Satellite Ocean Colour: Current Status and Future Perspective

TLDR

Ocean‑colour measurements of water‑leaving radiances and chlorophyll are essential for tracking phytoplankton dynamics, marine biogeochemistry, and climate impacts, yet the 21‑year record is fragmented across heterogeneous sensors, requiring careful merging to avoid artefacts and to enable a consistent time series that will become long enough by 2029 to separate climate change from natural variability. This paper surveys the present state and future outlook of large‑to‑medium‑resolution ocean‑colour observations for oceans and coastal seas. It reviews user needs for products and uncertainties, details current and forthcoming satellite sensors, emphasizes in‑situ validation and ground‑segment processing, and illustrates applications in climate records, water‑quality monitoring, and model assimilation. The authors report ongoing capacity‑building and training initiatives and conclude with a concise outlook on future developments in the field.

Abstract

Spectrally-resolved water-leaving radiances (ocean colour) and inferred chlorophyll concentration are key to studying phytoplankton dynamics at seasonal and inter-annual scales, for a better understanding of the role of phytoplankton in marine biogeochemistry; the global carbon cycle; and the response of marine ecosystems to climate variability, change and feedback processes. Ocean colour data also have a critical role in operational observation systems monitoring coastal eutrophication, harmful algal blooms, and sediment plumes. The contiguous ocean-colour record reached 21 years in 2018; however, it is comprised of a number of one-off missions such that creating a consistent time-series of ocean-colour data requires merging of the individual sensors (including MERIS, Aqua-MODIS, SeaWiFS, VIIRS and OLCI) with differing sensor characteristics, without introducing artefacts. By contrast, the next decade will see consistent observations from operational ocean colour series with sensors of similar design and with a replacement strategy. Also, by 2029 the record will start to be of sufficient duration to discriminate climate change impacts from natural variability, at least in some regions. This paper describes current status and future prospects in the field of ocean colour focussing on large to medium resolution observations of oceans and coastal seas. It reviews the user requirements in terms of products and uncertainty characteristics and then describes features of current and future satellite ocean-colour sensors, both operational and innovative. The key role of in situ validation and calibration is highlighted as are ground segments that process the data received from the ocean-colour sensors and deliver analysis-ready products to end-users. Example applications of the ocean-colour data are presented, focussing on the climate data record and operational applications including water quality and assimilation into numerical models. Current capacity building and training activities pertinent to ocean are described and finally a summary of future perspectives is provided.