MODIS Atmosphere Daily Global 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 over 500 gridded statistical parameters within each 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. The Summary Table (at the bottom of the page) details this relationship.


Daily Global Product Parameter List

AEROSOL: LAND & OCEAN (Y.KAUFMAN)

1. Scattering_Angle	Derived from the MOD04_L2 SDS "Scattering_Angle".
2. Optical_Depth_Land_And_Ocean	Derived from the MOD04_L2 SDS "Optical_Depth_Land_And_Ocean".
3. Optical_Depth_Ratio_Small_Land_And_Ocean	Derived from the MOD04_L2 SDS "Optical_Depth_Ratio_Small_Land_And_Ocean".
4. Reflected_Flux_Land_And_Ocean	Derived from the MOD04_L2 SDS "Reflected_Flux_Land_And_Ocean".

AEROSOL: LAND ONLY (Y.KAUFMAN)

5. Corrected_Optical_Depth_Land	Derived from the MOD04_L2 SDS "Corrected_Optical_Depth_Land". 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 at 5x5 intervals for each.
6. Optical_Depth_Ratio_Small_Land	Derived from the MOD04_L2 SDS "Optical_Depth_Ratio_Small_Land".
7. Mass_Concentration_Land	Derived from the MOD04_L2 SDS "Mass_Concentration_Land".
8. Angstrom_Exponent_Land	Derived from the MOD04_L2 SDS "Angstrom_Exponent".
9. Transmitted_Flux_Land	Derived from the MOD04_L2 SDS "Transmitted_Flux_Land".
10. Reflected_Flux_Land	Derived from the MOD04_L2 SDS "Reflected_Flux_Land".
11. Mean_Reflectance_Land_All	Derived from the MOD04_L2 SDS "Mean_Reflectance_Land_All". The parameter has three spectral band solutions (.47, .66, and 2.13 microns) Two groups of statistics are available in MOD08, one group is associated with QA for .47 microns, the other is associated with QA for .66 microns. The parameter groups are called Mean_Reflectance_Land_All_QA47 and Mean_Reflectance_Land_All_QA66, respectively.
12. Path_Radiance_Land	Derived from the MOD04_L2 SDS "Path_Radiance_Land". The parameter has two spectral band solutions (.47 and .66 microns) Two groups of statistics are available in MOD08, one group is associated with QA for .47 microns, the other is associated with QA for .66 microns. The parameter groups are called Path_Radiance_Land_QA47 and Path_Radiance_Land_QA66, respectively.
13. Critical_Reflectance_Land	Derived from the MOD04_L2 SDS "Critical_Reflectance_Land". The parameter has two spectral band solutions (.47 and .66 microns) Two groups of statistics are available in MOD08, one group is associated with QA for .47 microns, the other is associated with QA for .66 microns. The parameter groups are called Critical_Reflectance_Land_QA47 and Critical_Reflectance_Land_QA66, respectively.

AEROSOL: OCEAN ONLY (D.TANRE)

14. Mass_Concentration_Ocean	Derived from the MOD04_L2 SDS "Mass_Concentration_Ocean ".
15. Effective_Optical_Depth_Average_Ocean	Derived from the MOD04_L2 SDS "Effective_Optical_Depth_Average_Ocean".
16. Optical_Depth_Ratio_Small_860_Ocean	Derived from the MOD04_L2 SDS "Optical_Depth_Ratio_Small_Ocean_0.86micron". There are two solutions (dimensions), one for best and one for average. (The now defunct parameter "Optical_Depth_Ratio_Small_Ocean" was derived at 0.55 and was replaced by this parameter in Spring 2002.)
17. Effective_Radius_Ocean	Derived from the MOD04_L2 SDS "Effective_Radius_Ocean".
18. Cloud_Condensation_Nuclei_Ocean	Derived from the MOD04_L2 SDS "Cloud_Condensation_Nuclei_Ocean".
19. Angstrom_Exponent_1_Ocean 20. Angstrom_Exponent_2_Ocean	Derived from the MOD04_L2 SDS "Angstrom_Exponent_1_Ocean" and "Angstrom_Exponent_2_Ocean", respectively.
21. Asymmetry_Factor_Average_Ocean	Derived from the MOD04_L2 SDS "Asymmetry_Factor_Average_Ocean".
22. Backscattering_Ratio_Average_Ocean	Derived from the MOD04_L2 SDS "Backscattering_Ratio_Average_Ocean".
23. Transmitted_Flux_Average_Ocean	Derived from the MOD04_L2 SDS "Transmitted_Flux_Average_Ocean".
24. Reflected_Flux_Average_Ocean	Derived from the MOD04_L2 SDS "Reflected_Flux_Average_Ocean".
25. Optical_Depth_by_models_ocean	Derived from the MOD04_L2 SDS "Optical_Depth_by_models_ocean". The parameter has solutions at 9 models.

WATER VAPOR (B.GAO)

26. Water_Vapor_Near_Infrared_Clear 27. Water_Vapor_Near_Infrared_Cloud

Derived from the MOD05_L2 SDS "Water_Vapor_Near_Infrared" and aggregated into a clear or cloud category from the MOD05_L2 SDS "Quality_Assurance_Near_Infrared".

CIRRUS DETECTION (B.GAO)

28. Cirrus_Reflectance 29. Contrail_Reflectance	Derived from the MOD06_L2 SDS "Cirrus_Reflectance" and aggregated into a cirrus or contrail category from the MOD06_L2 SDS "Cirrus_Reflectance_Flag".
30. Cirrus_Fraction_SWIR 31. Contrail_Fraction_SWIR	Derived from the MOD06_L2 SDS "Cirrus_Reflectance_Flag" and aggregated into a cirrus or contrail category from the MOD06_L2 SDS "Cirrus_Reflectance_Flag". This flag differentiates between BadData, Non-Cirrus, Cirrus, or Contrail at 1km resolution.

CLOUD TOP PROPERITES (P.MENZEL)

32. Cloud_Top_Temperature 33. Cloud_Top_Temperature_Day 34. Cloud_Top_Temperature_Night	Derived from the MOD06_L2 SDS "Cloud_Top_Temperature" and aggregated into Day or Night categories from the MOD06_L2 SDS "Cloud_Mask_5km".
35. Cloud_Top_Pressure 36. Cloud_Top_Pressure_Day 37. Cloud_Top_Pressure_Night	Derived from the MOD06_L2 SDS "Cloud_Top_Pressure" and aggregated into Day or Night categories from the MOD06_L2 SDS "Cloud_Mask_5km".
38. Cloud_Effective_Emissivity 39. Cloud_Effective_Emissivity_Day 40. Cloud_Effective_Emissivity_Night	Derived from the MOD06_L2 SDS "Cloud_Effective_Emissivity" and aggregated into Day or Night categories from the MOD06_L2 SDS "Cloud_Mask_5km".
41. Cloud_Phase_Infrared 42. Cloud_Phase_Infrared_Day 43. Cloud_Phase_Infrared_Night	Derived from the MOD06_L2 SDS "Cloud_Phase_Infrared" and aggregated into Day or Night categories from the MOD06_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.
44. Cloud_Fraction_Infrared 45. Cloud_Fraction_Infrared_Day 46. Cloud_Fraction_Infrared_Night	Derived from the MOD06_L2 SDS "Cloud_Fraction" and aggregated into Day or Night categories from the MOD06_L2 SDS "Cloud_Mask_5km".
47. Cirrus_Fraction_Infrared 48. High_Cloud_Fraction_Infrared	Derived from the MOD06_L2 SDS "Quality_Assurance_5km" The SDS's are an interpretation of the Retrieval Processing Path Flags: Cirrus/NoCirrus or HighCloud/NoHighCloud.

CLOUD OPTICAL PROPERTIES (M.KING)

49. Cloud_Optical_Thickness_Water 50. Cloud_Optical_Thickness_Ice 51. Cloud_Optical_Thickness_Undetermined 52. Cloud_Optical_Thickness_Mixed_Phase 53. Cloud_Optical_Thickness_Combined	Derived from the MOD06_L2 SDS "Cloud_Optical_Thickness" and aggregated into Cloud Phase categories (water, ice, undetermined, mixed, combined) from the MOD06_L2 SDS "Quality_Assurance_1km". Note that the liquid water cloud parameter contains three joint histograms for COT vs Cloud Effective Radius, COT vs Cloud Top Temperature, and COT vs Effective Emissivity at 11x10, 11x12, and 11x10 intervals, respectively; and the ice cloud parameter also contains the same three joint histograms but at 11x12, 11x10, and 11x10 intervals, respectively.
54. Cloud_Effective_Radius_Water 55. Cloud_Effective_Radius_Ice 56. Cloud_Effective_Radius_Undetermined 57. Cloud_Effective_Radius_Mixed_Phase 58. Cloud_Effective_Radius_Combined	Derived from the MOD06_L2 SDS "Effective_Particle_Radius" and aggregated into Cloud Phase categories (water, ice, undetermined, mixed, combined) from the MOD06_L2 SDS "Quality_Assurance_1km". Note that the liquid water cloud parameter contains two joint histograms for CER vs Cloud Top Temperature and CER vs Effective Emissivity at 10x12 and 10x10 intervals, respectively; and the ice cloud parameter also contains the same two joint histograms but at 12x10 and 12x10 intervals, respectively.
59. Water_Path_Liquid 60. Water_Path_Ice 61. Water_Path_Undetermined 62. Water_Path_Mixed_Phase 63. Water_Path_Combined	Derived from the MOD06_L2 SDS "Water_Path" and aggregated into Cloud Phase categories (water, ice, undetermined, mixed, combined) from the MOD06_L2 SDS "Quality_Assurance_1km".
64. Cloud_Fraction_Water 65. Cloud_Fraction_Ice 66. Cloud_Fraction_Undetermined 67. Cloud_Fraction_Mixed_Phase 68. Cloud_Fraction_Total	Derived (and aggregated into Cloud Phase categories: water, ice, undetermined, mixed, combined) from the MOD06_L2 SDS "Quality_Assurance_1km". The SDS's are an interpretation of the Retrieval Processing Path Flags (decision tree outcome) that is determined from the Cloud Mask, IR and SWIR tests.
69. Cloud_Fraction_SWIR_Water 70. Cloud_Fraction_SWIR_Ice 71. Cloud_Fraction_SWIR_Undetermined 72. Cloud_Fraction_SWIR_Total	Derived (and aggregated into Cloud Phase categories: water, ice, undetermined, combined) from the MOD06_L2 SDS "Quality_Assurance_1km". The SDS's are an interpretation of the Determination of Cloud Phase from the SWIR test only. Note that as of March 2001, the SWIR algorithm is still under development, so these SDS parameters contain all missing data.

ATMOSPHERE PROFILE (P.MENZEL)

73. Total_Ozone	Derived from the MOD07_L2 SDS "Total_Ozone".
74. Total_Totals	Derived from the MOD07_L2 SDS "Total_Totals". The Total Totals Index, like the K-Index, is computed using discreet pressure level information, but is more indicative of severe weather potential. It's formula is: TT=(T850+TD850)-2(T500) Generally, TT values below 40-45 are indicators of little or no thunderstorm activity, while values exceeding 55 in the East and Central or 65 in the West are indicators of considerable severe weather,including the potential for tornadic activity. Total Totals values tend to be somewhat higher over higher elevations, therefore higher TT values in the Western U.S. are required to indicate the same level of storm severity as lower TT values in the Central and Eastern U.S.
75. Lifted_Index	Derived from the MOD07_L2 SDS "Lifted_Index". The Lifted Index is calculated by lifting (frontal, orographic, upper air dynamics, etc.) a parcel of air dry adiabatically while conserving moisture until it reaches saturation. At that point the parcel is lifted moist adiabtically up to 500mb. The Lifted Index is the ambient air temperature minus the lifted parcel temperature at 500mb. If the parcel is warmer than the environment (negative L.I.), it has positive buoyancy, and will tend to continue to rise, favoring convection. L.I. values less than -5C indicate very unstable conditions. A positive L.I. value indicates negative parcel buoyancy, and the parcel will tend to sink. This is representative of stable conditions where convection is unlikely. Increasingly negative numbers correspond to increasing instability and likelihood of severe weather. At times, very high (stable) lifted index values in cold air are indicative of frozen or freezing precipitation versus rain during warm advection events. The extreme stability does not allow air to lift out, resulting in cold air "damming", which restricts the advance of warm air at the surface.
76. K_Index	Derived from the MOD07_L2 SDS "K_Index".
77. Atmospheric_Water_Vapor 78. Atmospheric_Water_Vapor_Low 79. Atmospheric_Water_Vapor_High	Derived from the MOD07_L2 SDS's "Water_Vapor, "Water_Vapor_Low", and "Water_Vapor_High", respectively. This is also sometimes refered to as "Precipitable Water". The keyword "Low" refers to an integration from the surface to 920 hPa and "High" refers to an integration from 700 to 300 hPa. Water_Vapor is the total column precipitable water vapor, which is integrated from a complete set of retrieved profiles at 101 discrete levels. (Note that only 20 levels are stored in the atmospheric profile in MOD07_L2, so if users integrate the L2 profiles themselves they likely will not get the same total column value as reported here).

MOD08_D3 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

• Mean
• Minimum
• Maximum
• Standard_Deviation

QA Weighted Statistics

• QA_Mean
• QA_Standard_Deviation

Histograms of the quantity within each grid box

• Histogram_Counts

Histograms of the confidence placed in each measurement

• Confidence_Histograms

Fraction of pixels that satisfy some condition (e.g. cloudy, clear)

• (Fraction)

Total number of observations (pixels) within each grid box

• Pixel_Counts

Parameters of Log-Normal Distributions

• Log_Mean
• Log_Standard_Deviation

Parameters of QA Weighted Log-Normal Distributions

• QA_Log_Mean
• QA_Log_Standard_Deviation

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

• Regression_Slope
• Regression_Intercept
• Regression_R_Squared
• Regression_Mean_Square_Error
• Joint_Histogram_vs_Effect_Radius
• Joint_Histogram_vs_Temperature
• Joint_Histogram_vs_Emissivity

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).