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The operation of
optical surveillance systems at night time needs additional
illumination. For some areas like airports, however, visible
illumination cannot be used.
To cover also this situation, the cameras of the DNC series are
equipped with a sophisticated single CCD image sensor which
operates during daytime in coloured mode and switches at night
time automatically into a high sensitive black and white mode.
In this mode the spectral sensitivity is extended to the near
infrared range (NIR). Therefore light sources which are emitting
radiation in this range can be used to illuminate the night
without being seen by the human eye.
This concept is termed as active night vision (ANV) in contrast
to passive night vision which exploits image intensifier,
however yielding a poor image quality. Within the system
PSS-20-04 active night vision is applied in general, NIR light
sources are either LED (Light Emitting Diode) arrays or for
special arrangements NIR Laser are used.
LED arrays are suitable for distances up to 100 m with a broad
illumination angle.
The figure on the right shows an LED beamer with an optical
power of 60 Watts, allowing a distance of app. 100 m to be
covered. The actual range depends also on the sensitivity of the
used camera system. The spectral emission is centred around 850
nm with a spectral width of 80 nm.
Operation at day and night with active night vision is the
domain of the “Desert Owl”. It combines a high sensitivity
camera with a special Laser system to illuminate the dark with
invisible light. The design is weather proof wherever the
“Desert Owl” will do its duty. The ruggedised housing protects
the valuable interior against vandalism.
To avoid the recognition of a camera as a camera the observation
line - meaning the orientation of the camera with respect to the
object – must be different. The vertical orientation of a camera
completely disguises the appearance as a “camera eye”. The
figure displayed in the middle has been taken from the roof of a
building with active night vision support by means of the Laser
source. The figure on the left shows the same scenery whereby
the Laser has been switched off. The sequence of the pictures
are recorded with the “Desert Owl” camera demonstrating the
excellent night operation capabilities. Similar results are also
obtainable with LED beamer, provided the distance does not
exceed 100 m.
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