Ships of Opportunity for PACE (SO-PACE): Validation of water-leaving reflectances, IOPs, and plankton community metrics

SO-PACE will make use of opportunistic instrument deployments on research vessels to produce measurements of hyperspectral Rrs spanning 350 nm - 750 nm using the pySAS system, a continuous above-water autonomous solar tracking platform to collect water-leaving and sky radiances and downwelling irradiance, from which Rrs is calculated. Complementary measurements of IOPs will be made using underway flow-through systems and using pumps that minimize particle damage. IOP measurements will provide several products including: chlorophyll-a concentrations and spectral absorption of phytoplankton (both derived from particulate absorption), and spectral backscattering coefficients. The slope of particulate attenuation will provide estimates of trends in both bulk particle and phytoplankton size distributions. Concentrations of chlorophyll-a as well as additional phytoplankton accessory pigments will be estimated from both particulate absorption and Rrs spectra. Additionally, discrete water samples will be collected from flow-through systems and prepared for onshore laboratory HPLC analysis of phytoplankton pigments. Continuous measurements of phytoplankton communities will be made using two well-established instruments: an Imaging FlowCytobot (IFCB) and a SeaFlow (a continuous flow cytometer). These two instruments will also be deployed on shipboard flow-through systems, and have a combined range of ~ 0.6-150 microns for quantitative phytoplankton assessment.