Authors: Adrian Turner, Mat Maltrud

Tools for smoothing bathymetry in an MPAS-Ocean with a Gaussian filter with a
characteristic length scale (stdDeviation) and cut-off distance
(distanceLimit). Smoothing is applied over a given number of iterations
(numSmoothingPasses). The tools do not currently work on meshes without
ice-shelf cavities.

The smooth_topo_skip_land_ice tool can be applied to topography after an
initial condition has been created.  The smoothing is only applied if the
original maxLevelCell is deeper than a given threshold (minLevelForSmoothing)
and ice-shelf cavities are ignored.

The smooth_topo_before_init tool is used to smooth topography data on the MPAS
mesh before an initial condition has been created.

An example namelist file (smooth_depth_in) is:

&smooth
    filename_depth_in  = "mpaso.IcoswISC30E3r2.20230901.nc"
    filename_depth_out = "smooth.IcoswISC30E3r2.r200e100.1pass.min5.skipLandIce.231115.nc"
    filename_mpas_mesh   = "mpaso.IcoswISC30E3r2.20230901.nc"
    distanceLimit    = 200.
    stdDeviation     = 100.
    numSmoothingPasses = 1
    minLevelForSmoothing = 5
/

The minLevelForSmoothing namelist option only applies to
smooth_topo_skip_land_ice.
