RFM Driver Table Sections

*SFC Section: Surface Parameters

24JUL17

Type
Secondary Section - activated by SFC Flag.

Description
Surface temperature and (optionally) emissivity.

Format
Up to 3 fields, identified by order.
Field#1 ('REL') is optional
Field#2 (TEMSFC) is mandatory
Field#3 (EMSSFC or FILSFC) is optional (assume emissivity = 1 if not specified)
FieldTypeDescription Range
1. 'REL' C*3 (optional) Flag for relative temperature Case insensitive [available from RFM v4.33 onwards]
2. TEMSFC R*4 Surface Temperature [K] >0 unless Field#1='REL'
3. EMSSFC R*4 (optional) Surface Emissivity [dimensionless] 0:1
or FILSFC C*80 Name of .sfc file containing EMSSFC values NB: Format changed with RFM v4.35
RFM v5: in addition to the above, the following PARAM=VALUE fields can be used (no space either side of '='), all optional, arbitrary order
ParamValueDescriptionRange
TEMSFC R*4 Surface temperature [K] ≥ 0
TEMREL R*4 Surface relative temperature [K]
EMSSFC R*8 Surface emissivity [dimensionless] 0:1
or C*193 File of spectral surface emissivity values 0:1
HGTSFC R*4 Surface altitude [km] Within *HGT internal profile
PRESFC R*4 Surface pressure [mb] Within *PRE internal profile

Notes
  1. The surface is considered to lie just below the lowest altitude specified in the first height profile loaded in the *ATM section, i.e. not necessarily at 0 km (0 km is the altitude surface for which the radius of curvature applies).
  2. (RFM v4.33 onwards) The *SFC section itself is optional, if it is not included in the Driver Table then default values are used
    • TEMSFC = Temperature of lowest atmospheric level
    • EMSSFC = 1.0
  3. 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.
  4. (RFM v4.33 onwards) If the first field is the character string REL (mixed case) the following temperature is interpreted as relative to the lowest atmospheric profile temperature, otherwise it is absolute temperature.
  5. A warning message is issued if the surface temperature differs TEMSFC from the lower boundary atmospheric profile temperature by more than TEMDEL=10 K (set in module inpsfc.for) since this is an unphysically large temperature discontinuity.
  6. 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
  7. For EMSSFC <1, for flux calculations (FLX Flag) the reflection is treated as diffuse but for other calculations it is treated as specular so that the observer-surface path is mirrored by the surface-space path beyond the reflection point.
  8. FILSFC (RFM v4.35 onwards) 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 (see .sfc file format for use with earlier versions of the RFM).
  9. 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.
  10. RFM v5, while supporting the original format, also allows surface parameters to be specified as a rather more straightforward set of PARAM=VALUE pairs. It is recommended that these be used.
  11. RFM v5: also allows two additional parameters, PRESFC or HGTSFC, which allow the surface to be specified at some level other than the lowest level of the input atmosphere.

Examples
*SFC
      250 0.999 ! T_sfc = 250 K, reflectivity=0.001
*SFC
   REL 10.0 data.sfc   ! 10K above atm.temp, external emissivity spectrum
*SFC
   REL 0.0 1.0  ! Equivalent default values if no *SFC section present
RFM v5: example
*SFC
   TEMREL=0.0
   EMSSFC=1.0  ! Equivalent default values if no *SFC section present
   HGTSFC=2.0  ! Set surface at 2km altitude
Example of a regularly gridded emissivity data file (eg data.sfc from above). Note that these examples apply to RFM v4.35 onwards, older versions of the RFM used the .sfc format.
! 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#25 (Fixed v4.12)
Bug#10 (Fixed v4.10)
Bug#6 (Fixed v4.04)
Bug#1 (Fixed v4.01)