Bottom and Suspended Sediment Backscatter Measurements in a Flume—Towards Quantitative Bed and Water Column Properties

For health and impact studies of water systems, monitoring underwater environments is essential, for which multi-frequency single- and multibeam echosounders are commonly used state-of-the-art technologies. However, the current scarcity of sediment reference datasets of both bottom backscatter angular response and water column scattering hampers empirical data interpretation. Comprehensive reference data derived from measurements in a controlled environment should optimize the use of empirical backscatter data. To prepare for such innovative experiments, we conducted a feasibility experiment in the Delta Flume (Deltares, The Netherlands). Several configurations of sonar data were recorded of the flume floor and suspended sediment plumes. The results revealed that flume reverberation was sufficiently low and that the differential settling of fine-sand plumes in the water column was clearly detected. Following this successful feasibility test, future comprehensive experiments will feature multi-frequency multi-angle measurements on a variety of sediment types, additional scatterers and sediment plumes, resulting in reference datasets for an improved interpretation of underwater backscatter measurements for scientific observation and sustainable management

Advanced Processing Methods for Image-Based Displacement Field Measurement

International audienceWe present recent developments in data processing for velocity field estimation and visualization originating from computer vision. We review the current paradigm of PIV data processing, based on window correlation, and the regularization or variational approach which is dominant in optical flow estimation. We propose a novel unifying framework via the optimization of a compound regularized criterion written in terms of a dense displacement (or velocity) field. The paper then focuses on algorithmic issues.A fast iterative window correlation method leading to a highly parallel lgorithm termed FOLKI is described. Thanks to a GPU (Graphical Processing Unit) implementation, FOLKI reaches video rate for typical PIV data. Then we present more sophisticated solvers able to deal with the regularization term of the criterion, notably multigrid methods.In our view, these two components form the foundation of a video rate velocity field visualization and interpretation toolbox which, together with recent advances in experimental apparatus and numerical simulation, opens the way to a major development in experimental fluid science

Experimental evaluation of seven quality control phantoms for digital breast tomosynthesis

International audiencePurposes: The introduction of digital breast tomosynthesis (DBT) into the French breast cancer screening program is forecast by the authorities. The aim of the present study was to evaluate image quality phantoms to be used as internal quality controls. Methods: Seven breast phantoms dedicated to quality control in mammography were evaluated on reconstructed DBT images: ACR Model 015, BR3D, DBT QC model 021, Mam/Digi-EPQC, MTM100, TOMOMAM® and TOMOPHAN®. Two representative image parameters of DBT images were studied: image score and z-resolution, when inserts were included in the phantom, on five DBT systems of three different brands. Three observers were involved. Results: The MTM100, Mam/Digi-EPQC, BR3D, DBT QC model 021 phantoms' images presented artefacts affecting the image score. The ACR Model 015, TOMOMAM® and TOMOPHAN® phantoms appeared to be pertinent for DBT image score analysis. Due to saturation artefacts, Z-resolution results were not coherent with the theory for all phantoms except by using aluminium beads in the TOMOMAM® phantom. Conclusions: Phantom manufacturers should be encouraged to collaborate with DBT system manufacturers in order to design universal phantoms suitable for all systems for more complete quality control. From our study we can propose several specifications for an ideal and universal phantom designed for internal quality control in DBT. Phantoms should allow sensitive image score measurements. The background structure should be realistic to avoid artefacts. Phantoms should have a standard breast-like shape and size. © 2019 Associazione Italiana di Fisica Medic