Autonomous Long-Term In-Situ Particle Sizing Using A New Laser Diffraction Instrument

A new sensor system is described for unattended long-term observation of particle size spectra in the sea. The instrument is based on the principle that, at small angles, scattering by a particle is substantially identical to diffraction through an aperture of equal diameter, regardless of the particle refractive index. A CCD array records near-forward scattering of light from a laser beam. The inversion of observed scattered intensity over a range of small angles is required to obtain size data. A survey of the inverse methods is included. The data from the CCD line array permits a new level of detail in analysis of the in-situ data. The sensor system can be easily programmed for an arbitrary schedule of sampling. Furthermore, by incorporating the concepts of a settling tube, the settling velocity spectrum of the particles can be determined independently.