Image Processing Reference
LWIR image onto the windshield to assist in low-light-level driving conditions. In
recent years, BMW has installed thermal imaging cameras on their 7-series sedans
as a must-have option for the tech crowd. Uncooled IR cameras can be extremely
small and lightweight with low power requirements. Other applications for these
miniature cameras include helmet-mounted imaging systems for firefighters and
as a payload on unmanned aerial vehicles for military reconnaissance. Thermal
imaging in the LWIR band gives a firefighter the ability to see through smoke,
since smoke particles are too small to strongly scatter long-wavelength IR light.
The firefighter observes a helmet-mounted video display of the thermal image, and
can detect people from their body heat as well as hot spots in doors, walls, floors
and ceilings that may indicate that a fire is still burning. Figure 2.14 shows a view
of a person imaged through smoke by a miniature uncooled camera.
The ability to see through smoke is useful for long-range reconnaissance of
forest fires. The Jesusita fire in Santa Barbara, California in 2009 was particularly
destructive. The smoke was impenetrable to the eye from 10 km away, but the seats
of the fires were easily visible with a MWIR camera, as shown in Fig. 2.15. MWIR
light penetrates through smoke quite well, though generally not as well as LWIR
light. The longer wavelengths of LWIR are less scattered by smoke particles for a
typical bush fire like this.
Surveillance and Law Enforcement
Thermal imaging technology development has been driven mainly by the military,
for the following reasons: infrared cameras can see objects that are well
camouflaged in the visible band, and they can also image through smoke, haze
and other battlefield obscurants. Initially, only the military could afford to buy
high-speed FPA cameras, but as the cost of thermal imaging systems drops with
the advent of new technologies and fabrication techniques, law enforcement is
making increasing use of them for surveillance. Thermal imaging can detect a
suspect hiding in the bushes; identify a car that just pulled into a parking garage
late at night; or find recently fired weapons and other warm objects in darkness
and in partially concealed places. Figure 2.16 shows two views of a warm handgun
dropped into the bushes outside my house. The gun was in my waistband for an
hour before the picture was taken, heating up to over90 F(32 C). The gun is
nearly invisible in the visible-light image even though it was illuminated with a
flash, while the LWIR thermal image has high contrast between the gun and the
vegetation in total darkness.
Figure 2.17 shows a man sneaking around the back of a house. Even though
the scene is completely dark as viewed in visible light and the man is impossible
to see in the shadows, he glows brightly in the MWIR band because he is about
10 C(50 F)hotter than the other objects in the scene. The rear windshield trim is
reflective in the MWIR band, and since it is canted at an angle, it reflects the cold
sky into the camera and thus appears black (cold) in this image.
Thermal imaging can also be used to detect density variations in materials,
since differences in heating and cooling can create surface temperature differences.