Nathalie Long

Monitoring the Topography of a Dynamic Tidal Inlet Using UAV Imagery

Unmanned Aerial Vehicles (UAVs) are being increasingly used to monitor topographic changes in coastal areas. Compared to Light Detection And Ranging (LiDAR) data or Terrestrial Laser Scanning data, this solution is low-cost and easy to use, while allowing the production of a Digital Surface Model (DSM) with a similar accuracy. Three campaigns were carried out within a three-month period at a lagoon-inlet system (Bonne-Anse Bay, La Palmyre, France), with a flying wing (eBee) combined with a digital camera. Ground Control Points (GCPs), surveyed by the Global Navigation Satellite System (GNSS) and post-processed by differential correction, allowed georeferencing DSMs. Using a photogrammetry process (Structure From Motion algorithm), DSMs and orthomosaics were produced. The DSM accuracy was assessed against the ellipsoidal height of a GNSS profile and Independent Control Points (ICPs) and the root mean square discrepancies were about 10 and 17 cm, respectively. Compared to traditional topographic surveys, this solution allows the accurate representation of bedforms with a wavelength of the order of 1 m and a height of 0.1 m. Finally, changes identified between both main campaigns revealed erosion/accretion areas and the progradation of a sandspit. These results open new perspectives to validate detailed morphological predictions or to parameterize bottom friction in coastal numerical models.

Sensitivity of Spatial Indicators for Urban Terrain Characterization

To develop and manage urban territories and to analyze urbanisation impact on environment, an accurate knowledge of the city and its urban fabric is necessary. A physical description like building morphology or land cover/use allows some characterization of the urban terrain. A specific package for a GIS software is developed for urban analysis: UrbSAT (Urban Spatial Analysis Tool). It allows extracting knowledge from various data sources and gives some indicators to real applications (sustainable development, management policy, air quality improvement, etc). It raises issues such as database accuracy and quality, cell shape, size and orientation for the construction of spatial indicators. We present some tests to address those issues.

Participatory simulation to foster social learning on coastal flooding prevention

Abstract Due to the increase in coastal flooding risk associated with sea-level rise and increasing population along the coasts, there is a strong need to develop efficient and long-term management strategies. In partnership with the local administration of Oleron Island in France, a participatory simulation model was developed to foster social learning about coastal risk prevention measures with local authorities and managers. This simulation integrates a coastal flooding model and a spatially explicit agent-based model that simulates the development of the area and the management of prevention measures. The participatory set-up includes an immersive environment for participants to remember the coastal flooding simulation displayed and a role game mechanism that simulates the coordination issues between the different decision bodies involved in coastal risk management. A first application proved that participants learn about the water expansion dynamics during flood events and the effects of building, raising and restoring dikes.

A multi-scale, morphological interpretation of the sustainable city

This article seeks to highlight a shift in development of the city towards a sustainable model through the prism of morphology. It presents multi-scale, morphological keys for understanding, making it possible to identify and detail the physical and structural elements which comprise the sustainable city. Via these keys for understanding, the article endeavours to identify the various physical elements and structures of this urban landscape which is undergoing radical transformation. On what scale is the drive towards a sustainable city the most noteworthy? Does the slogan \“act locally, think globally” also apply to the urban territory? This paper begins by outlining the concepts of the sustainable city. There then follows a description and analysis of morphological keys for understanding the sustainable city. Finally, the concluding part covers application of these keys to the city of Nantes, which hosts several sustainable development projects and will assume the mantle of European Green Capital in 2013.

A combined approach to detect urban features from multi-spectral and radardata

With increase of urban population, the cities have an impact more and more important on environment. Because of artificial surface, building morphology, economical activities, traffic several natural ecosystem are modified. To analyze this impact, the land covers/land uses have to be identified exactly in an urban area. To reach this objective, remote sensing represents an important and complete source of information. Joint use of radar and optical data allows improving results of classical classification to identify the cover mode. Re-sampled to 1m resolution, the difference between the two classifications is analyzed to detect the confusion in each class corresponding to a land cover/land use. Finally, a vector process allowed to transform the geometry of the results: a polygon aggregates several pixels. Combination of results is also possible with GIS functionalities like contains, intersect, cut, and permits to propose aland cover/ land use description on the study area.