Laser Scattering Instrument for Measurement of Oceanic Particle Size Distribution from Submicron to Mesoplankton

Size distributions of ocean particles indicate marine biodiversity, ecosystem health, and the state of the oceanic carbon cycle. Satellite measurements of particle size distribution (PSD) are vital for our understanding of these global processes on large spatial and temporal scales. Ocean color satellites capture synoptic views of marine ecosystems that cannot be obtained by conventional ship and aircraft sampling methods. However, satellite algorithms for estimating PSD remain largely unvalidated due to the lack of appropriate in situ “ground truth” datasets.
We present a particle sizing instrument under investigation that combines measurements of near-forward light scattering with polarized side scattering to cover a wide particle size range from approximately 0.1 to 500 micron. The measurement is an ensemble-averaging laser scattering technique that acts on a bulk water sample and, therefore, can analyze large volumes of sample water continuously. Consequently, the instrument is favorable to integration into shipboard flow-through/underway systems and can cover a wide dynamic range of particle sizes and concentrations without the need to change microscope objectives or sensing orifices as is needed in other commonly-used particle sizing techniques.