Environmental Monitoring of Harbour Dredging Using EO Data
Sipelgas, Liis; Uiboupin, Rivo; Raag, Laura; Lagemaa, Priidik; Alari, Victor
Marine Systems Institute at Tallinn University of Technology, ESTONIA

In 2011 the Estonian PECS program supported the project 'Environmental Monitoring of Harbor Dredging'. The goal of the project is to develop a tool for environmental monitoring during harbour dredging activities using Earth Observation (EO) data, in situ measurements and hydrodynamical modeling. Second objective of the project is to analyze the suspended matter distribution in the vicinity of the ports during 10 years period to asses the background levels of suspended matter concentration and to evaluate the environmental impact of port development and maintenance. Sub-objectives of the project are: (a) Development of site specific algorithms for retrieval of water quality parameters (e.g. total suspended matter) from multi sensor EO data. (b) Integration of EO data, in situ measurements and numerical model outputs to characterize and forecast water quality during the dredging activities. (c) Creation of an online GIS based user interface where the EO data, in situ measurements and model outputs are presented/updated operationally to provide overview of the water quality in the dredging region for interested parties (decision makers, port authorities, environmental agencies).
We assessed the site specific processors/algorithms for retrieving of water quality parameters (suspended matter concentration, chlorophyll concentration) as well as the size and type distribution of suspended particles from EO data. Finally EO data from MERIS (Medium Resolution Imaging Spectrometer) were used. 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 implemented at the time of dredging operation was done. Analysis showed good correlation between satellite data and in situ TSM measurements at the time of dredging operations when only one type of particles were dominant in water mass. However, in case there were particles of different origin and with no dominant particle type present, the algorithm provided insufficient results. The mean maps describing concentration of total suspended matter in the harbour region were calculated for further analysis. The maps cover different timeframes: annual mean, monthly mean, season mean, dredging period mean and non-dredging period mean. The average maps are based on MERIS data from years 2006-2009 that was provided by project CoastColour (Brocmann Consult; http://www.coastcolour.org/). Mean maps will be used in the monitoring system (final outcome of project) to describe the background TSM levels (''normal conditions'') in case there is no dredging impact.
The information about wind and currents is extracted from the HIROMB model (High Resolution Operational Model for the Baltic Sea). HIROMB model provides 48 h forecast from which only 24 h forecast will be used as the quality of the forecast is higher for shorter time period. The spatial resolution of the HIROMB model data is 0.5 nautical miles (900m) which is coarser compared to remote sensing data (250m). However, it is sufficient to describe the wind and current conditions in the harbour area. The forecast data is necessary for operational planning and monitoring purposes. Also the model data time series are used that enable to carry out retrospective analysis of the dredging activities (effect of physical conditions on dredging bloom).The wave data is included because wave conditions influence resuspensioon of particles in the shallow areas thus causing increasing TSM concentration values in the surface layer. The wave field information (significant wave height and wave direction) with 1 km horizontal resolution is provided by SWAN model (www.swan.tudelft.nl) which is running operationally at Marine Systems Institute and covers the entire Baltic Sea. The 1 km resolution is currently the state of the art for the Baltic Sea region. Subsets of wave information near dredging sites are extracted from the model outputs for the harbour dredging monitoring purposes.
Online user interface was developed to provide the harbour developers operational information about water quality and physical parameters during dredging activities. The on-line user interface will provide graphical information about the following parameters: (a) daily total suspended matter obtained from EO data, (b) background levels of total suspended matter obtained from mean monthly average satellite data, (c) total suspended matter obtained from in situ measurements, (d) significant wave height and (e) wind speed. As a result of the project the EO data and outputs of operational models are now routinely available and can be used for dredging monitoring purposes. EO data from MODIS and MERIS sensors are validated and calibrated for two main harbours areas in Paldiski and Muuga. Monthly mean suspended matter maps for Estonian coastal area are ready and can used as reference to evaluate the environmental impact caused by ongoing dredging.
The developed dredging monitoring system will be implemented, tested and adjusted in real-time dredging monitoring in spring 2013. It is planned to use the data from Sentinel-2 and Sentinel-3 missions for monitoring of suspended matter load in the coastal waters when the data becomes available in late 2013 - early 2014