INTRODUCTION TO NIGHT VISION DEVICES
NIGHT VISION DEVICES. These devices have revolutionized night flying by permitting
vastly expanded night operations. Daytime like tactics can now be covertly carried out under
the cover of darkness. Such maneuvers as low level flight, air drops, target acquisition and
engagement, threat detection, multi-ship or formation flights, and air-to-air operations that
would otherwise be impossible are now possible using night vision devices (NVDs).
At the present time, the USAF is using two different technologies for night vision imagery.
The most common of these is the night vision goggle (NVG). This helmet mounted device
uses two image intensifier tubes, one for each eye, to amplify reflected or emitted ambient
light including short wavelength infrared. The intensified image is displayed on a screen
resembling a black and white television, except that it is in shades of green rather than gray
due to the selected display phosphor. The second system is Forward Looking Infrared (FLIR)
which is a thermal sensor that images long wavelength infrared radiation. Present FLIR
systems use an externally mounted IR sensor and display their image on the Head-Up Display
(HUD) or on a Head-Down Display (HDD) on the instrument panel.
FLIR SYSTEMS. FLIR technology emerged during the Vietnam War and is based on the fact
that all objects warmer than absolute zero emit heat, or long wavelength infrared (IR) energy
(1 to 15 microns). Objects in a scene will have different temperatures and will emit IR energy
at different rates. The FLIR image is a computer generated picture of the "thermal contrast"
created by the different temperatures and the varying IR emission rates of the objects in the
scene. FLIR systems are capable of differentiating between objects with a temperature
difference of as little as one degree or even objects with the same temperature if the rate of
energy emission is different.
Unlike NVGs, FLIR systems are totally independent of ambient light. They are able to
penetrate smoke and haze somewhat but are attenuated by moisture. The visual limitations of
the FLIR systems include small field-of-view, reduced resolution, decreased depth perception,
and lack of color contrast. Environmental conditions such as precipitation, fog, or even high
humidity can severely effect the performance of FLIR systems.
FLIR systems are much larger and heavier than NVGs and must, therefore, be aircraft
mounted rather than helmet mounted. An example of a fielded FLIR system is the Low
Altitude Navigation & Targeting Infrared for Night (LANTIRN) found on some Air Force
F-15, F-16, and Navy F-14 fighter aircraft. LANTIRN consists of a FLIR camera pod for
navigation and another FLIR camera pod for targeting. The targeting pod can independently
maintain a lock on the target and provides a stabilized image as the aircraft maneuvers. The
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FLIR image is displayed on the aircraft’s HUD, providing the pilot with a 21° by 28° view
of the night world.
NIGHT VISION GOGGLES. During the mid 1960’s first generation (GEN I) image
intensifiers were developed for night observation by ground troops. An attempt was made to
use these devices in Forward Air Control aircraft during the Vietnam War but they were much
too large and heavy to be used effectively in the cockpit. In the late 1960’s, second generation
(GEN II) image intensifiers became available. This technology was much smaller and lighter
than GEN I and led to the development of the night vision goggle. These were head mounted
binocular systems originally designed for truck and tank drivers. In the early 1970’s, the
AN/PVS-5 NVG was adapted for use in helicopter operations. This device demonstrated that
NVGs could significantly increase the operational capacity of helicopters by allowing pilots
to fly at high speed and low altitude on clear moonlit nights.
The success of the PVS-5 led the Army to develop the AN/AVS-6 or Aviators Night Vision
Imaging System (ANVIS) specifically designed for helicopter pilots. The ANVIS goggle is
third generation (GEN III) technology which is lighter, provides better resolution, and has
greater low light capability than GEN II image intensifiers. The AN/AVS-6 NVG was fielded
in the early 1980’s and remains in use today. Presently, the AN/AVS-9, often called the
F4949, is the NVG of choice for new acquisitions. Sometimes called the ANVIS-9, the
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AN/AVS-9 has upgraded features including better objective and eyepiece focusing
mechanisms, monocular PD adjustment, and improved resolution.
The British proved that NVGs could be successfully used to enhance night operations in high
performance fixed wing aircraft during the Falkland Islands War. Since then, the USAF,
USMC, and USN have been routinely using NVGs in both rotary and fixed wing night
operations. As demonstrated by Operation Desert Storm, and over Bosnia and Kosovo, night
war fighting capability has become a reality. With a greater emphasis on night operations by
the USAF, the number and types of aircraft utilizing this technology is increasing rapidly. If a
unit at the base where you are assigned is not already flying an NVG mission, it may by only
a matter of time before one or more of them receives such a mission. Since NVGs are vision
enhancing systems, you may be asked by Flight Medicine to assist the unit in preparing its
aircrew for their night mission. It is therefore important for you to be knowledgeable about
these systems and understand their visual capabilities and limitations
Unlike FLIR systems, GEN III NVGs are sensitive to visible light and near infrared energy
(600 to 900nm) and image "reflective contrast" rather than "thermal contrast." As stated
earlier, NVGs amplify ambient light (up to 5,000X) and therefore some visible or near IR
light must be present for the NVGs to work. The present GEN III systems can operate quite
well under starlight and will function even in overcast starlight conditions. Due to the ability
of IR energy to penetrate moisture in the atmosphere, NVGs can function in thin clouds, light
fog and even light rain quite effectively. They are, however, attenuated by atmospheric smoke
and haze. Lighted objects can easily be seen from distances of 30 miles or more while bright
lights such as aircraft strobe lights may be seen from distances of 100 miles or more. Even a
lighted cigarette may be seen from as far away as 5 miles. However, detail such as power
lines or objects with low reflectivity are virtually invisible to the goggles even under optimum
lighting conditions.
Some of the visual limitations of NVGs include limited field-of-view, reduced visual acuity,
reduced depth perception, and lack of color contrast. Visual acuity with early models of
AN/AVS-6 or F4949 goggles, though significantly better than unaided visual acuity, would be
about 20/40 under optimum conditions (quarter moon or better illumination). Newer models
of NVGs are capable of resolving details at 20/25 or better under ideal lighting conditions. As
illumination decreases, goggle performance decreases resulting in reduced visual acuity.
Since NVGs are often used in conditions that are less than optimum, visual acuity will often
be much worse than 20/40 during many night operations. Current NVGs provide a maximum
field-of-view (FOV) of 40° . To maintain situational awareness and spatial orientation with
this small FOV, the pilot must increase his/her head movements to adequately scan the full
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field of regard. The FOV is further reduced as the goggle is moved away from the eye as it
would be if spectacles were worn under them. For this reason, soft contact lenses are
approved for aircrew using NVGs if they meet other requirements of the contact lens program.
Even under optimum conditions, depth perception and distance estimation can be significantly
degraded when using NVGs. Anything that adversely affects the NVG image will further
degrade the user's depth perception. Studies have shown that stereopsis may be reduced while
wearing NVGs and the user must learn to rely on monocular cues to depth. Due to the
monochromatic phosphor screen used to present the NVG image, color contrast is absent. All
objects viewed through the goggles appear as shades of green.
NVGs AND THE ROLE OF THE OPTOMETRIST
INITIAL CERTIFICATION OF AIRCREW USING NVGs. AFI 48-123, Attachment 8.7,
Duty Requiring Use of Night Vision Goggles (NVG), provides instruction to the flight
surgeon and the optometrist for evaluating aircrew using NVGs. AFI 48-123 states that NVG
users are required to meet "no additional vision standards over and above already required for
their duty AFSC…" Studies have shown that around 85% or more of users can achieve 20/50
with early generation III NVGs (Silberman, et., al., 1994). Improved models of currently
fielded NVGs should provide at least 20/50 vision for all users who have best corrected
Snellen acuity of at least 20/20 (Baldwin, et. al., 1999). In the past, some MAJCOMs or
individual squadrons have had acuity standards for NVG flying. Check local flying
regulations for references to unit specific NVG acuity standards. Before approving an aircrew
member for initial NVG duty, the flight surgeon must review the medical records to ensure
that the individual meets the vision standards required for their flying class. This record
review is repeated periodically thereafter to ensure that the individual has passed the most
recent annual vision screening. Documentation of the initial review and all periodic reviews
should be entered into the medical records. Measurement of visual acuity with the NVGs in
the eye clinic by an optometrist or ophthalmologist is no longer required. Aircrew members
who fail the yearly vision screening, complain of visual problems with or without NVGs, or
fail to achieve 20/50 visual acuity in the NVG pre-flight test lane should be referred to the eye
clinic for a routine eye examination.
PROFICIENCY TESTING. According to AFI 11-202V3, General Flight Rules, 1 June 1998:
"Crewmembers must undergo an initial certification course, emphasizing preflight procedures
and goggle optimization or limitations, prior to their initial flight with NVGs. An
appropriately trained instructor, assisted by a flight surgeon or a designated representative,
will conduct this course (see AFI 48-123, Medical Examination and Standards)." You may be
asked to be that representative or at least become involved in some aspects of the initial NVG
training. As part of this training, the flight surgeon or designated representative should ensure
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that the aircrew members understand how to properly fit, adjust, and focus their NVG. A one
and one-half day course at Luke AFB entitled "NVG Instructor Course" is open to anyone
who might be tasked with training aircrew in NVG operations. For information on registering
for this course contact Col William Berkley, 602-988-6561, or see
http://www.williams.af.mil/html/nvgup.htm.
The squadron life-support section is responsible for maintaining an NVG test lane for
preflight assessment of the NVGs and for aircrew proficiency evaluation and training. AFI
11-202V3 states, "Aircrew will preflight NVGs prior to each use to ensure proper operation
and optimum night visual enhancement." Proficiency at using the NVGs is evaluated by the
individual crewmembers and life-support personnel. This testing does not have to be
accomplished by the flight surgeon or optometrist, but it is suggested that the flight surgeon or
a designated representative (possibly you) occasionally verify the calibration of the NVG test
lane, the accuracy of the preflight testing procedures, and the performance of the squadron
personnel.
SAFETY LENSES AND CONTACT LENSES FOR NVG USERS. Aircrew members can
wear either soft contact lenses, IAW the Aircrew Soft Contact Lens Program, rigid lenses if
medically waivered, or spectacles, when correction is required using NVGs. The eyepiece of
the ANVIS goggle can be adjusted to compensate for spherical refractive errors from +2.00D
to -5.00D. Individuals outside this range or with astigmatism of greater than 0.75D should
wear corrective lenses when using NVGs. NVG users look under the NVGs to see the cockpit
display, and often look out of the window without NVGs (for example during landing) and
therefore should wear corrective lenses if the refractive error is significant. Spectacles worn
with NVGs should have safety lenses, either 3.0mm minimal thickness CR-39, or
polycarbonate. IAW AFI 48-123, aircrew who wear NVGs in the performance of their duties
are authorized two pair of aircrew frames with safety lenses for use with NVGs. These may
be obtained by mailing a properly completed DD Form 771 to the Optical Research Unit,
USAFSAM/AFCO, 2507 Kennedy Circle, Brooks AFB, TX 78235-5117, or by sending the
order electronically with SRTS. Air National Guard and Air Force Reserve Units must
include a fund cite with their request. All orders must clearly indicate within the "Remarks"
section that the request is for "safety lenses for use with night vision goggles." Refer to AFI
48-123, Attachment 8, for more detailed guidance concerning safety lenses for NVG users, or
call the Optical Research Unit at DSN 240-3852.
EDUCATION AND SUPPORT. The optometrist’s role in the night vision program is
education, trouble shooting, and support. Flying operations with NVGs are inherently
hazardous with accident rates for NVG flights considerably greater than conventional flying.
From October 1995 to October 1999 there were 6 class-A mishaps resulting in 16 deaths of
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Air Force personnel. Therefore, every Air Force optometrist should be aware of the
requirements, functions, safety concerns, and the routine operation of their unit’s NVG
program in order to help maximize safety and performance. In addition to the NVG
instructor's course mentioned above there are other sources of training materials available on
the web. The AF optometry website includes the Night Vision Manual for the Flight Surgeon,
AL-SR-1992-0002:
http://chppm-www.apgea.army.mil/dcpm/vcp/afopnet/ISSUES/NVG/TOC.HTM
A set of Powerpoint slides is available on the USAFSAM Aerospace Medicine webpage at:
http://wwwsam.brooks.af.mil/web/ram/NVG/nvgtoc.htm
AN/AVS-6
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AN/AVS-9
References:
JB Baldwin, RC Tutt, JT Yates, DJ Ivan, FJ LoRusso, PL Hiers, B Thompson, TJ Tredici
(1999) Predicting which users will have optimal visual performance with night vision goggles
(NVG). Optometry and Vision Science, Supplement (Presented at the 1999 Annual Meeting).
W Silberman, D Apsey, D Ivan, W Jackson, G Mitchell (1994) The effect of test chart design
and human factors on visual performance with night vision goggles. Aviation, Space, and
Environmental medicine, 65: 12, 1077-1081.
AFI 11-202V3, General Flight Rules, 1 June 1998
AFI 48-123, Medical Examination and Standards
AFM 11-217, V2, Instrument Flight Procedures, Chapter 3 (A comprehensive review of
NVG performance capabilities and limitations)
Night Vision Manual for the Flight Surgeon, AL-SR-1992-0002
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http://wwwsam.brooks.af.mil/web/ram/NVG/nvgtoc.htm (Downloadable Powerpoint slides,
and NVG resolution chart maker software)
http://chppm-www.apgea.army.mil/dcpm/vcp/afopnet/ISSUES/NVG/TOC.HTM (AF
optometry page containing Night Vision Manual for the Flight Surgeon, AL-SR-1992-0002 )
http://www.lmco.com/LANTIRN/home.html (Lockheed Martin, FLIR web page)
http://www.ittnv.com/military/index.html (ITT Night Vision, makers of NVGs and
accessories)
http://www.littoneos.com/products/usmilitary/usaviation.htm (Litton Electro-Optical Systems,
makers of NVGs and accessories)
For additional information, contact:
LtCol J. Bruce Baldwin
Maj Ron Tutt
MSgt Paul Hiers
USAF School of Aerospace Medicine
2507 Kennedy Circle
Brooks AFB, TX 78235-5117
DSN 240-4453/2735
vision.aaerospace@brooks.af.mil
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