RFM Driver Table Sections

*SFC Section

26MAY22

Type
Secondary Section — activated by SFC Flag.

Description
Specify surface characteristics: temperature, emissivity, height/pressure

Format
Multiple records, any order, each containing a PARAM=VALUE pair. PARAM is case insensitive.
ParamValueDescriptionRange Default
TEMSFC R Surface temperature [K] ≥ 0 Temperature at base of atmosphere
or
TEMREL R Surface relative temperature [K] [n/a] 0
EMSSFC D Surface emissivity [dimensionless] 0:1 1
or C193 File of spectral surface emissivity values 0:1
HGTSFC R Surface altitude [km] Within *HGT profile Height of base of atmosphere
or
PRESFC R Surface pressure [mb] Within *PRE profile Pressure of base of atmosphere
RFLSFC C Surface reflectivity model RFM v5.10 onwards SPECULAR or DIFFUSE (case insensitive) SPECULAR
Type: I=Integer; R=Real; D=Double Precision; Cn=character string, length n.

Notes
  1. Since all surface parameters have default values it is possible to have the SFC flag enabled without any *SFC section. However the SFC Flag remains mandatory if any ray-paths intersect the surface (in case the user was unaware that the surface is being encountered), which is always the case for nadir viewing in a plane-parellel atmosphere (NAD, FLX flags), and may be the case for 'limb-viewing' (ie curved atmosphere) rays which intersect the lower boundary of the specified height profile (including any rays required for FOV convolution). If in doubt, add the SFC flag anyway.
  2. Surface temperature can either be specified to have an absolute value TEMSFC, or a value TEMREL relative to the temperature at the base of the atmosphere. A warning message is issued if the surface temperature differs TEMSFC from the lower boundary atmospheric profile temperature by more than 10 K (set in module drvsfc_sub.f90)
  3. Unless moved (upwards) by the HGTSFC or PRESFC parameters, the surface is considered to lie at the the lowest altitude/highest pressure specified in the first profile loaded in the *ATM section, i.e. not necessarily at 0 km. (The absolute altitude is only significant for circular geometries when it is combined with the radius of curvature)
  4. Either the HGTSFC or PRESFC parameters (but not both) can be used to adjust the surface level, in which case an extra profile level is inserted at the new values (although any original levels below the new surface are retained, e.g. in the PRF output). The default surface temperature, or value specified with TEMREL, are also adjusted appropriately
  5. For versions prior to RFM v5.10: With the NAD option, a surface emissivity of 1.0 (i.e. a perfect Black Body) is treated differently to values <1.0:
    • EMSSFC=1: .tra, .abs, .opt all refer just to the downward atmospheric path without including the surface (otherwise these spectra would be completely flat)
    • EMSSFC<1: spectra refer to complete downward + upward path including surface reflection
    RFM v5.10: always just refer to the downward path, independent of surface emissivity
  6. For flux calculations (FLX Flag) any surface reflection is always treated as diffuse (Lambertian). For other calculations, prior to RFM v5.10, surface reflections were always treated as specular (i.e., mirror-like). RFM v5.10 onwards: the default is specular (set in sfccom_dat.f90) but the RFLSFC parameter can be used to change this to diffuse.
  7. FILSFC Spectrally varying surface emissivity values can be supplied using a standard RFM Spectral file (regularly or irregularly spaced) - see Example below. Linear interpolation is assumed between the tabulated values, and the emissivity outside the tabulated range is assumed to be constant at the edge value of the table (i.e., not extrapolated). A file containing a single emissivity value (labelled with any spectral wavenumber) is equivalent to specifying the EMSSFC value directly in the driver table
  8. To test whether EMSSFC/FILSFC is a value or a filename, the RFM first attempts to open it as a file. If this fails, a value is assumed. Consequently any fatal error message arising from an incorrect filename/path could be misleading.

Examples
*SFC
   TEMREL=0.0  ! Equivalent to default value
   EMSSFC=data.sfc  
   HGTSFC=2.0  ! Set surface at 2km altitude
Example of a regularly gridded emissivity data file (eg data.sfc from above) in RFM Spectral File Format for regularly gridded data
! Surface emissivity spectrum
!N.Pts  WNO1  WNOD  WNO2
     5    800.0 50.0 1000.0
0.995 0.996 0.995 0.994 0.993
[eof]
The same data could be represented as an 'irregularly' gridded file
! Surface emissivity spectrum
!N.Pts  WNO1  WNOD  WNO2
     5    800.0 0.0 1000.0
800.0  0.995
850.0  0.996
900.0  0.995
950.0  0.994
1000.0 0.993
[eof]

Bugs
Bug#28 (Fixed v5.11)