Experimental scattering matrices of clouds and randomly oriented particles

In the atmospheres of planets and satellites, liquid particles may occur in the form of clouds, hazes, fog, and rain. The liquid can be water as is the case in the atmosphere of the Earth but also other materials, like sulfuric acid that occurs in the atmosphere of Venus. These liquid particles can be safely assumed to be homogeneous spherical particles. There is, however, also a large variety of non-spherical particles in very different astronomical environments ranging from the Earth’s atmosphere to other planetary and cometary atmospheres in the solar system, the interplanetary medium, reflection nebulae, atmospheres of brown dwarfs, etc. In these cases, the assumption of spherical particles is highly unrealistic. This is well known for the Earth’s atmosphere where mineral dust is one of the most prominent aerosol classes. The main sources of mineral dust are the big deserts and their margins (Mishchenko et al. 2002; Nousiainen 2009). In addition, volcanic eruptions inject gas and volcanic ash into the Earth’s atmosphere affecting its radiative balance. Moreover, a large number of cloud particles consist of non-spherical ice crystals (see, e.g., Yang and Liou 2006; Baran 2009). There are other examples in the solar system where we can find small irregular (mineral) particles. This is the case for the atmosphere of Mars, where dust particles from its surface are regularly swept up into its atmosphere by winds (e.g. Wolff and Clancy 2003; and Chapter 17). The atmospheres of the giant planets such as Jupiter and Saturn, and satellites like Titan have solid particles of condensed material in clouds and hazes (e.g. West and Smith 1991; and Chapter 19). In studies of solar system objects, light scattered by those particles is usually the only tool we have for determining their physical characteristics, such as size, shape, and refractive index. By analyzing the spectral dependence of the observed intensity and polarization of the scattered light we can retrieve information on the physical characteristics and location in the atmosphere of the scattering particles.