subroutine get_cloud_waterphase_fraction(debug, line, elem, along_track_idx,
     *                                 across_track_idx, cloud_phase,
     *                                 wtrcld_frc)

c-----------------------------------------------------------------------------------
c
c Description: Calculate fraction of HIRS IFOV that is covered by water clouds
c              according to the PATMOS-X "cloud_phase" data set.
c
c Input parameters:
c debug                     Debug write flag
c line                      HIRS line number (1-1100)
c elem                      HIRS pixel number (1-56)
c along_track_idx           AVHRR scan line numbers of collocated pixels
c across_track_idx          AVHRR element numbers of collocated pixels
c cloud_phase               AVHRR cloud phase index from PATMOS-X data
c
c Output parameters:
c wtrcld_frc                Fraction of HIRS IFOV that is covered by water clouds      
c
c Revision history:         12/13       R. Frey       Original version
c
c Calls                     None
c
c----------------------------------------------------------------------------------

      implicit none
      save

c----------------------------------------------------------------------------------

c     Calling arguments.
      real*4  wtrcld_frc
      integer cloud_phase(409,15000)
      integer across_track_idx(100,56,1100), along_track_idx(100,56,1100)
      integer debug, line, elem

c     Local variables.
      integer wtr, ntot, nwtr
      integer i, j, k

c-----------------------------------------------------------------------------------

c     Get land cover indecis from collocated PATMOS-X data.

      nwtr = 0
      ntot = 0

      do i = 1, 100

        j = along_track_idx(i,elem,line)
        k = across_track_idx(i,elem,line)

        wtr = -1.0
        if(j .ne. 0 .and. k .ne. 0) then

          wtr = cloud_phase(k,j)

          if(wtr .ge. 1 .and. wtr .le. 5) then
            ntot = ntot + 1

            if(wtr .eq. 1) then
              nwtr = nwtr + 1.0
            end if

          end if

        end if

c----------------------------------------------------------------------------------

        if(debug .gt. 1) then
          write(*,'(6i6)') i, j, k, wtr, ntot, nwtr
        end if

c----------------------------------------------------------------------------------

      enddo

c-----------------------------------------------------------------------------------

c     Calculate land fraction.
 
      if(ntot .gt. 0.0) then
        wtrcld_frc = real(nwtr) / real(ntot)
      else
        wtrcld_frc = -99.99
      end if

c-----------------------------------------------------------------------------------

      if(debug .gt. 0) then
        write(*,'(''Collocated AVHRR water cloud fraction at line '', i5, '' and element '',
     *            i5, '': '', f8.3)') line, elem, wtrcld_frc
      end if

c-----------------------------------------------------------------------------------

      return
      end