THE MEASUREMENT OF SUSPENDED PARTICULATE CONCENTRATIONS FROM REMOTELY-SENSED DATA

Knowledge of the distribution of SPM is recognised to be of increasing importance in relation to the prediction of the fate of pollutants in the shelf seas. Persistent patterns in SPM and a marked annual cycle are observed in the shelf seas around the United Kingdom. Although concentrations of surface suspended particulate material can be related to the imagery, little insight into the processes causing the variations can be gained without knowledge of the depth variability. Assessment of the spatial variation was facilitated by regular conductivity, temperature, depth (CTD) and transmissometer surveys from March to October 1987, in an area of the Irish Sea where there were marked gradients in the sea surface reflectance. This showed that although surface concentrations showed similar trends to sea surface reflectance, vertical gradients in suspended particulate material were associated with the seasonal pycnocline. The time dependance of beam attenuation and its control by tidal currents were assessed by the analysis of a six month record of transmissometer and current meter data from a mixed-water site. Beam attenuation was found to be significantly related to the springs-neaps cycle, advective processes and to the time of year. The study shows that remotely-sensed sea surface reflectance data have a significant part to play in the measurement of suspended particulate material if they are coupled with a carefully planned survey of in situ optical and oceanographic measurements.