Sequoia LISST-100X, Руководство пользователя

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2 LISST-100X User’s Guide
The LISST-100X records the scattering intensity over a range of
small angles using a specially constructed multi-ring detector
shown in the graphic below. This measurement is also known to
optical scientists as the
volume scattering function and can be
used as such for studies of underwater image propagation and
beam spread. A growing number of publications of measurements
using the LISST-100X instrument is available on our website:
http://www.sequoiasci.com/library/technical.aspx?SectionName=lib
rary
A collimated laser
beam enters
water, light is
scattered by
particles and
sensed by a multi-
ring detector
behind a receiving
lens. A
photodiode placed
behind a centered
hole measures
optical
transmission
The conversion of the multi-angle scattering to size distribution
involves a mathematical
inversion . In this step, a size-distribution
is found that would produce multi-angle scattering that fits the
observation. There exists a vast literature on the subject of this
inversion. For the stout-hearted user interested in learning all
about it, we recommend the most germane study of the subject:
"Optimal scaling of the inverse Fraunhofer diffraction
particle sizing problem: The linear system produced by
quadrature," by E. D. Hirleman,
Particle Characterization ,
4, 128-133, 1987.
The main conclusions are that the information content of the data is
most stably retrieved by use of ring-type detectors, with each ring
measuring the scattering over a sub-range of angles, and that the
resolution is limited to relatively few size classes depending on the
noise in the data. For example, for the dynamic range in scattering
angles of 200:1 that is built into the LISST systems, typically only
12-14 truly
independent size classes can be resolved.