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.