light and the microwave region used for
high-definition radar. The IR region of the
electromagnetic spectrum lies between wavelengths
of 0.72 and 1,000 micrometers. Discussion of the IR
region is usually in terms of wavelength rather than
frequency.
NOTE: A basic knowledge of IR detection
principles is essential to understanding
thermal imaging and the FLIR system as
discussed in this chapter. If needed, you
should review IR detection principles in
Aviation Electronics Technician 3,
NAVEDTRA 12329, before reading this
chapter.
THERMAL IMAGING
Learning Objective:
Recognize functions,
characteristics, components, and operating
principles of thermal or infrared imaging.
Infrared radiation is also known as thermal or
heat radiation. Most materials emit, absorb, and/or
reflect radiation in the IR region of the
electromagnetic spectrum. For example, an aircraft
parked on a sunlit runway absorbs and radiates
varying amounts of IR radiation. After the sun sets,
the aircraft continues to radiate the absorbed heat,
making detection at night possible. Even if the
aircraft is moved, detection of the aircraft is possible
because the runway surface, which was directly
below the aircraft, will be cooler than the surrounding
runway.
Thermal imaging is referenced in terms of
temperature instead of reflectivity (radar) or color
(visible light). Variations of the temperature in a
scene tend to correspond to details that can be visually
detected. The IR imaging system processes this
information and converts it into information that the
system operator can use. Currently, the types of
imaging systems generally used are mechanical-
scanning, fast-framing devices. They use the frame
rate (information update rate) that is similar to
television. They are known as forward-looking
infrared (FLIR) devices.
Before a target can be detected, it must exchange
energy with its environment, be self-heating, have
emissivity differences, and reflect other sources.
Look at figure 6-2. Notice the atmosphere between
Figure 6-2.-Thermal imaging.
6-2
