Analysis of Historical MERIS Data to Evaluate the Impact of Dredging to Monthly Mean Surface TSM Concentration
Raag, Laura; Uiboupin, Rivo; Sipelgas, Liis
Marine Systems Institute at Tallinn University of Technology, ESTONIA
Dredging operations in coastal waters affect water quality through an increase in suspended matter concentration. Total Suspended Matter (TSM) is determined by the backward scattering of light in the visible region, which can be retrieved using satellite data. The relation between scattering and TSM depends on the region. We studied the changes of TSM distribution in Estonian coastal sea with special interest in Muuga and Paldiski bay, where two biggest harbors of Estonia are located. The purpose of current study was to examine the suitability of remote sensing data to detect the turbidity differences caused by dredged sediments and to evaluate the impact of monthly mean dredging cubage to the surface TSM concentration retrieved from satellite images. We used MERIS (Medium Resolution Imaging Spectrometer) Full Swath Geo-located (FSG) products with 300m resolution from years 2006-2010 in our analysis. Images with L1P processing were downloaded and analyzed for detection of water turbidity over the Estonian coastal sea. Images were further processed using the Case-2 waters processors developed by Free University of Berlin (FUB) to calculate the TSM concentration. Validation of the FUB processor with in situ measurements of TSM at the time of dredging operation was implemented. Analysis showed good correlation between satellite data and in situ TSM measurements (correlation (r2) 0,89) at the time of dredging operations when only one type of particles were dominant in water mass. But in case there were particles of different origin and with no dominant particle type present, the algorithm provided insufficient results. For further analysis of environmental impact the average TSM maps in the harbor region were calculated from MERIS data. The maps covered different timeframes: annual mean, monthly mean, season mean, dredging period mean and non-dredging period mean. These maps were compared to the monthly mean dredging cubage. Comparison reviled that in case of monthly mean dredging cubage more than 5250 m3 the changes in monthly mean TSM maps can be detected.