LISST-100 (Sequoia Scientific, Inc.) is an instrument designed for in-situ measurement of particle size spectra. The instrument uses the principle of laser diffraction to measure volume content of suspended particles in each of 32 logarithmically spaced size classes from 1.25 to 250 microns. The LISST-100 was critically evaluated in the laboratory to examine its capability of resolving (1) particle size distribution, and (2) total volume (mass) concentration of test samples. In order to simulate field conditions, a test chamber was designed that utilizes the full laser path length of the instrument and allows for continuous mixing of particle suspensions. The small volume of the test chamber minimizes the amount of polymer standard needed for each sample analysis. Suspensions of single sized polymer particles (5, 20, 50, 100, and 140 microns), combinations of single sized particles, and a size distribution (1-40 microns) at various concentrations were analyzed in the laboratory using the test chamber. Results from the analysis were interpreted using vendor software. Mean particle size was correctly determined by the LISST-100 for all samples of single size particles. The instrument correctly identified peaks in mixtures of single-sized particles and the distribution of particles within a size range. Changes in volume concentration were correctly identified as a percent change. An instrument calibration constant was determined from linear regression for determination of total mass concentration of field samples.

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An abstract presented at AGU 1998 Fall meeting, special session on Dynamics of Sediment-Laden Flows.