Ocean-Color Remote Sensing from the First Earth-Sun Lagrange Point

The EPIC camera onboard the DSCOVR observatory in Lagrange-1 (L1) orbit provides imagery of the Earth's surface lit by the Sun at a cadence of 13 to 22 images/day and optical resolution of about 20 km in 10 spectral bands from 317 to 780 nm. The data can be used to estimate surface solar irradiance and water reflectance, basic variables from which a variety of optical and biogeochemical products can be derived. Measuring at practically the same scattering angle, a characteristic of the L1 orbit, offers a unique capability to handle atmospheric influence using multi-directional observations, a concept that may be exploited in future remote sensing systems. EPIC-derived global products for ocean biology/biogeochemistry are presented and, whenever possible, evaluated against other satellite estimates. They include surface fluxes in the ultraviolet, photosynthetically available radiation (PAR), water reflectance, near surface chlorophyll-a concentration, diffuse attenuation coefficient, backscattering and absorption coefficients, and the fraction of PAR absorbed by live algae, a key variable controlling primary production. Observing frequently the sunlit part of the ocean has the advantage of maximizing temporal coverage. Space agencies should consider utilizing the L1 orbit for future satellite ocean-color missions.