Determination of ice crystal habits for application to the cirrus cloud remote sensing

The single scattering properties of ice crystals are fundamental in the radiative transfer simulations of the ice clouds, in assessing the radiative forcing of ice clouds, and in retrieval of the microphysical and optical properties of ice clouds from satellite sensors (Baum et al. 2011; Yang et al. 2013). Yang et al. (2005) developed a ice crystals scattering database for droxtals, plates, columns, hollow columns, 3D bullet rosettes, and compact aggregates of columns at 49 discrete wavelengths between 3 and 100 μm by using the scattering calculation models of the finite-difference time domain method (FDTD) and the improved geometric optics method (IGOM). Ice crystal habits were determined based on the ice partial samples by aircraft observations. Furthermore, Yang et al. (2013) published the scattering, absorption, and polarization properties of ice particles for 11 ice crystal habits with three surface roughness conditions in the spectral range from 0.2 to 100 μm. The aim of this study is to determine the effective ice crystal habits employed in retrieval of the ice cloud microphysical properties for Global Change Observation Mission (GCOM-C)/ Second generation GLobal Imager (SGLI) satellite mission. The GCOM-C satellite is scheduled to launch in around 2016 by the Japan Aerospace Exploration Agency (JAXA). The SGLI sensor is a successor of the Global Imager (GLI) aboard the ADEOS-II satellite. The GCOM-C satellite measures essential geophysical parameters on the Earth' s surface and in the atmosphere to facilitate understanding of the global radiation budget. There are 19 channels in SGLI, including two polarized channels. The instantaneous fields of view of the SGLI are 0.25, 0.5, and 1.0 km. First we developed a ice crystal scattering database with varied habits based on the specifications of the SGLI channels. The single scattering properties were calculated by a combination of three scattering computational models: FDTD (Ishimoto et al., 2012), Geometric-Optics-Integral-Equation (GOIE) (Ishimoto et al., 2012) and GOM (Mastuda et al., 2012). Based on the ice crystal habit used in MODIS collection 5 product and aircraft observations samples, 5 ice crystal habits (Plate, Colum, Voronoi, Droxtal, and Bullet rosettes) were selected for developing the scattering properties database. According to the optimization results of the SGLI specification by Letu et al., (2012), 28 wavelengths in SGLI channels were selected for developing the scattering database. Cole et al., 2013 compared the Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar (PARASOL) observations with polarized reflectance simulated using different ice habit mixtures model (IHMM) that has severely roughened surfaces. It is suggested that an ice model incorporating an ensemble of different habits with severely roughened surfaces would potentially be an adequate choice for global ice cloud retrievals. For determination the ice crystal habits used in the ice cloud retrievals, we then simulated the polarized PARASOL reflectance using six ice crystal models developed in this study. As a result, simulations by Voronoï habit model with large effective radius have a most closely agreement with the polarized reflectance observed by PARASOL. It is proved that Voronoï habit model is efficient for retrieval of the ice cloud microphysical and optical properties that have large effective particle radius. Finally, we investigated the influence of various ice crystal habits on retrieval of the ice cloud optical thickness and effective particle radius.

Key words: ice crystal, scattering properties, cloud remote sensing, cloud microphysical properties

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