Reconstruction bathymétrique sonar en présence de trajets multiples et de bruit impulsif

National audienceCet article propose une méthode de poursuite de l'angle d'arrivée de l'écho principal rétrodiffusé par le fond marin pour la reconstruction bathymétrique. Cette méthode présente certains avantages par rapport aux techniques classiques d'estimation de l'angle d'arrivée et permet en particulier de régulariser la trajectoire de l'angle estimé et ainsi réduire le niveau d'interférence causé par les échos secondaires

Control of the repeatability of high frequency multibeam echosounder backscatter by using natural reference areas

The increased use of backscatter measurements in time series for environmental monitoring necessitates the comparability of individual results. With the current lack of pre-calibrated multibeam echosounder systems for absolute backscatter measurement, a pragmatic solution is the use of natural reference areas for ensuring regular assessment of the backscatter measurement repeatability. This method mainly relies on the assumption of a sufficiently stable reference area regarding its backscatter signature. The aptitude of a natural area to provide a stable and uniform backscatter response must be carefully considered and demonstrated by a sufficiently long time-series of measurements. Furthermore, this approach requires a strict control of the acquisition and processing parameters. If all these conditions are met, stability check and relative calibration of a system are possible by comparison with the averaged backscatter values for the area. Based on a common multibeam echosounder and sampling campaign completed by available bathymetric and backscatter time series, the suitability as a backscatter reference area of three different candidates was evaluated. Two among them, Carré Renard and Kwinte, prove to be excellent choices, while the third one, Western Solent, lacks sufficient data over time, but remains a valuable candidate. The case studies and the available backscatter data on these areas prove the applicability of this method. The expansion of the number of commonly used reference areas and the growth of the number of multibeam echosounder controlled thereon could greatly contribute to the further development of quantitative applications based on multibeam echosounder backscatter measurements

WIKWIO Portal: An online resource on weeds for sugarcane growers

Efficient control of weeds is only achievable through a clear and sound knowledge of their biology and ecology. The Weed Identification and Knowledge in the Western Indian Ocean (WIKWIO) portal (http://portal.wikwio.org/) has been developed to meet this objective. It aims at building and leveraging a science and technology network to consolidate existing scientific and technical knowledge, and facilitating the sharing of new information. Although the portal currently covers the Indian Ocean region, most of the tropical weeds that are documented are also present in many other sugarcane-producing countries. This paper highlights the benefits that this resource can have to growers for managing weeds in their fields. The WIKWIO portal is the outcome of a three-year collaboration among weed scientists of CIRAD (France), CNDRS (Comoros), FOFIFA (Madagascar), IFP (India) and MSIRI (Mauritius). A community of stakeholders involved in weed knowledge and management, also collaborated in the action. Experts from the six research institutions worked on a list of nearly 470 species of tropical weeds. They compiled and validated information on the biology, ecology, distribution, agronomic importance and management of each weed species in datasheets in both English and French. Each weed has been fully illustrated with high- resolution pictures and scanned herbarium sheets to provide additional details. Botanists and computer engineers set up an information system to host these data, in addition to other tools that facilitate rapid weed recognition and documentation. The portal became operational in early 2014 and was improved with various options at the completion of the project in February 2017. More than 750 users have registered on the WIKWIO network, contributing over 10,000 observations of weeds, many of them encountered in sugarcane fields in various parts of the world. All the observations posted on the website are geo-referenced, thus providing useful data on their ecological distribution. Identified species are linked to the appropriate datasheets, giving insights into their management and control. Weed identification is possible via a computer-aided tool (IDAO) available on the portal. This resource and the possibility of uploading observations onto the network are accessible through applications (apps) on mobile devices enabling easy use in the field for rapid weed control decision and intervention. The WIKWIO portal enhances a collaborative and participative approach by sharing knowledge and providing practical information. It can serve as a platform for establishing and reinforcing a community of sugarcane growers seeking help or exchanging experience on weed management issues. Nowadays, with the easy and rapid access to internet connectivity, timely assistance may be obtained through the portal. The latter takes place in a 'numerical agriculture' approach that is expected to evolve into a website for tropical weeds

Enjeux et contraintes du partage et de la diffusion des connaissances en malherbologie tropicale pour une meilleure gestion des enherbements, exemple du portail collaboratif Wiktrop

La production agricole tropicale est en pleine mutation et la gestion des enherbements est un élément majeur de la stratégie de l'agriculteur. L'élaboration d'itinéraires de gestion des adventices requiert de plus en plus de connaissances, sur la biologie des espèces, leur comportement dans les milieux cultivés et l'efficacité des pratiques de désherbage. L'accès à l'information est maintenant facilité par les infrastructures numériques en constante évolution, mais nécessite que la connaissance soit partagée, mise à jour et diffusée de façon continue. Une part de connaissance est présente chez chacun des acteurs (producteurs, vulgarisateurs, chercheurs, enseignants), mais sa compilation et sa diffusion présentent différentes contraintes d'ordre réglementaire, humain et technologique. Le portail collaboratif WIKTROP permet à tous les acteurs du monde agricole tropical de partager et diffuser leurs connaissances et leurs questionnements sur les adventices tropicales et leur gestion. Il est associé à des applications mobiles facilitant son utilisation au bureau, sur le terrain ou pour des formations

What does the world look like according to superdeterminism?

The violation of Bell inequalities seems to establish an important fact about the world: that it is non-local. However, this result relies on the assumption of the statistical independence of the measurement settings with respect to potential past events that might have determined them. Superdeterminism refers to the view that a local, and determinist, account of Bell inequalities violations is possible, by rejecting this assumption of statistical independence. We examine and clarify various problems with superdeterminism, looking in particular at its consequences on the nature of scientific laws and scientific reasoning. We argue that the view requires a neo-Humean account of at least some laws, and creates a significant problem for the use of statistical independence in other parts of physics and science more generally

Charm2000: A >10^8-charm experiment for the turn of the millennium

I discuss the physics reach of a fixed-target charm experiment which can reconstruct >10^8 charm decays, three orders of magnitude beyond the largest extant sample. Such an experiment may run at Fermilab shortly after the Year 2000. In addition to "programmatic" charm physics such as spectroscopy, lifetimes, and tests of QCD, this "Charm2000" experiment will have significant sensitivity to new physics in the areas of CP violation, flavor-changing neutral-current and lepton-number-violating decays, and mixing, and could observe direct CP violation in Cabibbo-suppressed decays at the level predicted by the Standard Model.Comment: 10 pages, 3 PostScript figure