Monitoring North Sea Coastal Waters:
from Radiance at Sensor Data to a Web Mapping Service

M.A. Eleveld (1), A.J. Wagtendonk(2), R. Pasterkamp (1), A.Q.A. Omtzigt (2)

(1) Programme Unit Remote Sensing (PERS), Institute for Environmental Studies, Vrije Universiteit Amsterdam (NL)
(2) SPatial INformation laboratory (SPINlab), Vrije Universiteit Amsterdam (NL)

Monitoring is a prerequisite for assessment of changes in the state of the North Sea. Various ocean colour satellite sensors collect data sets of the North Sea every day. These data sets need to be processed to extract information on water quality parameters. Processing needs to be optimised when using remote sensing for monitoring purposes. This paper presents the development of a processing chain for the monitoring of Total Suspended Matter (TSM) in the southern North Sea with Sea-viewing Wide Field-of-view Sensor (SeaWiFS) data. All 2001 SeaWiFS data of the research area were acquired and processed using the SeaWiFS Data Analysis System (SeaDAS 4.0) with MUMM's turbid water extended atmospheric correction algorithm. Subsequently, the POWERS TSM algorithm was used to derive TSM concentration (in mg l­1) from SeaWiFS sub-surface irradiance reflectance, R(0­), in band 5. This resulted in 491 TSM products: on average more than one image a day. Seasonal variation in TSM concentration was extracted from composites, and statistics on TSM concentrations were produced for any location within the research area. The data were exported as tables with comma separated values. In ArcView 3.3 with the Spatial Analyst extension, these values were imported as Event themes into a View with Universal Transverse Mercator (UTM) WGS 84 projection. The points were converted to grids using the Nearest Neighbour algorithm, and exported as georeferenced images. Scripts were used to incorporate the grids into the IVM map layout for an atlas. The grids were also provided on CD to enable further GIS analysis. Images from the previous year (2000) were used in an ArcIMS application. The IVM processing chain enabled us to process 491 data sets within a few weeks time. The results are useful for monitoring, because of their 2D spatial and temporal coverage (an average sampling of 107 data sets per pixel over a total of 491 TSM data sets for 2001). These results led to new insights into some of the large scale processes in the North Sea. Unfortunately, the processing chain cannot automatically be adapted for the processing of data from other ocean colour sensors, but certain components can be plugged into new processing chains. The monitoring data are currently available in different formats for different users: as a hardcopy atlas accompanied by a CD with the data in ArcView format for the coastal management authorities that commissioned the work, and (for the 2000 data) as a Web mapping service that allows anyone with an Internet connection to interactively combine the TSM data with other geographical information. User preferences for these products will be further investigated using the CoastBase User Requirements Study approach.