Topic 3c - Ocean Colour overview (part 1) - why and how it is measured
Oceans can be difficult to monitor because of their large expanse and because they are often shrouded in cloud. However, good quality measurements of sea level and ocean colour have been achieved from space – and have been backed up with surface measurements by intrepid ocean-going crews and floating buoys. As we mentioned at the start of the course, our picture of the Earth often relies on a variety of measurements from space including optical EO. Ocean temperature is one of these key measurements – vital for climate science – and we use thermal signatures for it. Sea level is also important and is measured using radar and lidar altimetry.
Ocean colour science measures reflected sunlight scattered back from the ocean, from the surface, and also from material within the water column. Ocean colour observations allow us to work out both the concentration and type of material in the water column, usually via some type of scattering model. Colour changes based on different things dissolved in water, sediments, and phytoplankton – plants which float on the surface and are fundamental to ocean life because they form the base of the oceanic food chain.
In the satellite era, the variety of different ocean colours over small areas has become much more obvious, as have changes in phytoplankton behaviour due to the currents connected to the El Nino and La Nina phenomenon in the Pacific Ocean. Satellites reveal ocean conditions in remote places like the polar seas, and can show clearly the relationship between land and ocean. In addition, optical observations can show the extent and dynamics of sediment released into the sea, from distances of hundreds or even thousands of kilometres upstream. This allows us to study large scale hydrological processes, agricultural runoff and habitat quality .
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