Earth Planets Space, Vol. 65 (No. 10), pp. 1133-1137, 2013
Robert S. Botet1 and Rakesh K. Rai1,2
1Laboratoire de Physique des Solides - Bât.510 - CNRS UMR8502, Université Paris-Sud, 91405 Orsay, France
2D. D. U. Gorakhpur University, 273009 Gorakhpur, India
(Received October 31, 2012; Revised March 15, 2013; Accepted March 20, 2013; Online published October 24, 2013)
We present optical features characteristic of the shape of composite dust particles, such as grain-aggregates formed under cosmic or atmospheric conditions. The discussion develops along two examples of realistic models for the formation of the composite particles, and constant refractive indices. That way, particular features exhibited in the optical cross section behaviors result from the particle structure only. The role of the ratio between optical particle cross section and the corresponding cross section of the coated sphere of same composition and volume is highlighted. Limited wavelength ranges are defined where the coated sphere model can be used to obtain the effective radius or the volume composition of the particle. Other wavelength domains are very dependent on the particle formation mechanisms, then giving constraints on the possible formation processes. Therefore, such an approach is able to provide inverse methods to obtain the actual values of physical parameters from definite features of optical quantities.
Key words: Aggregate aerosol, composite particles, cosmic dust, extinction, fractal aggregates.