To the right is a thermal image of an old office building in Lime Street in London in winter. It is apparent that one of the windows is emitting a lot more heat than any of the others. This is the standard perception of what thermal imaging can do, but it can also do much more. From helping to diagnose medical conditions in people and animals, through preempting failures in machines and buildings, to informing effective business and public energy policies, over the coming weeks this page will present a growing number of examples of how thermal imaging can be of value. See the energy and technology pages for more relevant information.

The current article collection on this page will be slowly revised over the coming months. Contributions are invited from anybody who thinks they might have relevant information of interest. Any third party images and comments used will be marked and hyperlinked as requested. Please see the About page for details of how to contact


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BELOW: Aerial thermal imaging of cities and towns
BELOW: The case for regular aerial thermal imaging of towns and cities

This article is based on material kindly submitted by Nick Reilly of Ren Solutions - a UK -based thermal imaging and sustainability consulting service. Except where otherwise stated in this section, copyright for all images resides with Ren Solutions
A thermal bridge is a thermally conducting material which penetrates or bypasses an insulation system; such as a metal fastener, concrete beam, slab or column. Heat will flow the easiest path from the heated space to the outside - the path with least resistance. Very often heat will "short circuit" through an element which has a much higher conductivity than surrounding material, which can be described as a thermal bridge.

Typical effects of thermal bridges are:

  • Decreased interior surface temperatures; in the worst cases this can result condensation problems, particularly at corners. 
  • Significantly increased heat losses. 
  • Cold areas in buildings

Such problems need to be identified properly first, before they can be resolved.

A thermal bridge caused by a structural beam in a first floor bed room

External shot of a floor slab acting as a thermal bridge.

Mineral wool snagged on a roof joist allows a small area of air circulation for this bridge.
This steel column going through the roof to a balcony above is a major thermal bridge.

A common problem - insulation is not installed appropriately, up to near the eves.

A similar problem to the left, this time with installed bat insulation rather than roles.

Here, the bridging is between the ceiling framing and the plaster board on the walls.

This article is based on material from Horton Levi Ltd and Hotmapping Ltd who combined their skills to create a geo-rectified aerial heat-loss survey of London. In addition to providing immediately useful information, their survey underpins a strong case for such surveys being conducted on a regular basis in the future. (see below)

First off, Horton Levi Ltd, used military specification thermal imaging equipment to capture over 600 aerial images of London from an aircraft flying at 2,000 feet in 2000.

Known geographic reference points in each image were then identified and the images were rescaled so that they could then be overlaid upon standard mapping data. The composite thermal image was then, effectively, 'georectified', as every geographic point within it, corresponded to standard mapping data, for automatic plotting and mapping purposes. The process is explained by Hotmapping Limited in the column to the right.

Part of a seamless 'georectified' thermal image from Hotmapping Ltd and Horton Levi Ltd.

Although the big London aerial image set acquired by Horton Levi dates back to 2000 and a lot of building, demolition, construction and maintenance has taken place since, it still generates valuable data. The following examples are drawn from both Hotmapping and Horton Levi's websites and used with permission.

The surveys can be used for many purposes. Housing stock can be analysed for efficiency and larger individual buildings can be analysed for weak insulation points. Heat emissions from factories can be identified and remedial action taken. Housing Associations and local authorities can study their entire stock from one data set. Poorly heated housing can be identified to help prevent winter deaths.
The benefits of insulation programmes can be seen, and housing in need of attention is easily highlighted

Thermal data is recorded in monochrome to retain full resolution. Conversion to colour is useful for specific analysis and presentation purposes.
This image clearly highlights an underground heating system. The highlighted area reveals a leak in the system which would otherwise be undetected.

Source = Hotmapping Ltd  

Numerous different false-colour representations of captured thermal data can be presented. There are more examples below and on the other pages of this website.



How aerial thermal imaging data is georectified (Courtesy Hotmapping Limited)

Step 1  Formatting the image and map data ready for georectifying.

Step 2  Using multiple Ground Control Points, individual images are aligned with the map data.

Step 3  The rectified images are joined together to form a seamless mosaic.

Step 4  The combined image map is projected using map co-ordinates so that it can overlay the map data in GIS (Geographic Information Systems = Mapping) software.

A case study of how Hotmapping has georectified Horton Levi's thermal imagery for Chester-le-Street District Council, can be accessed here.


The above thermal image has been both georectified and then subjected to further image analysis so that an average identified temperature has been colour coded for each known address. The final output is shown to the right. Note how the pattern of streets confirms the pictures are related.


The image to the bottom left is part of Horton Levy and Hotmapping's Heat Loss Survey for the London Borough of Haringey. Horton Levy's thermal image set was processed by Hotmapping to provide a colour code to 65,000 buildings.

You can click here to view the complete survey on-line. And here to get to a Horton Levi web page to access copies of newspaper articles about this. 

Note. Although Thermalcities is of the opinion that cities would benefit from regular updated aerial thermal surveys (Say every 5 years) Policy makers need to realise the limitations as well as benefits of such data. 

Due to how the technology works, and as intimated by the colour-code on the right, the best it can do, is to indicate areas for further review. 


Source = Horton Levi Ltd  

The case for regular aerial thermal imaging surveys of cities

Regular, repeated georectified surveys of towns and cities will allow many different types of analysis to be conducted, which, in turn, can inform everybody from people living in flats and houses, through facilities managers and architects, to policy makers.

Regularly updated aerial surveys of this kind can provide, effectively, for many different kinds of time series analyses. The fact that climactic conditions will vary from over-flight to over-flight can be accommodated in part by introducing known, ground-level control points. 

Thereafter, with georectification, beyond the simple point-by-point analysis available from a single over-flight, it becomes possible, for example, to: benchmark how, within different classes of buildings, some might have improved thermally, better than others, and also to evaluate changes in aggregated thermal data for assorted collections of buildings. 

Aggregated housing-heat data will, for example, be much easier than a single dwelling to calibrate against known 'environmental control points'. Meaningful time series analyses can be run. These, in turn, could be used to review the relative impact, over time, of different regional energy-efficiency policies, practices and technologies.

To the right is another image from Horton Levi Ltd. This is of The Royal Free Hospital, London. The clearly distinguishable hot spots aid its property maintenance programme.

Copyright for all images and text resides with Steve Lowe/ Thermalcities, except where otherwise stated.


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