In situmeasurements of water quality, collected by two ships and a helicopter, and remotely sensed data provided by a Daedalus Airborne Thematic Mapper have been compared in order to generate a calibration algorithm for Chlorophyll-a in the Bristol Channel off the South Gower Coastline. Statistical analyses showed that pigment concentration can be retrieved from the received radiances at channels 1 (0-42-0-45 μm), 3 (0- 52-0-60 μm) and 5 (0-673-0-69 μm), despite the high tidal stress in the area. Comparisons are made between the algorithm and previous ocean-colour experiments. It is concluded that, although the acuracy of determining Chtorophyll-a concentration in this case is lower, there is a great similarity between the slopes in a logarithmic form. Valuable information about the variability of Chlorophyll-a over a tidal cycle was obtained by airborne remote sensing, demonstrating its feasibility for monitoring water quality parameters.