NVG

Question 1

What do NVG do

Answer 1

Sensitive to near IR range of EMR
Reflected energy detected by NVGs
- intensified: multiplied/applied
- projected onto phosphor screen

NVG- enhanced image produced

Question 2

Structure of NVG

Answer 2

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

Question 3

Issue with fibre-optic bundle

Answer 3

Over time can get to distortion due to fibres falling out

Question 4

What are the lens on NVG

Answer 4

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

Question 5

Automatic brightness control pros and con

Answer 5

Automatic to prevent blinding from bright light
- will adjust gain

Issues with flying at dusk

Question 6

Blooming and halos?

Answer 6

Protect again exposure to bright light
Results in halo effect on light

result of auto brightness

Question 7

What is scintillation

Answer 7

Due too gain control features.. looks like snow on the screen as low light and trying to take in more and more light.

Question 8

Three major variable that influence NVG performance

Answer 8

Illumination
Terrain
Atmospheric conditions

Question 9

What are the types of Natural illumination

Answer 9

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

Question 10

What is cultural illumination

Answer 10

All artificial sources of light - building, roads, vehicles

Advantages: provide illumination to NVG, assist in nav and feature recognition

Disadvantage: paradoxical image degradation (blooming)

Question 11

3 main factors determin appearance of terrain throgh NVG

Answer 11

Reflectivity - albedo
Contrast
Shadowing

Question 12

Advantages of NVG

Answer 12

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

Question 13

Disadvantages of NVG

Answer 13

Limited field of view
Difficult depth, distance and closure
Monochromatic display
Susceptibility to visual illusions
Visual acuity half normal

Question 14

Aeromedical issues with NVG

Answer 14

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

Question 15

Visual acuity with and without NVG

Answer 15

Day 6/6 night >6/120

NVG
Day 6/9
Typical moonlight 6/12
Typical starlight >6/24

Question 16

Field of view with night vision

Answer 16

40 degree

Question 17

How do we do depth perception with NVG

Answer 17

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

Question 18

Aeromedical concern for depth perception with NVG

Answer 18

Inaccurate depth perception and hazard avoidance formation flying

Loss of situational awareness

Question 19

Issues with NVG mounted onto helmet

Answer 19

Overall weight
Centre of gravity by 30mm. Needs counter weight
Muscle fatigue
Manoeuverability and impaired dynamic scan
Acceleration forces

Question 20

Injuries from night vision goggles.

Answer 20

Neck injuries 
eye injuries
Facial fractures
Eye fatigue
Transient colour distortion

Question 21

Types of fatigue from NVG

Answer 21

Visual fatigue
Psychological fatigue
Physical fatigue
Circadian fatigue

Question 22

NVG and SD

Answer 22

5 fold increase in SD with NVG

Due to

• loss of peripheral vision
• dynamic scan and reconstituted field of regards
• instruments
• other crew member

Question 23

Time it takes for cones to adjust to dark

Answer 23

5-7 mins

Question 24

What type of eye injuries occur due to NVG

Answer 24

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.

Question 25

How to set NVG up

Answer 25

Inter-pupillary distance
vertical adjustment
Tilt
eye-relief distance
don't adjust for 10 mins

Can also use Hoffman