Sequoia Scientific has completed a NASA-sponsored phase II small business innovation research (SBIR) project spearheaded by Principle Investigator Dr. Wayne Slade, who proposed an instrument for continuous and automated measurement of suspended particle size distribution (PSD) in flow-through systems on research vessels. PSD is a key environmental parameter with diverse biogeochemical applicability, and estimation of particle size is a goal of next-generation ocean color remote sensors. However, presently, PSD variability in the ocean is not well understood due to the challenges of routine measurement, and minimal ground truth data exists for ocean color validation efforts.

Slade aims to bridge the known data gap with his design of the new LISST-Horizon instrument. Initially known as the flow through extended range particle sizer (FERPS), the LISST-Horizon is designed for installation in ship-based flow-through systems, allowing collection of PSD data over large space and time scales. The LISST-Horizon uses laser scattering to estimate PSD across a wide range of particle sizes from submicron to hundreds of microns, covering pico- to mesoplankton size scales. A prototype LISST-Horizon instrument has been delivered to NASA for testing.

The LISST-Horizon is a self-contained instrument for bench-top deployment in a research vessel laboratory. Plumbed to continuous underway uncontaminated seawater, it continuously measures PSD and particle concentration, as well as inherent optical properties (IOPs) beam attenuation (c) and volume scattering function (VSF, β) at 520 nm. From these IOPs, scattering (b), backscattering (bb), backscattering ratio (bb/b), and by difference, absorption (a = c – b), can be derived. LISST-Horizon is configured and controlled via a touch-panel graphical user interface, data and logs are accessed via a network connection, and the instrument’s raw data files are processed and viewed on a PC using included software.

LISST-Horizon has wide applicability in the field of ocean optics, ocean biology and biogeochemistry; and currently no purpose-built systems exist for underway measurement of PSD on research vessels. Methods currently used in oceanographic settings are time-consuming, expensive and non-automated. The LISST-Horizon will therefore be an attractive option for particle size measurement and advancing the state of the art in ocean color and biogeochemistry. —Sequoia Scientific Inc.

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