Optical remote sensing in support of water quality monitoring in the southern North Sea

S J Dury, J H M Hakvoort, R W L Jordans
Rijkswaterstaat, AGI , Derde Wereldreef 1, 2622 HA Delft, The Netherlands

ABSTRACT

The quality of surface water in the Dutch coastal zone is currently monitored through periodical ship-based measurements of a number of parameters at a network of fixed stations. However, representative spatial patterns of water quality parameters cannot be produced using these traditional in situ sampling techniques. Furthermore, because of budget constraints cost-effective alternatives to the very expensive ship cruises are urgently needed. Parameters such as the concentration of total chlorophyll or total suspended matter can alternatively be measured using optical remote sensing. In this study the potential use of water quality products from the space-borne instruments MERIS, MODIS and SeaWiFS is assessed, in the framework of the EU project OROMA and the ESA GSE Coastwatch initiative. Standard products from these instruments are compared with in situ data, and improvements in the quality of the results are obtained through consideration of appropriate atmospheric correction for turbid coastal waters and the use of local inherent optical properties. The selected cases show that space-borne remote sensing techniques are at least complementary to the traditional monitoring techniques. The accuracy of concentration maps obtained with remote sensing techniques is comparable with the accuracy of maps obtained with the classical monitoring techniques. Maps of total suspended matter and chlorophyll concentration derived from satellite-based sensors can therefore provide a valuable supplement to the existing in situ programme for monitoring of water quality in Dutch waters. In particular, a thorough assessment of spatial variability of the ecosystem becomes feasible and, even allowing for cloudy periods, the temporal coverage is comparable to that of the in situ sampling at the stations. Statistical evaluation of time series data enables comparison of water quality products from each of the three sensors studied.

Last Update: 2005-04-7