The colour of the water in an estuary depends upon the optical properties of the water itself and on the concentrations of the materials, both dissolved and suspended, near the water surface. Recent developments based on in situ radiometry have shown how measurements of estuarine colour can be interpreted in terms of the concentrations of dissolved organic material, and how, in turn, this can be related to salinity (Bowers et al., 2000, Binding and Bowers, 2003). The aim of this proposal is to apply this technique to airborne visible band remote sensing to produce synoptic, two-dimensional maps of surface salinity in an estuary. Such maps, which are not presently available, will, in turn be invaluable tools for providing new insights into mixing processes in estuaries.