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MOD05_L2 (Water Vapor Product)
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Format and Content
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QA Information
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Format and Content

File Format Basics

MOD05_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. Each of the gridded parameters listed below is stored as a Scientific Data Set (SDS) within the HDF file.

The values stored in the SDS (other then the geolocation arrays) are short integer values in order to save storage space. To calculate the real data value, the scale_factor and the add_offset are needed to apply to the stored value. These are local attributes attached to each SDS. The following equation should be used to get to the real value:

value = scale_factor * ( stored_value - add_offset )

Regarding to the quality assurance of the Water_Vapor_Infrared (07_L2) products copied into the 05_L2 file, there are either have sufficient data (e.g. at least 5 out of 25 pixels defined as confident clear) and the "Best Quality Data" retrievals are produced or the retrievals are flagged missing. The MOD07 retrievals are thus considered to be best quality.

The Water Vapor and Quality Assurance SDS's are stored at both 1 and 5 kilometer pixel resolution. All other SDS's (those relating to time, geolocation, and viewing geometry) are stored only at 5 kilometer pixel resolution. The Cloud Mask SDS, copied from the MOD35_L2 Product is stored at 1 kilometer resolution.




MOD05_L2 Dimension List

  1. Cell_Along_Swath_5km = 406 (typical)
  2. Cell_Across_Swath_5km = 270 (typical)
  3. Cell_Along_Swath_1km = 2030 (typical)
  4. Cell_Across_Swath_1km = 1354 (typical)
  5. QA_Byte_NIR = 1
  6. QA_Byte_IR = 5
  7. Number_of_Instrument_Scans = 203 (typical)
  8. Maximum_Number_of_1km_Frames = 1354 (typical)



MOD05_L2 Scientific Data Set (SDS) List

    Geolocation and Time Parameters

  1. Latitude
      Description: Geodetic Latitude
      Dimensions: (Cell_Along_Swath_5km, Cell_Across_Swath_5km)
      Valid Range: -90 to +90 degrees north
  2. Longitude
      Description: Geodetic Longitude
      Dimensions: (Cell_Along_Swath_5km, Cell_Across_Swath_5km)
      Valid Range: -180 to +180 degrees east
  3. Scan_Start_Time
      Description: International Atomic Time at Start of Scan replicated across the Swath
      Dimensions: (Cell_Along_Swath_5km, Cell_Across_Swath_5km)
      Valid Range: 0.0 to 3.1558E+9 seconds since 1 January 1993 00:00:00

    Solar and Viewing Geometry Parameters

  4. Solar_Zenith
      Description: Solar Zenith Angle, Cell to Sun
      Dimensions: (Cell_Along_Swath_5km, Cell_Across_Swath_5km)
      Valid Range: 0 to +180 degrees
  5. Solar_Azimuth
      Description: Solar Azimuth Angle, Cell to Sun
      Dimensions: (Cell_Along_Swath_5km, Cell_Across_Swath_5km)
      Valid Range: -180 to +180 degrees
  6. Sensor_Zenith
      Description: Sensor Zenith Angle, Cell to Sensor
      Dimensions: (Cell_Along_Swath_5km, Cell_Across_Swath_5km)
      Valid Range: 0 to 180 degrees
  7. Sensor_Azimuth
      Description: Sensor Azimuth Angle, Cell to Sensor
      Dimensions: (Cell_Along_Swath_5km, Cell_Across_Swath_5km)
      Valid Range: -180 to 180 degrees

    Science Parameters

      Water Vapor

  8. Water_Vapor_Near_Infrared
      Description: Total Column Precipitable Water Vapor - Near Infrared Retrieval
      Dimensions: (Cell_Along_Swath_1km, Cell_Across_Swath_1km)
      Valid Range: 0 to 20 cm

  9. Water_Vapor_Infrared
      Description: Total Column Precipitable Water Vapor - IR Retrieval
      Dimensions: (Cell_Along_Swath_5km, Cell_Across_Swath_5km)
      Valid Range: 0 to 20 cm

  10. Water_Vapor_Correction_Factors
      Description: Water Vapor Retrieval Algorithm Correction Factors
      Dimensions: (Cell_Along_Swath_1km, Cell_Across_Swath_1km)
      Valid Range: (byte array)

      Quality Assurance

  11. Quality_Assurance_Near_Infrared
      Description: Runtime Quality Assurance flags for Water_Vapor_Near_Infrared
      Dimensions: (Cell_Along_Swath_1km, Cell_Across_Swath_1km, QA_Byte_NIR)
      Valid Range: bit field (see MODIS Atmosphere QA Plan for details)

  12. Quality_Assurance_Infrared
      Description: Runtime Quality Assurance flags for Water_Vapor_Infrared
      Dimensions: (Cell_Along_Swath_5km, Cell_Across_Swath_5km, QA_Byte_IR)
      Valid Range: bit field

      Cloud Mask (1km)

  13. Cloud_Mask
      Description: MODIS Cloud Mask , First Byte
      Dimensions: (Cell_Along_Swath_1km, Cell_Across_Swath_1km)
      Valid Range: bit field




Cloud_Mask Bit-Field Interpretation

The Cloud_Mask SDS is copied from a portion of the complete MODIS Cloud Mask SDS in the MOD35_L2 Product. Each pixel in the Cloud_Mask SDS is assigned a 1 byte (8 bit) array. Individual bits or groups of bits are set to denote various cloud conditions and characteristics for that pixel.

All bit and byte numbering, in the table below, will start with 0.

Cloud_Mask Bit-Field Interpretation
Byte #0
(1km Cloud Mask & Processing Path Flags)
Bits Field Description Bit Interpretation Key
0 Cloud Mask Flag 0 = Not Determined
1 = Determined
1-2 Unobstructed FOV Quality Flag 0 = Confident Cloudy
1 = Probably Cloudy
2 = Probably Clear
3 = Confident Clear
3 Day/Night Flag 0 = Night
1 = Day
4 Sunglint Flag 0 = Yes
1 = No
5 Snow/Ice Background Flag 0 = Yes
1 = No
6-7 Land/Water Background Flag 0=Water
1=Coastal
2=Desert
3=Land




Quality_Assurance_Infrared Bit-Field Interpretation

Each pixel in the Quality_Assurance_Infrared SDS is assigned a 5 byte (40 bit) array. Individual bits or groups of bits are set to denote various quality run-time characteristics for that pixel.

All bit and byte numbering, in the table below, will start with 0.

Quality_Assurance_Infrared Bit-Field Interpretation
Byte #0
Bits Field Description Bit Interpretation Key
0 IR Water Vapor QA 0 = Not Useful
1 = Useful
1-3 IR Water Vapor Confidence QA (1km) 0 = Fill (Bad or Cloudy)
1 = Best Quality
2-7 = Not Used
4-7 (spares) n/a
Byte #1
Bits Field Description Bit Interpretation Key
0-7 Number of Cloudy Pixels within 5x5 km box valid range: 0 to 25
Byte #2
Bits Field Description Bit Interpretation Key
0-7 Number of Clear Pixels within 5x5 km box valid range: 0 to 25
Byte #3
Bits Field Description Bit Interpretation Key
0-7 Number of Missing Pixels within 5x5 km box valid range: 0 to 25
Byte #4
Bits Field Description Bit Interpretation Key
0-1 IR Water Vapor Retrieval Method Used 0 = Split Window (11-12)
1 = Moisture Profile Integration
2 = Other
3 = No Retrieval
2-7 (spares) n/a



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