFS Version: 2.0.1 Date: 2020 November 25 Author(s): C. Li, N. Krotkov, P. Leonard, S. Carn, A.J. Krueger PGE Version: 2.0.0 Lead Algorithm Scientists: C. Li, N. Krotkov Other Algorithm Scientist: P. Leonard Lead PGE Developer: P. Leonard Description: > This document specifies the format of the Ozone Monitoring Instrument (OMI) OMSO2e product, which is the daily Level 3e gridded data product that corresponds to the OMSO2 product. The latter is the U.S. OMI Science Team's Level 2 (L2) total column sulfur dioxide orbital swath data product based on Principal Component Analysis (References 1 and 2). The OMSO2e algorithm uses a "best pixel" approach to populate each L3e grid-cell. The data in each OMSO2e file are drawn from the ensemble of L2 ground pixels that have the same local calendar date on the ground, which is significantly different from the set of ground pixels that correspond to 24 consecutive UTC hours for a given UTC date. The adopted L3e grid is a 0.25-degree by 0.25-degree grid in longitude and latitude. The dimensions of this grid are 1440 by 720. The grid cell with coordinates (1, 1) is centered at (longitude = -179.875 , latitude = -89.875), and the grid cell with coordinates (1440, 720) is centered at (longitude = 179.875 , latitude = 89.875). The center of the grid is located at (longitude = 0.000 , latitude = 0.000), and corresponds to the corners of four L3e grid cells. The adopted L3e 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. (Reference 3). Each grid cell in the L3e product contains the data for the "best pixel", selected from all "good" L2 observations that overlap with the L3e grid cell, and has the shortest "path length", which is defined as follows: path length = 1/cos(solar zenith angle) + 1/cos(viewing zenith angle) . The overlap algorithm is based on a simple model for the OMI ground pixels corners and is consistent with the heritage TOMS L3 products. An L2 observation can be mapped onto more than one L3e grid cell, if the L2 observation overlaps with and has the shortest path length for more than one L3e grid cell. If no "good" overlaps are found, then all fields are set to fill values for the L3e grid cell. A "good" OMSO2 L2 scene is defined as one that passes both Step 1 filtering: 1) has an SO2 column amount that is not equal to the missing value, 2) has a solar eclipse possibility flag that is not set, 3) has an OMTO3 row-anomaly flag that is not set, 4) has a cross-track scene number between 3 and 58 (1-based, inclusive), 5) has a cloud radiance fraction that is less than or equal to 0.2, 6) has a solar zenith angle that is less than or equal to 70.0 degrees, 7) has a calculated air mass factor that is greater than or equal to 0.3, and Step 2 filtering: 8) does not lie within the SAA region. The L3e product currently excludes L2 data collected in spatial and spectral zoom modes. Each OMSO2e product file is stored as one HDF-EOS 5 grid file, and has a size range of 4 to 7 MB. The format of the L3e product file is consistent with the document entitled "A File Format for Satellite Atmospheric Chemistry Data Based On Aura File Format Guidelines" by C. Craig et al. (Reference 4). Global Metadata: - Metadata Name: EndUTC Mandatory: T Data Type: HE5T_NATIVE_CHAR Number of Values: 1 Data Source: PGE Description: > UTC at the end of the L3e granule in "YYYY-MM-DDTHH:MM:SS.SSSSSSZ" format. - Metadata Name: GranuleDay Mandatory: T Data Type: HE5T_NATIVE_INT Number of Values: 1 Minimum Value: 1 Maximum Value: 31 Data Source: PGE Description: The day of the month at the start of the L3e granule. - Metadata Name: GranuleDayOfYear Mandatory: T Data Type: HE5T_NATIVE_INT Number of Values: 1 Minimum Value: 1 Maximum Value: 366 Data Source: PGE Description: The day of the year at the start of the L3e granule. - Metadata Name: GranuleMonth Mandatory: T Data Type: HE5T_NATIVE_INT Number of Values: 1 Minimum Value: 1 Maximum Value: 12 Data Source: PGE Description: The month of the year at the start of the L3e granule. - Metadata Name: GranuleYear Mandatory: T Data Type: HE5T_NATIVE_INT Number of Values: 1 Minimum Value: 2000 Maximum Value: 2099 Data Source: PGE Description: The (four-digit) year at the start of the L3e granule. - Metadata Name: HDFEOSVersion Mandatory: T Data Type: HE5T_NATIVE_CHAR Number of Values: 1 Data Source: HE Description: > The version of HDF-EOS 5 used in production. Example is "HDFEOS_5.1.8". - Metadata Name: InputPointer Mandatory: T Data Type: HE5T_NATIVE_CHAR Number of Values: 1 Data Source: PGE Description: > A space-separated list of the L2G input granules. - Metadata Name: InstrumentName Mandatory: T Data Type: HE5T_NATIVE_CHAR Number of Values: 1 Valids: OMI Data Source: PGE Description: Actual is "OMI" (see Section 6.1 of Reference 4). - Metadata Name: OrbitNumber Mandatory: T Data Type: HE5T_NATIVE_INT Number of Values: 1,60 Minimum Value: 1 Maximum Value: 999999 Data Source: L2G Description: The OMI orbit number for each L2 input granule. - Metadata Name: OrbitPeriod Mandatory: T Data Type: HE5T_NATIVE_DOUBLE Number of Values: 1,60 Minimum Value: 5000.0 Maximum Value: 7000.0 Data Source: L2G Description: > The Aura orbital period for each L2 input granule (in seconds). - Metadata Name: Period Mandatory: T Data Type: HE5T_NATIVE_CHAR Number of Values: 1 Valids: Daily,Weekly,Monthly Data Source: PGE Description: The duration of the L3e granule. Actual is "Daily". - Metadata Name: PGEVERSION Mandatory: T Data Type: HE5T_NATIVE_CHAR Number of Values: 1 Data Source: PCF Description: Example is "2.0.0" (see Appendix K of Reference 5). - Metadata Name: ProcessLevel Mandatory: T Data Type: HE5T_NATIVE_CHAR Number of Values: 1 Valids: 3e Data Source: PGE Description: Actual is "3e". - Metadata Name: StartUTC Mandatory: T Data Type: HE5T_NATIVE_CHAR Number of Values: 1 Data Source: PGE Description: > UTC at the start of the L3e granule in "YYYY-MM-DDTHH:MM:SS.SSSSSSZ" format. - Metadata Name: TAI93At0zOfGranule Mandatory: T Data Type: HE5T_NATIVE_DOUBLE Number of Values: 1 Minimum Value: 0.0 Maximum Value: 1.0e+30 Data Source: PGE Description: > The TAI93 time at 0z of the L3e granule (see Section 6.1 of Reference 4). Grid Metadata: - Metadata Name: GCTPProjectionCode Mandatory: T Data Type: HE5T_NATIVE_INT Number of Values: 1 Minimum Value: 0 Maximum Value: 99 Data Source: PGE Description: > The GCTP projection code of the L3e grid. Actual is 0, which corresponds to the geographic projection. - Metadata Name: GridName Mandatory: T Data Type: HE5T_NATIVE_CHAR Number of Values: 1 Valids: OMI Total Column Amount SO2 Data Source: PGE Description: Actual is "OMI Total Column Amount SO2". - Metadata Name: GridOrigin Mandatory: T Data Type: HE5T_NATIVE_CHAR Number of Values: 1 Valids: Center Data Source: PGE Description: > The origin of the L3e grid. Actual is "Center" (see Section 6.2 of Reference 4). - Metadata Name: GridSpacing Mandatory: T Data Type: HE5T_NATIVE_CHAR Number of Values: 1 Data Source: PGE Description: > Spacing of L3e grid (in degrees). Actual is "(0.25,0.25)". - Metadata Name: GridSpacingUnit Mandatory: T Data Type: HE5T_NATIVE_CHAR Number of Values: 1 Valids: deg Data Source: PGE Description: > Unit for GridSpacing. Actual is "deg". - Metadata Name: GridSpan Mandatory: T Data Type: HE5T_NATIVE_CHAR Number of Values: 1 Data Source: PGE Description: > Span of L3e grid (in degrees). Actual is "(-180,180,-90,90)". - Metadata Name: GridSpanUnit Mandatory: T Data Type: HE5T_NATIVE_CHAR Number of Values: 1 Valids: deg Data Source: PGE Description: > Unit for GridSpan. Actual is "deg". - Metadata Name: NumberOfLatitudesInGrid Mandatory: T Data Type: HE5T_NATIVE_INT Number of Values: 1 Minimum Value: 1 Maximum Value: 720 Data Source: PGE Description: The number of latitude bins in the L3e grid. - Metadata Name: NumberOfLongitudesInGrid Mandatory: T Data Type: HE5T_NATIVE_INT Number of Values: 1 Minimum Value: 1 Maximum Value: 1440 Data Source: PGE Description: The number of longitude bins in the L3e grid. - Metadata Name: Projection Mandatory: T Data Type: HE5T_NATIVE_CHAR Number of Values: 1 Valids: Geographic Data Source: PGE Description: > The map projection of the L3e grid. Actual is "Geographic" (see Section 6.2 of Reference 4). Grid Dimensions: - Dimension Name: XDim Data Type: HE5T_NATIVE_INT Dimension Type: FIXED Number of Values: 1 Minimum Value: 1 Maximum Value: 1440 Data Source: PGE Description: > The longitudes dimension of the L3e grid. There are currently 1440 0.25-degree-wide bins between longitudes -180.0 and 180.0 degrees. - Dimension Name: YDim Data Type: HE5T_NATIVE_INT Dimension Type: FIXED Number of Values: 1 Minimum Value: 1 Maximum Value: 720 Data Source: PGE Description: > The latitudes dimension of the L3e grid. There are currently 720 0.25-degree-wide bins between latitudes -90.0 and 90.0 degrees. Geolocation Fields: - Field Name: Latitude Data Type: HE5T_NATIVE_FLOAT Dimensions: YDim,XDim Minimum Value: -90.0 Maximum Value: 90.0 Missing Value: -1.2676506e+30 Units: deg Data Source: L2G Title: Geodetic Latitude Description: > The geodetic latitude (in degrees) at the center of each L3e grid cell. - Field Name: LineNumber Data Type: HE5T_NATIVE_INT Dimensions: YDim,XDim Minimum Value: 1 Maximum Value: 1700 Missing Value: -2147483648 Units: NoUnits Data Source: L2G Title: Line Number Description: > The line number for the best L2 scene in each L3e grid cell. - Field Name: Longitude Data Type: HE5T_NATIVE_FLOAT Dimensions: YDim,XDim Minimum Value: -180.0 Maximum Value: 180.0 Missing Value: -1.2676506e+30 Units: deg Data Source: L2G Title: Geodetic Longitude Description: > The geodetic longitude (in degrees) at the center of each L3e grid cell. - Field Name: OrbitNumber Data Type: HE5T_NATIVE_INT Dimensions: YDim,XDim Minimum Value: 1 Maximum Value: 999999 Missing Value: -2147483648 Units: NoUnits Data Source: L2G Title: Orbit Number of L2 Scene Description: > The orbit number for the best L2 scene in each L3e grid cell. - Field Name: RelativeAzimuthAngle Data Type: HE5T_NATIVE_FLOAT Dimensions: YDim,XDim Minimum Value: -180.0 Maximum Value: 180.0 Missing Value: -1.2676506e+30 Units: deg(EastofNorth) Data Source: L2G Title: Relative Azimuth Angle (sun + 180 - view) Description: > The relative (sun + 180 - view) azimuth angle (in degrees) on the ground at the center of the best L2 scene in each L3e grid cell (negative values correspond to the satellite being on the left hand side for an observer on the ground facing in the solar direction). - Field Name: SceneNumber Data Type: HE5T_NATIVE_INT Dimensions: YDim,XDim Minimum Value: 1 Maximum Value: 60 Missing Value: -2147483648 Units: NoUnits Data Source: L2G Title: Scene Number of Candidate Scene Description: > The cross-track ground-pixel number for the best L2 scene in each L3e grid cell. - Field Name: SolarZenithAngle Data Type: HE5T_NATIVE_FLOAT Dimensions: YDim,XDim Minimum Value: 0.0 Maximum Value: 180.0 Missing Value: -1.2676506e+30 Units: deg Data Source: L2 Title: Solar Zenith Angle Description: > The solar zenith angle (in degrees) on the ground at the center of the best L2 scene in each L3e grid cell. - Field Name: TerrainHeight Data Type: HE5T_NATIVE_INT16 Dimensions: YDim,XDim Minimum Value: -200 Maximum Value: 10000 Missing Value: -32767 Units: m Data Source: L2 Title: Terrain Height Description: > The terrain height (in meters) for the best L2 scene in each L3e grid cell. - Field Name: Time Data Type: HE5T_NATIVE_DOUBLE Dimensions: YDim,XDim Minimum Value: -5.0e+09 Maximum Value: 1.0e+10 Missing Value: -1.2676506002282294e+30 Units: s Data Source: L2 Title: Time of Scan (TAI93) Description: > The TAI93 time (in seconds) for the best L2 scene in each L3e grid cell. - Field Name: ViewingZenithAngle Data Type: HE5T_NATIVE_FLOAT Dimensions: YDim,XDim Minimum Value: 0.0 Maximum Value: 70.0 Missing Value: -1.2676506e+30 Units: deg Data Source: L2 Title: Viewing Zenith Angle Description: > The viewing zenith angle (in degrees) on the ground at the center of the best L2 scene in each L3e grid cell. Data Fields: - Field Name: CloudRadianceFraction Data Type: HE5T_NATIVE_FLOAT Dimensions: YDim,XDim Minimum Value: 0.0 Maximum Value: 1.0 Missing Value: -1.2676506e+30 Units: NoUnits Data Source: L2 Title: Cloud Radiance Fraction at 313 nm Description: > The cloud radiance fraction at 313 nm for the best L2 scene in each L3e grid cell. - Field Name: ColumnAmountO3 Data Type: HE5T_NATIVE_FLOAT Dimensions: YDim,XDim Minimum Value: 50.0 Maximum Value: 700.0 Missing Value: -1.2676506e+30 Units: DU Data Source: L2 Title: Best Total Ozone Solution (from OMTO3) Description: > The best total ozone solution (in DU) from OMTO3 for the best L2 scene in each L3e grid cell. - Field Name: ColumnAmountSO2 Data Type: HE5T_NATIVE_FLOAT Dimensions: YDim,XDim Minimum Value: -10.0 Maximum Value: 2000.0 Missing Value: -1.2676506e+30 Units: DU Data Source: L2 Title: Vertical Column Amount SO2 (GEOS-5 Profile) Description: > The total vertical column amount SO2 (in DU) for the best L2 scene in each L3e grid cell retrieved using the NASA Principal Component Analysis (PCA) SO2 retrieval algorithm and monthly mean a priori SO2 profile from GEOS-5 model simulations. - Field Name: QualityFlags_SO2 Data Type: HE5T_NATIVE_INT Dimensions: YDim,XDim Minimum Value: 0 Maximum Value: 2 Missing Value: -2147483648 Units: NoUnits Data Source: PGE Title: Quality Flags for Column Amount SO2 Description: > The quality flags for column amount SO2 in each L3e grid cell: 0 - no quality issues 1 - eliminated in Step 1 2 - eliminated in Step 2 Core Metadata: None Archived Metadata: None. References: > 1. "README Document for OMSO2: Aura/OMI Sulfur DioxideLevel 2 Product" Updated 2020 February 29 https://aura.gesdisc.eosdis.nasa.gov/data/Aura_OMI_Level2/OMSO2.003/doc/OMSO2Readme_V2.pdf 2. Li, C., Krotkov, N. A., Leonard, P. J. T., et al., (2020) Version 2 Ozone Monitoring Instrument SO2 product (OMSO2 V2): new anthropogenic SO2 vertical column density dataset Atmos. Meas. Tech., 13, 6175–6191 https://doi.org/10.5194/amt-13-6175-2020 3. "Definition of OMI Grids for Level 3 and Level 4 Data Products" OMI-Grids_L3L4, SD-OMIE-KNMI-443, 2005 January 25 4. "A File Format for Satellite Atmospheric Chemistry Data Based On Aura File Format Guidelines" ESDS-RFC-009, 2008 May https://earthdata.nasa.gov/esdis/eso/standards-and-references/aura-file-format-satellite-atmospheric-chemistry-data 5. "OMI Science Software Delivery Guide for Version 0.9" OMI-SSDG-0.9.10, Version 0.9.10, 2005 June 22