Sedze M.,CNRS Paris Institute of Global Physics |
Sedze M.,Institute National Of Linformation Geographique Et Forestiere |
Heggy E.,Jet Propulsion Laboratory |
Bretar F.,Normandie Center |
And 2 more authors.
International Geoscience and Remote Sensing Symposium (IGARSS) | Year: 2012
We combine ALOS-PALSAR coherence images with airborne LiDAR data, both acquired over the Piton de la Fournaise volcano (Reunion Island, France), to study the main errors affecting repeat-pass InSAR measurements and understand their causes. The high resolution DTM generated using LiDAR data is used to subtract out the topographic contribution from the interferogram and to improve the radar coherence maps. The relationship between LiDAR intensity and radar coherence is then analyzed over several typical volcanic surfaces: it helps to evaluate the coherence loss terms. Additionally, the geometric and physical properties of these surfaces have been measured in situ. Coherence deteriorates over pyroclastic deposits and rough lava flows due to volume and surface scattering. In the presence of vegetation, it is directly related to plant density: the higher the Leaf Area Index (LAI), the lower the coherence. The accuracy of InSAR measurements strongly decreases for LAI higher than 7. © 2012 IEEE.
Mecheri S.,University Paris Est Creteil |
Rosey F.,Normandie Center |
Lobjois R.,University Paris Est Creteil
Accident Analysis and Prevention | Year: 2017
Previous research has shown that lane-width reduction makes drivers operate vehicles closer to the center of the road whereas hard-shoulder widening induces a position farther away from the road's center. The goal of the present driving-simulator study was twofold. First, it was aimed at further investigating the respective effects of lane and shoulder width on in-lane positioning strategies, by examining vehicle distance from the center of the lane. The second aim was to assess the impact on safety of three possible cross-sectional reallocations of the width of the road (i.e., three lane-width reductions with concomitant shoulder widening at a fixed cross-sectional width) as compared to a control road. The results confirmed that lane-width reduction made participants drive closer to the road's center. However, in-lane position was affected differently by lane narrowing, depending on the traffic situation. In the absence of oncoming traffic, lane narrowing gave rise to significant shifts in the car's distance from the lane's center toward the edge line, whereas this distance remained similar across lane widths during traffic periods. When the shoulders were at least 0.50 m wide, participants drove farther away from both the road center and the lane center. Road reallocation operations resulted in vehicles positioned farther away from the edge of the road and less swerving behavior, without generating higher driving speeds. Finally, it is argued that road-space reallocation may serve as a good low-cost tool for providing a recovery area for steering errors, without impairing drivers’ behavior. © 2017 Elsevier Ltd
Bretar F.,Normandie Center |
Bretar F.,Laboratoire Of Geomatique Appliquee |
Arab-Sedze M.,University Paris Diderot |
Arab-Sedze M.,Laboratoire MATIS |
And 4 more authors.
Remote Sensing of Environment | Year: 2013
We present a rapid in situ photogrammetric method to characterize surface roughness by taking overlapping photographs of a scene. The method uses a single digital camera to create a high-resolution digital terrain model (pixel size of ~1.32mm) by means of a free open-source stereovision software. It is based on an auto-calibration process, which calculates the 3D geometry of the images, and an efficient multi-image correlation algorithm. The method is successfully applied to four different volcanic surfaces-namely, a'a lava flows, pahoehoe lava flows, slabby pahoehoe lava flows, and lapilli deposits. These surfaces were sampled in the Piton de la Fournaise volcano (Reunion Island) in October, 2011, and displayed various terrain roughnesses. Our in situ measurements allow deriving digital terrain models that reproduce the millimeter-scale height variations of the surfaces over about 12m2. Five parameters characterizing surface topography are derived along unidirectional profiles: the root-mean-square height (ξ), the correlation length (Lc), the ratio Zs=ξ2/Lc, the tortuosity index (τ), and the fractal dimension (D). Anisotropy in the surface roughness has been first investigated using 1-m-long profiles circularly arranged around a central point. The results show that Lc, Zs and D effectively catch preferential directions in the structure of bare surfaces. Secondly, we studied the variation of these parameters as a function of the profile length by drawing random profiles from 1 to 12m in length. We verified that ξ and Lc increase with the profile length and, therefore, are not appropriate to characterize surface roughness variation. We conclude that Zs and D are better suited to extract roughness information for multiple eruptive terrains with complex surface texture. © 2013 Elsevier Inc.
Ferraz A.,University Paris Est Creteil |
Ferraz A.,University Paris Diderot |
Ferraz A.,Polytechnic Institute of Coimbra |
Bretar F.,Normandie Center |
And 6 more authors.
Remote Sensing of Environment | Year: 2012
This study presents a robust approach for characterization of multi-layered forests using airborne laser scanning (ALS) data. Fuel mapping or biomass estimation requires knowing the diversity and boundaries of the forest patches, as well as their spatial pattern. This includes the thickness of the main vegetation layers, but also the spatial arrangement and size of the individual plants that compose each stratum. In order to decompose the ALS point cloud into genuine 3-D segments corresponding to individual vegetation features, such as shrubs or tree crowns, we apply a statistical approach based on the mean shift algorithm. The segments are progressively assigned to a forest layer: ground vegetation, understory or overstory. Our method relies on a single biophysically meaningful parameter, the kernel bandwidth, which is related to the local forest structure. It is validated on 44 plots of a Portuguese forest, composed mainly of eucalyptus (Eucalyptus globulus Labill.) and maritime pine (Pinus pinaster Ait.) trees. The number of detected trees varies with the dominance position: from 98.6% for the dominant trees to 12.8% for the suppressed trees. Linear regression models explain up to 70% of the variability associated with ground vegetation and understory height. © 2012 Elsevier Inc.
Rosey F.,Normandie Center |
Auberlet J.-M.,University Paris Est Creteil
Safety Science | Year: 2012
The analysis of the variability of vehicle trajectories can reveal important information about how situational constraints influence drivers' behaviour (e.g., lateral position and/or speed). Variability in the lateral position using a driving simulator was examined. Forty-two participants had to drive on two road environments: a 3. km straight road with a crest vertical curve (CVC) with perceptual treatments and narrowed lane width with subsequent provision of a hard shoulder, by relocation of the road markings. The results showed that, on the one hand the lateral position variability was greater when driving on the test CVC, before meeting oncoming vehicle and on the narrowed lane width; and on the other hand it was limited according to the perceptual treatment used. The lateral position variability would be a difficulty indicator of road geometry which would inform road managers of the presence of a risk zone on their road network. © 2012 Elsevier Ltd.
Auberlet J.-M.,University Paris Est Creteil |
Rosey F.,Normandie Center |
Anceaux F.,University of Valenciennes and Hainaut‑Cambresis |
Aubin S.,CER ESEO |
And 3 more authors.
Accident Analysis and Prevention | Year: 2012
Our study focused on the lateral position of drivers in relation to risk on rural crest vertical curves, using a field site proposed by a local operator of the French road network (Conseil Général de Maine-et-Loire, 49). The final goal was to test one road treatment on this field site. The study consisted of three stages. The first, using driving simulators, selected two perceptual treatments (i.e.; rumble strips on both sides of the centerline and sealed shoulders) from five that were tested in order to help drivers maintain lateral control when driving on crest vertical curves. The rumble strips were installed first on the field site. The second stage was to develop a diagnostic device specifically in order to evaluate, on the field site, the impact of a perceptual treatment on the driver's performance (i.e.; lateral position). This diagnostic device was installed in the field upstream and downstream of the target crest vertical curve. The third stage was to collect the data during two periods, before and after the centerline rumble strips were installed. We then compared the results obtained in the field study with those from the driving simulator studies. The comparison showed that, as in the simulator studies, the centerline rumble strips on the crest vertical curve affected lateral positions, causing the participants to drive closer to the center of the lane. Finally, the results showed the usefulness of driving simulators in the road design process. © 2011 Elsevier Ltd. All rights reserved.
Prabhakar Y.,Normandie Center |
Prabhakar Y.,LITIS Laboratory |
Subirats P.,Normandie Center |
Lecomte C.,LITIS Laboratory |
And 3 more authors.
IEEE Conference on Intelligent Transportation Systems, Proceedings, ITSC | Year: 2013
The safety of Powered Two Wheelers (PTWs) is an issue of concern for public authorities and road administrators around the world. In 2011, the official figures show that the PTW is estimated to represent only 2% of the total traffic but represents 30% of the deaths on the roads in France. The ambiguity in the values is due to the fact that the PTWs are particularly difficult to detect because of their unknown interactions with the other vehicles on the road. To date, there is no overall definite solution to this problem that uses a single sensor to detect and count this category of vehicle in the traffic. In this paper we present a robust method for detecting and counting PTWs in real time and real traffic, named the Last Line Check (LLC) method. This method can adapt to the angle at which the laser scanner is tilted with respect to the road and can estimate the non-observed values in the data. We can obtain data with an accuracy, which eases the extraction process. After extraction, a Support Vector Machine (SVM) is used for classification of laser scanner data. The approach gives encouraging results even when the traffic moves at up to 130 km/h with a precision of 98.5%. © 2013 IEEE.
Gombert P.,INERIS |
Orsat J.,INERIS |
Mathon D.,Normandie Center |
Alboresha R.,University of Lorraine |
And 2 more authors.
Bulletin of Engineering Geology and the Environment | Year: 2014
About 4 million people live on the alluvial plain of the Loire, the main river located in the centre of France. Their protection against flooding is mainly based on the construction of 650 km of old levees. During the last 100 year flood of the nineteenth century, these levees were repeatedly broken. This led to catastrophic flooding, especially in the Val d'Orléans. No new 100 year flood occurred during the twentieth and twentyfirst centuries and the likely response of these old levees to future major floods is poorly understood. Located midway along the river, the study area is 35 km long and 1–7 km wide. It is protected by 42 km of embankments that have already suffered 35 breaches. In the Val d'Orléans, 6-10 m of sandy alluvium cover a karstified limestone bedrock. Nearly 600 collapses were reported whose diameter varies from 0.50 to 18 m. 62 [%] occurred at <2 km from the river, that is to say, close to the levees. Statistically, 35 collapses should have occurred on the levees but only ten of them have been observed. No major consequences resulted because these collapses did not occur during a flood event. The question that arises here is to estimate the potential role of karst in levees breaches occurring during flooding. However, most of these collapses appeared in the nineteenth and early twentieth centuries and the role of karst was not looked at. The risk scenario is as follows: the Loire flooding causes karst flooding (because kasrtic channels are connected to the river), which induces or reactivates collapses. For the ‘karst collapse’ hazard, some predisposing factors can be listed: density of ancient collapses, thickness and nature of the alluvium, hydroclimatic conditions (frost, snow, heavy rain, floods, low water period etc.). This paper examines this issue and seeks to determine the potential role of karst in the levee breaches. The intensity and probability of this hazard is then characterised. Several mechanisms of levee instability, potentially due to karst, are reviewed. If a causal link between flood, karst and collapse is established, it will enable us to monitor the risk of breaches during the next major flood. © 2014, Springer-Verlag Berlin Heidelberg.
Kaouane C.,Ecole Polytechnique de Montréal |
Kaouane C.,Normandie Center |
Chouteau M.,Ecole Polytechnique de Montréal
RILEM Bookseries | Year: 2012
Severe climatic conditions and poor methodology of maintenance and rehabilitation in Quebec make assessment survey of pavement a necessary however difficult task. In order to support prior results obtained with numerical modeling and to address optimal design of equipments, we determined physical properties of concrete, asphalt and foundation soil. These materials have been sampled from a street in the city of Montreal for which pavement had to undergo complete rehabilitation. The last complete rehabilitation of this street was done more than 30 years ago and material properties and composition were largely unknown. Before removal of pavement, we carried out a GPR survey with two distinct pairs of antennae (450MHz and 900MHz). Laboratory tests on concrete and asphalt were conducted on wet and dried samples, trying to reproduce the variability of physical properties due to changes in climatic conditions for a whole year. We measured complex dielectric constants in the range 50MHz-900MHz with a recently developed dielectric probe, and electrical resistivity using a simple laboratory system. Results show low variability of properties of asphalt depending of the saturation compared to larger variability in concrete. Finally all collected data are used as input to numerical modeling, and results compared with the survey data. © RILEM 2013.
Fargier Y.,Électricité de France |
Palma sLopes S.,LUNAM University |
Fauchard C.,Normandie Center |
Francois D.,Électricité de France |
Cote P.,LUNAM University
Near Surface Geoscience 2012 | Year: 2012
In France, EDF (Électricité De France) is in charge of managing the large hydraulic structure stock dedicated to producing hydroelectricity. This responsability is associated with high economical and safety issues. Electrical Resistivity Imaging (ERI) is being widely used on earth embankment dikes, either for extensive survey of large sections (a few km) or for higher resolution surveys on shorter sections (a few 100m). However, the processing of extensive longitudinal survey with conventional 2.5D software is likely to yield image artefacts. This study aims to show that a bad management of the dike complexity in the inversion process is the origin of these artifacts. To overcome this limitation, a new inversion algorithm specially created to take into account the complex behaviour of the dike is presented. This development aims at filling the gap between more classical 2D and purely 3D approaches, by optimising a compromise between acquisition cost and model reliability. Applied to real data sets this tool supplies a new understanding of the interpretation capability of the inversion results.