module topography_mod

! <CONTACT EMAIL="Bruce.Wyman@noaa.gov">
!   Bruce Wyman
! </CONTACT>

! <HISTORY SRC="http://www.gfdl.noaa.gov/fms-cgi-bin/cvsweb.cgi/FMS/"/>

! <OVERVIEW>
!   Routines for creating land surface topography fields and land-water masks
!   for latitude-longitude grids.
! </OVERVIEW>

! <DESCRIPTION>
!   This module generates realistic mountains and land-water masks
!   on a specified latitude-longitude grid by interpolating from the
!   1/6 degree Navy mean topography and percent water data sets.
!   The fields that can be generated are mean and standard deviation
!   of topography within the specified grid boxes; and land-ocean (or
!   water) mask and land-ocean (or water) fractional area.
!
!   The interpolation scheme conserves the area-weighted average
!   of the input data by using module horiz_interp.
!
!   The interfaces get_gaussian_topog and gaussian_topog_init are documented in <LINK SRC="gaussian_topog.html">gaussian_topog_mod</LINK>.
! </DESCRIPTION>

use gaussian_topog_mod, only: gaussian_topog_init, get_gaussian_topog
use   horiz_interp_mod, only: horiz_interp_type, horiz_interp_new, &
                              horiz_interp, horiz_interp_del

use            fms_mod, only: file_exist, check_nml_error,               &
                              open_namelist_file, close_file, stdlog,    &
                              mpp_pe, mpp_root_pe, write_version_number, &
                              open_ieee32_file, error_mesg, FATAL, NOTE, &
                              mpp_error
use         fms_io_mod, only: read_data
use      constants_mod, only: PI
use            mpp_mod, only: input_nml_file

implicit none
private

public :: topography_init,                 &
          get_topog_mean, get_topog_stdev, &
          get_ocean_frac, get_ocean_mask,  &
          get_water_frac, get_water_mask,  &
          gaussian_topog_init, get_gaussian_topog

interface get_topog_mean
  module procedure get_topog_mean_1d, get_topog_mean_2d
end interface
interface get_topog_stdev
  module procedure get_topog_stdev_1d, get_topog_stdev_2d
end interface
interface get_ocean_frac
  module procedure get_ocean_frac_1d, get_ocean_frac_2d
end interface
interface get_ocean_mask
  module procedure get_ocean_mask_1d, get_ocean_mask_2d
end interface
interface get_water_frac
  module procedure get_water_frac_1d, get_water_frac_2d
end interface
interface get_water_mask
  module procedure get_water_mask_1d, get_water_mask_2d
end interface

!-----------------------------------------------------------------------
! <NAMELIST NAME="topography_nml">
!   <DATA NAME="topog_file" TYPE="character" DEFAULT="DATA/navy_topography.data">
!       Name of topography file.
!   </DATA>
!   <DATA NAME="water_file" TYPE="character" DEFAULT="DATA/navy_pctwater.data">
!       Name of percent water file.
!   </DATA>

   character(len=128) :: topog_file = 'DATA/navy_topography.data', &
                         water_file = 'DATA/navy_pctwater.data'
   namelist /topography_nml/ topog_file, water_file
! </NAMELIST>

!-----------------------------------------------------------------------
! --- resolution of the topography data set ---
! <DATASET NAME="">
!   This module uses the 1/6 degree U.S. Navy mean topography
!   and percent water data sets.
!
!   These data sets have been re-formatted to separate 32-bit IEEE files.
!   The names of these files is specified by the <LINK SRC="#NAMELIST">namelist</LINK> input.
!
!The format for both files is as follows:
! <PRE>
!     record = 1    nlon, nlat
!     record = 2    blon, blat
!     record = 3    data
! </PRE>
!where:
! <PRE>
!     nlon, nlat = The number of longitude and latitude points
!                  in the horizontal grid.  For the 1/6 degree
!                  data sets this is 2160 x 1080. [integer]
!     blon, blat = The longitude and latitude grid box boundaries in degrees.
!                     [real :: blon(nlon+1), blat(nlat+1)]
!
!     data       = The topography or percent water data.
!                    [real :: data(nlon,nlat)]
! </PRE>
! </DATASET>
  integer :: unit
  integer :: ipts, jpts
  integer, parameter :: COMPUTE_STDEV = 123  ! use this flag to
                                             !   compute st dev

!-----------------------------------------------------------------------

 character(len=128) :: version = '$Id$'
 character(len=128) :: tagname = '$Name$'

 logical :: module_is_initialized = .FALSE.

!-----------------------------------------------------------------------

 contains

!#######################################################################

   subroutine topography_init ()

     if ( module_is_initialized ) return

     call write_version_number (version,tagname)
     call read_namelist
     module_is_initialized = .TRUE.

   end subroutine topography_init

!#######################################################################

! <FUNCTION NAME="get_topog_mean">

!   <OVERVIEW>
!     Returns a "realistic" mean surface height field. 
!   </OVERVIEW>
!   <DESCRIPTION>
!     Returns realistic mountains on a latitude-longtude grid.
!     The returned field is the mean topography for the given grid boxes.
!     Computed using a conserving area-weighted interpolation.
!     The current input data set is the 1/6 degree Navy mean topography.
!   </DESCRIPTION>
!   <TEMPLATE>
!     flag = <B>get_topog_mean</B> ( blon, blat, zmean )
!   </TEMPLATE>

!   <IN NAME="blon" TYPE="real" DIM="(:)">
!     The longitude (in radians) at grid box boundaries.
!   </IN>
!   <IN NAME="blat" TYPE="real" DIM="(:)">
!     The latitude (in radians) at grid box boundaries.
!   </IN>
!   <OUT NAME="zmean" UNIT=" meter" TYPE="real" DIM="(:,:)">
!     The mean surface height (meters).
!     The size of this field must be size(blon)-1 by size(blat)-1.
!   </OUT>
!   <OUT NAME="get_topog_mean" TYPE="logical">
!     A logical value of TRUE is returned if the surface height field
!     was successfully created. A value of FALSE may be returned if the
!     input topography data set was not readable.
!   </OUT>

!   <ERROR MSG="shape(zmean) is not equal to (/size(blon)-1,size(blat)-1/))" STATUS="FATAL">
!     Check the input grid size and output field size.
!   </ERROR>

 function get_topog_mean_1d (blon, blat, zmean)

   real, intent(in),  dimension(:)   :: blon, blat
   real, intent(out), dimension(:,:) :: zmean
   logical :: get_topog_mean_1d

!-----------------------------------------------------------------------
   if (.not. module_is_initialized) call topography_init()

   if ( any(shape(zmean(:,:)) /= (/size(blon(:))-1,size(blat(:))-1/)) ) &
        call error_mesg('get_topog_mean_1d','shape(zmean) is not&
            & equal to (/size(blon)-1,size(blat)-1/))', FATAL)

   if ( open_topog_file(topog_file) ) then
       call interp_topog_1d ( blon, blat, zmean )
       get_topog_mean_1d = .true.
   else
       get_topog_mean_1d = .false.
   endif

!-----------------------------------------------------------------------

 end function get_topog_mean_1d

!############################################################

 function get_topog_mean_2d (blon, blat, zmean)

   real, intent(in),  dimension(:,:) :: blon, blat
   real, intent(out), dimension(:,:) :: zmean
   logical :: get_topog_mean_2d

!-----------------------------------------------------------------------
   if (.not. module_is_initialized) call topography_init()

   if ( any(shape(zmean(:,:)) /= (/size(blon,1)-1,size(blon,2)-1/)) .or. &
        any(shape(zmean(:,:)) /= (/size(blat,1)-1,size(blat,2)-1/)) ) &
        call error_mesg('get_topog_mean_2d','shape(zmean) is not&
            & equal to (/size(blon,1)-1,size(blon,2)-1/))', FATAL)

   if ( open_topog_file(topog_file) ) then
       call interp_topog_2d ( blon, blat, zmean )
       get_topog_mean_2d = .true.
   else
       get_topog_mean_2d = .false.
   endif

!-----------------------------------------------------------------------

 end function get_topog_mean_2d

! </FUNCTION>
!#######################################################################

! <FUNCTION NAME="get_topog_stdev">

!   <OVERVIEW>
!     Returns a standard deviation of higher resolution topography with 
!     the given model grid boxes. 
!   </OVERVIEW>
!   <DESCRIPTION>
!     Returns the standard deviation of the "finer" input topography data set,
!     currently the Navy 1/6 degree mean topography data, within the
!     boundaries of the given input grid.
!   </DESCRIPTION>
!   <TEMPLATE>
!     flag = <B>get_topog_stdev</B> ( blon, blat, stdev )
!   </TEMPLATE>
!   <IN NAME="blon" TYPE="real" DIM="(:)">
!     The longitude (in radians) at grid box boundaries.
!   </IN>
!   <IN NAME="blat" TYPE="real" DIM="(:)">
!     The latitude (in radians) at grid box boundaries.
!   </IN>
!   <OUT NAME="stdev" UNITS="meter" TYPE="real" DIM="(:,:)">
!     The standard deviation of surface height (in meters) within
!     given input model grid boxes.
!     The size of this field must be size(blon)-1 by size(blat)-1.
!   </OUT>
!   <OUT NAME="get_topog_stdev" TYPE="logical">
!     A logical value of TRUE is returned if the output field was
!     successfully created. A value of FALSE may be returned if the
!     input topography data set was not readable.
!   </OUT>

 function get_topog_stdev_1d (blon, blat, stdev)

   real, intent(in),  dimension(:)   :: blon, blat
   real, intent(out), dimension(:,:) :: stdev
   logical :: get_topog_stdev_1d

!-----------------------------------------------------------------------
   if (.not. module_is_initialized) call topography_init()

   if ( any(shape(stdev(:,:)) /= (/size(blon(:))-1,size(blat(:))-1/)) ) &
       call error_mesg('get_topog_stdev','shape(stdev) is not&
            & equal to (/size(blon)-1,size(blat)-1/))', FATAL)

   if ( open_topog_file(topog_file) ) then
       call interp_topog_1d ( blon, blat, stdev, flag=COMPUTE_STDEV )
       get_topog_stdev_1d = .true.
   else
       get_topog_stdev_1d = .false.
   endif

!-----------------------------------------------------------------------

 end function get_topog_stdev_1d

!#######################################################################

 function get_topog_stdev_2d (blon, blat, stdev)

   real, intent(in),  dimension(:,:) :: blon, blat
   real, intent(out), dimension(:,:) :: stdev
   logical :: get_topog_stdev_2d

!-----------------------------------------------------------------------
   if (.not. module_is_initialized) call topography_init()

   if ( any(shape(stdev(:,:)) /= (/size(blon,1)-1,size(blon,2)-1/)) .or. &
        any(shape(stdev(:,:)) /= (/size(blat,1)-1,size(blat,2)-1/)) ) &
        call error_mesg('get_topog_stdev_2d','shape(stdev) is not&
            & equal to (/size(blon,1)-1,size(blon,2)-1/))', FATAL)

   if ( open_topog_file(topog_file) ) then
       call interp_topog_2d ( blon, blat, stdev, flag=COMPUTE_STDEV )
       get_topog_stdev_2d = .true.
   else
       get_topog_stdev_2d = .false.
   endif

!-----------------------------------------------------------------------

 end function get_topog_stdev_2d

! </FUNCTION>
!#######################################################################

! <FUNCTION NAME="get_ocean_frac">

!   <OVERVIEW>
!      Returns fractional area covered by ocean in a grid box.
!   </OVERVIEW>
!   <DESCRIPTION>
!     Returns fractional area covered by ocean in the given model grid boxes.
!   </DESCRIPTION>
!   <TEMPLATE>
!     flag = <B>get_ocean_frac</B> ( blon, blat, ocean_frac )
!   </TEMPLATE>

!   <IN NAME="blon" UNITS="radians" TYPE="real" DIM="(:)">
!     The longitude (in radians) at grid box boundaries.
!   </IN>
!   <IN NAME="blat" UNITS="radians" TYPE="real" DIM="(:)">
!     The latitude (in radians) at grid box boundaries.
!   </IN>
!   <OUT NAME="ocean_frac" TYPE="real" DIM="(:,:)">
!     The fractional amount (0 to 1) of ocean in a grid box.
!     The size of this field must be size(blon)-1 by size(blat)-1.
!   </OUT>
!   <OUT NAME="get_ocean_frac" TYPE="logical">
!     A logical value of TRUE is returned if the output field
!     was successfully created. A value of FALSE may be returned
!     if the Navy 1/6 degree percent water data set was not readable.
!   </OUT>

 function get_ocean_frac_1d (blon, blat, ocean_frac)

 real, intent(in),  dimension(:)   :: blon, blat
 real, intent(out), dimension(:,:) :: ocean_frac
 logical :: get_ocean_frac_1d

!-----------------------------------------------------------------------
   if (.not. module_is_initialized) call topography_init()

   if ( any(shape(ocean_frac(:,:)) /= (/size(blon(:))-1,size(blat(:))-1/)) ) &
        call error_mesg('get_ocean_frac','shape(ocean_frac) is not&
                 & equal to (/size(blon)-1,size(blat)-1/))', FATAL)

   if ( open_topog_file(water_file) ) then
       call interp_water_1d ( blon, blat, ocean_frac, do_ocean=.true. )
       get_ocean_frac_1d = .true.
   else
       get_ocean_frac_1d = .false.
   endif

!-----------------------------------------------------------------------

 end function get_ocean_frac_1d

!#######################################################################

 function get_ocean_frac_2d (blon, blat, ocean_frac)

 real, intent(in),  dimension(:,:) :: blon, blat
 real, intent(out), dimension(:,:) :: ocean_frac
 logical :: get_ocean_frac_2d

!-----------------------------------------------------------------------
   if (.not. module_is_initialized) call topography_init()

   if ( any(shape(ocean_frac(:,:)) /= (/size(blon,1)-1,size(blon,2)-1/)) .or. &
        any(shape(ocean_frac(:,:)) /= (/size(blat,1)-1,size(blat,2)-1/)) ) &
        call error_mesg('get_ocean_frac_2d','shape(ocean_frac) is not&
            & equal to (/size(blon,1)-1,size(blon,2)-1/))', FATAL)

   if ( open_topog_file(water_file) ) then
       call interp_water_2d ( blon, blat, ocean_frac, do_ocean=.true. )
       get_ocean_frac_2d = .true.
   else
       get_ocean_frac_2d = .false.
   endif

!-----------------------------------------------------------------------

 end function get_ocean_frac_2d

! </FUNCTION>
!#######################################################################
! <FUNCTION NAME="get_ocean_mask">

!   <OVERVIEW>
!     Returns a land-ocean mask in a grid box.
!   </OVERVIEW>
!   <DESCRIPTION>
!     Returns a land-ocean mask in the given model grid boxes.
!   </DESCRIPTION>
!   <TEMPLATE>
!     flag = <B>get_ocean_mask</B> ( blon, blat, ocean_mask )
!   </TEMPLATE>

!   <IN NAME="blon" UNITS="radians" TYPE="real" DIM="(:)">
!     The longitude (in radians) at grid box boundaries.
!   </IN>
!   <IN NAME="blat" UNITS="radians" TYPE="real" DIM="(:)">
!     The latitude (in radians) at grid box boundaries.
!   </IN>
!   <OUT NAME="ocean_frac" TYPE="real" DIM="(:,:)">
!     The fractional amount (0 to 1) of ocean in a grid box.
!     The size of this field must be size(blon)-1 by size(blat)-1.
!   </OUT>
!   <OUT NAME="get_ocean_mask" TYPE="logical">
!     A logical value of TRUE is returned if the output field
!     was successfully created. A value of FALSE may be returned
!     if the Navy 1/6 degree percent water data set was not readable.
!   </OUT>

 function get_ocean_mask_1d (blon, blat, ocean_mask)

 real   , intent(in),  dimension(:)   :: blon, blat
 logical, intent(out), dimension(:,:) :: ocean_mask
 logical :: get_ocean_mask_1d

 real, dimension(size(ocean_mask,1),size(ocean_mask,2)) :: ocean_frac
!-----------------------------------------------------------------------
   if (.not. module_is_initialized) call topography_init()

 if ( get_ocean_frac(blon, blat, ocean_frac) ) then
   where (ocean_frac > 0.50)
     ocean_mask = .true.
   elsewhere
     ocean_mask = .false.
   end where
   get_ocean_mask_1d = .true.
 else
   get_ocean_mask_1d = .false.
 endif

!-----------------------------------------------------------------------

 end function get_ocean_mask_1d

!#######################################################################

 function get_ocean_mask_2d (blon, blat, ocean_mask)

 real   , intent(in),  dimension(:,:) :: blon, blat
 logical, intent(out), dimension(:,:) :: ocean_mask
 logical :: get_ocean_mask_2d

 real, dimension(size(ocean_mask,1),size(ocean_mask,2)) :: ocean_frac
!-----------------------------------------------------------------------
   if (.not. module_is_initialized) call topography_init()

 if ( get_ocean_frac(blon, blat, ocean_frac) ) then
   where (ocean_frac > 0.50)
     ocean_mask = .true.
   elsewhere
     ocean_mask = .false.
   end where
   get_ocean_mask_2d = .true.
 else
   get_ocean_mask_2d = .false.
 endif

!-----------------------------------------------------------------------

 end function get_ocean_mask_2d

! </FUNCTION>
!#######################################################################
! <FUNCTION NAME="get_water_frac">

!   <OVERVIEW>
!     Returns fractional area covered by water.
!   </OVERVIEW>
!   <DESCRIPTION>
!     Returns the percent of water in a grid box.
!   </DESCRIPTION>
!   <TEMPLATE>
!     flag = <B>get_water_frac</B> ( blon, blat, water_frac )
!   </TEMPLATE>

!   <IN NAME="blon" UNITS="radians" TYPE="real" DIM="(:)">
!     The longitude (in radians) at grid box boundaries.
!   </IN>
!   <IN NAME="blat" UNITS="radians" TYPE="real" DIM="(:)">
!     The latitude (in radians) at grid box boundaries.
!   </IN>
!   <OUT NAME="water_frac" TYPE="real" DIM="(:,:)">
!     The fractional amount (0 to 1) of water in a grid box.
!     The size of this field must be size(blon)-1 by size(blat)-1.
!   </OUT>
!   <OUT NAME="get_water_frac" TYPE="logical">
!     A logical value of TRUE is returned if the output field
!     was successfully created. A value of FALSE may be returned
!     if the Navy 1/6 degree percent water data set was not readable.
!   </OUT>
!   <ERROR MSG="shape(water_frac) is not equal to (/size(blon)-1,size(blat)-1/))" STATUS="FATAL">
!      Check the input grid size and output field size.
!   </ERROR>

 function get_water_frac_1d (blon, blat, water_frac)

 real, intent(in),  dimension(:)   :: blon, blat
 real, intent(out), dimension(:,:) :: water_frac
 logical :: get_water_frac_1d

!-----------------------------------------------------------------------
   if (.not. module_is_initialized) call topography_init()

   if ( any(shape(water_frac(:,:)) /= (/size(blon(:))-1,size(blat(:))-1/)) ) &
        call error_mesg('get_water_frac_1d','shape(water_frac) is not&
                 & equal to (/size(blon)-1,size(blat)-1/))', FATAL)

   if ( open_topog_file(water_file) ) then
       call interp_water_1d ( blon, blat, water_frac )
       get_water_frac_1d = .true.
   else
       get_water_frac_1d = .false.
   endif

!-----------------------------------------------------------------------

 end function get_water_frac_1d

!#######################################################################

 function get_water_frac_2d (blon, blat, water_frac)

 real, intent(in),  dimension(:,:) :: blon, blat
 real, intent(out), dimension(:,:) :: water_frac
 logical :: get_water_frac_2d

!-----------------------------------------------------------------------
   if (.not. module_is_initialized) call topography_init()

   if ( any(shape(water_frac(:,:)) /= (/size(blon,1)-1,size(blon,2)-1/)) .or. &
        any(shape(water_frac(:,:)) /= (/size(blat,1)-1,size(blat,2)-1/)) ) &
        call error_mesg('get_water_frac_2d','shape(water_frac) is not&
            & equal to (/size(blon,1)-1,size(blon,2)-1/))', FATAL)

   if ( open_topog_file(water_file) ) then
       call interp_water_2d ( blon, blat, water_frac )
       get_water_frac_2d = .true.
   else
       get_water_frac_2d = .false.
   endif

!-----------------------------------------------------------------------

 end function get_water_frac_2d

! </FUNCTION>
!#######################################################################
! <FUNCTION NAME="get_water_mask">

!   <OVERVIEW>
!     Returns a land-water mask in a grid box.
!   </OVERVIEW>
!   <DESCRIPTION>
!     Returns a land-water mask in the given model grid boxes.
!   </DESCRIPTION>
!   <TEMPLATE>
!     flag = <B>get_water_mask</B> ( blon, blat, water_mask )
!   </TEMPLATE>

!   <IN NAME="blon" UNITS="radians" TYPE="real" DIM="(:)">
!     The longitude (in radians) at grid box boundaries.
!   </IN>
!   <IN NAME="blat" UNITS="radians" TYPE="real" DIM="(:)">
!     The latitude (in radians) at grid box boundaries.
!   </IN>
!   <OUT NAME="water_mask" TYPE="real" DIM="(:,:)">
!     A binary mask for water (true) or land (false).
!     The size of this field must be size(blon)-1 by size(blat)-1.
!   </OUT>
!   <OUT NAME="get_water_mask" TYPE="logical">
!     A logical value of TRUE is returned if the output field
!     was successfully created. A value of FALSE may be returned
!     if the Navy 1/6 degree percent water data set was not readable.
!   </OUT>

 function get_water_mask_1d (blon, blat, water_mask)

 real   , intent(in),  dimension(:)   :: blon, blat
 logical, intent(out), dimension(:,:) :: water_mask
 logical :: get_water_mask_1d

 real, dimension(size(water_mask,1),size(water_mask,2)) :: water_frac
!-----------------------------------------------------------------------
   if (.not. module_is_initialized) call topography_init()

 if ( get_water_frac(blon, blat, water_frac) ) then
   where (water_frac > 0.50)
     water_mask = .true.
   elsewhere
     water_mask = .false.
   end where
   get_water_mask_1d = .true.
 else
   get_water_mask_1d = .false.
 endif

!-----------------------------------------------------------------------

 end function get_water_mask_1d

!#######################################################################

 function get_water_mask_2d (blon, blat, water_mask)

 real   , intent(in),  dimension(:,:) :: blon, blat
 logical, intent(out), dimension(:,:) :: water_mask
 logical :: get_water_mask_2d

 real, dimension(size(water_mask,1),size(water_mask,2)) :: water_frac
!-----------------------------------------------------------------------
   if (.not. module_is_initialized) call topography_init()

 if ( get_water_frac(blon, blat, water_frac) ) then
   where (water_frac > 0.50)
     water_mask = .true.
   elsewhere
     water_mask = .false.
   end where
   get_water_mask_2d = .true.
 else
   get_water_mask_2d = .false.
 endif

!-----------------------------------------------------------------------

 end function get_water_mask_2d

! </FUNCTION>

!#######################################################################
!##################   private interfaces below here   ##################
!#######################################################################

 function open_topog_file ( filename )
 character(len=*), intent(in) :: filename
 logical :: open_topog_file
 real    :: r_ipts, r_jpts
 integer :: namelen

 namelen = len(trim(filename))
  if ( file_exist(filename) .AND. filename(namelen-2:namelen) == '.nc') then
     if (mpp_pe() == mpp_root_pe()) call mpp_error ('topography_mod', &
            'Reading NetCDF formatted input data file: '//filename, NOTE)
     call read_data(filename, 'ipts', r_ipts, no_domain=.true.)
     call read_data(filename, 'jpts', r_jpts, no_domain=.true.)
     ipts = nint(r_ipts)
     jpts = nint(r_jpts)
     open_topog_file = .true.
  else
     if ( file_exist(filename) ) then
        if (mpp_pe() == mpp_root_pe()) call mpp_error ('topography_mod', &
             'Reading native formatted input data file: '//filename, NOTE)
        unit = open_ieee32_file (trim(filename), 'read')
        read (unit) ipts, jpts
        open_topog_file = .true.
     else
        open_topog_file = .false.
     endif
  endif

 end function open_topog_file

!#######################################################################

 subroutine interp_topog_1d ( blon, blat, zout, flag )
 real   , intent(in)  :: blon(:), blat(:)
 real   , intent(out) :: zout(:,:)
 integer, intent(in), optional :: flag

 real :: xdat(ipts+1), ydat(jpts+1)
 real :: zdat(ipts,jpts)
 real :: zout2(size(zout,1),size(zout,2))

    call input_data ( topog_file, xdat, ydat, zdat )

    call horiz_interp ( zdat, xdat, ydat, blon, blat, zout )

! compute standard deviation if necessary
    if (present(flag)) then
       if (flag == COMPUTE_STDEV) then
           zdat = zdat*zdat
           call horiz_interp ( zdat, xdat, ydat, blon, blat, zout2 )
           zout = zout2 - zout*zout
           where (zout > 0.0)
             zout = sqrt ( zout )
           elsewhere
             zout = 0.0
           endwhere
       endif
    endif

 end subroutine interp_topog_1d

!#######################################################################

 subroutine interp_topog_2d ( blon, blat, zout, flag )
 real   , intent(in)  :: blon(:,:), blat(:,:)
 real   , intent(out) :: zout(:,:)
 integer, intent(in), optional :: flag

 real :: xdat(ipts+1), ydat(jpts+1)
 real :: zdat(ipts,jpts)
 real :: zout2(size(zout,1),size(zout,2))
 integer :: js, je
 type (horiz_interp_type) :: Interp

    call input_data ( topog_file, xdat, ydat, zdat )
    call find_indices ( minval(blat), maxval(blat), ydat, js, je )

    call horiz_interp_new ( Interp, xdat, ydat(js:je+1), blon, blat )
    call horiz_interp     ( Interp, zdat(:,js:je), zout )

! compute standard deviation if necessary
    if (present(flag)) then
       if (flag == COMPUTE_STDEV) then
           zdat = zdat*zdat
           call horiz_interp ( Interp, zdat(:,js:je), zout2 )
           zout = zout2 - zout*zout
           where (zout > 0.0)
             zout = sqrt ( zout )
           elsewhere
             zout = 0.0
           endwhere
       endif
    endif

    call horiz_interp_del ( Interp )

 end subroutine interp_topog_2d

!#######################################################################

 subroutine find_indices ( ybeg, yend, ydat, js, je )
 real,    intent(in)  :: ybeg, yend, ydat(:)
 integer, intent(out) :: js, je
 integer :: j

   js = 1
   do j = 1, size(ydat(:))-1
      if (ybeg >= ydat(j) .and. ybeg <= ydat(j+1)) then
         js = j
         exit
      endif
   enddo

   je = size(ydat(:))-1
   do j = js, size(ydat(:))-1
      if (yend >= ydat(j) .and. yend <= ydat(j+1)) then
         je = j
         exit
      endif
   enddo

   !print '(a,i2,2(a,f10.5),2(a,i4))', "PE=",mpp_pe(),"  phs=",ybeg,"  phn=",yend,"  js=",js,"  je=",je

 end subroutine find_indices

!#######################################################################

 subroutine input_data ( ifile, xdat, ydat, zdat )
 character(len=*), intent(in) :: ifile
 real, intent(out) :: xdat(ipts+1), ydat(jpts+1), zdat(ipts,jpts)
 integer :: nc

   nc = len_trim(ifile)

! note: ipts,jpts,unit are global

  if ( file_exist(trim(ifile)) .AND. ifile(nc-2:nc) == '.nc') then
     call read_data(trim(ifile), 'xdat', xdat, no_domain=.true.)
     call read_data(trim(ifile), 'ydat', ydat, no_domain=.true.)
     call read_data(trim(ifile), 'zdat', zdat, no_domain=.true.)
  else
    read (unit) xdat, ydat    ! read lon/lat edges in radians
    read (unit) zdat          ! read land surface height in meters
    call close_file (unit)
 endif

 end subroutine input_data

!#######################################################################

 subroutine interp_water_1d ( blon, blat, zout, do_ocean )
 real   , intent(in)  :: blon(:), blat(:)
 real   , intent(out) :: zout(:,:)
 logical, intent(in), optional :: do_ocean

 real :: xdat(ipts+1), ydat(jpts+1), zdat(ipts,jpts)

    call input_data ( water_file, xdat, ydat, zdat )

! only use designated ocean points
    if (present(do_ocean)) then
        if (do_ocean) call determine_ocean_points (zdat)
    endif

! interpolate onto output grid
    call horiz_interp ( zdat, xdat, ydat, blon, blat, zout )

 end subroutine interp_water_1d

!#######################################################################

 subroutine interp_water_2d ( blon, blat, zout, do_ocean )
 real   , intent(in)  :: blon(:,:), blat(:,:)
 real   , intent(out) :: zout(:,:)
 logical, intent(in), optional :: do_ocean

 real :: xdat(ipts+1), ydat(jpts+1), zdat(ipts,jpts)

    call input_data ( water_file, xdat, ydat, zdat )

! only use designated ocean points
    if (present(do_ocean)) then
        if (do_ocean) call determine_ocean_points (zdat)
    endif

! interpolate onto output grid
    call horiz_interp ( zdat, xdat, ydat, blon, blat, zout )

 end subroutine interp_water_2d

!#######################################################################

 subroutine determine_ocean_points ( pctwater )
 real, intent(inout) :: pctwater(:,:)
 logical :: ocean(size(pctwater,1),size(pctwater,2))
 integer :: i, j, m, n, im, ip, jm, jp, new 

 real :: ocean_pct_crit = .500

  ! resolution of the grid
    m = size(pctwater,1)
    n = size(pctwater,2)

  ! the 1/6 degree navy percent water data set
  ! designates ocean grid boxes as 100 percent water
  ! all other grid boxes have <= 99 percent water

  ! set a mask for ocean grid boxes
    ocean = (pctwater > .999) 
    new = count(ocean)

  ! set land grid boxes that have sufficient amount of water
  ! to ocean grid boxes when they are adjacent to ocean points
  ! iterate until there are no new ocean points
    do 
    if (new == 0) exit 
    new = 0 

       do j = 1, n
       do i = 1, m
          if (.not.ocean(i,j) .and. pctwater(i,j) > ocean_pct_crit) then
             im = i-1; ip = i+1; jm = j-1; jp = j+1
             if (im == 0)   im = m  
             if (ip == m+1) ip = 1
             if (jm == 0)   jm = 1
             if (jp == n+1) jp = n
           ! check the 8 grid boxes that surround this grid box
             if (ocean(im,j ) .or. ocean(ip,j ) .or. ocean(i ,jm) .or. ocean(i ,jp) .or. &
                 ocean(im,jm) .or. ocean(ip,jm) .or. ocean(ip,jp) .or. ocean(im,jp)) then
                 ocean(i,j) = .true.
                 new = new + 1
             endif
          endif
       enddo
       enddo
      !print *, 'new=',new

    enddo

  ! final step is to elimate water percentage if land
    where (.not.ocean) pctwater = 0.

 end subroutine determine_ocean_points

!#######################################################################
! reads the namelist file, write namelist to log file, 
! and initializes constants

subroutine read_namelist

   integer :: unit, ierr, io

!  read namelist

#ifdef INTERNAL_FILE_NML
      read (input_nml_file, topography_nml, iostat=io)
      ierr = check_nml_error(io,'topography_nml')
#else
   if ( file_exist('input.nml')) then
      unit = open_namelist_file ( )
      ierr=1; do while (ierr /= 0)
         read  (unit, nml=topography_nml, iostat=io, end=10)
         ierr = check_nml_error(io,'topography_nml')
      enddo
 10   call close_file (unit)
   endif
#endif

!  write version and namelist to log file

   if (mpp_pe() == mpp_root_pe()) then
     unit = stdlog()
     write (unit, nml=topography_nml)
   endif

end subroutine read_namelist

!#######################################################################

end module topography_mod

! <INFO>

!   <TESTPROGRAM NAME="">  
!  
!  To run this program you will need the topography and percent water
!  data sets and use the following namelist (in file input.nml).
!  
!   &amp;gaussian_topog_nml
!     height = 5000., 3000., 3000., 3000.,
!     olon   =   90.,  255.,  285.,    0.,
!     olat   =   45.,   45.,  -15.,  -90.,
!     wlon   =   15.,   10.,    5.,  180.,
!     wlat   =   15.,   25.,   25.,   20., /
!  
!  program test
!  
!  ! test program for topography and gaussian_topog modules
!  <PRE>  
!  use topography_mod
!  implicit none
!  
!  integer, parameter :: nlon=24, nlat=18
!  real :: x(nlon), y(nlat), xb(nlon+1), yb(nlat+1), z(nlon,nlat)
!  real :: hpi, rtd
!  integer :: i,j
!  logical :: a
!  
!  ! gaussian mountain parameters
!  real, parameter :: ht=4000.
!  real, parameter :: x0=90., y0=45. ! origin in degrees
!  real, parameter :: xw=15., yw=15. ! half-width in degees
!  real, parameter :: xr=30., yr= 0. ! ridge-width in degrees
!  
!  ! create lat/lon grid in radians
!    hpi = acos(0.0)
!    rtd = 90./hpi ! rad to deg
!    do i=1,nlon
!      xb(i) = 4.*hpi*real(i-1)/real(nlon)
!    enddo
!      xb(nlon+1) = xb(1)+4.*hpi
!      yb(1) = -hpi
!    do j=2,nlat
!      yb(j) = yb(j-1) + 2.*hpi/real(nlat)
!    enddo
!      yb(nlat+1) = hpi
!  ! mid-point of grid boxes
!    x(1:nlon) = 0.5*(xb(1:nlon)+xb(2:nlon+1))
!    y(1:nlat) = 0.5*(yb(1:nlat)+yb(2:nlat+1))
!  ! test topography_mod routines
!    a = get_topog_mean(xb,yb,z)
!    call printz ('get_topog_mean')
!  
!    a = get_water_frac(xb,yb,z)
!    z = z*100. ! in percent
!    call printz ('get_water_frac')
!  
!    a = get_ocean_frac(xb,yb,z)
!    z = z*100. ! in percent
!    call printz ('get_ocean_frac')
!  
!  ! test gaussian_topog_mod routines
!    a = .true.
!    z = get_gaussian_topog(x,y,ht,x0,y0,xw,yw,xr,yr)
!    call printz ('get_gaussian_topog')
!  
!    call gaussian_topog_init (x,y,z)
!    call printz ('gaussian_topog_init')
!  
!  contains
!  
!  ! simple printout of topog/water array
!    subroutine printz (lab)
!    character(len=*), intent(in) :: lab
!     if (a) then
!        print '(/a)', trim(lab)
!     else
!        print '(/a)', 'no data available: '//trim(lab)
!        return
!     endif
!      ! print full grid
!        print '(3x,25i5)', (nint(x(i)*rtd),i=1,nlon)
!      do j=nlat,1,-1
!        print '(i3,25i5)', nint(y(j)*rtd), (nint(z(i,j)),i=1,nlon)
!      enddo
!    end subroutine printz
!  
!  end program test
!   </PRE>
!   </TESTPROGRAM>

!   <BUG>                  
!      Water mask produces some possible erroneous water points along
!      the coast of Antarctic (at about 90W).
!   </BUG>

!   <FUTURE>Use of netcdf data sets. </FUTURE>
!   <FUTURE>Incorporate other topography and ocean data sets. </FUTURE>
! 
! </INFO>