Using a digital camera for water quality measurements in Galway Bay

A method for using the red–green–blue (RGB) digital output from a digital camera, a Nikon Coolpix 885, to estimate water quality parameters is described. To eliminate reflection from the water surface, a tube is fitted around the camera lens which breaks the surface such that only the upwelling light from below is measured. To obtain consistency between stations, RGB values used for analysis are taken where the total cameras response (R + G + B) is a constant value, derived from pictures taken at a range of exposures.The method has been successfully used in Galway Bay, where the optical characteristics of the coastal water are dominated by yellow substance (or coloured dissolved organic material – CDOM) and chlorophyll. A strong linear relationship was found between CDOM and the Red/Blue camera output. The form of the relationship was consistent with previous measurements using more conventional narrow band irradiance sensors. In addition, a log–log relationship between chlorophyll and the Green/Blue camera output was also found. Some problems exist with the use of the camera, particularly with the cameras automatic functions such as ‘white balance’ which may artificially change the RGB output. Nevertheless, the use of a camera for simple water quality measurements has been demonstrated.