FLIR Image Enhancement by Automatic Low Frequency Gain Limiting,
ARMY ELECTRONICS RESEARCH AND DEVELOPMENT COMMAND FORT BELVOIR VA NIGHT VISION AND ELECTRO-OPTICS LABS*
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An inherent problem with existing Military FLIR Common Module systems is that the dynamic range of the thermal scenes far exceeds that of the system display. Current displays used in FLIR systems have a dynamic range of approximately 30 dB 321 and typical infrared scenes can be several orders of magnitude greater. A common example being the terrain-sky horizon which an Airborne FLIR encounters when the helicopter or aircraft makes a steep bank. In this scenario some of the channels in the vertical array of detectors will be viewing both the hot terrain and cold sky. This scene dynamic range can be as high as 500 to 1, or 54 db, with a temperature difference, delta T of 100 C and the noise equivalent differential temperature NE delta T of 0.2 C. The display of the channels will be such that the terrain saturates to white and the sky is suppressed to black, assuming that the system polarity switch is in the whitehot mode. Now if the operator attempts to reduce the gain of the system, such that both areas are within the dynamic range of the display, he is unable to perceive detail in both regions due to a lack of contrast. At this moment the operator may adjust the brightness level and maintain the contrast high enough to perceive either the terrain or the sky detail but not both simultaneously.
- Infrared Detection and Detectors