Ice Cloud Bulk Scattering Models in the Visible (VIS) to Shortwave Infrared (SWIR) Spectral Region

The models provided through this web page are intended for use in the retrieval of ice cloud properties in the visible (VIS) to shortwave infrared (SWIR) spectral region. The models are provided over the spectral range from 0.4 to 2.2 microns at 0.01 micron resolution. While there are a few spectral gaps, bulk scattering models are available for 144 wavelengths. The difference between this set of models and those provided for specific imagers such as MODIS is that these models are provided at specific wavelengths, whereas those for the imagers have been integrated over each imager channel's spectral response function.

A listing is provided here of the available wavelengths as well as the index of refraction for ice (both real and imaginary indices) used in the ice particle scattering calculations. The bulk scattering models provide bulk microphysical and optical properties such as ice water content (IWC), median mass diameter, extinction efficiency, asymmetry factor, and single scattering albedo.

The bulk scattering models are the result of a multiyear team effort to derive new ice cloud scattering models based on reanalysis of in-situ data from a variety of midlatitude and tropical ice cloud field experiments. Here are a few details about the models:

  1. Size distributions are based on 45 size bins (particle size ranges from 2 to 9500 microns).
  2. Ice particle habit distributions vary as a function of maximum dimension.
  3. New ice crystal scattering property libraries have been calculated for a variety of habits, including droxtals, plates, hollow and solid columns, 3-D bullet rosettes, and aggregates.
  4. Each model contains the mean and standard deviation of each microphysical and optical property, including ice water content, mean mass diameter, single scattering albedo, asymmetry factor, extinction efficiency, and the scattering phase function in selected wavenumber regions.

In situ Microphysical Ice Cloud Data

More complete descriptions of the in situ data are provided in the following links.

Description of the field experiments and data sources

Particle size distributions

Ice crystal habit "recipe" implemented for these models

The percentage of each habit used in the integration of a given property over a particle size distribution is based on the particle's maximum dimension.

D < 60 microns:
100% droxtals

60 microns < D < 1000 microns:
15% 3D bullet rosettes
50% solid columns
35% plates

1000 microns < D < 2500 microns:
45% hollow columns
45% solid columns
10% aggregates

2500 microns < D < 9500 microns
97% 3D bullet rosettes
3% aggregates

VIS-SWIR Spectral Models:

A set of 18 text files have been prepared, each one specific to a given effective diameter (De). The De span a range from 10 to 180 microns in increments of 10 microns. Each file contains entries for each of the 144 wavelengths for which properties are available. The habit mixture as described above is used for all calculations of microphysical and optical properties.

Each of these files contains the following properties.

Microphysical properties provided once per file as they are not wavelength dependent:

  • De
  • Ice Water Content (IWC)
  • Total ice particle projected area
  • Total ice particle volume
  • Median mass diameter

Mean and standard deviation of optical properties for each wavelength.

  • Asymmetry factor (g)
  • Single scattering albedo (omega)
  • Extinction efficiency (Qe)
  • Scattering cross section (sig_scat)
  • Extinction cross section (sig_ext)

Note: the files provided above do NOT contain scattering phase functions (both means and standard deviations). The scattering phase files are provided in a tar file through the link below; a file is available for each individual wavelength within the tar file.

Scattering Phase Functions- tar file

Note: Format of scattering phase function files:

Within each of the (ascii) files, the first line is wavelength; the 2nd line provides column titles. Beginning with the 3rd line, you have the following:

1st column: scattering angle (from 0 to 180 degrees with 498 angles)
2nd column: mean value of scattering phase function at De = 10 microns
3rd column: standard deviation of phase function at De = 10 microns
4th column: mean value of scattering phase function at De = 20 microns
5th column: standard deviation of phase function at De = 20 microns
and so forth for the rest of the De values up to 180 microns

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