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Format & Content

Collection 6 File Format Basics

MOD08_M3 product files are stored in Hierarchical Data Format (HDF). HDF is a multi-object file format for sharing scientific data in multi-platform distributed environments. HDF files should only be accessed through HDF library subroutine and function calls, which can be downloaded from the HDF web site.

Each of the gridded statistical fields within the HDF file is stored as a Scientific Data Set (SDS). Only a subset of statistics outlined in the Statistic List (see below) are computed for each parameter.


Monthly (08_M3) Parameter List (primary parameters only)

Parameters derived from the L2 Aerosol (04_L2) Product
AEROSOL: LAND & OCEAN (L.A.Remer)
Scattering_Angle Derived from the 04_L2 SDS "Scattering_Angle".
Aerosol_Optical_Depth_Land_Ocean Derived from the 04_L2 SDS "Optical_Depth_Land_And_Ocean". Note that the land part of this SDS is taken from the 04_L2 SDS Corrected_Optical_Depth_Land at 0.55 microns and the ocean part of this SDS is taken from the 04_L2 SDS Effective_Optical_Depth_Best_Ocean (a parameter that is not propagated into L3 by itself).
AEROSOL: LAND ONLY (L.A.Remer)
Aerosol_Optical_Depth_Land
Derived from the 04_L2 SDS "Corrected_Optical_Depth_Land". Three solutions (computed at 0.47, 0.55, and 0.66 microns) are retained. Note that this parameter group contains three joint histograms for optical depth computed using 0.47 vs. 0.55 microns, 0.47 vs. 0.66 microns, and 0.55 vs. 0.66 microns.
AEROSOL: OCEAN ONLY (L.A.Remer & D.Tanre)
Aerosol_Optical_Depth_Average_Ocean Derived from the 04_L2 SDS "Effective_Optical_Depth_Average_Ocean".
Aerosol_Optical_Depth_Small_Ocean Derived from the 04_L2 SDS "Optical_Depth_Ratio_Small_Ocean_0.55micron". Only the L2 "best" solution is retained in L3. The "average" solution is computed in L2 but not propagated to L3.
Aerosol_PSML003_Ocean Derived from the 04_L2 SDS "Cloud_Condensation_Nuclei_Ocean".
Aerosol_Optical_Depth_by_models_ocean Derived from the 04_L2 SDS "Optical_Depth_by_models_ocean". The parameter has solutions at 9 models.
AEROSOL: DEEP BLUE ()
Deep_Blue_Aerosol_Optical_Depth_Land Derived from the 04_L2 SDS "Deep_Blue_Aerosol_Optical_Depth_Land ".
AOD_550_Dark_Target_Deep_Blue_Combined Derived from the 04_L2 SDS "". Combines Dark Target and Deep Blue Aerosol.
Parameters derived from the L2 Water Vapor (05_L2) Product
WATER VAPOR (B.Gao)
Water_Vapor_Near_Infrared_Clear
Water_Vapor_Near_Infrared_Cloud
Derived from the 05_L2 SDS "Water_Vapor_Near_Infrared" and aggregated into a clear or cloud category from the 05_L2 SDS "Quality_Assurance_Near_Infrared".
Parameters derived from the L2 Cloud (06_L2) Product
CIRRUS DETECTION (B.Gao)
Cirrus_Reflectance
Contrail_Reflectance
Derived from the 06_L2 SDS "Cirrus_Reflectance" and aggregated into a cirrus or contrail category from the 06_L2 SDS "Cirrus_Reflectance_Flag".
Cirrus_Fraction_SWIR
Contrail_Fraction_SWIR
Derived from the 06_L2 SDS "Cirrus_Reflectance_Flag" and aggregated into a cirrus or contrail category from the 06_L2 SDS "Cirrus_Reflectance_Flag". This flag differentiates between BadData, Non-Cirrus, Cirrus, or Contrail at 1km resolution.
CLOUD TOP PROPERITES (P.Menzel)
Cloud_Top_Temperature
Cloud_Top_Temperature_Day
Cloud_Top_Temperature_Night
Derived from the 06_L2 SDS "Cloud_Top_Temperature" and aggregated into Day or Night categories from the 06_L2 SDS "Cloud_Mask_5km".
Cloud_Top_Pressure
Cloud_Top_Pressure_Day
Cloud_Top_Pressure_Night
Derived from the 06_L2 SDS "Cloud_Top_Pressure" and aggregated into Day or Night categories from the 06_L2 SDS "Cloud_Mask_5km".
Cloud_Top_Height
Cloud_Top_Height_Day
Cloud_Top_Height_Night
Derived from the 06_L2 SDS "Cloud_Top_Height" and aggregated into Day or Night categories from the 06_L2 SDS "Cloud_Mask_5km".
Cloud_Effective_Emissivity
Cloud_Effective_Emissivity_Day
Cloud_Effective_Emissivity_Night
Derived from the 06_L2 SDS "Cloud_Effective_Emissivity" and aggregated into Day or Night categories from the 06_L2 SDS "Cloud_Mask_5km".
Cloud_Phase_Infrared
Cloud_Phase_Infrared_Day
Cloud_Phase_Infrared_Night
Derived from the 06_L2 SDS "Cloud_Phase_Infrared" and aggregated into Day or Night categories from the 06_L2 SDS "Cloud_Mask_5km". The various dimensions of the Histogram Counts statistic corresponds to clear = 0, water = 1 or 5, ice = 2 or 4, mixed = 3, and uncertain = 6. Note that categories 4 and 5 were eliminated in a year 2000 L2 code delivery.
Cloud_Fraction
Cloud_Fraction_Day
Cloud_Fraction_Night
This is the primary L3 Cloud Fraction parameter from Cloud Mask. This is derived from the 06_L2 SDS "Cloud_Fraction" and aggregated into Day or Night categories using the day/night flag from the 06_L2 SDS "Cloud_Mask_5km".
Cirrus_Fraction_Infrared
High_Cloud_Fraction_Infrared
Derived from the Cirrus and High Cloud Flags in the 06_L2 SDS "Quality_Assurance_5km". The numbers computed are actually ratios of cirrus clouds (or high clouds) to all clouds. They are not true cloud fractions, where clear sky pixels are accounted for in the denominator. (Note that in the upcoming Collection 006, these numbers will change to true cloud fractions where clear sky pixels will be accounted for in the denominator.)
CLOUD OPTICAL PROPERTIES (M.King & S.Platnick)
Cloud_Optical_Thickness_Liquid
Cloud_Optical_Thickness_Ice
Cloud_Optical_Thickness_Undetermined
Cloud_Optical_Thickness_Combined
Derived from the 06_L2 SDS "Cloud_Optical_Thickness" and aggregated into Cloud Phase categories (liquid water, ice, undetermined, & combined) using the Primary Cloud Retrieval Phase Flag from the 06_L2 SDS "Quality_Assurance_1km". Note that the liquid water and ice cloud parameters contain joint histograms vs. Cloud Effective Radius, vs. Cloud Top Temperature, vs. Cloud Top Pressure, & vs. Cloud Effective Emissivity (for ice clouds only)
Cloud_Effective_Radius_Liquid
Cloud_Effective_Radius_Ice
Cloud_Effective_Radius_Undetermined
Cloud_Effective_Radius_Combined
Derived from the 06_L2 SDS "Cloud_Effective_Radius" and aggregated into Cloud Phase categories (liquid water, ice, undetermined, & combined) using the Primary Cloud Retrieval Phase Flag from the 06_L2 SDS "Quality_Assurance_1km". Note that the liquid water and ice cloud parameters contain joint histograms vs. Cloud Top Temperature & vs. Cloud Top Pressure
Cloud_Water_Path_Liquid
Cloud_Water_Path_Ice
Cloud_Water_Path_Undetermined
Cloud_Water_Path_Combined
Derived from the 06_L2 SDS "Cloud_Water_Path" and aggregated into Cloud Phase categories (liquid water, ice, undetermined, & combined) using the Primary Cloud Retrieval Phase Flag from the 06_L2 SDS "Quality_Assurance_1km".
Cloud_Fraction_Liquid
Cloud_Fraction_Ice
Cloud_Fraction_Undetermined
Cloud_Fraction_Combined
This is the Cloud Fraction (really the successful cloud retrieval fraction) from the Cloud Optical Properties retrieval aggregated into Cloud Phase categories: liquid water, ice, undetermined, combined from the 06_L2 SDS "Quality_Assurance_1km". The SDS's are an interpretation of the Primary Cloud Retrieval Phase Flag (cloud optical properties decision tree outcome) determined from the Cloud Mask, IR and SWIR tests, which is read from the 06_L2 SDS "Quality_Assurance_1km".
Parameters derived from the L2 Profiles (07_L2) Product
ATMOSPHERE PROFILE (P.Menzel)
Total_Ozone Derived from the 07_L2 SDS "Total_Ozone".
Total_Totals Derived from the 07_L2 SDS "Total_Totals".
Lifted_Index Derived from the 07_L2 SDS "Lifted_Index".
K_Index Derived from the 07_L2 SDS "K_Index".
Atmospheric_Water_Vapor
Atmospheric_Water_Vapor_Low
Atmospheric_Water_Vapor_High
Derived from the 07_L2 SDS's "Water_Vapor, "Water_Vapor_Low", and "Water_Vapor_High", respectively. The keywords "Low" and "High" refer to the lower and higher portions of the atmospheric column. Note that the parameter "Water Vapor" is also refered to as "Precipitable Water".



MOD08_M3 Statistic List

A number of statistical summaries are computed, depending on the science parameter being considered. Statistics for a given Level-2 measurement might include:

    Simple Statistics of the Mean

  1. Mean_Mean
  2. Mean_Min
  3. Mean_Max
  4. Mean_Std

    Mean of the Standard Deviation

  5. Std_Deviation_Mean

    QA Weighted Statistics

  6. QA_Mean_Mean
  7. QA_Mean_Std
  8. QA_Mean_Min
  9. QA_Mean_Max
  10. QA_Std_Deviation_Mean

    Histograms of the quantity within each grid box

  11. Histogram_Counts

    Histograms of the confidence placed in each measurement

  12. Confidence_Histograms

    Mean and Standard Deviation of the Fraction of pixels that satisfy some condition (e.g. cloudy, clear)

  13. FMean
  14. FStd

    Total number of observations (pixels) within each grid box

  15. Pixel_Counts

    Parameters of Log-Normal Distributions

  16. Log_Mean_Mean
  17. Log_Mean_Std
  18. Log_Mean_Min
  19. Log_Mean_Max
  20. Log_Std_Deviation_Mean

    Parameters of QA Weighted Log-Normal Distributions

  21. QA_Log_Mean_Mean
  22. QA_Log_Mean_Std
  23. QA_Log_Mean_Min
  24. QA_Log_Mean_Max
  25. QA_Log_Std_Deviation_Mean

    Regressions and/or Histograms derived from comparing one science parameter to another, statistics may be computed for a subset that satisfies some condition

  26. Regression_Slope
  27. Regression_Intercept
  28. Regression_R_Squared
  29. Regression_Mean_Square_Error
  30. Joint_Histogram_vs_Effect_Radius
  31. Joint_Histogram_vs_Temperature
  32. Joint_Histogram_vs_Emissivity
  33. Joint_Histogram_47vs55
  34. Joint_Histogram_47vs66
  35. Joint_Histogram_55vs66


Statistic Computation Details

Below are more details on the computation of each statistic:

For the daily product, assume that x1, x2, , xn represent the retrieved pixel values of a Level-2 parameter over a 1 x 1 degree grid box, Qi is the quality flag for each retrieved pixel value, and wi is the weighting factor (1 for the daily case), then the simple statistics are defined as:

In these equations, (1) will be referred to as the 'regular' mean, (2) as the QA weighted mean, (3) as the regular standard deviation, (4) as the QA weighted standard deviation, (5) as the minimum, and (6) as the maximum.

The simple statistics also include daily log regular mean, log standard deviation, log QA mean, and log QA standard deviation. These log quantities are calculated as shown in equations (1 - 4), except that x1, x2, , xn are replaced by their logarithms.

Regression statistics, based on the pixels within each 1 by 1 degree grid cell, includes the slope, intercept, mean-squared-error (MSE), and the coefficient of determination (R2).

The histograms and joint histograms report the counts of the pixels falling into predetermined numerical intervals.

The pixel counts are used to represent the number of pixels for the parameters which do not have QA flags, while the confidence-histograms-counts are used to represent the number of counts for each parameter that falls within each QA bin (e.g., questionable, good, very good, and total).