# Format & Content

Aerosol Product (04_L2) File Format Basics

Aerosol (04_L2) 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 parameters listed below is stored as a Scientific Data Set (SDS) within the HDF file.

Note to Aerosol Data Users: We are permitting small negative Aerosol Optical Depth values in order to avoid an arbitrary negative bias at the low AOD end in long term statistics. This is because MODIS does not have sensitivity over land to retrieve aerosol to better than +/-0.05. This means in very clean conditions the algorithm cannot determine if the AOD = 0, 0.05 or -0.05. If we eliminate all the negative numbers and keep all the positive numbers, we introduce an artificial bias. Thus, we allow negative retrievals up to -0.05. To interpret these: If you are calculating long-term statistics, simply add the negatives into the mix and don't worry about them. If you were looking at individual retrievals then count negative retrievals as 'very clean'. You could force them to be AOD = 0, for example. It really depends on the application. However, these small negative AOD values are good retrievals and do contain information.

Aerosol Product (04_L2) Scientific Data Sets
(Primary SDS's only, not a complete list)

Dimensions

• Cell_Along_Swath = 204 (typical size)
• Cell_Across_Swath = 135 (typical size)
• Cell_Along_Swath_500 = 4080 (typical size)
• Cell_Across_Swath_500 = 2700 (typical size)
• Solution_2_Land = 3 (470, 555, 659 nm)
• Solution_3_Land = 3 (470, 659, 2130 nm)
• Solution_Index = 9 (1, 2, 3, 4, 5, 6, 7, 8, 9)
• Solution_Ocean = 2 (1, 2)
• Solution_Index = 9
• MODIS_Band_Land = 7 (470, 555, 659, 865, 1240, 1640, 2130 nm)
• MODIS_Band_Ocean = 7 (470, 555, 659, 865, 1240, 1640, 2130 nm)
• MODIS_Band_AND_NPP_Extra = 10
• Num_DeepBlue_Wavelengths = 3
• QA_Byte_Land = 6
• QA_Byte_Ocean = 5

Geolocation and Time Parameters

• Longitude
Description: Geodetic Longitude
Dimensions: (Cell_Along_Swath, Cell_Across_Swath)
Valid Range: -180 to +180 degrees east
• Latitude
Description: Geodetic Latitude
Dimensions: (Cell_Along_Swath, Cell_Across_Swath)
Valid Range: -90 to +90 degrees north
• Scan_Start_Time
Description: International Atomic Time at Start of Scan replicated across the Swath
Dimensions: (Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0.0 to 3.1558E+9 seconds since 1 January 1993 00:00:00

Solar and Viewing Geometry Parameters

• Solar_Zenith
Description: Solar Zenith Angle, Cell to Sun
Dimensions: (Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0 to +180 degrees
• Solar_Azimuth
Description: Solar Azimuth Angle, Cell to Sun
Dimensions: (Cell_Along_Swath, Cell_Across_Swath)
Valid Range: -180 to +180 degrees
• Sensor_Zenith
Description: Sensor Zenith Angle, Cell to Sensor
Dimensions: (Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0 to 180 degrees
• Sensor_Azimuth
Description: Sensor Azimuth Angle, Cell to Sensor
Dimensions: (Cell_Along_Swath, Cell_Across_Swath)
Valid Range: -180 to 180 degrees

Aerosol Combined Land and Ocean Parameters

• AOD_550_Dark_Target_Deep_Blue_Combined
Description: Combined Dark Target, Deep Blue AOT at 0.55 micron for land and ocean.
Dimension: (Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0.0 to 5.0
• Optical_Depth_Land_And_Ocean
Description: Aerosol Optical Thickness at 0.55 µm for both Ocean (average) and Land (corrected) with best quality data (QA Confidence Flag = 3)
Dimensions: (Cell_Along_Swath, Cell_Across_Swath)
Valid Range: -0.05 to 5.0
• Image_Optical_Depth_Land_And_Ocean
Description: Aerosol Optical Thickness at 0.55 µm for both Ocean (average) and Land (corrected) with all quality data (QA Confidence Flag = 0, 1, 2, 3)
Dimensions: (Cell_Along_Swath, Cell_Across_Swath)
Valid Range: -0.05 to 5.0
• Scattering_Angle
Description: Scattering Angle
Dimensions: (Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0 to 180 degrees

Aerosol Land Only Parameters

• Aerosol_Type_Land
Description: Aerosol Type
Dimensions: (Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 1 to 5  (1 = Continental, 2 = Moderate Absorption Fine, 3 = Strong Absorption Fine,4 = Weak Absorption Fine, 5 = Dust Coarse)
• Fitting_Error_Land
Description: Spectral Fitting Error for inversion over land
Dimensions: (Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0 to 1.0
• Surface_Reflectance_Land
Description: Fitting Error for Land
Dimensions: (Solution_2_Land, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0 to 5.0
• Corrected_Optical_Depth_Land
Description: Corrected Optical Thickness at 0.47, 0.55, and 0.66 µm
Dimensions: (Solution_3_Land, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: -0.05 to 5.0
• Corrected_Optical_Depth_Land_wav2pl
Description: Corrected Optical Thickness at 2.13 µm
Dimensions: (Cell_Along_Swath, Cell_Across_Swath)
Valid Range: -0.05 to 5.0
• Optical_Depth_Small_Land
Description: Corrected Optical Thickness for small mode at 0.47, 0.55, 0.66, and 2.13 µm
Dimensions: (Solution_4_Land, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: -0.05 to 5.0
• Optical_Depth_Ratio_Small_Land
Description: Small mode aerosol fraction
Dimensions: (Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0 to 1
• Number_Pixels_Used_Land
Description: Number of good pixels used for retrieval at 470 and 659 nm
Dimensions: (Solution_1_Land, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 1 to 400
• Mass_Concentration_Land
Description: Mass Concentration over Land
Dimensions: (Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0 to 1000 x 1.0e-6g/cm^2
• Angstrom_Exponent_Land
Description: Angstrom Exponent at 0.47 and 0.67 µm
Dimensions: (Cell_Along_Swath, Cell_Across_Swath)
Valid Range: -1.0 to 5.0
• Mean_Reflectance_Land
Description: Mean reflectance at 0.47, 0.55, 0.66, 0.87, 1.24, 1.64, and 2.13 µm
Dimensions: (MODIS_Band_Land, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0.0 to 1.0
• STD_Reflectance_Land
Description: Standard deviation of reflectance at 0.47, 0.66, and 2.1 µm after cloud screening
Dimensions: (Solution_3_Land, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0.0 to 1.0
• STD_Reflectance_Land
Description: Standard Deviation of reflectance at at 0.47, 0.55, 0.66, 0.87, 1.24, 1.64, and 2.13 µm
Dimensions: (MODIS_Band_Land, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0 to 2

Aerosol Ocean Only Parameters

• Solution_Index_Ocean_Small
Description: Solution number index (1 through 4) for small particles. Indices of ocean models 1 through 4 correspond to accumulation (small) mode models with effective radii 0.10, 0.15, 0.20, 0.25 µm, respectively.
Dimensions: (Solution_Ocean, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 1 to 4
• Solution_Index_Ocean_Large
Description: Solution number index (5 through 9) for large particles. Indices of ocean models 5 through 7 correspond to coarse (large) mode models of marine (sea salt) particles with effective radii 1.0, 1.5, 2.0 µm, respectively. Indices of ocean models 8 and 9 correspond to coarse (large) mode models of mineral dust particles with effective radii 1.5 and 2.5 µm, respectively.
Dimensions: (Solution_Ocean, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 5 to 9
• Effective_Optical_Depth_Best_Ocean
Description: Aerosol Optical Thickness for Best Solution at 7 bands 0.47, 0.55, 0.66, 0.86, 1.24, 1.63, and 2.13 µm
Dimensions: (MODIS_Band_Ocean, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: -0.05 to 5.0
• Effective_Optical_Depth_Average_Ocean
Description: Aerosol Optical Thickness for Average Solution at 7 bands 0.47, 0.55, 0.66, 0.86, 1.24, 1.63, and 2.13 µm
Dimensions: (MODIS_Band_Ocean, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: -0.05 to 5.0
• Optical_Depth_Small_Best_Ocean
Description: Aerosol Optical Thickness for Small Mode of Best Solution at 7 bands 0.47, 0.55, 0.66, 0.86, 1.24, 1.63, and 2.13 µm
Dimensions: (MODIS_Band_Ocean, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: -0.05 to 5.0
• Optical_Depth_Small_Average_Ocean
Description: Aerosol Optical Thickness for Small Mode of Average Solution at 7 bands 0.47, 0.55, 0.66, 0.86, 1.24, 1.63, and 2.13 µm
Dimensions: (MODIS_Band_Ocean, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: -0.05 to 5.0
• Optical_Depth_Large_Best_Ocean
Description: Aerosol Optical Thickness for Large Mode of Best Solution at 7 bands 0.47, 0.55, 0.66, 0.86, 1.24, 1.63, and 2.13 µm
Dimensions: (MODIS_Band_Ocean, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: -0.05 to 5.0
• Optical_Depth_Large_Average_Ocean
Description: Aerosol Optical Thickness at 7 bands 0.47, 0.55, 0.66, 0.86, 1.24, 1.63, and 2.13 µm for large mode of average solution
Dimensions: (MODIS_Band_Ocean, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: -0.05 to 5.0
• Mass_Concentration_Ocean
Description: Mass Concentration for Best and Average Solutions
Dimensions: (Solution_Ocean, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0 to 1000 x 1.0e-6g/cm^2
Description: Effective Radius of Both Solutions at 0.55 µm
Dimensions: (Solution_Ocean, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0 to 5 µm
• PSML003_Ocean
Description: Inferred column concentration (number per area) of particles larger than 0.03 micron for best (1) and average (2) solutions
Dimensions: (Solution_Ocean, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0.0 to 9.999E+10 CCN/cm^2
• Asymmetry_Factor_Best_Ocean
Description: Asymmetry Factor for Best Solution at 7 bands 0.47, 0.55, 0.66, 0.86, 1.24, 1.63, and 2.13 µm
Dimensions: (MODIS_Band_Ocean, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0 to 3
• Asymmetry_Factor_Average_Ocean
Description: Asymmetry Factor for Average Solution at 7 bands 0.47, 0.55, 0.66, 0.86, 1.24, 1.63, and 2.13 µm
Dimensions: (MODIS_Band_Ocean, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0 to 3
• Backscattering_Ratio_Best_Ocean
Description: Backscattering Ratio of Best Solution at 7 bands 0.47, 0.55, 0.66, 0.86, 1.24, 1.63, and 2.13 µm
Dimensions: (MODIS_Band_Ocean, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0 to 3
• Backscattering_Ratio_Average_Ocean
Description: Backscattering Ratio of Average Solution at 7 bands 0.47, 0.55, 0.66, 0.86, 1.24, 1.63, and 2.13 µm
Dimensions: (MODIS_Band_Ocean, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0 to 3
• Angstrom_Exponent_1_Ocean
Description: Angstrom Exponent for 0.55 and 0.86 µm
Dimensions: (Solution_Ocean, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: -1.0 to 5.0
• Angstrom_Exponent_2_Ocean
Description: Angstrom Exponent for 0.865 and 2.130 µm
Dimensions: (Solution_Ocean, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: -1.0 to 5.0
• Least_Squares_Error_Ocean
Description: Least Square Error Estimate
Dimensions: (Solution_Ocean, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0 to 1
• Optical_Depth_Ratio_Small_Ocean
Description: Ratio of Optical Depth of Small Mode vs Effective Optical Depth at .55 µm for best (1) and average (2) solutions
Dimensions: (Solution_Ocean, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0 to 1
• Optical_Depth_by_models_Ocean
Description: Retrieved AOD (at 0.55 micron) partioned by mode index (for Average solution)
Dimensions: (Solution_Index, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0 to 1
• Number_Pixels_Used_Ocean
Description: Number of good pixels used for retrieval at at 865 nm
Dimensions: (Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 1 to 400
• Mean_Reflectance_Ocean
Description: Mean Reflectances at 7 bands 0.47, 0.55, 0.66, 0.86, 1.24, 1.63, and 2.13 µm
Dimensions: (MODIS_Band_Ocean, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0 to 1
• STD_Reflectance_Ocean
Description: Standard Deviation of Reflectances at 7 bands 0.47, 0.55, 0.66, 0.86, 1.24, 1.63, and 2.13 µm
Dimensions: (MODIS_Band_Ocean, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0 to 2

Deep Blue Aerosol

• Deep_Blue_Aerosol_Optical_Depth_550_Land
Description: Aerosol Optical Thickness at 0.55 micron for land (corrected) with all quality data (QA Confidence Flag = 1, 2, 3)
Dimensions: (Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0.0 to 5.0
• Deep_Blue_Spectral_Aerosol_Optical_Depth_Land
Description: AOD at 0.412, 0.47, and 0.66 micron for land with all quality data (QA Confidence Flag=1, 2, 3)
Dimensions: (Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0.0 to 5.0
• Deep_Blue_Aerosol_Optical_Depth_Land
Description: Aerosol Optical Thickness at 0.412, 0.47, and 0.66 micron for land (corrected) with all quality data (QA Confidence Flag = 1, 2, 3)
Dimensions: (Num_DeepBlue_Wavelengths, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0.0 to 5.0
• Deep_Blue_Angstrom_Exponent_Land
Description: Deep Blue Angstrom Exponent for Land (0.412-0.47 micron) with all quality data (QA Confidence Flag = 1, 2, 3)
Dimensions: (Cell_Along_Swath, Cell_Across_Swath)
Valid Range: -0.5 to 5.0
• Deep_Blue_Single_Scattering_Albedo_Land
Description: Deep Blue Single Scattering Albedo for Land at 0.412, 0.47, and 0.66 micron with all quality data (QA Confidence Flag = 1, 2, 3)
Dimensions: (Num_DeepBlue_Wavelengths, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0.7 to 1.0
• Deep_Blue_Single_Surface_Reflectance_Land
Description: Deep Blue Surface Reflectance for Land at 0.412, 0.47, and 0.66 micron with all quality data (QA Confidence Flag = 1, 2, 3)
Dimensions: (Num_DeepBlue_Wavelengths, Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0.0 to 1.0
• Deep_Blue_Cloud_Fraction_Land
Description: Cloud Fraction from Deep Blue Aerosol Cloud Mask over land
Dimensions: (Cell_Along_Swath, Cell_Across_Swath)
Valid Range: 0.0 to 1.0

Aerosol Cloud Mask and QA Parameters