subroutine get_satnode(lat1, lat2, debug, sat_node)

c-----------------------------------------------------------------------------------
c Description: Calculate satellite node (ascending or descending).
c
c Input parameters:
c lat1                latitude of sub-satellite point for initial point
c lat2                latitude of sub-satellite point for second point
c debug               debug message index
c
c Output parameters:
c sat_node            satellite node (1 = ascending node, 2 = descending node,
c                                     0 = invalid latitude)
c
c Revision history:
c                     10/10       R. Frey        Original version
c
c Calls               None
c
c-----------------------------------------------------------------------------------

      IMPLICIT NONE
      save

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

c     Calling arguments.
      integer sat_node, debug
      real lat1, lat2

c     Local variables.
      character*160 errmsg
      integer status, level
      real dlat

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

      dlat = 0.0

c     Check latitude values.
      if(lat1 .gt. 90.0 .or. lat1 .lt. -90.0 .or. lat2 .gt. 90.0 .or.
     *   lat2 .lt. -90.0) then

c       Invalid latitude found.
        sat_node = 0
        level = 2
        status = -1
        write( errmsg,'('' WARNING - invalid latitude '',2f10.2)') lat1, lat2
        call message( 'get_satnode', errmsg, status, level )

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

      else

c       Calculate node.
        dlat = lat1 - lat2
        if(dlat .gt. 0.0) then
          sat_node = 2
        else
          sat_node = 1
        end if
    
      end if

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

      if(debug .gt. 0) then
        write(*,'(/,''get_satnode: '')')
        write(*,'(''Input latitudes: '',2f12.3)') lat1, lat2
        write(*,'(''Lat. difference and node index: '',f10.3,i5)') dlat, sat_node
      end if
 
c-----------------------------------------------------------------------------------

      return
      end