@BeginModule
@NewPage
@Name      = Intvert
@Title     = Vertical interpolation
@Section   = Interpolation
@Class     = Interpolation
@Arguments = ifile ofile
@Operators = ml2pl ml2hl

@BeginDescription
Interpolate 3D variables on hybrid model levels to pressure or height levels.
The input file should contain the log. surface pressure or the surface pressure.
To interpolate the temperature, the orography (surface geopotential) is also needed.
The pressure, temperature, and orography are identified by their code numbers.
Supported parameter tables are: WMO standard table number 2 and ECMWF local table number 128.
Use the alias  @bold{ml2plx}/@bold{ml2hlx} or the environment variable @env{EXTRAPOLATE}
to extrapolate missing values. All input fields have to be on the same horizontal grid.
@EndDescription
@EndModule


@BeginOperator_ml2pl
@Title     = Model to pressure level interpolation
@Parameter = plevels

@BeginDescription
Interpolates 3D variables on hybrid model levels to pressure levels.
@EndDescription
@EndOperator


@BeginOperator_ml2hl
@Title     = Model to height level interpolation
@Parameter = hlevels

@BeginDescription
Interpolates 3D variables on hybrid model levels to height levels.
The procedure is the same as for the operator @oper{mh2pl} except for
the pressure levels being calculated from the heights by:
@math{plevel = 101325*exp(hlevel/-7000)}
@EndDescription
@EndOperator


@BeginParameter
@Item = plevels
FLOAT  Pressure levels in pascal
@Item = hlevels
FLOAT  Height levels in meter (max level: 65535 m)
@EndParameter


@BeginEnvironment
@Item = EXTRAPOLATE
If set to 1 extrapolate missing values.
@EndEnvironment


@BeginNote
The netCDF CF convention for vertical hybrid coordinates is 
not supported, yet!
@EndNote


@BeginExample
To interpolate hybrid model level data to pressure levels of
925, 850, 500 and 200 hPa use:
@BeginVerbatim
   cdo ml2pl,92500,85000,50000,20000 ifile ofile
@EndVerbatim
@EndExample
