Determination of the particle size range in the visible spectrum from spectral extinction measurements

The problem of determining the particle size range in the visible spectrum is studied. The forward-scattering corrections are considered in the spectral extinction measurements. The monomodal and bimodal particle size distributions are retrieved in the independent model and dependent model algorithms, respectively. The constrained least-squares inversion method developed by Phillips and Twomey is applied in the independent model, and the genetic algorithm (GA) optimization method is employed in the dependent model. In the independent model, it is found that the particle size distributions can be retrieved very well in the size range from 0.1 νm to 12 νm for latex particles dispersed in water. The light scattering will enter the Rayleigh scattering region for particles below 0.1 νm and the diffraction scattering region for particles above 12 νm. The relation between the size range and relative refractive index of particles is also investigated. In the dependent model, the GA method can be successfully applied to retrieve the particle size distribution with high stability in the range from 0.01 νm to 350 νm for water particles dispersed in air even in the case where the bimodal distributions are retrieved.