Thermal Mapping is a vehicle-based survey technique, scientifically proven to identify and quantify the distribution of temperature differences across a highway network.
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 utilized 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 color-coded temperature categories.
Vaisala has over 20 years experience in the provision and development of Thermal Mapping services. Vaisala expertise is utilized 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.