NOTE: 120 shown in Figure 1-4 indicates the scan angle for this system.
(1) The basic IR scanner consists of a rotating scan mirror and a series of
reflecting and focusing mirrors. The scan mirror rotates at high speed vertical to the aircraft
track. At the start of a line scan only objects at the left end of the scan are focused into the
detector. Energy from other areas is reflected away from the folding mirrors. After the scan
mirror has rotated halfway through the scan, only energy from objects directly below the
aircraft are reflected to the detector. Further rotation of the scan mirror feeds energy into the
detector' from objects located at the right end of the scan line. All other energy Is reflected
away from the folding mirrors, thus eliminating its detection. When one face of the scan mirror
is parallel to the horizon, all energy is reflected to the ground. At this time the Image from the
aircraft is reflected on itself. Because of the cool-down of the detector a sharp cold spike is
generated in the system. Shortly after this the scan mirror Is in position to start another scan.