Characteristic of the ice crystal scattering database for GCOMC/SGLI satellite mission

In this study, we developed the ice crystal scattering database for ice cloud remote sensing and radiative transfer calculation of the Global Change Observation Mission (GCOMC)/Second Generation Global Imager (SGLI) satellite mission using light scattering methods of the LIght Scattering solver Applicable to particles of arbitrary Shape (LISAS)/ Geometrical-Optics Approximation (GOA), Surface Integral Equations Method of Müller-type (SIEMM), Finite-Difference Time Domain (FDTD), and Improved Geometrical-Optics Method (IGOM). The GCOMC/SGLI mission measures essential geophysical parameters on the Earth's surface and in the atmosphere to facilitate understanding of the global radiation budget, which is scheduled to launch in around 2014 by the JAXA. Computing time and retrieval error of the effective particle radius is a main subject for developing the ice crystal scattering database for GCOMC satellite mission. For developing the suitable database, it is important to optimize the light scattering database based on the specification of the satellite sensor. There are two approaches to optimize a light scattering database: optimizing the complex refractive index grid system and optimizing the wavelength bin for a specific sensor channel. In the former method, a suitable grid system is determined by investigating the radiance error of radiative transfer calculations caused by differing fineness of step size of the complex refractive index. This study focuses on the former case. The grid system of the complex refractive index in the 1.6-μm (SW3) channel of the GCOMC/SGLI satellite sensor was investigated for optimizing the ice crystal scattering database. This grid system is separated into twelve patterns according to the step size of the real and imaginary parts of the refractive index. Specifically, the LISAS/ GOA technique is used to simulate the scattering of light by randomly oriented large hexagonal ice crystals. The difference of radiance with different ice cloud optical thickness and step size of the refractive index is calculated from developed light scattering database using the radiative transfer (R-STAR) solver. The results indicated that the step size of the real part is a significant factor in the difference of radiance. Furthermore, retrieval error of the effective particle radius caused by the sensor noise and error caused by refractive index grid system are investigated. Result indicated that, when step size of the real part is 0.04 with ice cloud optical thickness 8, total error of the effective particle radius is generally smaller than 2-μm. Hence, optimization of the refractive index in the SGLI channel is a significant step toward developing a suitable light scattering database for non-spherical ice crystals. Based on the above result, we developed the ice crystal scattering database for GCOMC satellite mission. Characteristic of the ice crystal scattering database for GCOMC/SGLI was investigated finally. Keywords: GCOMC/SGLI, ice crystal, light scattering method, effective particle radius