The Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) Mission will deliver the first NASA-supported ocean color satellite that is designed to study aspects of the marine carbon cycle. PACE offers unprecedented improvements in technology and sampling capabilities compared to previous missions. Heritage ocean color sensors with limited bandsets have been either proof-of-concept missions (e.g., the Coastal Zone Color Scanner) or focused on a limited set of geophysical retrievals, with pigment concentration being the singularly important climate data record. Accordingly, these sensors have been insufficient for comprehensive carbon cycle studies. The science conducted by PACE data will yield a decidedly "carbon-centric" revelation in ocean color science.
A cornerstone property in marine carbon cycle science is the rate of phytoplankton net primary production (NPP). NPP in the sunlit layer of the ocean fuels marine ecosystems, providing the source material (particulate and dissolved) for trophic transfer and export to the ocean interior. Significant effort during the satellite era (~1990 - present) has been invested in estimating NPP from remote sensing measurements, but the unique and advanced observational capabilities of the PACE Mission now offer a long-awaited opportunity to significantly reduce uncertainties in global NPP estimates and thus refine our understanding of ocean carbon cycling. The importance of this opportunity is emphasized in the very first Threshold Mission Ocean Science Question (SQ-1), "What are the standing stocks, compositions, and productivity of ocean ecosystems? How and why are they changing?" To address these science questions, the PACE Threshold Ocean Mission approach explicitly calls for, "... estimates of productivity using bio-optical models, chlorophyll fluorescence, & ancillary physical properties (e.g., SST, MLD)." (see Science Traceability Matrix in final PACE Science Definition Team Report). PACE's emphasis on carbon cycle parameters quite simply requires a launch-ready algorithm for NPP that is designed to exploit the mission's unique capabilities.
Here we propose to deliver a state-of-the-art algorithm for estimating NPP that capitalizes on the hyperspectral retrievals of the PACE Ocean Color Instrument (OCI). Our approach focuses on three targeted advances:
- Use of directly retrieved hyperspectral estimates of phytoplankton absorption to initiate an "absorption-based" NPP model
- Use of retrieved hyperspectral particulate backscattering to improve estimates of phytoplankton biomass through links with the particle size distribution
- Use of hyperspectral resolution around the chlorophyll fluorescence emission region (~650-800 nm) to refine fluorescence line height (FLH) and its use in NPP modeling