Wednesday, 26 May 2010

Pilot IR/Thermal imaging scheme in Scotland

The single thing most people get confused about, as far as infrared is concerned, is the difference between near infrared photography and far infrared thermal imaging. This is especially apparent from the occasional emails I get, and forum postings I see, asking how to use infrared photography to study heat-loss from a building.

So I was interested to read on the BBC web site about a pilot project in Scotland, involving ten thousand homes, to use thermal imaging to 'scan' their external heat pattern and pinpoint areas where heat is being lost from the building. It's a 15 month pilot being carried out by IRT Surveys of Dundee and rather than aiming to help individual home owners the scheme wants to provide an overview of how effective various methods of insulation are.

It strikes me that one cause of the confusion is terminology. We call everything from 700 nm (just beyond red) down to the edge of microwaves by the term infrared, even though the sources of the radiation and the ways we can render it visible change significantly as we move from the photographic infrared to the thermal infrared. I found this terminological inexactitude particularly confusing while going through wartime papers to research my paper on the history of infrared photography for the RPS. One of the best sources of information on this is RV Jones, who was a senior scientist in British scientific intelligence: senior enough to have regular contact with Churchill. Jones's papers are in Churchill College in Cambridge and he also wrote a fascinating book called Most Secret War, which is still in print. Like many others, Jones refers to both ends of the infrared spectrum as simply infra-red. I had to read between the lines to try to see whether he was referring to thermal or near infrared technology ... and possibly got it wrong sometimes.

Jones told a nice story about a meeting sometime after the war with the American military where they began to tell him about a new missile they had started work on called the Sidewinder. 'So this is a heat-seeking missile then?' says Jones, somewhat startling the Americans who immediately think that their security is compromised. Jones explains that the sidewinder rattlesnake detects prey using rudimentary thermal sensors in its head, so he has surmised that this missile does likewise. Sighs of relief from the military, who have named the missile after the rattlesnake because of its striking prowess and are unaware that it uses infrared. So it goes.

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