Satellite observations of ocean colour

Abstract

Ocean colour is unique among the properties of the sea that can be measured from satellites because visible wavelength radiation penetrates below the surface skin and contains direct information about the bulk water quality in the upper few metres of the sea. With reference to Nimbus czcs and Landsat MSS data, this review examines three aspects of ocean-colour monitoring: the removal of atmospheric effects, which make up a large proportion of the visible signal reaching the satellite; the calibration of the ocean colour signal in terms of more useful ocean parameters such as sediment load, chlorophyll concentration, water depth or the depth of the euphotic zone; and the potential applications of colour-monitoring satellites to oceanography. Algorithms for atmospheric correction are now well developed, but calibration for chlorophyll or sediment is less certain, particularly where inorganic sediments or land-derived yellow substance, as well as the local phytoplankton population, are present in the sea. Oceanographic applications include the estimate of total productivity, the identification of blooms, and the location of productive areas to assist ship surveys. The greatest potential for satellite observations of ocean colour may lie in the synoptic spatial information contained in the images, but this awaits serious exploitation by dynamical oceanographers.