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Hyperspectral/Multispectral Ice Cloud Microphysical and Optical Models. Bryan A. Baum 1 Ping Yang 2 , Andrew Heymsfield 3 1 NASA Langley Research Center, Hampton, VA 2 Texas A&M University, College Station, TX

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Hyperspectral/Multispectral Ice Cloud Microphysical and Optical Models

Bryan A.Baum1

Ping Yang2, Andrew Heymsfield3

1 NASA Langley Research Center, Hampton, VA

2 Texas A&M University, College Station, TX

3 National Center for Atmospheric Research, Boulder, CO

Goal: Provide ice cloud bulk scattering models that are developed consistently for suite of multispectral and hyperspectral instruments

5th Workshop on Hyperspectral Science

June 7-9, 2005


Bulk Scattering Models

Operational satellite-based cloud retrievals require the ability to simulate realistic ice cloud radiances quickly

Simulations require bulk scattering parameters such as

single-scattering albedo

scattering phase function or asymmetry factor

extinction efficiency or scattering/absorption cross sections

Scattering parameters in turn are based on the

cloud phase (ice, water, or mixed)

particle size distribution

particle habit distribution


Have libraries of scattering properties from Ping Yang & colleagues


Library of SWIR to Far-IR Scattering Properties

100 to 3250 cm-1

Library of ice particle scattering properties include

Hexagonal plates

Solid and hollow columns



3D bullet rosettes

45 size bins ranging from 2 to 9500 m

Spectral range: 100 to 3250 cm-1 at 1-cm-1 resolution

Properties for each habit/size bin include volume, projected area,

maximum dimension, single-scattering albedo, asymmetry factor,

and extinction efficiency

* Yang, P., H. Wei, H. L Huang, B. A. Baum, Y. X. Hu, M. I. Mishchenko, and Q. Fu, Scattering and absorption property database of various nonspherical ice particles in the infrared and far-infrared spectral region. In press, Applied Optics.


Particle Size Distributions

Gamma size distribution* has the form:

N(D) = NoDe-D

whereD = max diameter

No = intercept

 = dispersion

 = slope

The intercept, slope, and dispersion values are derived for each PSD by matching three moments (specifically, the 1st, 2nd, and 6th moments)

Note: when  = 0, the PSD reduces to an exponential distribution

*Heymsfield et al., Observations and parameterizations of particle size distributions in deep tropical cirrus and stratiform precipitating clouds: Results from in situ observations in TRMM field campaigns. J. Atmos. Sci., 59, 3457-3491, 2002.


Field Campaign Information

Probe size ranges are: 2D-C, 40-1000 m; 2D-P, 200-6400 m; HVPS (High Volume Precipitation Spectrometer), 200–6100 m; CPI (Cloud Particle Imager), 20-2000 m; Replicator, 10-800 m; VIPS (Video Ice Particle Sampler): 20-200 m.


Particle Size Distributions

From Gamma Fits

  • Midlatitude cirrus characteristics
  • Size sorting more pronounced
  • Small crystals at cloud top
  • More often find pristine particles
  • Tropical cirrus anvil characteristics
  • Form in an environment having much higher vertical velocities
  • Size sorting is not as well pronounced
  • Large crystals often present at cloud top
  • Crystals may approach cm in size.
  • Habits tend to be more complex
  • Note that CRYSTAL distributions tend to be the narrowest overall

Ice Particle Habit Distribution

At this point, we have

- ice particle scattering library

- wealth of microphysical data for ice clouds (1117 PSDs)

Next issue: develop a ice particle habit distribution that makes sense

Note: each idealized ice particle has a prescribed volume, and hence mass

Compare IWC and Dm computed from integrating over the habit and size distributions to those values estimated from techniques developed by Heymsfield and colleagues from analyses of their in situ data


Ice Particle Habit Percentages Based on Comparison of Calculated to In-situ Dm and IWC


4 size domains defined by particle maximum length

Droxtals: used only for smallest particles

Aggregates: only for particles > 1000 m

Plates: used only for particles of intermediate size

Proposed ice particle

habit mixture

Max length < 60 m

100% droxtals

60 mm < Max length < 1000 m

15% bullet rosettes

35% hexagonal plates

50% solid columns

1000 mm < Max length < 2500 m

45% solid columns

45% hollow columns

10% aggregates

Max length > 2500 m

97% bullet rosettes

3% aggregates


Small Particle Sensitivity Study

Note that CRYSTAL distributions tend to be the narrowest overall

For all 41 CRYSTAL size distributions, increase the number of particles with Dmax < 20 m by a factor of 100 or 1000


Development of Discrete Set of Models

For building look-up tables for operational retrievals, want discrete set of models that are evenly spaced in effective diameter


Bulk Scattering Models

Available for Multiple Instruments

Provide bulk properties (mean and std. dev.) evenly spaced in Deff from 10 to 180 m for

asymmetry factor phase function

single-scattering albedo extinction efficiency& cross sections


Models available at for

IR Spectral Models (100 to 3250 cm-1)


VIRS MAS (MODIS Airborne Simulator)

ABI (Advanced Baseline Imager) POLDER (Polarization)

SEVIRI (Spinning Enhanced Visible InfraRed Imager)