Published on 10 November 2022
Monitoring turbid areas in the Belgian part of the North Sea is important as it is one of the key parameters that can have a detrimental ecological impact. Increasing human activities like the construction of offshore windmill parks and dredging activities may significantly influence Suspended Particulate Matter (SPM) variability. Improving our understanding of both natural and human-induced SPM variability is therefore essential for sustainable coastal management.
The team behind STEREO III project TIMBERS (3D Turbidity assessment through Integration of MultiBeam Echo-sounding and optical Remote Sensing), composed of researchers from VITO and VLIZ (Vlaams Instituut voor de Zee), investigated the possibility of generating 3D vertical turbidity profiles within the seawater column by combining two techniques, i.e. optical remote sensing and MultiBeam Echo-Sounding (MBES).
Yoyo-movement of the turbidity measurements with simultaneous multibeam water column data collection.
Satellite-derived turbidity is already a product in the portfolio of companies specialized in Earth observation and provides information of turbidity at the upper layers in the water column.
On the other hand, MBES-derived turbidity is a relatively new technique that is not yet applied in the field and opens the possibility of obtaining information on turbidity in lower layers of the water column.
Within the framework of the TIMBERS project, multiple field campaigns were organised in the Belgian part of the North Sea, a well-known dynamic area with high turbidity. The team collected hyperspectral radiometric data from the water surface as well as turbidity and SPM information from the water column (e.g. their particle size distribution and optical backscatter characteristics).
A first cube of merged surface ORS (Optical Remote Sensing) and underwater MBES (Multibeam echo-sounding) data has been generated based on data from the February 2021 campaign.
Drone image acquired during one of the TIMBERS field campaigns (21.04.2021). Right shows the True colour image, while on the left the derived turbidity map is given. The vessel generates a turbidity plume and impacts the in-situ measurements collected.
The TIMBERS team defined optimised protocols for collecting and processing multibeam water column data for turbidity extraction. Similarly, they developed protocols for assessing the quality of hyperspectral radiometric data (QWIP score, Dierssen et al., 2022). The most suitable algorithms for turbidity retrieval in the North Sea from satellite and drone data were also evaluated. The TIMBERS workflow resulted in the generation of 3D SPM cubes (mg/l) composed of multibeam-derived data for the bottom part and turbidity values retrieved from satellite data for the top part.