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MOD05_L2 (Water Vapor Product)
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Data Volume

The MODIS Atmosphere Water Vapor Product (MOD05_L2) will be produced at the MODAPS facility at the NASA Goddard Space Flight Center.

MODAPS will produce 100% of the MOD05_L2 product. Approximately 288 MOD04_L2 HDF files are produced per day, however daytime granules are quite a bit larger than their nighttime counterparts. Since both MODIS terminator granules (for both ascending and descending nodes) are counted as day, a full 55% of all MODIS granules are labeled daytime. With each daytime HDF file roughly 14.6 MB in size and each nighttime HDF file roughly 3.6 MB in size, the total data volume is approximately 2.9 GB per day.

Production Rules

The production rules of combined MOD_PR04 and MOD_PR05 are based upon input time check of required inputs (such as L1B, geolocation and cloud mask), and solar zenith angle (i.e., the minimum solar zenith angle retrieved from cloud mask metadata). No retrieval of aerosol or near-infrared total precipitable water will be performed if inputs time checking fails, or if minimum solar zenith angle is greater than 72 degrees. For solar zenith angle greater than 72 degrees, only the MOD_PR05 copying procedure will be executed in order to copy the total precipitable water derived from infrared channels from MOD_PR07 (which is processed day and night).

The MOD_PR07 generated HDF file should exist before this process in order to copy column water vapor results derived from infrared wavelength to MOD_PR05 HDF file. However, MOD_PR04 and MOD_PR05 processes will still continue if MOD_PR07 generated HDF file does not exist by simply not copying the infrared column water vapor results (error message will be written to LogStatus and Fill value will be filled to the array).

The required inputs are MODIS L1B, geolocation, and cloud mask data data. Individually, other than the required inputs, for MOD_PR04 aerosol retrieval, MOD05 near infrared total precipitable water and MOD_PR07 total ozone are also needed for the gas absorption correction. However, if MOD05 near infrared total precipitable water and/or MOD_PR07 total ozone are not generated correctly, the MOD_PR04 aerosol retrieval will still continue to use ancillary inputs (shown below). continue to check whether ancillary inputs are available (as shown next). This process requires other ancillary (non-MODIS) inputs as well, such as NCEP data (and later DAO data becomes available). It is however that the combined MOD_PR04 and MOD_PR05 process will still continue if NCEP (or DAO) data is unavailable. In this case, climatological data will be used instead.

For each execution:

  • Input File Characterization

      The combined run of MOD_PR04 and MOD_PR05 requires only one granule of data (e.g., 200 scan lines) at a time, including L1B, geolocation, and cloud mask. It will process all the granules satisfied by the production rule. In addition, MOD_PR05 near infrared total precipitable water and MOD_PR07 total ozone are used as inputs for MOD_PR04 process.

  • Dynamic Ancillary Data Needs

      Currently, four ancillary data (i.e., ozone, ice, meteorology and sea surface temperature and ice) from NCEP are needed. Later, when DAO data becomes available, it will be used as ancillary inputs.

  • Static Ancillary Data Needs

      For MOD_PR05 (total precipitable water and correction) the look-up tables are:

    • TRANSM_H2O.MDL_1
    • TRANSM_H2O.MDL_3
    • TRANSM_H2O.MDL_5
    • TRANSM_H2O.MDL_2
    • TRANSM_H2O.MDL_4
    • TRANSM_H2O.MDL_6
    • Refl_Ch2_Ascii
    • Ratio_Ch19_To_Ch2_Ascii

  • Output Product Characterization

      Both MOD_PR04 and MOD_PR05 processes generate HDF products (i.e., mod04_L2.hdf and mod05_L2.hdf) along with .met metadata files. Diagnostic files will be generated when debugging mode is turned on. For each diagnostic file, associated metadata will also be generated.

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