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The civil security sirens are used by the authorities in a wide range of countries to signal an imminent or ongoing threat. Even if their sound level is known, it is nevertheless difficult to evaluate their audibility across a given zone, especially in complex urban environments. An experimental protocol was deployed around a siren installed in a town in France, to assess its audibility perceptually and through modeling. Sound level measurements during source activation were made with the NoiseCapture smartphone application at different distances and on several axes by a group of 25 participants. They were also asked to fill in a questionnaire on perceptual information about the siren such as its audibility, the perceived sound level, or the masking of the siren by passing vehicles. A comparison between acoustic measurement levels using NoiseCapture and simulated sound levels using NoiseModelling was performed. The results of this study validate the use of the Common Noise Assessment Methods in Europe model to evaluate the audibility of a warning system located in an urban environment within a radius of 2.8 km around the siren. Finally, a metric linking audibility to modeled sound level is proposed, enabling the development of siren audibility maps in the study area.

The mapping of the damage caused by natural disasters is a crucial step in deciding on the actions to take at the international, national, and local levels. The large variety of representations that we have observed leads to problems of transfer and variations in analysis. In this article, we propose a representation, Regular Dot map (RD), and we compare it to 4 others routinely used to visualise post-disaster damage. Our comparison is based on a user study in which a set of participants carried out various tasks on multiple datasets using the various visualisations. We then analysed the behaviour during the experiment using three approaches: (1) quantitative analysis of user answers according to the reality on the ground, (2) quantitative analysis of user preferences in terms of perceived effectiveness and appearance, and (3) qualitative analysis of the data collected using an eye tracker. The results of this study lead us to believe that RD is the best compromise in terms of effectiveness among the various representations studied. [ABSTRACT FROM AUTHOR]

In post-disaster context, air assets represent an effective solution to act quickly in a devastated environment. Among these means, the flexibility, the economic advantage and the possibilities offered by Unmanned Aircraft System, also known as UAS, particularly in terms of 3D reconstructions and cartography, make them an alternative investigation tool that is rapidly expanding. Five applications of these UAV surveys are illustrated in this article after the passage of Hurricane Irma over the French North West Indies in September 2017 (Saint-Martin and Saint-Barthélemy). They illustrate the technical and scientific potentialities of these new tools, the modalities of their implementation, and give us also the opportunity to discuss about their limitations in the context of post-disaster feedback. The results obtained are multiple and offer a high operational value for the prevention of cyclonic risks. They concern the spatial analysis of debris dispersal and the reconstruction of associated volumes, the reliability of damage estimates on buildings, the monitoring of the reconstruction process, and the understanding of geomorphological impacts on the coastline. [ABSTRACT FROM AUTHOR]

In view of the high vulnerability of the Lesser Antilles small islands to cyclonic hazards, realistic very fine scale numerical simulation of hurricane-induced winds is essential to prevent and manage risks. The present innovative modeling aims at combining the most realistic simulated strongest gusts driven by tornado-scale vortices within the eyewall and the most realistic complex terrain effects. The Weather Research and Forecasting (WRF) model with the Nonlinear Backscatter and Anisotropy (NBA) Large Eddy Simulation (LES) configuration was used to reconstruct the devastating landfall of category 5 Hurricane Irma (2017) on Saint Barthélemy and Saint Martin islands. The results pointed out that the 30-m scale seems necessary to simulate intense 400-m scale vortices leading to extreme peak gusts like 132 m s-1 over sea. Risk areas associated with terrain gust speed-up factors greater than one have been identified for the two islands. The comparison between the simulated gusts and the remote sensing building damages highlighted the major role of structure strength linked with the socio-economic development of the territory. The present modeling method could be easily extended to other small mountainous islands to improve the understanding of observed past damages and to develop safer urban management and appropriate building standards. [ABSTRACT FROM AUTHOR]

This study aims to better understand coastal processes associated with extreme cyclonic events through the study of the coastal changes, flooding and damage that resulted from the passage of a category 5 hurricane (Irma) on 6 September 2017 over the islands of Saint-Martin and Saint-Barthélemy in the Lesser Antilles. Hurricane Irma was contextualized from tropical cyclone track data and local weather observations collected by Météo-France, as well as high-resolution numerical modelling. Field work involved the study of accretion coasts through qualitative observations, topo-morphological and sedimentary surveys, as well as image acquisition with Unmanned Aerial Vehicle (UAV) surveys during two trips that were made 2 and 8 months after the catastrophe. Wave propagation and flood numerical models are presented and compared to field data. Our field analysis also reports on the devastating impacts of storm surges and waves, which reached 4 and 10 meters height, respectively, especially along east-facing shores. The approaches reveal a variety of morpho-sedimentary responses over both natural and highly urbanized coasts. The analysis shows the effects of coastal structures and streets on flow channeling, on the amplification of some erosion types, and on water level increase. Positive spatial correlation is found between damage intensity and marine flood depth. The signatures of ocean-induced damage are clear and tend to validate the relevance of the intensity scale used in this study. [ABSTRACT FROM AUTHOR]