A sea is not always blue
The sea is generally blue or green, but in certain circumstances it can take on a white, brown or yellow hue. This variation is because it is not only the interaction of light with the water itself that determines the sea colour, but also its interaction with the components that are present in the sea, via processes of refl ection, absorption and diffusion on the sea surface, within the water column or on the seabed. As a result, the optical properties of algae, of dissolved organic substances and of suspended non-organic particles – such as sand, mud and clay – can have a considerable effect on the colour of the sea. This means that by taking precise measurements of sea water colour (or of spectral refl ectance to be more precise) – for example using a satellite-based measuring instrument – and using the appropriate mathematical models, scientists are able to estimate the concentration of these components.