For decades oceanographers have used passive upwelling light to estimate phytoplankton distributions across the world ocean. Elaborate algorithms have been developed to estimate in situ quantities based upon the spectral properties of the up-welled light. But passive upwelled light says nothing about the vertical distribution of the plankton, and of course it depends upon a clear sky to see the surface.
For quite some time now lidar (light detection and ranging) has been used on aircraft and satellites to scan surface waters for horizontal and vertical distributions of plankton and particulate matter. What I can’t understand is why oceanographers haven’t adopted the same approach on research vessels, and ultimately on merchant marine vessels. Think about it, a lidar on a vessel in regular traffic, would give us a high-resolution view of plankton and particulates in the top 10-50 m of water along its route and how these vary with location and season. By high resolution I mean one meter in the vertical and sub-kilometer in horizontal – ceaselessly over time. Seems to me going from a satellite to a vessel in regular traffic would be like going from binoculars to a scanning microscope.
Lidars have been around for a long time; the technology is well-known. It has been used on research vessels, but attempts to broaden its usage have met bumps in the road, why? I submit it is because we lack an agency that can argue for and fund research for sustained observation on research vessels and the merchant marine fleet. It may also be that the community is still unaware of what an incredible resource the merchant marine for sustained ocean observation? Everyone I have spoken with about this agrees that a program of sustained observation of the vertical distribution of backscattered light could lead to a major improvement in our understanding of ocean color and biogeochemical processes in the upper ocean. Given the enormous interest in euphotic zone you would think the funding agencies would be putting out calls to the community to develop such a capability. Yes, to bring the technology out of the research laboratory into usage on a sustained basis will require streamlining the hardware and developing software to process the raw optical data into user-understandable scientific units on a routine basis. But that is what we do with all new technologies! A recent study by Collister and co-authors (2024) gives us a good hint of the possibilities. Take a look at their recent paper and references therein.
Collister, B, and co-authors (2024). Assessing the utility of high spectral resolution lidar for measuring particulate backscatter in the ocean and evaluating satellite ocean color retrievals. Remote Sensing of Environment, 300. https://www.sciencedirect.com/science/article/abs/pii/S0034425723004492