Vaisala IceCast Thermal Mapping
On a typical winter night the differences in temperature
across a road or runway network can vary by as much as
10ºC/18ºF. Consequently some sections may be below freezing while
others may not.
Thermal Mapping is a process by which the
spatial variation of minimum night-time road surface temperature is measured,
using a high resolution infrared thermometer. Vaisala Thermal
Mapping is the only proven and established technique to determine
surface temperature relationships likely to occur across an entire road or
runway network. It is a technique, which has been utilised worldwide, to
enhance the information available to both highway authorities and supporting
forecast providers. Thermal Mapping is an integral part
of an effective Ice Prediction system as it provides a mechanism for extending
point specific sensor site information between individual weather stations and
across a road network.
Thermal Mapping identifies patterns of
temperature variation, by undertaking accurate measurements of winter night time
surface temperatures across pre-defined sections of a highway or runway network
under a range of different weather conditions. This pattern and
distribution of warm and cold sections is determined by local environmental
factors and prevailing weather conditions. The occurrence of frost or ice
is determined by the balance of energy a surface receives and loses in
conjunction with the amount of available moisture. This is influenced by the
complex relationship between a number of factors including:
Prevailing weather conditions.
Sky view factor (exposure). This will be dictated by
features such as vegetation, buildings and tunnels etc. A low sky view
indicates features overhanging or close to the road or runway. Such
features will inhibit night-time cooling and may help the surface to retain
some of its heat. A high sky view will relate to an open environment that
will exhibit cold night-time road temperatures, as there is nothing
to prevent the surface cooling.
Altitude (temperatures decrease with height).
Proximity to the coast and major water bodies.
Urban heat island effect.
Cuttings, embankments, elevated sections. These are
localized features that will affect the energy flux of the road/runway at that
point.
Road/runway construction (surface material e.g.
concrete/asphalt/open asphalt, and depth of construction).
Traffic volume and flow.
The combination of these factors generates a unique
temperature fingerprint for each road/runway. Thermal Mapping
establishes the relationship between these variables and how they interact under
different weather scenarios.
The surveys produce Thermal Fingerprints - temperature
profiles unique to a road or runway. Thermal Maps are
constructed from analysis of the Fingerprints, in conjunction with information
on the specific survey weather conditions. The Thermal
Map for each weather condition identifies the pattern and magnitude of
surface temperature variations, indicating the relative differences as
colour-coded temperature categories.
Vaisala has over 20 years experience in the provision and
development of Thermal Mapping services. Vaisala
expertise is utilised throughout an international client base of more than 1000
users, operating in a variety of different winter climates including; Western
Europe, North America, Japan, Eastern Europe, Scandinavia, and New
Zealand. Thermal Mapping is now established Best Practice for many highway
authorities throughout the world.
Thermal Mapping and the use of Thermal Maps provides the winter service engineer with key operational and financial benefits.
Under similar weather conditions a highway or runway will exhibit a constant and predictable pattern of surface temperature variations. Thermal Mapping uses three distinct weather categories to identify the changes in surface temperature variation.
Facts, figures and key points regarding Vaisala's Thermal Mapping operations.