Diffuse Attenuation Coefficient

The diffuse attenuation coefficient (K490) is an indicator of the turbidity of the water column – how visible light in the blue-green part of the spectrum penetrates the water column. It is directly related to the presence of scattering particles in the water column. Since there is a direct relationship between the diffuse attenuation coefficient and the more traditionally used expression ‘secchi depth’ which is a direct measure of how many meters the light penetrates the water column. Below is given an example of a secchi depth map.

GRAS can provide worldwide daily maps of diffuse attenuation coefficient distributions derived from either SeaWiFS or MODIS.

The diffuse attenuation coefficient maps can be used for a wide range of applications related to water quality and turbidity. All areas where knowledge about the light availability at different depths is needed will benefit from the diffuse attenuation coefficient data. Examples could be: primary production models which require information on the vertical distribution of photosynthetically available radiation (PAR) or input to models of fish predation behaviour, since the latter depends on the light conditions.