PACE: read the ocean and atmosphere through light

NASA’s PACE mission launched in February 2024 to investigate connections among plankton, aerosols, clouds and ocean ecosystems. Microscopic phytoplankton influence marine food webs and the movement of carbon. Suspended particles and dissolved substances also affect the light leaving the ocean. Measuring that light across many wavelengths provides clues about a changing ecosystem rather than a direct photograph of each organism.

The Ocean Color Instrument, OCI, measures a broad spectral range with fine wavelength sampling. Different constituents leave different patterns in the observed spectrum. Comparing those patterns can help scientists distinguish properties that a simple three-color picture would combine. The value comes from calibrated measurements and defensible retrieval methods, not from making an image appear more colorful.

PACE also carries SPEXone and HARP2, polarimeters that observe properties of light including polarization and viewing-angle dependence. Their measurements help characterize aerosols and clouds and offer information useful for interpreting the atmospheric contribution to ocean observations. The mission’s atmosphere and ocean investigations are therefore physically connected by the path the light takes to the spacecraft.

Imagine two fictional observations of the same water, one through clear air and one through a smoke layer. A difference at the satellite might partly reflect the atmosphere instead of a change in the water. Atmospheric correction — open definition and quality screening help distinguish these contributions. A blocked or unreliable observation should not be presented as a precise ocean result simply because a map has space for another colored pixel.

Suppose a coastal image becomes greener. Plausible explanations include changes in phytoplankton, suspended sediment or other optically active constituents. A broader spectrum, suitable algorithms and observations collected in the water help test the explanation. Even a supported phytoplankton increase does not establish that the bloom is toxic; that claim requires evidence appropriate to the organisms and their effects.

PACE data products differ in processing level and scientific meaning. An instrument signal, a corrected reflectance and an estimated biological property are not interchangeable. Preserve product versions, uncertainty and observation dates when comparing scenes. The PACE spacecraft preparation photograph introduces the hardware, while the mission’s science depends on connecting its measurements to validated interpretations of the ocean and atmosphere.