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belcolour project




Introduction to the belcolour project

The colour of the sea is usually thought of as blue or green though may in certain circumstances be white, red, yellow, brown and black or any intermediate shade. In fact the colour of water is determined by the electromagnetic interaction of light with the constituent components of water via absorption or scattering processes either within the water column or at the sea surface or bottom. Thus, the optical properties of matter such as algae, certain dissolved organic substances, inorganic suspended particles (e.g. sand, mud, clay) may all affect the water colour. Conversely, by careful measurement of colour, or, more precisely, spectral reflectance, for example by a satellite-based spectroradiometer, and use of appropriate inversion models, it may be possible to estimate remotely these water constituents. This phenomenon is the physical basis for global satellite-based mapping of oceanic chlorophyll concentration, allowing thereby a quantification of phytoplankton at the surface of the world’s oceans and its contribution to the global carbon cycle and hence climate.

Such deep oceanic waters have been classified as "Case 1" by Morel and Prieur because their colour varies essentially only with chlorophyll concentration and chlorophyll estimation from spectral reflectance is now relatively well-established. In contrast, the colour of most coastal waters are also affected by dissolved organic matter originating, for example, from river outflows and from non-algae particles in the water such as resuspended bottom sediments or from river outflows. These are classified as "Case 2" and there is increasing interest in mapping parameters such as chlorophyll in such waters for example to assess the extent and degree of eutrophication and, more generally, the state of the ecosystem.

BELCOLOUR-2 further expands the scientific knowledge, infrastructure and working relationships built up during the BELCOLOUR-1 project (15th December 2001-30th June 2006). Major outcomes of the BELCOLOUR-1 project include an extensive online optical remote sensing products database for the North Sea, improved algorithms to retrieve chlorophyll (De Cauwer et al., 2004) and total suspended matter concentration (Ruddick et al., 2003) in "Case 2" waters from satellite images and characterisation of optical properties of Belgian waters, especially phytoplankton (Astoreca et al., 2006).

The objective of the BELCOLOUR-2 project is to further improve the quality of existing optical remote sensing products for marine, coastal and inland waters and to develop innovative products including primary production and partial pressure of CO2 for key applications such as aquaculture and air-sea CO2 fluxes.

Belgian seawater of various colours, photographed from a ship.

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The BELCOLOUR-2 PROJECT is funded by the Belgian Federal Science Policy Office under the STEREO program