1 Spatial Modelling of the Terrestrial Environment - Georeferencial

228 Spatial Modelling of theTerrestrial Environment
A National Atmospheric Emissions Inventory (NAIE) has been established along with a
network of monitoring stations which provide a basis for national mapping (see Bush et al.,
2001) and monitoring. Whilst direct measurement of emissions is an expensive process,
there has been a proliferation of models which take into account line and area sources of
emissions and these provide a basis for local evaluation and testing (see Hassea, 2000).
As a result of this increasing awareness and understanding, the emissions problem is
becoming less acute. However, despite the major progress which is being made with the
implementation of standards and cleaner, more efficient forms of engine technology, road
traffic continues to increase in volume and continued progress is needed if widely supported
objectives of long-term sustainable development are going to be achieved (Mazmanian
and Kraft, 1999). It is particularly important that sustainable planning strategies which
tend to reduce the level of emissions can be identified. It is also critical that there is a clear
understanding of the impact of emissions on both the population at large and the landscape
ecology of the local environment.
This chapter presents a case study illustrating how a powerful methodology for testing
sustainable planning policy can be created within the framework of a GIS (SHIRE 2000)
containing a wide range of remotely sensed data linked to socioeconomic sources derived
from the UK Census and ground-based surveys. The modelling system is used to examine
planning strategy within the County of Cambridgeshire, UK, between 1991 and 2006 with
a view to evaluating the impact of different planning strategies on exposure to road traffic
emissions. The results demonstrate the value of LANDSAT TM satellite imagery and
associated land cover information derived by automated classification techniques as a basis
for evaluating and visualizing the impact of emissions on settlement patterns. Furthermore,
they raise important questions about whether supposedly sustainable planning policy will
always lead to sustainable outcomes.
11.2 Integrating Models within the Framework of the SHIRE 2000 GIS
In order to measure the impact of road traffic emissions on the population at large it is
necessary to have accurate maps of long-run, annual concentration over wide areas and to
be able to overlay and compare these maps with settlement and population distributions.
Given the relatively low density of the national network of monitoring stations, the high
cost of ground-based monitoring and the high levels of spatial variability that emissions
exhibit, it is extremely difficult to produce and validate detailed concentration surfaces.
Furthermore, population is also extremely variable in its spatial pattern and the highest
level of resolution available from major sources such as the 10 yearly population census
(Enumeration Districts) is too low to enable a reliable linkage between population and
concentration to be established.
The approach adopted here to resolve these problems makes two key assumptions:
First, detailed maps of settlement boundaries derived from an automated, maximum
likelihood classification of widely available satellite imagery can provide a surrogate
variable that provides a basis for an index of population exposure.
Second, current methods of modelling emissions concentrations are sufficiently accurate
to provide a reliable indication of spatial patterns in concentration. In particular, the
reliance of such models on estimates of traffic speed, volume and mode by road link
generated by transport modelling systems leads to robust results.