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TOVS PATH B DATA SUMMARY: 3. DATA ORGANIZATION


The TOVS Pathfinder Path B gridded output consists of binary files containing 2- and 3-dimensional geophysical parameters mapped to a 1 degree rectangular latitude-longitude grid. For each parameter, each cell in the grid is characterized by a mean value of that parameter, the associated standard deviation, and the number of observations used in computing the first two quantities. These statistics are stored as Scientific Data Sets (SDSs) in the Hierarchical Data Format (HDF). Means and standard deviations are stored as 32-bit floating point words, while the number of observations or "counts" are represented as 16 bit integers. Version 3.3 release 2 of HDF (HDF3.3r2) was used to create all level 3 files. The schematic below shows the overall structure of a TOVS Path B HDF file:

                            --------------------------
                            |     FILE IDENTIFIER    |
                            --------------------------
                            |     FILE DESCRIPTION   |
                            --------------------------
                            |      DAAC METADATA     |
         -----------        --------------------------        -----------
         |  SDS 37 |        |     SCIENCE METADATA   |        |  SDS 38 |
         | AIRMASS |------------------------------------------|  FLAGS  |    

         -----------       /             |            \       -----------
                          /              |             \     
                         /               |              \
                        /                |               \
                       /                 |                \
            -----------             -----------            -----------         
            |Parameter|             |Parameter|            |Parameter|    
            |  Means  |             | Std Dev |            |  Counts |
            -----------             -----------            -----------
               /   \                   /   \                   /   \
              / ... \                 / ... \                 / ... \
       ---------   ---------   ---------   ----------  ---------   ----------
       | SDS 1 |...|SDS 12 |   |SDS 13 |...| SDS 24 |  |SDS 25 |...| SDS 36 |
       | TEMP  |   | EMISS |   |TEMP_SD|   |EMISS_SD|  |TEMP_CT|   |EMISS_CT|
       ---------   ---------   ---------   ----------  ---------   ----------
            |  .....  |             |  .....  |             |  .....  |
            |         |             |         |             |         |
        --------   --------     --------   --------     --------   --------
        |Labels|   |Labels|     |Labels|   |Labels|     |Labels|   |Labels|
        --------   --------     --------   --------     --------   --------
        |Scales|   |Scales|     |Scales|   |Scales|     |Scales|   |Scales|
        --------   --------     --------   --------     --------   --------
        |Type  |   |Type  |     |Type  |   |Type  |     |Type  |   |Type  |
        --------   --------     --------   --------     --------   --------

        

Each file includes the following parameter SDSs (written out in that order):


    SDS Name   Units   Dimension   Description
    --------   -----   ---------   ----------
    (1) MTEMP    K     360x180x9   Vertically averaged dry-air temperatures 
                                   between the 1000-850, 850-700, 700-500, 
                                   500-300, 300-100, 100-70, 70-50, 50-30, 
                                   and 30-10 mb mandatory levels 

    (2) VTEMP    K     360x180x9   Vertically averaged virtual temperatures 
                                   between the 1000-850, 850-700, 700-500,
                                   500-300, 300-100, 100-70, 70-50, 50-30, 
                                   and 30-10 mb mandatory levels 

    (3) CLTEMP   K     360x180x4   Coarse layer mean temperature for the 
                                   surface-500, 500-300, 300-100, 100-30 mb
                                   layers      

    (4) PRWAT    cm    360x180x5   Total precipitable water values above 
                                   the surface, 850, 700, 500, and 300 mb 


    (5) TSURF    K     360x180     Surface skin temperature 

    (6) FCLD     0-1   360x180     Total cloud fraction *

    (7) FCLDP    0-1   360x180x7   Cloud fraction in 7 ISSCP layers *
                                    180 mb to top of atmosphere
                                    180 mb to 310 mb     
                                    310 mb to 440 mb     
                                    440 mb to 560 mb     
                                    560 mb to 680 mb     
                                    680 mb to 800 mb     
                                    800 mb to surface          

    (8) PCLD     mb    360x180      Cloud top pressure *

    (9) TCLD     K     360x180      Cloud top temperature *

   (10) ZANGLE   deg   360x180      Effective satellite zenith angle defined 
                                    as the arccosine of the average value of 
                                    the cosines of the individual satellite 
                                    zenith angles

   (11) TIME     hrs   360x180      Time of observation in Z hours (HH.hh)

   (12) EMISS    0-1   360x180      Microwave surface emissivity (fraction) *

   (13 - 24)                        Repeat for Standard Deviations 
                                    (e.g., MTEMP_STD)

   (25 - 36)                        Repeat for Sample Counts 
                                    (e.g., MTEMP_COUNT)

   (37) AIRMASS  1-5   360x180      Frequency of occurrence 5 air mass
                                    types within the grid cell (bit-encoded)

   (38) FLAGS          360x180      Flags indicating profile rejection 
                                    percentages for selected criteria

        

The asterisks '*' indicate that these parameters were designated as experimental by the TOVS Implementation Team. The last two SDSs (SDS 37 and SDS 38) contain additional useful information pertaining to the retrievals that were used to derive the grid cell statistics. The AIRMASS SDS consists of a 2-dimensional, 32 bit integer array of values providing information on the frequency of occurence of each of 5 air mass types in each gridbox, bit-encoded as follows:


             Bit Positions          Air Mass Type (Frequency)      
             -------------          -------------------------
                1 -  6                      polar-1 
                7 - 12                      polar-2 
               13 - 18                      midlat-2
               19 - 24                      midlat-1 
               21 - 30                      tropical 

        

The FLAGS SDS also consists of a 2-dimensional, 32 bit integer array of values indicating the percentage of rejected retrievals due to various conditions, bit-encoded as follows:



             Bit Positions          Rejections (Percentage)      
             -------------          -----------------------
                1 -  4                   temperature 
                5 -  9                   clouds 
               10 - 14                   surface skin temp 
               15 - 19                   water vapor
               20 - 31                   number of events

        

Associated with each SDS is a set of ASCII labels containing the name, units, display format, and a brief description of the data in that array. The axes scales for each dimension of the SDS are also stored in the same representation as that used for the data, i.e., if the data are represented as 16-bit integers, then the scales are also stored as 16-bit integers. For the TOVS data, x-axis scales refer to longitude, the y-axis scales to latitude, and (for 3-dimensional SDSs) the z-axis scales to pressure altitude. It should be noted that in the case of layer quantities such as CLTEMP and FCLDP, the values for the z-axis scales denote the midpoints of the layers rather than the upper or lower boundaries.

There are 6 level 3 data product files, each representing a different averaging time period. The spatial and temporal resolutions of the data are listed below:


        Averaging periods   :  daily, 5-day and monthly AM (descending nodes)
                               daily, 5-day and monthly PM (ascending nodes)   
        Gridbox dimensions  :  1 degree latitude by 1 degree longitude          
        Center of gridbox 1 :  (-179.5,-89.5), with negative longitudes         
                               west of the Greenwich meridian                   
        Gridbox progression :  proceeds from (-179.5,-89.5) to (179.5,-89.5),   
                               continuing northward and ending at the gridbox   
                               with central coordinates (179.5,89.5)          

        

An HDF file identifier has been included with each of the 6 files which indicates the type of data set, the satellite, the time period and the date pertaining to the data. This label takes the following form (using March 1988 AM as an example) :


          TOVS_NOAA10_PATHB_GLOBAL_GRIDDED_DAILY_AM_880320           (daily)
          TOVS_NOAA10_PATHB_GLOBAL_GRIDDED_5DAYS_AM_B880317.E880321  (5day)
          TOVS_NOAA10_PATHB_GLOBAL_GRIDDED_MONTHLY_AM_8803          (monthly)

The HDF file identifiers for the PM files are named in an analagous manner. There are also two HDF ASCII annotations in each file. The first contains a general file description containing useful information related to the contents of the file and the Path B methodology. The second contains a short list of ASCII keywords (metadata) extracted by the Goddard DAAC as part of the archive process and used to populate a database for inventory purposes.

Local equator crossing time for even numbered satellites such as NOAA-10 is nominally 7:30 PM for the ascending node and 7:30 AM for the descending node. For gridding purposes, the global AM (PM) map is not created by including data from all descending (ascending) portions of the orbits between 00Z and 24Z. This would result in data from 2 consecutive days being included in either map since the satellite crosses the date line during this 24-hour period. Rather, the gridding is based upon the local date and time of the orbits, e.g., only those ascending orbits with the same local day and time (which is always 7:30 PM) are used in the construction of the PM map. A similar procedure is used in the construction of the AM map.

Each level 2 spot retrieval is assigned to a single gridbox according to which gridbox the spatial coordinates of the center of the level 2 FOV falls within. For a gridbox with multiple observations, a simple unweighted average of all points within the box is used for determining mean values. No interpolation or data filling is used. For all mean and standard deviation arrays, a fill of -9999. is used to indicate that data for that gridbox is either missing, invalid or suspect. For the count arrays, a corresponding fill value of 0 is used under these circumstances.


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Last updated: Nov 23, 2009 02:26 PM ET
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