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The Principles of Using Targets for Infrared Measurement in Avionics

28 November, 2017

Thermal imaging cameras comprise a vitally important technological category within military avionics, but they can only be used properly if they are calibrated and tested before being deployed. One of the simplest ways to carry out infrared measurement within the confines of electro-optical test systems is to use specially developed targets. Take a look at the various kinds of targets that are typically used for a range of testing methods.

The Main Types of Targets Used for Infrared Measurement

Whether you are just learning about electro-optical systems, or you are already highly familiar with this aspect of avionics, infrared measurement is something that has no doubt not escaped your attention. Electro-optical testing generally requires the use of an integrating sphere subsystem and a source of blackbody radiationalongside special infrared targets.

While plenty of time is spent on learning the principles of this kind of radiation, vital objects like these targets are often left relatively untouched. Consider the main target types below and discover more about their role in your infrared measurement device:

  • It’s a good idea to work out the minimum resolvable temperature difference (MRTD) for your infrared camera. Bar targets are used in this case to help you calculate the detection, recognition and identification ranges of your imaging device.
  • Many people assume that MRTD is the same thing as minimum detectable temperature difference (MDTD), but actually there is a significant albeit subtle difference. The main fact to remember is that MDTD is a measure of visibility rather than resolvability. You can carry out tests for this factor manually with the help of pinholes.
  • Thermal resolution should be measured for all infrared cameras, and the noise equivalent temperature difference (NETD) is what tells you the difference in temperature between a given object and its surroundings. Square-shaped targets are used for this purpose.
  • Modulation transfer function (MTF) is particularly worth your time as it essentially allows you to combine the properties of resolution and contrast. When the line spacing on your slit targets decreases, the lens in your infrared optical device cannot transfer the reduced contrast as well as when the line spacing is greater. This is often also described as a decrease in MTF.
  • Alignment and bore sighting requires the use of cross targets. When you use an electro-optical testing system to guarantee a reliable boresight, you end up with a much higher first round hit probability. Whether your thermal imaging device is going to be used in aircraft, ground vehicles or even naval vessels, you’ll want to be sure that your alignment and bore sighting is as accurate as possible.

The Importance of Selecting the Right Target

The targets used for infrared measurement are of specific shapes and sizes for very good reasons. The patterns and dimensions used for any given test are chosen depending on the characteristics of the test itself plus those of the infrared imaging device that is being tested and calibrated.

Generally speaking, you can get targets that have been designed at the microscopic level to be suitable for your chosen equipment and testing mechanisms. It’s all a matter of thoroughly understanding the workings of each calibration method, and then picking exactly the right kind of target to guarantee the accuracy and reliability of each individual characteristic of your camera or imaging device.

Make sure you get to grips with all the various target types that are used to test electro-optical systems.

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