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SCENE
MANAGEMENT
obtain the maximum performance from the AD1562
To
in camera and scene management that vastly reduce the
number of nuisance alarms. Methods for dealing with
common scene problems are described below.
Scene Illumination at Night
Even a carefully camouflaged intruder can do nothing to hide
his shadow. Shadows can be used to the system's advantage to
aid in detection by strategically positioning cameras and
lighting for optimal nighttime performance.
The AD1562 DuoTect-C can be used to maximum effect at
night if the lighting used to illuminate a secure area is located
at right angles to the camera. This ensures that the shadow of
the intruder is visible to the camera, and so aids in detection.
The least desirable arrangement is for the camera and lights to
be mounted together, because an intruder's shadow will then be
cast behind him, away from the camera, and may not be seen at
all by the system.
If camera and lighting must be mounted in close proximity,
then wherever possible the distance between them should be
If lighting
than six
show up as bright moving objects at night. In some
circumstances these objects can be detected and cause nuisance
alarms. If not detected, they may affect the auto-iris lens,
causing the background to darken and thus lessen the
possibility of detection of actual intruders.
The DuoTect-C requires a full l.OV p-p video signal with
reasonable contrast to ensure a high probability of target
detection. The combination of camera type and scene
illumination level under the worst case conditions should be
chosen to achieve this signal level.
Camera Mounting
The DuoTect-C system works best with fixed cameras. These
should be mounted as solidly as possible to minimize wind
induced movement. A moving camera gives the impression
that the viewed scene is moving and may cause nuisance alarm
activation. Camera Pan, Tilt, or Zoom actions cause alarms
unless the camera channel is disarmed during such operations.
Some steps can be taken to minimize alarms if it is known that
excessive camera movement is a problem and it is not possible
to solidly mount the camera.
is closer than this. insects.
Camera movement causes alarms where Detection Zones cover
sharp contrast boundaries. To minimize such problems,
carefully modify the Detection Zone pattern by removing
detection cells that lie along these boundaries (such as edges of
structures or lines painted on surfaces). Leave as many
detection cells as possible covering areas of even contrast, as
these will not be affected by camera movement. The EDGE
REJECTION feature (page 7) may also be used to minimize
jitter or camera problems at sharp contrast boundaries.
Effects of Rain
During a rainstorm water may collect on the top of a camera
housing. This water will then periodically run off as a trickle
from the lowest point. Often this run-off occurs over the
inclined front of the camera housing and is visible to the
camera. This run-off may cause nuisance alarms. Alarms
triggered this way usually appear on a freeze-frame output as a
vertical stripe of the Detection Trace. Without a freeze-frame
unit the source of the alarm may be difficult to ascertain,
Placement of a bead of rubber, silicone sealant, or similar
material along the front edge of the camera housing will direct
the run-off away from the front of the camera and thus prevent
alarms from this source.
Small numbers of raindrops adhering
housing should not cause nuisance alarms unless they are
affected by wind. However, if the raindrops coalesce, a trickle
effect may result, with the same problem as above.
Rain puddles can cause a problem if they fill a significant part
of the field of view of the camera. Nuisance alarms may result
from ripples of the water surface caused by wind and rain and
by reflections of lights or moving objects (such as clouds) on
the surface of the water.
These problems are best dealt with as follows:
their reflections.
Path and Location of Movement
Objects moving across the scene and near the camera are more
easily detected than those moving to and from the camera, or
those far from the camera. Objects having high contrast with
their background are more easily detected than those with low
contrast.
C
SCENE
MANAGEMENT
to the face of a camera
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