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LISST-ST

(Laser In-Situ Scattering and Transmissometry)

The LISST-ST is a new instrument for in-situ measurement of the settling velocity distribution of suspended particles in the aquatic environment. The settling velocity is of importance in estimation of sediment transport rates as well as in the estimation of particle settling in bio-geochemical studies. The settling velocity of particles depends on the particle size and density. In the complexity of the natural environment, there may exist particles which are of identical size but differ in composition so that the settling velocity itself is not a unique function of size alone. The LISST-ST measures not only the settling velocity at high size-resolution, it also captures the non-unique variability of settling velocity within each size class.

The LISST-ST incorporates our unique motorized sliding-door with 'O'-ring seal design. This feature maintains complete isolation of the trapped water sample from the outside, ensuring that currents which might be created by leakage are non-existent. The result is reliable data on the settling velocity of even the smallest particles. Additionally, a second motorized ducted propeller is also exploited to clean the instrument windows after each settling experiment. Particle disruption by the propeller is avoided by careful timing of the interval between drawing a sample and closing of settling tube doors.

The instrument contains batteries, data logger, and pressure and temperature sensors. Specifications of the instrument itself are an extension of the basic LISST-100.

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