al
Video Tape Recording:
Quite a lot of work has gone into converting the AGA
Thermovision signals into TV compatible waveforms, and
it is possible to record directly onto tape electro
But chiefly due to the 4-field interlace format,
playback must be done through the Thermovision display -
not standard TV monitors. We chose the pragmatic approach
of simply picking up the Thermovision imagery with a
small black-and-white TV camera, together with the
visible terrain optically superimposed, virtually imaged
at the distance of the terrain features being examined.
The raster sweeep inconsistancies between the Thermo-
vision and the CCTV systems, it turned out, are practically
undetectable on the TV monitor, in realtime as well as
playback.
One thing is still lacking: the 'colour dimension' which is
lost through the use of the small black-and-white camera.
Smaller colour CCTV cameras which will fit the top of the
Superviewer (and not collide with the roof OF the heli-
copter) are anticipated before the end of 1978. This
will be the final 'breakthrough'. For the present, the
slight flicker which can be noticed in the thermal
imagery is helpful in separating it from the visible
light imagery on the TV monitor screen. Simultaneous
soundtrack recording of the cabin-intercom crew conver-
sation also aids in identifying what is happening on the
video tape during ground playback.
Photorecording on Colour Film:
The natural colours in the hybrid view make it a simple
matter for the instrument operator to follow terrain
features while studying the thermal pattern distribu-
tion. Exact locations of thermal anomalies, hot or cold
relative to the surrounding terrain, generally appear
as abstract forms or spots, unrecognizable by themselves
on the Thermovision screen. By superimposing them on a
background of natural colours visible through the Super-
viewer, recognition is often automatic. Registering the
same view on colour film was a primary object of the
development, for use in instructing new operators.
The advent of fast negative colour film (Kodacolor 400)
with ASA 400/DIN 27 exposure index, at the time of our
initial flight-photography trials over forest fires in
North America (the summer of 1977) must be attributed
to our success - right from the beginning. That, and the
appearance of a new 35 mm SLR camera with automatic
aperture exposure control (Canon AE-1). The automatic
aperture was a great advantage, since the instrument
operator's hands are full, preventing a check of critical
exposure parameters during fast flybys at low altitudes
over patrol objectives.