Particle size distribution (PSD) is a fundamental oceanographic measurement, with diverse biogeochemical applications including carbon cycle science, ecosystem and fisheries modeling, and harmful algal bloom (HAB) detection/prediction. There is optimism that estimates of PSD will be available from ocean color measurements (such as NASA’s upcoming PACE mission), and will be able to help constrain global-scale ecosystem/carbon models and estimates of primary production. However, natural PSD variability is not well understood due to the challenges of routine measurement, and there exists little field data over large space and time scales.

Sequoia Scientific is working to bridge this gap by developing an instrument (FERPS—Flow-through Extended Range Particle Sizer) that expands upon laser diffraction technology, using wide angle scattering, multiple source wavelengths, and polarization. FERPS is designed around autonomous deployment in flow-through systems: cleaning and background measurements are automated.

Making measurements of particle size over a wide range of space and time scales, such as in ship-based underway systems or observatories, is highly beneficial to researchers in ocean science and coastal monitoring. Example applications include collecting ground truth PSD data for development of phytoplankton functional group algorithms and/or increasingly complex biogeochemical models, as well as routine monitoring of changes in PSD as a tool for detecting harmful algal blooms and shifts in plankton community structure.

FERPS is being developed through the NASA SBIR Program.

FERPS is built around a flow-through sample cell, surrounded on one side by wide angle scattering detectors. Conventional LISST near-forward optics are coupled with a multi-wavelength and multi-polarization laser source. An embedded computer supervises operation of the instrument, along with a touch-panel interface used for instrument configuration and operational feedback. Data is easily accessible over a network connection.

Plumbing, including electrically actuated valves can cycle automate filtering of the sample through a 0.2-µm filter for periodic filtered seawater blanks, as well as periodic calibration and cleaning.