PLEASE NOTE: This program is no longer active and has been archived in SSEC Research History as of 6/5/18: More info

Version 3: Models for Polar and Geostationary Imagers

Ice cloud bulk single-scattering property models are now available for 35 imagers (just added 4 more on April 30, 2012) from both polar-orbiting and geostationary platforms. This set of models is based on a general habit mixture (GHM) involving a set of 9 habits: solid/hollow bullet rosettes, solid/hollow columns, plates, droxtals, small/large aggregate of plates, and an aggregate of solid columns. The models are based on the assumption of severely roughened particles.

We are providing these models so that ice cloud properties can be obtained more consistently from various imagers, which should in turn help scientists assess products during sensor comparison least the ice cloud products can be based on ice models built consistently from sensor to sensor.

The files are in NetCDF format, with a single file per imager. The properties are developed first for a set of discrete wavelengths (i.e., spectral models); subsequently the imager band-averaged single-scattering properties are obtained through integration over each imager's spectral response functions (SRF), also called radiance spectral response (RSR) functions.

Properties are provided for each imager band as a function of imager channel and effective diameter, and includes the asymmetry parameter, single-scattering albedo, scattering phase function at 498 angles (also provided), the average ice water content inferred from idealized habits and the microphysical data used to generate the models (provided for general information), and the extinction coefficient (β) divided by the IWC. The person who asked me to include this parameter has since retired, but perhaps someone else will find it useful. To help me keep organized, an average wavenumber is provided for each channel - this may be slightly different from the central wavenumber you may be used to stating, but is simply derived from taking an average of the wavelengths for each of the spectral models employed in the development of the band averaged models.

Because the particle scattering properties are based on severe surface roughening, the phase functions will be much smoother (e.g., no haloes) and the asymmetry parameters will be lower in the shortwave region than those based on smooth-faceted particles. We anticipate that if shortwave channels are used to infer optical thickness and effective radius/diameter, the optical thicknesses based on these roughened particles will be lower and the effective radius/diameter will be larger than if smooth particles are assumed.

This list can be expanded to other sensors by request, but it may take a bit of time. For me to build additional models, you will need to provide me with the response functions for each band. Thanks to Richard Siddans (Rutherford Appleton Lab), we now have the response functions for ATSR-1/2 and AATSR, enabling me to build models for these sensors. MISR is now included too.

The AVHRR imagers on NOAA 4-8 and NOAA 10 have 4 channels, while those on NOAA 9 and NOAA 11-14 have 5 channels; the AVHRR imagers on NOAA 15-19 and MetOp-A/B have 6 channels.

The imager models are combined in a tar file - for access to the compressed (gzip) tar file, click on the "Download Models" button at the top of the page. Note that there is a new system in place at SSEC and we now ask that you register before downloading data - all we ask for is your name and email address. Since there will be updates in the future, we hope that you will permit us to include you on an email list so that we can send a brief note with what has changed in each subsequent version. So when you register, there will be a box that asks you whether you want to be on this email list - it is voluntary on your part.

The version number of the models (currently at 3.5) and the creation date are in the NetCDF files. The tar file is about 10 MB and has the date of its creation in the filename so you can always find out if you have the current models. Note that if you pulled over this file before April 30, 2012, it will not have the most up-to-date listing.

Important note: The availability of these models does not in any way imply that they might be used operationally by one team or another. We also need to emphasize that the models and look-up tables employed for the eventual MODIS Collection 6 (C6) optical property products will be provided by Dr. Steven Platnick at NASA Goddard Space Flight Center. We anticipate that the models used for MODIS C6 will be different from those offered here.

Polar-orbiting imagers: AVHRR on MetOp-B AVHRR on MetOp-A AVHRR on NOAA-5 AVHRR on NOAA-6 AVHRR on NOAA-7 AVHRR on NOAA-8 AVHRR on NOAA-9 AVHRR on NOAA-10 AVHRR on NOAA-11 AVHRR on NOAA-12 AVHRR on NOAA-14 AVHRR on NOAA-15 AVHRR on NOAA-16 AVHRR on NOAA-17 AVHRR on NOAA-18 AVHRR on NOAA-19 MODIS on Terra platform MODIS on Aqua platform VIIRS imager on Suomi-NPP platform Imaging Infrared Radiometer on the CALIPSO platform

These 4 imagers were added on April 30, 2012: MISR on the EOS Terra platform AATSR (7 channels) ATSR-1 (4 channels) ATSR-2 (7 channels)

Geostationary imagers: METEO SG-1 METEO SG-2 future GOES-R Advanced Baseline Imager GOES-8 imager GOES-9 imager GOES-10 imager GOES-11 imager GOES-12 imager GOES-13 imager MTSAT-1 MTSAT-2

Documentation of the Models:

The microphysical data are documented in Heymsfield et al. (2013). The derivation of single scattering properties for individual ice habits from 0.2 to 100 µm is discussed in Yang et al. (2013). The derivation of ice cloud bulk optical property models from 0.2 to 100 µm is discussed in Baum et al. (2014), although an earlier paper (Baum et al. 2011) describes more limited progress on this topic.

Baum, B. A., P. Yang, A. J. Heymsfield, A. Bansemer, A. Merrelli, C. Schmitt, and C. Wang, 2014: Ice cloud bulk single-scattering property models with the full phase matrix at wavelengths from 0.2 to 100 µm. Submitted to J. Quant. Spectrosc. Radiant. Transfer, Special Issue ELS-XIV.

Heymsfield, A. J., C. Schmitt, and A. Bansemer, 2013: Ice cloud particle size distributions and pressure dependent terminal velocities from in situ observations at temperatures from 0˚ to -86˚C. J. Atmos. Sci., 70, 4123-4154.

Yang, P., L. Bi, B. A. Baum, K.-N. Liou, G. Kattawar, and M. Mishchenko, 2013: Spectrally consistent scattering, absorption, and polarization properties of atmospheric ice crystals at wavelengths from 0.2 µm to 100 µm. J. Atmos. Sci., 70, 330-347.

Baum, B. A., P. Yang, A. J. Heymsfield, C. Schmitt, Y. Xie, A. Bansemer, Y. X. Hu, and Z. Zhang, 2011: Improvements to shortwave bulk scattering and absorption models for the remote sensing of ice clouds. J. Appl. Meteor. Clim., 50, 1037-1056.

Note, however, that we are only providing models using a general habit mixture (GHM) at this time. Imager models based on only a single habit might be provided at some future point if funding and time permit.

Also, we will not be supplying additional models specifically for midlatitude or tropical clouds as discussed in Baum et al. (2011) - the general habit mixture seems to compare well with measured polarized reflectances from POLDER/PARASOL so we are limiting ourselves to this for now.

Note: if you have questions or find problems, please let me know (send email to Bryan Baum) so I can look into the issue. If there is a problem, I want to get it fixed.