Abstract
<jats:p>We introduce the LISST-Horizon, a new bench-top instrument for measuring polarized angular scattering in water which provides the volume scattering function from 0.05° to 150° and the degree of linear polarization from 30° to 150°. This instrument can measure continuously for extended periods in a flow-through setting with minimal operator intervention. We present the instrument design, calibration procedure, processing of the data, and validation. Following calibration, the instrument shows excellent agreement with Mie theory for polystyrene beads and with the LISST-VSF for both beads and natural samples, though with higher uncertainty in the back angles (120°-150°) due to internal reflections. The instrument calibration factors are stable over 5 years including one full year where it was deployed at sea and collecting data continuously while the ship was underway. We suggest that this instrument provides a valuable new addition to the optical oceanographer's toolkit by rapidly measuring angular and polarized scattering properties, supporting marine particle characterization across space and time, and validating ocean products from new satellite multi-angle polarimeters such as PACE's HARP2 and SPEXone.</jats:p>