Abstract:
We present new observational data on small-angle light scattering properties of
natural, random shaped particles, as contrasted with spherical particles. The interest in
this "shape effect" on scattering arises from the need for a suitable kernel matrix for use
in the laser diffraction method (LD) of particle sizing. LD is now used broadly for
measuring size distribution of suspended marine particles. LD involves the measurement
of small-angle forward scattering at multiple angles. This data is inverted using the
kernel matrix to produce size distribution. In the absence of a suitable matrix for random
shaped particles, past practice has been to use a model based on Mie theory, applicable
strictly only to homogeneous spheres. The present work replaces Mie theory with
empirical data. The work was motivated in part by anomalous field observations of size
distribution and settling velocity distributions reported in literature. We show that a
kernel matrix for random shaped particles results in improved interpretation of field
multiangle scattering observations. In particular, a rising edge at the fine particle end of
the size spectrum is shown to be associated with shape effects.
