A database system for analysis of single scattering properties of irregular particles

Particles in the atmosphere that scatter radiation may display a variety of complex shapes other than a sphere, which is a good assumption only for cloud droplets. Mie theory has enabled accurate single-scattering calculation for a spherical particle since the early part of the last century. In the last twenty years, various single-scattering methods have also been developed for particles with irregular shapes. The discrete dipole approximation and the finite-difference time-domain method are probably the most versatile of these methods. However, existing single-scattering calculations generally focus on particles with shapes that can be described mathematically. To the authors best knowledge, no systematic analysis has even been done with aggregate particles composed of a number of component particles with simple, non-spherical geometry. The infinite combinations of particle shapes and geometrical compositions that are possible and indeed exhibited in nature would render their radiative transfer problem intractable, unless some parameterization scheme can found which requires only a small number of parameters which can essentially describe the single scattering characteristics of these complex particles. Extensive analysis of the single scattering properties of such realistic but complex particles is therefore needed in order to find such efficient and effective scattering parameterization schemes. To achieve this end a large catalog of complex individual and aggregate particles is needed, upon which single-scattering calculations can be carried out. Statistical analysis can then in turn be applied to the single-scattering calculation results to find effectual parameters for parameterization. We present here an integrated system with a database for the creation (interactive or programmed) of various geometric shapes, computation of their single-scattering properties, collection and organization of the shapes and computation results. This system consists of DDSCAT (a Fortran code for calculating scattering and absorption of light by irregular particles), an application which prepares arbitrary particle shape descriptions for use by DDSCAT and processes DDSCAT's output, a web-based interface which allows users to create new database entries in the system and retrieve information from the system and a selection of desktop computer application which may be used to generate specific particle shapes and aggregates to feed in to the web interface for processing. The generation of this large collection of particle descriptions is a rather enormous undertaking so we therefore expect this to be a community effort. Accordingly, we have envisioned and designed the system using freely available software and have made it web accessible. We present a basic statistical analysis on a small population of simple and aggregate shapes to illustrate the utility of this tool and its potential for future applications. We envision a particular use in interpreting the radar return signal from ice and other solid precipitation particles. We believe that with the help of this system the reliability and accuracy of of ice precipitation radar retrieval can be greatly improved.