Geoscience Reference
In-Depth Information
5.5. Urban climate monitoring methods
5.5.1.
Mobile surveys
In order to acquire detailed data, the first studies on climatology of the UCL
were based on mobile measurements carried out on foot, by bicycle, motor bicycle,
and eventually by car.
The observers stopped regularly during the traverses and
noted down the readings of meteorological parameters, using different types of
devices. The
Assmann
psychrometer (Figure 5.3a) was one of the most accurate
instruments for field observations of air temperature and humidity, despite its weight
and slow performance. Nowadays, values are recorded through the use of digital
devices during the mobile surveys (Figure 5.3b). Some research institutes use
vehicles equipped with meteorological instrumentation that record and plot data
continuously during the traverses, allowing for a much greater number and variety
of sampling points [MAT 01; KUT 04].
Figure 5.3.
Examples of instruments and shelters. a) Assmann psychrometer; b) portable
digital thermo-hygrometer; c) temperature and humidity sensor Gemini data-logger
and former shelter; d) plastic shelter and temperature data logger;
e) plastic shelter located on a lamp at 3.5 m high
Once sampling points are chosen, mobile surveys require decisions concerning
survey's timing (frequency). Traditionally measurements were carried out three
times a day: around noon (covering maximum temperature period), at dawn
(frequently minimum temperature time) and some hours after sunset in order to
sample the period when the intensity of UHI is at its highest.
5.5.2.
Fixed measurements
Mobile surveys have two main disadvantages: their temporal and spatial
discontinuity and the fact that the measurements cannot be carried out
simultaneously in every point, so that corrections have to be introduced. Nowadays,
“a set of data loggers installed in key points in towns has replaced most of the
mobile surveys” [GRI 06b].
Some studies are based on pre-existing meteorological network recording
continuously over time. However, meteorological stations (either traditional or
automatic), following the rules of the World Meteorological Organization [WMO
