BALIST : nearshore bathymetry
The space-derived nearshore bathymetry provides bathymetric information (bottom depth) over shallow waters (0-20 m) where there is a lack of data or need for updated data.
The applicative tool produces information about bottom depth at metric/decametric resolution using HR/VHR optical multispectral satellite imagery from a range of sensors (e.g. Landsat-7/8, Sentinel-2, SPOT, Pleiades, Worldview, Quickbird).
The underlying technology is based on ocean color algorithms that transform pixel radiometry into water depth under specific environmental and imagery conditions (clear waters, limited glint effects at sea surface). Benthic habitat maps (sediment type i.e. sandy, rocky, coral reefs) may be delivered as an intermediate thematic product needed for bathymetry production along heterogeneous seabed coastline (typically in tropical coral reefs).
The BALIST processing tool encompasses several sub-routines coded under Matlab© for imagery pre-processing (masking, radiometric calibration), retrieval of water depth following multiple algorithm strategies upon availability of ground truthing, data post-processing including quality control by a thematic expert.
Bathymetric data in nearshore (0-10 m) coastal areas are essential for many reasons and several end users :
• Assessment of shallow water bathymetry (as an entry to coastal modelling studies) and seabed stability in areas where strategic industrial activities are located or expected to be : harbours, Marine Renewable Energy (wind farms, well farms, hydroliennes), cable routes,…
• Assessment of coastal sediment dynamics through the enhancement of beach morphodynamics and shoreline evolution knowledge. Acquisition of frequent bathymetric data along very dynamic sandy shores are critical for the elaboration of shoreline management strategies.
• Support for updating and/or completing bathymetric charts realized through traditional bathymetric surveys.
The satellite-derived nearshore bathymetry product is a relevant alternative to traditional bathymetric surveys : frequent updates (up to several times a year) enabling catching of yearly coastal morphodynamics, regional coverage at (decametric) spatial resolution and overall very less expensive (ten times less in average).
RIVERCOLOR : water quality / turbidity from land to the ocean
The RIVERCOLOR solution provides information relative to the water content in Suspended Particulate Matter (SPM Concentrations or turbidity) over rivers, estuaries and coastal areas. The added value of this product is the dedicated tool boxes developed for processing respectively HR / MR optical multispectral datasets (HR : Sentinel-2, Landsat-7/8; MR: Sentinel-3, MODIS) that performs ideally when an enlarged vision (from catchment basin to coastal areas) is seeked.
For now, algorithm strategy implemented is based on regional empirically-driven models which uses ground truth (SPM concentrations from in situ network and/or couples of simultaneous reflectance/SPM data) for algorithm calibration and thus enables the production of accurate (20 – 40 % in average) surface SPM concentrations. Generic optical models can also be used, but this option is not yet implemented in the RIVERCOLOR processing chain.
The RIVERCOLOR tool is providing a software-like interface enabling automatic downloading of MR and HR satellite images over the area of interest, data processing (atmospheric corrections if needed i.e. for high-resolution top-of-atmospheric products, land and cloud masking) and production of a series of SPM maps (image format). Currently, post-processing is finalized under GIS software from which several product outputs are possible : first-level is a database of SPM concentration maps in image/GIS format, secondary outputs are Near Real Time flash report, seasonal / yearly statistics and percentiles, spatial gradients along river continuum, delineation of turbid plumes and other.
The RIVERCOLOR applicative tool provides series of SPM concentration maps and secondary derived products, for both a retrospective analysis of historical environmental conditions and near-real-time monitoring of sediment dynamics. This bring added-value information for a range of end users needing to :
• Acknowledge the behaviour of Maximum Turbidity Zones over very turbid (SPM-dominated) estuaries in particular at summertime during low water levels (critical time periods for fauna / fish population because of prolonged anoxic conditions and thus having impacts over traditional fishing + freshwater catchment issue)
• Enhance the understanding of sediment dynamics over estuaries and coastal areas for better management of dredging activities (harbours), site assessment studies and impact analysis (marine renewable energy infrastructure projects).
• Evaluate impacts of natural forcing factors and anthropic activities (dredging, offshore works) over water quality and benthic habitats (seagrass, corals)