Thermography: Through the lens of an Infrared camera

What is a thermal camera?

An infrared camera, thermal imaging camera or a thermographic camera is a camera that forms images using infrared radiation as opposed to visible light as used by normal cameras. Rather than the usual 400-700 nanometer range used by the visible light camera, thermal cameras use wavelengths as long as fourteen thousand nanometers. The use of infrared cameras is referred to as thermography.

Infrared rays were first discovered in 1800 as a radiation form beyond red light. At the time, infrared rays were used mainly as a way of thermal measurement. Until the First World War, the main focus on development of detectors was on the use of bolometers and thermometers. However, the first main advancement in its application was in 1913 when IR technology was patented as a device to identify the presence of steamships and icebergs. Subsequently, this technology was used in detecting forest fires in 1934 but the technology was not fully industrialized until 1935 when it was used to analyze uniform heating of hot steel strips.

In 1929, a Hungarian Physicist working for the British anti-aircraft defense system developed an electronic television camera sensitive to infrared. The initial thermographic cameras used were infrared line scanners. They were developed in The United States military in partnership with Texas Instruments in 1947. Similar advances were made in the UK in the fifties. An operation named the Yellow Duckling applied a perpetual rotating mirror and detector. Although it failed in its intended use of detecting submarines, it laid the groundwork for land based surveillance and eventually, military IR linescan.

How it works

One of the most important features of infrared technology was the ability for its users to intelligently decipher signals as well as giving warnings in the presence of any threats. It is for this reason that smart sensors encouraged by the United States Strategic Defense Initiative. These sensors eased the process of sensing signals, their extraction, processing and comprehension. Towards the start of the new millennium, infrared application was moving into civil operations. There was a sharp reduction in the cost of uncooled arrays. This together with the huge increase in developments resulted in a dual way use between civil and military markets. Such uses included medical function diagnostics, building and art analysis, environmental control and car guidance as well as collision avoidance systems.

Like other parts of the electromagnetic spectrum, Infrared energy is surrounded by x-rays, gamma rays, micro waves, radio waves, visible and ultraviolet light. All these waves are related and only differ in terms of their wavelength. However, all these rays produce a certain level of black body radiation. This radiation is a function of their temperatures. Generally, the higher the temperature of a given object, the higher its infrared radiation. A thermos camera can detect this radiation the same way common cameras detect light rays. Since infrared cameras are independent of ambient light, they can work even in total darkness. This makes it perfect for use in rescue missions in underground and smoke filled situations.

Unlike regular optimal cameras, a thermographic camera lens cannot be made of glass. This is because glass interferes with the infrared rays. Such cameras are usually fitted with sapphire crystals or germanium hence their heightened costs. While using thermographic cameras, the images are usually monochrome since the cameras usually use image sensors that do not differentiate the varying wavelengths of infrared radiation. These images are sometimes viewed in pseudo color. This allows differences in color to represent different signal levels. This technique is commonly referred to as density slicing.

While measuring temperature, the warmest parts of the image are usually colored white. Intermediate temperatures are indicated as either red or yellow while the dimmest parts of the image are labelled by black. A scale is usually provided to help relate the colors shown to the temperatures in the image. These unique traits make thermography very important and enables it to be applied in various activities such as firefighting for easier visibility through smoke, to locate would be victims of fires and to identify the source of fire. It also allows electrical technicians to easily identify overheating parts. Thermography adds another lens to our lives and allows us to see what we ordinarily would have missed.