Ocean colour radiometers and imaging spectrometers measure the radiance leaving marine waters in the visible and near IR spectrum in the range 400–800 nm, where the colour is characterised by the constituents of the water – typically phytoplankton, suspended particulate material and dissolved compounds. Differences in the intensity of light received in the different bands give information on the concentration of a variety of substances present in the ocean.
These instruments have very narrow detection channels, around 10 nm wide, to measure fine spectral details. The spatial resolution of these instruments is typically 0.3 to 1 km. The more recent ocean colour instruments have improved spatial, spectral and radiometric resolution. The trend towards multi-channel, multi-purpose sensors, such as MODIS and MERIS, is resulting in more instruments with an ‘ocean colour’ capability.
Significant calibration and validation activities, together with algorithm development for ocean colour instruments, continues – particularly with respect to measuring ocean productivity