Understanding Thermal Night Vision
Basically, you have the image sensor number of pixels ie. 640x480, the display number of pixels ie. 640x480, the pixel pitch measured in microns (uf) of the display and the sensor, and the refresh rate (Hz). The higher number of pixels the better, especially for zooming in, the lower number micron pixel pitch the better for a more dense image, and the higher number Hz the better for smooth image. Be careful of mistaking the display number of pixels and pixel pitch for the sensors data! Very detailed descriptions below, from Wikipedia.
Discovery and research of infrared radiation
Infrared was discovered in 1800 by Sir William Herschel as a form of radiation beyond red light. These "infrared rays" (infra is the Latin prefix for "below") were used mainly for thermal measurement. There are four basic laws of IR radiation: Kirchhoff's law of thermal radiation, Stefan-Boltzmann law, Planck’s law, and Wien’s displacement law. The development of detectors was mainly focused on the use of thermometer and bolometers until World War I. Leopoldo Nobili fabricated the first thermocouple in 1829, which paved the way for Macedonio Melloni to show that a person 10 meters away could be detected with his multielement thermopile. The bolometer was invented in 1878 by Langley. It had the capability to detect radiation from a cow from 400 meters away, and was sensitive to differences in temperature of one hundred thousandth of a degree Celsius.
The first advanced application of IR technology in the civil section may have been a device to detect the presence of icebergs and steamships using a mirror and thermopile, patented in 1913. This was soon outdone by the first true IR iceberg detector, which did not use thermopiles, patented in 1914 by R.D. Parker. This was followed up by G.A. Barker’s proposal to use the IR system to detect forest fires in 1934. The technique was not truly industrialized until it was used in the analysis of heating uniformity in hot steel strips in 1935.
First thermographic camera
In 1929, Hungarian physicist Kálmán Tihanyi invented the infrared-sensitive (night vision) electronic television camera for anti-aircraft defense in Britain. The first thermographic cameras began with the development of the first infrared line scanner. This was created by the US military and Texas Instruments in 1947, and took one hour to produce a single image. While several approaches were investigated to improve the speed and accuracy of the technology, one of the most crucial factors dealt with scanning an image, which the AGA company was able to commercialize using a cooled photoconductor.
The first infrared linescan system was the British Yellow Duckling of the mid 1950s. This used a continuously rotating mirror and detector, with Y axis scanning by the motion of the carrier aircraft. Although unsuccessful in its intended application of submarine tracking by wake detection, it was applied to land-based surveillance and became the foundation of military IR linescan.
This work was further developed at the Royal Signals and Radar Establishment in the UK when they discovered mercury cadmium telluride could be used as a conductor that required much less cooling. Honeywell in the United States also developed arrays of detectors which could cool at a lower temperature, but they scanned mechanically. This method had several disadvantages which could be overcome using an electronically scanning system. In 1969 Michael Francis Tompsett at English Electric Valve Company in the UK patented a camera which scanned pyro-electronically and which reached a high level of performance after several other breakthroughs throughout the 1970s. Tompsett also proposed an idea for solid-state thermal-imaging arrays, which eventually led to modern hybridized single-crystal-slice imaging devices.
One of the most important areas of development for security systems was for the ability to intelligently evaluate a signal, as well as warning for a threat's presence. Under the encouragement of the United States Strategic Defense Initiative, "smart sensors" began to appear. These are sensors that could integrate sensing, signal extraction, processing, and comprehension. There are two main types of Smart Sensors. One, similar to what are called "vision chips" when used in the visible range, allow for preprocessing using Smart Sensing techniques due to the increase in growth of integrated microcircuitry. The other technology is more oriented to a specific use and fulfills its preprocessing goal through its design and structure.
Towards the end of the 1990s the use of infrared was moving towards civil use. There was a dramatic lowering of costs for uncooled arrays, which along with the large increase in developments lead to a dual way use market between civil and military.These uses include environmental control, building/art analysis, medical functional diagnostics, and car guidance and collision avoidance systems.
Theory of operation
Infrared energy is just one part of the electromagnetic spectrum, which encompasses radiation from gamma rays, x-rays, ultra violet, a thin region of visible light, infrared, terahertz waves, microwaves, and radio waves. These are all related and differentiated in the length of their wave (wavelength). All objects emit a certain amount of black body radiation as a function of their temperatures.
Generally speaking, the higher an object's temperature, the more infrared radiation is emitted as black-body radiation. A special camera can detect this radiation in a way similar to the way an ordinary camera detects visible light. It works even in total darkness because ambient light level does not matter. This makes it useful for rescue operations in smoke-filled buildings and underground.
A major difference with optical cameras is that the focusing lenses cannot be made of glass, as glass blocks long-wave infrared light. Special materials such as Germanium or Sapphire crystals must be used. Germanium lenses are also quite fragile, so often have a hard coating to protect against accidental contact. The higher cost of these special lenses is one reason why thermographic cameras are more costly.
Some specification parameters of an infrared camera system are:
- Number of pixels
- Frame rate
- Noise-equivalent power
- Noise-equivalent temperature difference (NETD)
- Spectral band
- Distance-to-Spot Ratio (D:S)
- Minimum Focus Distance
- Sensor lifetime
- Minimum resolvable temperature difference (MRTD)
- Field of view
- Dynamic range
- Input power
- Mass and volume