french institute of science and technology for transport ... - Ifsttar

Research orientation S_Improving road safety and modernizing transport infrastructure
On the road
From video surveillance to meteorological
observation
In order to locate and forecast weather that may disrupt
traffic, for example fog, the French meteorological office
(Météo-France) relies on observations. Risk maps are
then drawn up by combining satellite observations with
observations made on the ground.
The latter are made using a network of about a hundred
weather stations spread all over mainland France. Unfortunately,
the resolution of this system is not sufficient to give reliable
data for a very localized phenomenon like fog. For this reason
critical areas such as airports are specifically instrumented in
order to measure meteorological visibility distances.
In contrast with airports, the linear nature of the road network
makes this kind of instrumentation economically problematic
not to say impossible. However, there is enormous potential
for meteorological observations of fog on roads as many
of them are equipped with video cameras for surveillance
purposes.
Raouf Babari’s thesis, which was jointly funded by Météo-
France and IFSTTAR and directed by IGN, set out to evaluate
this potential.
The outcome is a novel method for estimating the meteorological
visibility distance by processing images from convential
roadside cameras, which are inexpensive, robust to lighting
Fog observations using a video camera: (a) an image of fog from the Météo-France
instrumented site at Trappes; (b) X-axis: meteorological visibility distance measured
by Météo-France. Y-axis: an estimator based on the average normalized gradients
in the Lambertian zones of the image. The model that has been fitted to the data (blue)
has been plotted in red.
conditions and effective over a wide visibility range from road
fog to atmospheric pollution.
@ CONTACT
nicolas.hautiere@ifsttar.fr
a
Estimated Contrast (m)
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b
Meteorologie visibility distance (m)
61
Airport pavement design
With some help from Alizé
The development of a new design method for airport
pavements, in collaboration with STAC.
Traditionally, the French airport pavement design
methodology is empirical, based on the American CBR (California
Bearing Ration) method for flexible pavements. It uses
the CBR rating to characterize soils and applies coefficients
of equivalence between different materials. It does not take
account of the real configurations of aircraft landing gear or
the actual mechanical behaviour of the materials.
The collaborative project between IFSTTAR and STAC
(French Civil Aviation Technical Centre) is intended to overcome
these shortcoming and develop a new design method
for airport pavements. The method is founded on an “aeronautical”
version of the IFSTTAR Alizé pavement design software
package. As is the case with roads, the design process
involves computing the stresses within the pavement using
a linear elastic model. The main difference relates to the description
of the traffic, as in the case of the airport pavement,
the damage produced by each type of aircraft passing over
the pavement is computed separately. Miner’s law is then
applied to give the cumulative damage. The FICAV database
held by STAC is used to obtain the characteristics of different
airplanes. Their speed of passage and variations in their
transverse position are also taken into account.
A design manual for airport pavements which describes the
entire method was drafted in 2011, for asphalt pavements.
It is currently being validated by a group of experts from the
profession (contractors, project owners) and is due to be
published at the end of 2012. A second version, for pavements
with hydraulically bound foundations, is planned for
a later date.
@ CONTACT
pierre.hornych@ifsttar.fr
ANNUAL REPORT 2011 ifsttar.fr