signals from the control servomechanism. As shown
at the top of figure 6-12, one side scans the incoming
IR energy and reflects the signals into the IR imaging
optics, while the bottom side simultaneously scans
visible light signals from the collimating lens and
reflects the signal into the TV camera optics. The
mirror scans the horizontal axis, and is indexed in the
vertical axis to provide a 2:1 ratio interlace scan. The
mirror scan is synchronized to the TV camera by sync
signals.
IR TO VIDEO PROCESSING.— The IR signals
reflected from the scan mirror into the imaging optics
are focused onto an IR detector array located behind
an imaging lens. The lens is kept in focus much the
same as the afocal lenses. The IR detector array
consists of approximately 180 individual detectors
arranged in a linear array with a space between each
to allow for 2:1 interlacing. The scan mirror scans the
image across the detectors, and each detector
produces a single horizontal line of IR video. The
scan mirror is indexed one line width in the vertical
direction, making a total of 360 lines of video with
only 180 detectors and amplifier channels. Because
of the 2:1 interlacing, two full scans of the mirror are
required to reproduce the entire image. Each detector
conducts according to the amount of IR energy
impressed on it from the scan mirror. The resultant
output of the IR detector array is 180 parallel signals
representing 360 video lines of IR energy scanned by
the scan mirror.
The IR detectors are kept at cryogenic
temperatures by the refrigerator unit. The detectors
are biased to process the incoming IR energy into a
useable multichannel IR video signal. The low-level
output of the detector array is fed to a video amplifier
module. The module consists of one preamplifier and
three postamplifiers for each of the IR detectors in the
array. This is required to increase the IR signal to a
useable level. The output of the postamplifiers is
controlled by a dc level (+ or –) whose polarity is
controlled by a polarity switch on the IRDSC. The
purpose of the dc polarity is to have “hot” targets
appear either white or black on the video indicator.
Also, the outputs of the video amplifiers are gated on
or off in synchronization with the scan mirror and the
TV camera sweep.
Each video amplifier feeds a light-emitting diode
(LED) of the LED array. The LED array duplicates
the IR detector array.
The visible light intensity
output of one LED is proportional to the IR output of
the corresponding IR detector in the detector array.
The resultant output of the LED array comprises 180
parallel visible light beams (signals) representative of
the IR energy scanned by the scan mirror. In other
words, the resultant output of the LED array
represents the terrain or targets scanned.
The output of the LED array is applied to the
collimating lens unit. This unit focuses the visible
light while maintaining the light beams parallel to
each other rather than converging them to a focal
point, as shown in figure 6-13, views A and B.
The output of the collimating lens unit is scanned
by the back side of the scan mirror and is reflected
into the camera optics unit that focuses the light for
the TV vidicon camera. Also, a reticle light signal
from the reticle optics unit is applied simultaneously
to the TV camera to give an indication of the position
of the receiving head.
The TV vidicon camera
processes the visible light signals into a single
channel video signal. The video output of the camera
is fed to the power supply-video converter assembly
for further processing.
Figure 6-13.-Lens focusing patterns.
6-11
