Image Processing Reference
A comparative study has been conducted allowing the verification of several
hypotheses (Weber et al. 2001 ):
A strong correlation between the mobile means of measurement and the measur-
ing station has been established. A law was established allowing the use the
pseudo-stations as virtual stations. The behavior of the virtual stations was
similar to that of the measuring stations.
The influence of urban morphology on the spatial repartition of air pollutants
has been confirmed.
Using these virtual stations, it is now possible to make the network denser. Two
maps of PM 10 have been computed to show the benefits of the virtual stations
(Fig. 11.10 ). In both cases, the interpolator is a thin-plate operator. This interpolator
should not be used to preserve the information at both ends of the multiscale repre-
sentation (10 km and 10 m) but is used here in a didactic purpose. On the left
the map is obtained with three measuring stations (black dots in Fig. 11.10 left).
The background of these images is the TM4 channel of Landsat, for a visualization
of the network of streets, the highways, and the Rhine River. Due to a few number of
measurement points, this map is rather homogeneous and is not representative
of the complexity of the air pollution. The right part of Fig. 11.10 is a similar map,
but obtained using 301 pseudo-stations determined with less restrictive classifica-
tion rules. The relationship between the concentrations measured at the actual stations
and the virtual stations was established, thus providing an assessment of the con-
centration at each virtual station. Then, the same interpolation technique was
applied and a map is obtained (Fig. 11.10 right). Though the error in the pollutant
concentration can be high, the spatial repartition of the pollutants seems close to
reality and in any case, is much better than what can be obtained presently.
Fig. 11.10 Map of the concentration in PM10 obtained from interpolation of the measuring
stations ( left ) and of the measuring and virtual stations ( right )