Feasibility study of the use of digital cameras for water quality monitoring in the coastal zone

Abstract

The coastal zone is characteristically a turbid region of the sea with water clarity being an indicator of coastal dynamics. Turbidity affects water quality and aesthetic value. Previous investigations into water clarity in the Irish Sea have been conducted using imagery obtained from the Advanced Very High Resolution Radiometer (AVHRR). Good correlations were found between light reflectance and suspended sediment concentrations from this imagery. In order to investigate suspended sediment concentrations in the coastal zone, an area where satellite imagery does not ‘see well’, scientists from NUI, Galway, UW, Bangor and Compass Informatics Ltd. undertook a feasibility study to investigate the possibilities of using both in situ and airborne digital cameras to monitor water clarity in the coastal zone. The digital cameras capture visible spectrum imagery with assigned values for red, green and blue light, thus making a quantifiable measurement of the up-welling light of different colours in a similar manner to the UW, Bangor Ocean Colour Sensor used in this project and a previous INTERREG Project (White et al.; 2000). As suspended sediment concentrations were found to correlate well with in situ digital camera output values, it was anticipated that the camera would provide a successful method of monitoring Suspended Particulate Material (SPM) at fixed locations over a predetermined time period. In practice aerial imagery did not prove to be a feasible method for SPM monitoring in the type of dynamic coastal environment under this particular survey. A combination of sun glint, sky reflectance interference, strong tidal currents and time lapse between imagery capture and in situ data collection made the calibration of images very difficult. On the positive side, it was found that aerial imagery is ideally suited to observing coastal dynamical phenomena such as river plume development. These near shore dynamical processes cannot be monitored by satellite imagery and so aerial resolution and aircraft manoeuvrability are ideal for this type of coastal zone remote sensing.