by Chuck Husick
-Updated July 2009
Night vision light
amplifiers are one of the ultimate weapons in our battle against darkness, the other the infrared video camera. The light amplifiers work by exposing them to a moderately high voltage electrical field collecting and converting the light photons into electrons,
accelerating the electrons and focusing the electrons on a screen that
converts the electrons into visible light. The IR systems operate in a related manner, except that they are sensitive to the infrared energy that is emitted by the types of objects normally encountered in a marine environment. The IR sensitive viewing devices will work in situations where there is a total absence of visible light energy. (Most light amplifiers have a degree of IR sensitivity but it is very much inferior to that of a purpose designed IR viewing device.
Three levels of technology
are used in the light amplifiers. Generation I devices, by today's standards
fairly crude, provide the least amount of light amplification and the
poorest image quality. Generation II units provide very adequate sensitivity
and generally excellent image quality. Generation III, the latest technology,
provides the greatest sensitivity, image perfection, operating life and
ability to deal with the effects of scenes that may contain isolated,
very bright lights. Overall performance and quality go together. Most
Gen I units are imported while Gen II and Gen III products are made in
the U.S. Light amplification factors range from a few hundred times for
some Gen I units to more than 50,000 times for Gen III channel plate devices. Gen IV units are becoming available, however the performance advantage above the Gen III device is generally not sufficient to justify the significant cost increase.
Night vision light
amplifiers are moderately sensitive to normally invisible, infra-red light, the long
wavelengths of light at the far red end of the spectrum. This infra-red
sensitivity can be used to some advantage in marine navigation. An infra-red
light source, whose light is invisible to normal vision, can be used to illuminate a nearby object, making it clearly
visible through the night vision device, without degrading the dark adaptation
of other observers as would occur with use of a visible light beam. An
infra-red illuminator can be useful in locating things in a dark cabin,
without disturbing the occupants by turning on normal lighting. The infra-red
sensitivity of some viewing devices is sufficient to show hot areas of
a running or recently operated engine, however the sensitivity is not
sufficient for evaluation of thermal problems. You may notice that living
vegetation appears quite bright due to its high infra-red reflectivity,
however this aspect of night vision devices may have greater value for
detection of camouflage than for navigation.
Night vision devices
used for marine navigation should have as wide a field of view as possible.
The image should match as closely as possible what you see with your unaided
vision. Devices that magnify the image have unavoidably narrow fields
of view and although they may be useful for some applications, they are
not ideal for use on a boat. Most of the units intended for marine navigation
are monoculars, not binoculars. Using a monocular can be an economic and
operational advantage. The monocular is much less costly than a binocular
and if the device is always used with the same eye, much of the dark adaptation
of the other eye will be preserved, enhancing vision when not using the
device. The latest true IR viewing systems sufficiently sensitive to show the internal structural elements of a metal hull ship, where the presence of the supporting structure creates a very minor difference in the temperature of the metal hull plates. IR systems can provide a valuable visibility advantage in fog conditions since the temperature differences of objects visually obscured by the water droplets in the fog do not mask the underlying iR energy differences.
IR viewing systems are available in combination with various types of TV cameras and with gyro stabilized mounts.