Social Economical Impact of FogThe total social costs produced by fog in the region Veneto is of the order of 35M€ (total costs for accidents in Italy in 2003 is about 35G€, of which 1% attributed to fog, of which 10% attributed to Veneto).[Italian Central Institute of Statistics, Automobile Club Italia]

Objectives of the ROADIDEA Fog PilotThe main objectives of the ARPAV Fog Pilot in ROADIDEA are:

• to set up a cost effective, areal fog monitoring system for diagnosing reduced visibility conditions over an extended geographical region as alternative to the expensive in situ monitoring;

• set up a relatively low resolution network of direct visibility measurements (visibilimeter);

• set up of an information model to merge direct and indirect visibility information derived from satellite and meteorological surface stations;

• maintain open architecture to allow integration of complementary and innovative data sources for visibility (reports, intelligent cars, webcams, etc.).

Monitoring of fogFog monitoring is well known to be a significant challenge, not least due to the high spatial and temporal variability of the phenomenon. The development and refinement of fog forecast methods requires first a good monitoring system.

Present warning systemsDeployment of fog monitoring warning systems is generally limited to selected stretches of the main motorway networks, yielding only information on the local fog conditions, not however on its areal extension. Most of the regional to national road networks are not covered by such a service.

The FP7 project ROADIDEA studies the innovation potential of the European ITS sector by analysing available data sources, revealing existing problems for data utilisation and service build-up. The Fog Pilot, one of ROADIDEA’s pilots, constitutes a proof of concept, as well as a

practical application of how road safety can be improved by accounting for adverse meteorological conditions, in this case reduced visibility.

The combined Fog Monitoring System over the Veneto Region – Italy F. Zardini, F. Domenichini, A. Rossa, A. Della Valle, M. Calza, V. Gaspari, ARPAV – DRST, Meteorological Centre of Teolo - fzardini@arpa.veneto.it

Fog in the Po ValleyThe presence of fog is a frequent phenomenon in the Po Valley (up to 80-120 days per year), with consequent strong impact on road, air, ship and railway traffic, by dangerous reduction of visibility.

FOG PILOT

Visibility sensors (red boxes) used in the visibilimeter network for the Veneto Fog Pilot. An emitted infrared beam is scattered by the fog droplets. The instrument measures the scattered beam component, which is larger in presence of fog, and then estimates the visibility in meters.

The network of visibility sensorsFor the ROADIDEA Fog Pilot a network of 10 visibilimeters was installed. The siting is limited to the Veneto plain most prone to intense and persistent fog. Visibilimeters provide direct visibility measures which then are converted in a probability of fog (reduced visibility conditions) for merging with other data sources.

SAFN

WC

METEOSAT Satellite image. Cloud Type product derived by the SAFNWC software package.

Satellite information: elaboration by SAFNWCThe METEOSAT satellite images have the potential to provide areal fog information and were used to aid the spatial interpolation of the direct visibility measurements. The satellite information was processed by cloud classification algorithm of the Satellite Application Facility Nowcasting (SAFNWC), a software system developed over the last 13 years by a consortium of European national weather services.

CT product

Ground data statistical elaborationThe data obtained from the automatic surface meteorological stations network yields another, indirect probability estimate for fog occurrence based on current meteorological conditions by applying a statistical decision tree methodology (CART).

Tree 7 graph for Vis categNum. of non-terminal nodes: 11, Num. of terminal nodes: 12

ID=1 N=288551

ID=2 N=243341

ID=5 N=131541

ID=34 N=52621

ID=37 N=36251

ID=47 N=11144

ID=58 N=9984

ID=3 N=45214

ID=106 N=9111

ID=107 N=36104

ID=112 N=32724

ID=4 N=111801

ID=36 N=16371

ID=46 N=25111

ID=60 N=1505

ID=61 N=8484

ID=59 N=1161

ID=35 N=78921

ID=108 N=8251

ID=109 N=864

ID=114 N=2841

ID=115 N=29884

ID=113 N=3381

dT500PD

<= 0.004990 > 0.004990

RH

<= 94.500000 > 94.500000

T 2m (°C)

<= 3.850000 > 3.850000

WD categ

= N , ... = Other(s)

dTMtGr_Lgn

<= 0.005579 > 0.005579

P Teolo

<= 1008.100000 > 1008.100000

dT 12h

<= -6.500000 > -6.500000

RH

<= 95.500000 > 95.500000

dT500PD

<= 0.010707 > 0.010707

P Teolo

<= 1008.125000 > 1008.125000

P Teolo

<= 987.725000 > 987.725000

12345

Fog prob

=67%Fog prob

=0.5%

The decision tree obtained with the CART analysis allows us to derive a fog probability depending on the meteorological conditions (temperature, wind, humidity etc.) recorded by the ground stations. The fact that this method very rarely gives high fog probabilities limits its value in comparison to the other methods used in the Fog Pilot.

ARPAV (Regional Agency for Environmental Prevention and Protection of Veneto) is the regional meteorological service of the north-eastern Italian region Veneto and, as such, is responsible for meteorological support to institutional and private users. In the framework of ROADIDEA ARPAV developed pilot system for the fog monitoring.

ConclusionsThe main results of the ROADIDEA Fog Pilot can be summarized as follows:

• a probabilistic areal fog monitoring system has been built using a limited number of visibility sensors, a satellite cloud classification system and a meteorological surface station network;

• probabilistic verification of the Fog Pilot shows good performance with a probability of detection of about 75%, probability of false detection of about 10%;

• most value to the final product is brought by the direct visibility measurements, whereas the satellite information brings added value for the spatial interpolation; the impact of the meteorological surface observations appears to be limited, but has yet to be established more rigorously;

• to the knowledge of the authors, the Fog Pilot constitutes the first attempt of an areal combined fog monitoring system for road transport purposes, and has the potential to give a significant support for accident prevention and traffic management.

The Fog Pilot data mergingThe merging methodology for the different data sources was chosen to be probabilistic and can be divided into the following steps:

• estimate a fog probability map for each data source;

• attribute to each data source a relative quality, or weight, which accounts for the reliability for the current conditions;

• statistically combine the individual probability fields, accounting for the relative data quality.

The final product consists in a probability map of reduced visibility, which can yield fog alerts based on selected thresholds (e.g. 40%).

CART

Satellite

Visibilimeters

Merged Product

The output product of the Fog Pilot: on the left side the three products derived from single monitoring methods, while the large frame represents the merged final product. In each map the fog information is represented by the probability of having visibility under 500 meters.