You may or may not be a cricket fan – ( its not a crime, but late night listening to TMS is very addictive!), but there is no doubt that the advance of technology into sport is accelerating. From the early days of the Radar to give us ball speeds in Tennis, Cricket and Baseball, through to Hawkeye for predictive analysis of the route a ball may have taken, the use of technology by commentating teams enriches our viewing, and in the case of the Snickometer in cricket, our listening. 
The effects this may or may not have on the quality of umpiring decisions depends very much on your point of view, but the overall effect is to provide clarity. And herein lies the rub. As technology becomes more advanced, the average viewer / listener has less of an understanding of the basic principles behind it, and relies more and more on the presentation of the information to be fair, impartial and accurate.
As someone who has been involved in Thermography for some time, particularly in the sales of Thermal Imaging cameras, I believe I have a better than average understanding of the technology underpinning the use of Hotspot, and I would like to dispell a few myths behind it.
The cameras used for Hotspot are right at the top end of the market and their cost is very significant. The investment by the company presenting the information is to be admired (BBG Sports), and the image quality they deliver is superb (have a look at their website for some fantastic movies). The difficulty comes when we are trying to determine whether or not the ball has made contact with the bat and this relies on a some physics. Put simply, when the ball touches the surface of the bat, some energy is transferred. This energy typically manifests itself in two ways – as sound (the “snick”), and as heat. The larger the contact, the more energy is transferred, more noise and more heat.
Microphones embedded in the stump or ground near the stumps are only approx 1m away from the source and are very sensitive, but not directional. So while the visual (TV) image and the sound can be closely synchronised and a best guess delivered, there is no guarantee that the sound is not coming from another source such as a boot scuffing the ground at the same time, or a fielder treading on a stick.
The Thermal Imaging technology behind the HotSpot relies on a focal plane array detector – similar in concept to normal CCD in your digital camera, but only able to see in part of the Infrared spectrum. demand in this area is not as large as a consumer market, and evolution is very expensive and typically only paid for by military budgets, the detector pixel count is of the order of 350,000 pixels. However each of these pixels is able to determine a very small change in radiated energy – equivalent to 0.015°C, so you would expect this technology to be very sensitive to small energy changes and it is. However, there are factors affecting the information the camera recieves that need to be clearly understood before assuming that it will see every contact.
In the first instance, the cameras are sited outside the playing perimeter, and this will be approximately 60m and in many cases considerably more, from the point of contact. This means that the energy signal has to radiate quite some distance in order to be detected by the camera. Secondly, the lens required to get a detailed image needs to have a very narrow field of view – typically of the order of 1.5° – the reason for this is to ensure that you get enough pixels focussed onto the potential contact area to be able to detect a signal – one pixel isn’t really enough. So you then need to try to ensure that your pixel coverage of the contact area is sufficient. Thirdly you need to understand the effect of the various tapes and stickers that batsmen place on their bats to repair or strengthen them, or are placed there by sponsors. Some of these are highly reflective in the infrared and a small change of angle may appear like a flash of energy – but if it is a real energy source, then the energy signal will dissipate more slowly.
So while HotSpot is a great technology, and commentators such as former England captain Michael Vaughan are very keen to see it used more, there will be the odd occasion where it doesn’t give a definitive answer – and it not the fault of the technology, it the physics! The use of HotSpot has brought a richer viewing experience to many cricket fans, and enhanced the decision making of the Umpires, and while there is still the odd Luddite out there (Aggers!), generally progress is unavoidable.
images on this comment have been lifted whole heartedly from planetcricket.net (the snickometer images) and cricketupdates.org and remain the copyright of those sites.
