EXAMPLE USE OF THE IMAPP CLOUD MASK 
       -----------------------------------

	The MODIS cloud mask consists of a 6 byte (48 bit) array.
        For simply a cloud/clear discimination, you will need
        to extract only the first three bits. 
  
        This FORTRAN code excerpt shows how you would test a pixel 
        for cloudy or clear using the 95 % probability clear cutoff 
        ( 99%,95% - clear, 66%,1% - cloud ) given an array of pixels.
        It also demonstrates the extraction of the sunglint bit.
        This code is just an example.  Parts were taken from
        operational code, but it has not been compiled.

        This code excerpt utilizes the unix bit function iand.  

        If you wish to read the individual test result bits and
        use them, you will need to also look at the cloud mask 
        QA output file which will tell you whether or not that
        test was applied for a given pixel. For example, some tests 
        are not applied at night or in a given ecosystem.

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c       BOX_CLOUD   Clear/cloud flag array for box
c                   (-1 = undefined, 0 = Clear, 1 = Cloud)

c     Declaration
      byte mask_byte, mask_test, mask_value
c     Cloud mask array
      byte mask1( max_pixel, max_line )  
      integer box_cloud( isamp, isamp ) 
c     Number of sunglint contaminated pixels
      integer nglint

c     Number of good pixels (where first bit is set to 1)
      integer ngood_msk
        

      jbox = 1
      do j = line, line + isamp - 1
        ibox = 1
        do i = pixel, pixel + isamp - 1
c ...     Check that cloud mask was determined for this pixel, and if so
c ...     check cloud mask
c ...     (99% and 95% confidence clear pixels are classified CLEAR)
c ...     (Low confidence clear and cloudy pixels are classified CLOUD)

          mask_byte = mask1(  i, j )
          mask_test = 1

c         If first bit is set to 1, then mask has been determined
          mask_value = iand( mask_byte, mask_test )
          if ( mask_value .eq. 1 ) then
            ngood_msk = ngood_msk + 1
            mask_test = 6
            mask_value = iand( mask_byte, mask_test )

c           If both bits 2 and 3 are set or if bit 3 is set
c              (95 or 99% probability clear) then clear
            if ( mask_value .ge. 4 ) then
              box_cloud( ibox, jbox ) = 0
c           Else, cloudy
            else
              box_cloud( ibox, jbox ) = 1
            endif
          endif

c ...     Now check sunglint flag in cloud mask
          mask_byte = mask1( i, j )
          mask_test = 1
c         If first bit is set to 1, then mask has been determined
          mask_value = iand( mask_byte, mask_test )
          if ( mask_value .eq. 1 ) then
            mask_test = 16
c           If bit 5 is not set, then sunglint
            mask_value = iand( mask_byte, mask_test )
            if ( mask_value .lt. 16 ) nglint = nglint + 1
          endif

        enddo
      enddo