Langley DAAC Version Number:   LD_008_024_002_00_00_0_19990615
                                               
                                               

PRABHAKARA SMMR DERIVED INTEGRATED ATMOSPHERIC WATER VAPOR

     1.0  Introduction

     This README file contains information on the structure
     of the Prabhakara Scanning Multichannel Microwave Radiometer
     (SMMR) integrated atmospheric water vapor data, sample software
     to read the data files, and pertinent scientific references.

     The Prabhakara SMMR integrated atmospheric water vapor files
     were generated by Dr. Prabhakara Cuddapah at the Goddard Space
     Flight Center (GSFC) using the SMMR Antenna Temperatures.
     A discussion of the SMMR Antenna Temperatures is available
     from the Langely Research Center Distributed Active Archive
     Center (DAAC) User Services Office at 804-864-8656 or e-mail 
     at support-asdc@earthdata.nasa.gov.  Each integrated atmospheric water vapor 
     file contains one month of 3 degree by 5 degree gridded mean water 
     vapor.  The data spans the period from October 1979 to September 1983.  
     For a discussion of the data, see the scientific references in section 
     4.0.


     2.0  Monthly Integrated Atmospheric Water Vapor File Structure

     Each data file contains a header record and integer values in
     a 72 x 50 element array  (see Table 1).  Each element represents
     a gridded mean for a 3 x 5 degree grid, beginning at 75N, 180W and
     progressing to 75S, 180E.

     EXAMPLES:

          Element (1,1) corresponds to the mean for the grid
          defined as 72-75N, 175-180W.

          Element (50,72) corresponds to the mean for the grid
          defined as 72-75S, 175-180E.


                                Table 1.

        180E                                                      180W
     75N--------------------------------------------------------------
        |    ----------- 72 grids ----------                         |
        |    |                                                       |
        |    50 grids                                                |
        |    |                                                       |
        |    |                                                       |
     75S--------------------------------------------------------------


     A scale factor of 0.1 must be applied to convert the data into
     units of g/cm2.  Since the data are only computed over ocean,
     a value of 999.9 represents a land grid.


     3.0  Sample Software

     The following sample software to read the data is provided by
     Dr. Prabhakara Cuddapah.

     C
     C  Sample program to read and write header record
     C  and water vapor data
     C
            INTEGER WV(50,72), HDR(20)
     C
            READ(10,1000)(HDR(I),I=1,20)
      1000  FORMAT(20A4)
            WRITE(6,1000)(HDR(I),I=1,20)
C
            DO 10 I=1,50
             READ(10,1100)(WV(I,J),J=1,72)
             WRITE(6,1100)(WV(I,J),J=1,72)
      1100   FORMAT(72I4)
        10  CONTINUE
C
            STOP
            END

    4.0  Scientific References

    Prabhakara, C., H. D. Chang, and T. C. Chang, 1982:  Remote Sensing
    of Precipitable Water over the Oceans from Nimbus 7 Microwave
    Measurements. J. Appl. Meteor., Vol. 21, No. 1, 59-68.

    Prabhakara, C., G. Dalu, J. J., Nucciarone, and G. L. Liberti, 1992:
    Rainfall over Oceans:  Remote Sensing from Satellite Microwave
    Radiometers.  Meteorol. Atmos. Phys., 47, 177-199.