NVG Flashcards
What do NVG do
Sensitive to near IR range of EMR
Reflected energy detected by NVGs
- intensified: multiplied/applied
- projected onto phosphor screen
NVG- enhanced image produced
Structure of NVG
Objective lens - inverts image
Photocathode - turns light into electrons
Micro-channel plate - magnifies then
Phosphor screen - give you the green glow
Fibre-optic inverter - inverts image
Eye - piece lens
Issue with fibre-optic bundle
Over time can get to distortion due to fibres falling out
What are the lens on NVG
Objective lens
- bulk of focuses
- further lens
- Inverts image
Eyepiece diopter lens
- proximal lens
- allows the eyes to view the phosphor screen with relaxed accommodation
- 25mm lenses
- inverter image back
Need to focussing
Optimum eye-relief
Diopter adjustment ring allows for correction but we don’t use it
Automatic brightness control pros and con
Automatic to prevent blinding from bright light
- will adjust gain
Issues with flying at dusk
Blooming and halos?
Protect again exposure to bright light
Results in halo effect on light
result of auto brightness
What is scintillation
Due too gain control features.. looks like snow on the screen as low light and trying to take in more and more light.
Three major variable that influence NVG performance
Illumination
Terrain
Atmospheric conditions
What are the types of Natural illumination
lunar illumination: lunar cycle and moon angle
- stellar illumination: large amount of EMR- outside sensitivity of anatomical eye, NVGS designed to use stellar EMR
- other sources of night sky illumination: solar influence, sky glow
What is cultural illumination
All artificial sources of light - building, roads, vehicles
Advantages: provide illumination to NVG, assist in nav and feature recognition
Disadvantage: paradoxical image degradation (blooming)
3 main factors determin appearance of terrain throgh NVG
Reflectivity - albedo
Contrast
Shadowing
Advantages of NVG
A handed situational awareness Enhanced maneouvrability: terrain avoidance,masking and use of unconventional night tactics Enhanced safety with multi-ship ops Conduct of covert operations Tactical advantage in air-ground ops
Disadvantages of NVG
Limited field of view Difficult depth, distance and closure Monochromatic display Susceptibility to visual illusions Visual acuity half normal
Aeromedical issues with NVG
Dark adaptation Visual acuity FOV and dynamic scanning Depth perception Dynamic cues Head supported mass Spatial disorientation and loss of SA Fatigue, 1:2 ratio increase. Post-flight problems
Visual acuity with and without NVG
Day 6/6 night >6/120
NVG
Day 6/9
Typical moonlight 6/12
Typical starlight >6/24
Field of view with night vision
40 degree
How do we do depth perception with NVG
No convergence or accomodation cues
Very limited functional Stereopsis
Only have monocular causes which are limited by poor image quality, poor illumination, adjustment and focus
Aeromedical concern for depth perception with NVG
Inaccurate depth perception and hazard avoidance formation flying
Loss of situational awareness
Issues with NVG mounted onto helmet
Overall weight
Centre of gravity by 30mm. Needs counter weight
Muscle fatigue
Manoeuverability and impaired dynamic scan
Acceleration forces
Injuries from night vision goggles.
Neck injuries eye injuries Facial fractures Eye fatigue Transient colour distortion
Types of fatigue from NVG
Visual fatigue
Psychological fatigue
Physical fatigue
Circadian fatigue
NVG and SD
5 fold increase in SD with NVG
Due to
- loss of peripheral vision
- dynamic scan and reconstituted field of regards
- instruments
- other crew member
Time it takes for cones to adjust to dark
5-7 mins
What type of eye injuries occur due to NVG
increase risk of facial fracture
no protection from bird strike, dust etc
not compatible visors poorly tolerated
post flight visual problems eg eye fatigue and colour distortion.
