Introduction
The sun emits electromagnetic radiation that hits the Earth, and all of life on this planet depends on just a tiny portion of the electromagnetic spectrum - the colors of the rainbow (‘visible’ light). These are the specific wavelengths (400 -700 nm) by which plants on Earth photosynthesize and give us oxygen that we breathe. As this visible light hits the surface of the ocean and goes into the water, only one of two things can happen to that light - the light can either be scattered, or it can be absorbed by various constituents in the seawater. Pure water naturally absorbs more red light, leaving blue light to be scattered back to our eyes, and it is why the deep ocean appears blue. Conversely, other materials in the water – algae, dissolved organic material, dying or dead plant cells, floating seaweed, pollutants, suspended sediments from land, among other things - each uniquely absorb different amounts and types (wavelengths) of light, creating a color palette that we sense from discrete measurements of light from satellite sensors (Figure 1). How well we unravel the ocean composition from this signal largely depends on how well we can see these colors. Our heritage ocean color satellites detect anywhere from 5-10 wavelengths, which has limited our ability to distinguish some components from others. The launch of the Plankton, Aerosol, Cloud, and ocean Ecosystem (PACE) mission on February 8, 2024 introduced the satellite community to global ‘Hyper’-spectral measurements, meaning a spectrally continuous sampling of light. This has afforded the opportunity to sense the ocean through an entirely new lens by being able to resolve previously undetectable, subtle features unique to e.g. a particular phytoplankton class, or other ocean constituents. NOAA will be codifying these hyperspectral ocean color capabilities well into the 2050s with the launch of GeoXO, which will offer an even newer perspective from a geostationary orbit, where we can revisit the same area several times per day. This document is intended to familiarize readers with the capabilities and nuances of available and emergent ocean color data products to help guide use and implementation plans in NMFS.
