Thermal Display Unit: 
The thermal picture display renders the imagery in tones 
of gray on a black-and-white TV-type monitor screen. The 
normal mode of display is white = warmer, but other modes 
are possible: white = cooler (black = warmer) and 
brightened-up isotherm superimposition. Differing 
thermal ranges can be selected to depict greater or 
lesser thermal spans between black and white, and 
isothermal contours can be adjusted throughout the 
gray tonal range to enable evaluation of thermal 
differences between details in the picture. Probably 
most important for airborne remote sensing, thermal 
level adjustments remain constant so thermal sources 
separated from each other can be directly compared - 
by first flying over one, and then the other. 
Superposition Viewing Attachment: 
The IR camera and display units are mounted together 
so they can be panned as a single unit, held together 
by a unifying structure which incorporates a special 
viewing attachment, called the 'Superviewer'. Looking 
through the Superviewer, the instrument operator observes 
the thermal picture screen of the display unit superim- 
posed at the distance of the object of interest, and 
coincident with the visible object. The result is a sort 
of infrared-on-visible 'head-up display' with which one 
can look out of the side of the aircraft. 
Biocular viewer optics were adopted from the first, borrowing 
from modern 'head-up' technology, to increase the apparent 
brightness of the superimposed thermal imagery, and pro- 
vide relaxed seeing on prolonged patrol flights. Biocular 
(as opposed to binocular) optics have the added advantage 
of allowing operators with impared eyesight in one eye or 
the other to make use of the system. 
Registering the Hybrid View: 
To be useful to responsible authorities, whose organiza- 
tions would support the helicopter IR patrols, the hybrid 
view had to be registered in the air for later presenta- 
tion on the ground, either immediately,or in the form of 
reports. In the former case, video tape recording was 
adopted, using portable 1/2-inch reel-to-reel machines 
at first and just lately the new 1/2-inch cassette VTR 
models. For the latter, standard 35 mm colour photography 
was adopted, because of its accuracy in reproducing the 
operator's view in natural colour, suitable for reports. 
On forest surveys, however, only VTR moving picture playback 
can reproduce the 'picket fence' effect, which allows thermal 
anomalies warmer or cooler than the canopy to be observed 
through it, almost as though it were transparent. (It is 
this which allows forest fire holdover detection, big game 
censusing and even search and rescue operations to be carried 
out by the system.)