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Inproceedings Reference Backscatter stability and influence of water column conditions: estimation by multibeam echosounder and repeated oceanographic measurements, Belgian part of the North Sea
The European Union Marine Strategy Framework Directive requires Member States to monitor and assess the health status of their marine habitats. Belgium put forward that the spatial extent and distribution of the major habitats (sandy mud to mud, muddy sands to sands and coarse-grained sediments), as well as that of gravel beds may only fluctuate within a margin that is limited to the accuracy of the current sediment distribution maps. Due to their ability to provide simultaneous bathymetry and backscatter strength (BS), reflecting seabed nature, multibeam echosounder systems (MBES) provide a time- and costefficient solution to anticipate on this legal obligation. However, as there is no formal quality level scale for the BS and consequently no level of reliability of the final decibel values, evaluating the BS quantitative capabilities to monitor habitat changes remains challenging. In a monitoring context, it is absolutely necessary to investigate to what extent the mean MBES-measured BS variation -from one cruise to another- actually represents a significant change in seabed properties and not only a change in the conditions of the water column (e.g., variation in near-bed suspensions, biological effects, increased occurrence of micro bubbles in the sea surface due to wind) at the time of the measurement. In order to evaluate the relative accuracy and the repeatability of MBES BS and to examine the external sources of variance in acoustic signatures, repeated measurements combining MBES with an Acoustic Doppler current Profiler (ADP) have been performed during tidal cycles on reference areas in the Belgian part of the North Sea. Currents and BS in the water column and vertical profiling of oceanographic parameters have been investigated allowing studying the influence of water column conditions on the BS. Measurements were conducted using two MBES systems to evaluate repeatability between echosounders. Ultimate goal is to arrive at seabed mapping and analyses protocols to obtain harmonized data products from a collaborative seabed mapping community.
Located in Library / RBINS Staff Publications
Inproceedings Reference Influence of shells and shell debris on backscatter strength: investigation using modeling, sonar measurements and sampling on the Belgian Continental Shelf
Acoustic interaction theory and observation highlight the strong relation between the acoustic signal responses and the physical and biological processes acting on the seafloor and in the water column. Several descriptors such as sediment texture, porosity and surface roughness are identified as the main factors affecting the acoustic reverberation and backscatter signals. Shells can influence if not dominate the scattering on the seafloor(Jackson et al., 1986; Stanic et al., 1989 and Zhang, 1996). Scattering from both inclusions and partially buried shells on the sea-floor is described by Stanton (2000), and scattering from shells as a potential mechanism explaining the scattering above 200 kHz is highlighted by Ivakin (2009). In order to improve the knowledge on this matter, several institutions with different expertise are cooperating to integrate mathematical modeling and experimental results to better quantify the influence of shells and shell debris on the acoustic signal and scattering of sonar images. Mathematical 3D models of shell objects in a sediment matrix will be used to simulate the influence of the shells on acoustic signal and scattering. The physical arrangements of shells and their spatio-temporal population trends are also considered in the modeling. The models will be supported by direct sonar measurements of seafloor areas on the Belgian Continental Shelf, combined with sampling, visual observations, classification and shape analysis of the shells and shell debris.
Located in Library / RBINS Staff Publications
Inproceedings Reference New insights on Uppermost Famennian brachiopods from north-western France (Avesnois)
Located in Library / RBINS Staff Publications
Article Reference New insights on Uppermost Famennian brachiopods from north-western France (Avesnois).
Located in Library / RBINS Staff Publications
Article Reference Middle and Upper Devonian Events in Belgium: review and new insights.
Located in Library / RBINS Staff Publications
Article Reference The Red Marble of Baelen, an exceptional mid-Famennian mud mound complex in a carbonate ramp setting from Eastern Belgium
Located in Library / RBINS Staff Publications
Article Reference Pridolian–Lochkovian macrofaunas from southern Belgium and northern France: de Koninck (1876) revisited.
Located in Library / RBINS Staff Publications
Article Reference Diversity of athyridide brachiopods during the Late Devonian–Tournaisian in southern Belgium.
Located in Library / RBINS Staff Publications
Article Reference Orbitally forced sequences and climate reconstruction around the Devonian–Carboniferous boundary, and the Hangenberg Extinction Event
Located in Library / RBINS Staff Publications
Article Reference Hidden biodiversity in an ancient lake: phylogenetic congruence between Lake Tanganyika tropheine cichlids and their monogenean flatworm parasites
The stunning diversity of cichlid fishes has greatly enhanced our understanding of speciation and radiation. Little is known about the evolution of cichlid parasites. Parasites are abundant components of biodiversity, whose diversity typically exceeds that of their hosts. In the first comprehensive phylogenetic parasitological analysis of a vertebrate radiation, we study monogenean parasites infecting tropheine cichlids from Lake Tanganyika. Monogeneans are flatworms usually infecting the body surface and gills of fishes. In contrast to many other parasites, they depend only on a single host species to complete their lifecycle. Our spatially comprehensive combined nuclear-mitochondrial DNA dataset of the parasites covering almost all tropheine host species (N = 18), reveals species-rich parasite assemblages and shows consistent host-specificity. Statistical comparisons of host and parasite phylogenies based on distance and topology-based tests demonstrate significant congruence and suggest that host-switching is rare. Molecular rate evaluation indicates that species of Cichlidogyrus probably diverged synchronically with the initial radiation of the tropheines. They further diversified through within-host speciation into an overlooked species radiation. The unique life history and specialisation of certain parasite groups has profound evolutionary consequences. Hence, evolutionary parasitology adds a new dimension to the study of biodiversity hotspots like Lake Tanganyika.
Located in Library / RBINS Staff Publications