Define how liquid water content and effective droplet radius are translated
to optical properties.
wc_properties type
Possible choices for type are
- hu
-
Parameterization by Hu and Stamnes (1993);
this is the default setting. Note that
the parameterization is somewhat different for correlated_k FU than for all other
cases because in the latter case the parameterization from the newer (March 2000)
Fu and Liou code is used while otherwise the data are taken from the original
paper by Hu and Stamnes (1993). Note that this parameterization has been
developed to calculate irradiances, hence it is less suitable for radiances.
This is due to the use of the Henyey-Greenstein phase function as an approximation
of the real Mie phase function.
- echam4
-
Use the very simple two-band parameterization of the ECHAM4 climate model, described
in Roeckner et al. (1996); this is probably only meaningful if you want to compare
your results with ECHAM4, the two bands are 0.2 - 0.68 micrometer and 0.68 - 4.0 micrometer;
within these bands, the optical properties are assumed constant.
- mie
-
Use pre-calculated Mie tables; useful for correlated_k;
the tables are expected in data_files_path/correlated_k/../.For spectral or pseudo-spectral (correlated_k sbdart) calculations,
a set of pre-calculated tables is also available; the wavelength grid points of these
data has been carefully selected such that the extinction cross section,
single scattering albedo, and the asymmetry parameter are accurate to 1%
(compared to the fully-resolved Mie calculation) for all wavelengths
between 250nm and 100 micrometer. For spectral or pseudo-spectral
calculations wc_properties_interpolate has to be defined explicitely to
initiate the interpolation of the optical properties to the internal wavelength grid.
Please note that this option may be extremely memory-consuming because for each
internal wavelength a full set of Legendre moments of the phase function is
stored (up to several thousands). The Mie tables are not part of the standard distribution
(because of their large size) but they are freely available from http://www.libradtran.org.
This is the correct option to calculate radiances, to be preferred over the
Henyey-Greenstein approach of Hu and Stamnes (1993).
- filename
-
Read optical properties from specified filename; file format is as produced
by the mie-tool of the libRadtran package(see output_user cloudprp)
or by Frank Evans' cloudprp; for each of the internal (computational) wavelengths,
a separate file is expected. Use only if you really know what you are doing
(this option is subject to change).
Arve Kylling
2010-03-10