Ice Cloud Property Retrievals Using Far Infrared Upwelling Radiance Spectra
Abstract
Spectral measurements of the upwelling radiance in the mid-infrared (MIR, 8 - 12 μm wavelength) have proven sensitivity to microphysical and macrophysical parameters of ice clouds. This sensitivity is caused by the spectrally varying index of refraction, as well as the ice crystal shape and particle size parameter. Many methods have been demonstrated that utilize this sensitivity to retrieve bulk ice cloud microphysical properties such as effective ice particle size, and macrophysical properties such as optical depth and height. By extending the spectral observations into the far-infrared (FIR, 17 - 50 μm wavelength), additional information can be retrieved due to the different sensitivities exhibited by cloud ice at these longer wavelengths. Typically, in the far-infrared, ice exhibits stronger scattering across all particle sizes, due to a smaller complex index of refraction, and weaker forward scattering due to the smaller size parameter. In this research, a modeling framework is used to quantify the information content of the FIR spectrum for ice cloud property retrieval. The information content is quantitatively compared to the MIR, to show how ice cloud retrievals could be improved with FIR spectral measurements. For cases where the MIR spectrum contains a high amount of information (e.g., moderate optical depths with small particle size), the FIR spectrum adds only a marginal amount of information. In other cases where the MIR spectrum contains low information (e.g., high optical depth clouds), the FIR spectrum is shown to add significant information. The FIR spectrum can thus be shown to extend the region in state space where passive infrared measurements can effectively constrain ice cloud properties.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.A33J0286M
- Keywords:
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- 0360 ATMOSPHERIC COMPOSITION AND STRUCTURE / Radiation: transmission and scattering;
- 3311 ATMOSPHERIC PROCESSES / Clouds and aerosols;
- 3360 ATMOSPHERIC PROCESSES / Remote sensing