Ice Cloud Bulk Scattering Models for the GOES-R Advanced Baseline Imager (ABI)

The GOES-R notional baseline includes an Advanced Baseline Imager (ABI), a Hyperspectral Environmental Suite (HES), a lightning mapper, and advanced space and solar observing instruments. The ABI is a state of the art, 16-channel imager covering 6 visible to near-IR bands (0.47, 0.64, 0.86, 1.38, 1.61, and 2.26 microns), and 10 infrared (IR) bands (3.90 to 13.3 microns). Spatial resolutions are band dependent: 0.5 km at nadir for broadband visible, 1.0 km for near IR and 2.0 km for IR. The ABI will scan the Full Disk (FD) in approximately 5 minutes.

Characteristics of the imager's spectral response functions were used to derive these ice bulk scattering files. The spectral response functions are named for a "Gaussian Boxcar Hybrid" function. They are created using code from Mike Griffin at MIT Lincoln Labs. The curve is gaussian, forced to go through the 50% points (lower and upper wavelengths) and the top of the curve is flattened out like a boxcar function, hence the name. The notation 'v1' stands for version 1 (note that the current version of that algorithm on February 18, 2004 is the same as that of October 15, 2003). Channel numbers are not officially stated in the PoRD, but CIMSS has assumed a numbering convention for ease of use in software - the bands are numbered by increasing central wavelength (same convention has used on the current GOES series of imagers, but opposite as the current sounder). The SRFs are available by ftp at this site.

These 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 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 scatter albedo, asymmetry factor, fraction of delta transmitted energy, extinction efficiency, and the scattering phase function.

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

ABI Narrowband Models:

A tar file has been prepared for each of the ABI bands noted below. Each tar file contains a set of 18 models, with effective diameters (De) spanning a range from 10 to 180 microns in increments of 10 microns.

Naming convention of individual files: The channel (or band) number and effective diameter is in the file name. For example, a file named ABI_mix1_ch05_d080.dat means this: habit mixture 1 as described above, ABI channel 5 (1.61 micron wavelength), and a De of 80 microns.

Note: Channels 7, 11, 14, and 15 have been updated as of April 10, 2006. These new models incorporate a significant update in scattering libraries detailed in Yang et al. (2005), with the full reference below. These new models tend to have a higher asymmetry factor and a lower single scattering albedo than the previous models. There is no delta transmission energy in these new models, as this is primarily only important at shorter wavelengths.

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