>SECTION I: Anatomy & Physiology of the Eye
>SECTION II: Day vs. Night Vision
>SECTION III: Visual Deficiencies
>SECTION IV: Dark Adaptation
>SECTION V: Spatial Disorientation
>SECTION VI: Distance Estimation & Depth Perception
>SECTION VII: Operational Theory of the ANVIS
>SECTION VIII: Miscellaneous NVG Related Questions
>SECTION IX: Hypoxia and Aeromedical Considerations
>SECTION X: Hemispherical Illumination
*** Please post additions / corrections to the comments with current reference, if applicable. ***
– Rhodopsin is bleached out.
– Produces sharp images and color vision.
– Involves the cones only.
– Reduces color vision and decreases visual acuity.
– Involves both rods and cones.
– Most dangerous time to fly.
– Decreases visual acuity. 20/200 or less.
– Causes loss of color perception.
– Causes night blind spot.
– Requires us of peripheral vision and recognition of objects by silhouettes.
– Involves the rods only.
Time to Dark adapt
Time to Readapt after High Intensity Lighting
-Each person adapts at a different rate
-Exposure to intense sunlight for 2-5 hrs increases visual sensitivity for up to 5 hours
-Cumulative effect – the rate of dark adaptation and degree of night visual acuity decrease, may persist for several days.
Dilated pupil allowes 100,000 times more total eye sensitivity
– Red Lens Goggles and Red Lighting: Preserves up to 90% of dark adaptation, and starts dark adaptation if worn prior to flight.
– Oxygen supply: Rhodopsin is oxygen dependent
– Sunglasses: Neutral Density 15 (ND-15) lenses to minimize effects of sunlight on rhodopsin production.
– Cockpit Lighting: Adjust to lowest readable level
– Exterior Lighting: Dim or turn off if possible and mission permitting.
– Light Flash Compensation (CAAT)
* Close One Eye
* Auto Weapons Fire – use short bursts
* Alter Course – avoid built-up areas
*Turn Away – fly around flares, spotlights, etc.
Type II: (Recognized)
Type III: (Incapacitating, xfer controls)
– FALSE HORIZON – Clouds may be confused with the horizon.
– FASCINATION/FIXATION – Fascination (fixed inside, as on an instrument), Fixation (fixed outside, as on a target)
– FLICKER VERTIGO – A light flickering at 4 to 20 cycles per second can cause unpleasant feelings to make you sick.
– CONFUSION OF GROUND LIGHTS WITH STARS: When this happens, pilots may unknowingly position the aircraft in an unusual attitude trying to keep the stars (but really they are ground lights) above them.
– RELATIVE MOTION – You may mistake the motion of another object as your motion. An example is during formation flight when you notice another aircraft moving but you think it is your aircraft that is moving.
– AUTOKINESIS – When a static light is stared at for about 6 to 12 seconds in the dark, the light appears to move.
– STRUCTURAL ILLUSION: A straight line may be bent or 1 light may look like 2 lights. May be caused by looking through the curved windshield or through desert heat waves.
– HEIGHT/DEPTH PERCEPTION – When flying over low contrast areas such as desert, snow or water, you may think you are higher than you actually are.
– CRATER ILLUSION: While landing using NVGs, if the IR searchlight is pointed too far down, it appears the aircraft is landing in a crater. The pilot may continue lowering the collective, causing a hard landing.
– SIZE-DISTANCE – A false perception of distance. When you see an unfamiliar object (a runway not seen before), you may think of it as being the same size as a familiar object (a runway that you have seen before). Therefore, you may mistakenly judge that the runway is too far or too close.
– ALTERED PLANES OF REFERENCE: When approaching a line of mountains or clouds, you may feel the need to climb even though your altitude is adequate.
– REVERSIBLE PERSPECTIVE – This occurs when an aircraft appears to be going away from you when in fact it is actually coming toward you.
Semicircular Canals (sense angular acceleration)
-Oculogravic: Acceleration/deceleration causes perceptions of a nose-high attitude.
-Oculoagravic: Downward motion (such as autorotation) causes eyes to track upward and sense a nose-low attitude.
-Elevator: Upward acceleration causes eyes to track downward and percieve nose-high attitude.
-Leans: Most common form. After rolling into or out of bank, pilot may falsely perceive position and lean his body to compensate.
-Graveyard Spin: Usually occurs in fixed-wing aircraft. When recovering from a spin, pilot perceives spin in opposite direction, reenters spin and continues down.
-Coriolis Illusion: Overwhelming sensation caused by rotating head in an additional plane, causing fluid to rotate in different directions, resulting in head-over-heels tumbling sensation.
Never fly VMC / IMC at the same time
Never fly without reference to a horizon
Trust your instruments, develop a good cross-check
Avoid physiological stressors (DEATH – Drugs, Exhaustion, Anxiety, Tobacco, Hypoglycemia)
Delay intuitive reactions
Refer to instruments
Transfer the controls
– Geometric Perspective – an object may have a different shape when viewed at varying distances and different angles.
– Retinal Image Size – The brain perceives the actual size of an object from the size of an image on the retina.
– Aerial Perspective – The clarity of an object and the shadow cast by it are cues.
– Motion Parallax – The most important cue. While moving across the landscape, near objects appear to move backward while far objects seem to remain fixed. This motion difference is used to tell what objects are close and what objects are far.
– Linear Perspective – Parallel lines, such as runway lights and roads tend to converge as distance increases.
– Apparent Foreshortening – Distant objects appear elliptical. As you get closer, the true shape appears.
– Vertical Position in the Field – Farther away objects appear higher up on the horizon.
– Known Size of Objects – Familiar objects that are seen larger than usual are deemed to be close while smaller are deemed to be far away.
– Increasing or Decreasing Size of Objects – If the image size is increasing, the brain says the object is getting closer. If the size is decreasing, the object is getting farther away.
– Terrestrial Associaton – Comparing a known size object (like a helicopter) with another object associated with the object (like an airfield), then the objects are judged to be about the same distance.
– Overlapping Contours – When objects overlap, the overlapped object is farther away.
– Fading of Colors or Shades – The shade of an object is clar when closer to the object, but the object get blurry as distance increases.
– Loss of Detail/Texture – The farther away from an object, details become less apparent. Like leaves in a corn field can be seen when up close but become a solid mass when far away.
– Position of Lights and Shadows – When an object casts a shadow from a light source, the object is closer than the light source if the direction of the shadow is toward you.
-The Photocathode converts the photons into electrons.
-After passing through the Photocathode, the electrons then hit the Microchannel Plate where the electrons are multiplied. The Microchannel Plate multiplies the electrons by means of tiny glass tubes that bounce the electrons off the glass tubes sides, creating more electrons.
-These electrons (a lot of them now), then strike the Phosphor Screen. The Phosphor Screen turns the electrons back into photons (called “light”).
-The photons then go through the Fiber-Optic Inverter. The Fiber-Optic Inverter is a bunch of fiber optics that are twisted. This inverts the photons (and thus the image).
-This image is then sent to the eyepiece Lens.
-The human eye looks at the Eyepiece Lens and observes the image.
– Flickering or Flashing of one or both monoculars
– Edge Glow
– Emission Points
– Intermittent Operation
– Image Disparity: Defference in brightness between 2 tubes.
– Image Distortion: Trees or poles tend to wave or bend.
– Output Brightness Variation: Varying brightness across an image.
Definition – A helmet-mounted, light-intensification device that allows aircrews to conduct operations at terrain flight altitudes during low ambient light levels.
Amplification – ANVIS amplifies light 2,000 to 3,000 times.
Acuity – 20/25 under optimum conditions
Limited field of view – 40 degrees
Voltage Low Indicator – A red LED light on the helmet mount will come on when the battery is at 2.4 volts or less.
Power Supply – 3 sources:
1. Battery (2 x 1.5v lithium OR 2x 1.5v Alkaline)
2. Aircraft 3.8vdc
3. Clip On Power Source (COPS)
– Color Discrimination – There is no color when looking through the NVGs, only a green hue.
– Air/Ground Speed Limits – While wearing NVGs, you tend to overfly their capability to see.
– Lights – NVGs are affected by bright lights. The bright light may create: Whiteout, Halo effect, Tunnel Vision Performance is related to amount of available ambient light.
– Magnification – There is no magnification with the NVGs.
– Weather – Since the NVGs can see through fog and rain, you may fail to detect entry into IMC.
– Weapons – When rockets and machine guns are fired, the intensity of the light source may temporary degrade the NVGs.
– Aircraft Lighting –
* All cockpit red light must be extinguished.
* The use of blue-green aircraft instrument lights will not degrade the NVGs.
* Unless modified, the aircraft’s position lights degrade the NVGs.
– Depth Perception and Distance Estimation – Depth perception and distance estimation is difficult using NVGs. Rely upon the monocular cues to help.
– Scanning Techniques – NVG scanning is the same as for night unaided scanning.
– Obstruction Detection – Wires and small limbs are hard to see with NVGs. Locate wires by looking for the structural supports
– Spatial Disorientation – Avoid making drastic changes in attitude and bank angles since they tend to cause Spatial Disorientaion.
– Bright Source Protection (BSP): BSP does the same as ABC – protects the image intensifier from brightness damage. BSP lowers resolution on a bright night; therefore the images may not be a sharp as you may expect.
– AA alkaline batteries: 70 deg F and above = 10 to 22 hours
0 deg F = 5 to 10 hours
– AA Lithium batteries: 70 deg F and above = 34 hours
0 deg F = 28 hours
– Turn the power switch of the secondary compartmen to ON. The visor red light should come on or blink.
– Return the power switch to OFF and put the battery cap back on.
– Repeat the same procedure for the upper (Primary) compartment.
– Turn both Eyepiece Focus rings so that the Reference dot and “0” diopter mark are aligned.
– Turn on the ANVIS.
– Look at a high contrast target.
– Cup your hand over the left Objective Lens.
– Slowly rotate the right Objective Focus ring clockwise to the sharpest image.
– Turn the right Eyepiece Focus ring countercloskwise until the image blurs slightly. Then turn the Eyepiece slowly clockwise till you get a clear image.
– Cup your hand over the right Objective Lens and do the same procedures.
– Use both eyes and…
– Turn the left Objective Focus ring so it is slightly out of focus.
– Fine tune the right Eyepiece Focus ring to obtain a sharp image.
– Turn the left Objective Focus ring back to its original position.
– Still using both eyes, do the same for the right Objective Ring.
– Turn off the ANVIS.
– Increased Halo Effect.
– Increased “Image Noise” (like “snow” seen with poor TV reception).
– Rotate your head slowly left to right.
– At the same time, move your eyes from the left limit of vision seen inside the goggles to the right limit.
–This will cover about 80 degrees of viewing field while only turning your head 40 degrees
– Every 60 days, a 1 hour NVG flight at night in the aircraft.
(TC 3-04.33 2-6)
– NOE is up to 25 feet AHO at 40 KIAS
– Contour is between 25 – 80 feet AHO at 70 KIAS
– Low Level is between 80 – 200 feet AHO at up to VNE
Hypoxic – (Altitude) Occurs when not enough O2 is in the air or when decreasing partial pressure of O2 prevents diffusion across alveolar membranes.
Hypemic – (Anemia, Blood Loss, Chemical Interference) Reduction in O2 carrying capacity in the blood.
Histotoxic – (Alcohol, narcotics, poisons) Interference with tissues ability to receive O2 from blood.
Stagnant – (extreme G forces, blockage, trauma) Circulation is inadequate to deliver O2 to body tissues.
– Indifferent (0′ to 10,000′) – Night vision deteriorates ~4,000′
– Compensatory (10,000′ to 15,000′) – Pulse rate, blood pressure, circulation, and cardiac output increase to compensate for reduced O2. May become drowsy and make frequent errors in judgement.
– Disturbance (15,000′ to 20,000′) – Subjective/Objective symptoms present.
*Fatigue, dizziness, headache, breathlessness, euphoria
*Poor judgement, personality change, decreased coordination
– Critical (20,000′ to 25,000′) – Within 3 to 5 minutes, judgement and coordination deteriorate. Subsequently, confusion, dizziness, incapacitation, and unconciousness.
– Limit Time at Altitude
– Use Supplemental Oxygen
– Pressurize Cabin