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TM00358 Rev. A
Operator Use
Because of the sensor's thermographic imaging capabilities, its function is not restricted to daytime or night time
use. Operators would utilize this sensor in any lighting conditions to:
•
view subjects in daylight
•
view subjects at night or in low-light scenes
•
lock tracking on hot thermal signatures
For example, operators would use the IR sensor to locate an area of interest within a scene during night operation.
Or, during a search and rescue mission at sea, thermal energy would be more distinct than daylight color imagery
which would be very a monochromatic color scene.
Operating Temperature Limits
The IR sensor is thermally controlled but is also exposed to temperature fluctuations that occur inside the gimbal.
The system monitors the sensor's temperature and protects it from thermal extremes. The sensor will only be
operational within the following temperature control limits:
•
For cold operation, the sensor will shutdown below -55°C and not restart until -38°C.
•
For hot operation, the sensor will shutdown above 75°C and not restart until 58°C.
•
For cold starts below -38°C, the sensor will not operate until it has been warmed.
Operator's have the capability to control the following imaging parameters:
•
Sensor Calibration
•
Sensitivity
•
Offset
•
Scene Setup
•
Polarity
•
Initiate a BIT
Camera Cooler Assembly and Warm Area Electronics
The focal plane array – like the film in a camera or a CCD in a digital camera – converts infrared light into a human
visible image. Made up of a series of photodiodes, where each represents an image pixel, the focal plane array
converts infrared light into electrical signals where the measured energy is assigned a grayscale tone. The
combination of numerous grayscale pixels creates the overall monochromatic video image. The focal plane array is
contained within a vacuum-sealed, dewar assembly and is cryogenically cooled. During system startup, the housing
undergoes a cooling cycle that cools the focal plane array down to 77 K (-196.15°C or -321.07°F). Because the
focal plane array is much colder than subjects the operator might view, its detection capabilities are highly sensitive
and provide a high resolution image. The Warm Area Electronics (WAE) of the camera converts analog signals from
the focal plane array into an uncorrected digital signal. The digital data is transmitted over a HotLink™ interface for
later image processing enhancements prior to final video output.
Focal Plane Array Calibration
Infrared image quality will degrade with changing temperatures or from internal drifting of IR sensor hardware. The
image will either seem washed out or have non-responsive pixels or "spots" in the image. To restore image quality,
operators can re-calibrate the IR sensor and reset the dynamic range of thermal energy that is assigned to a
grayscale representation. If the dynamic range of the grayscale is too narrow, the sensor will lack the ability to
represent all measured infrared wavelengths and yield poor image quality. There are two types of calibration:
•
1-Point calibration
•
2-Point calibration
1-Point Calibration. Utilizes a single thermal signature profile for a de-focused scene. Utilized most often, it will
remove most common artifacts and optimizes the exposure time within about 15 seconds. A 1-Point calibration
L-3 WESCAM
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Chapter 3 - Payload Sensors
October 2007
59
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