Download Night Vision Sensors Electromagnetic Spectrum

Rotary Wing
Night Flight
Part III
Wings of Freedom
Reference
FM 3-04.203
Wings of Freedom
Contents
IV. Night Vision Sensors
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IV.Night Vision Sensors
A. Purpose
•
Enable friendly forces to sustain around-the-clock
operations
•
Allow the command to conduct offensive and
defensive operations against an enemy force with the
element of surprise
B. Types
•
Described as NVS or NVD and can either be thermal
imaging/FLIR or image intensifier (I2) systems
•
NVS’s are large and mounted to vehicles or aircraft
•
NVD’s are small, hand held or helmet mounted
devices
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IV.Night Vision Sensors
C. Electromagnetic Spectrum
•
Includes following range of wavelengths

Gamma Rays

X-Rays

Ultraviolet

Visible Light

Infrared

Microwaves

Radio waves
•
NVDs make use of visible light energy bands and IR
energy bands.
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Night Vision Systems
Electromagnetic Spectrum
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IV.Night Vision Sensors
C. Electromagnetic Spectrum
1. Visible Light
•
Amount of light reflected determines what human eye sees
•
Eyes see color due to the reflective and non-reflective
properties of the object being viewed
•
Sun is greatest source of visible light during daylight
•
After sunset, most naturally occurring light is reduced
creating a shift to scotopic vision
•
I2 systems amplify natural and artificial visible and near IR
energy
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IV.Night Vision Sensors
C. Electromagnetic Spectrum
2. Infrared Radiation
•
Sun emits energy across entire spectrum, not just
visible light.
•
IR energy that enters atmosphere is reflected or
absorbed to produce stimuli for NVDs.
•
I2 devices amplify this energy
•
Amount of IR energy radiated by object depends
on the exposure amount and how much thermal
energy is absorbed, reflected, or transmitted
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IV.Night Vision Sensors
C. Electromagnetic Spectrum
3. Infrared Energy- Reflectance, transmittance,
absorptance, and emissivity determine the amount of
IR energy an object will radiate when exposed to “x”
level of thermal energy for “x” amount of time.
•
Reflectance- The ratio of radiant energy reflected
by a body to the radiant energy incident upon it
•
Transmittance- The ratio of radiant energy that,
having entered a body, reaches its farther
boundary
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IV.Night Vision Sensors
C. Electromagnetic Spectrum
3. Infrared Energy (cont)
•
Absorptance The ratio of radiant energy absorbed by a
body to the radiant energy incident upon it
•
Emissivity- The relative power of a surface to emit heat
by radiation. The ratio of radiant energy emitted by a
body (temperature only) to that emitted by a reference
body (blackbody) at same temperature.
•
Significant regarding IR energy. A blackbody
completely absorbs 100% of the IR energy acting
upon it and emits 100% of its IR energy
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Night Vision Systems
Infrared Energy
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IV.Night Vision Sensors
D. Night Vision Devices
1. Operation
•
I2 device amplifies light energy
•
Light (photons) enters objective lens, is inverted
and focused onto photocathode
•
Photocathode converts photons to electrons
•
Electrons are accelerated away from
photocathode to the micro-channel plate (MCP)
via electrical field supplied by power source.
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IV.Night Vision Sensors
D. Night Vision Devices
1. Operation (cont)
•
MCP is a thin wafer of tiny glass tubes that are
tilted about 8 degrees.
•
Electrons enter these tubes and strike the walls,
creating an exponential increase in amount of
reaction
•
Electrons are then accelerated to the phosphor
screen
•
Phosphor screen emits an amount of photos
proportional to the number of electrons striking it
creating a lighted image.
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IV.Night Vision Sensors
D. Night Vision Devices
1. Operation (cont)
•
Image is then passed through fiber-optic inverter
which rotates the image 180 degrees
•
Image is then focused onto viewer’s eye through
an eyepiece lens
•
Power supply provides automatic brightness
control (ABC) that automatically adjusts MCP to
maintain image brightness
•
Bright Source Protection (BSP) reduces voltage
to photocathode when exposed to bright light
sources
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Night Vision Systems
Image Intensifier
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IV.Night Vision Sensors
D. Night Vision Devices
2. AN/AVS 6
•
Helmet mounted I2 Device
•
40 Degree FOV with 20/25 visual acuity under ideal
conditions
•
Amplifies light 2-3 thousand times
•
Powered by batteries or aircraft interface
•
Dual battery pack with a low voltage warning when
battery is at 2.4 volts or less
•
10-15G breakaway feature allowing goggles to
separate from attachment in crash sequence
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Night Vision Systems
AN/AVS 6 in Operational Position
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IV.Night Vision Sensors
D. Night Vision Devices
2. AN/AVS 6-Cont
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System Counterweights
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System consists of weight bag and counterweights
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Attachment of bag should be low on back of helmet
with battery pack mounted above it
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Recommended initial weight is 12 oz.
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Maximum weight is 22 oz.
•
Use caution as contents could become missile hazard
in crash sequence
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IV.Night Vision Sensors
D. Night Vision Devices
3.
Heads-Up Display
•
Displays flight, navigation, aircraft and weapons
system information onto NVG display
•
Enables aircrew member to concentrate vision
outside while maintaining ability to view critical
information
•
Aircrew member has ability to determine and
display different pages of critical information
within his FOV
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IV.Night Vision Sensors
D. Night Vision Devices
4. Operational Considerations
a)
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Magnification Versus Enhancement
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NVG Systems do not magnify an image; they
enhance the illumination of an object.
•
Objects viewed through the NVG system is
the same size as if seen with the naked eye
IV.Night Vision Sensors
D. Night Vision Devices
4. Operational Considerations
b)
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Lights and Lighting
•
Use of NVGs allows detection of light sources not
visible to unaided viewer
•
Performance of NVGs directly related to ambient
light.
•
As light levels increase, objects can be viewed
from greater distance, but too much light can
adversely affect NVGs.
IV.Night Vision Sensors
D. Night Vision Devices
4. Operational Considerations
b)
Lights and Lighting (Cont)
•
Fixed pattern noise (honeycomb) is usually evident at high
light levels. Internal circuitry automatically adjusts output
brightness to a preset level restricting peak display
luminance.
•
The ability to see objects within a lighted area depends on
the intensity of the light and distance of the object from the
viewer
•
To prevent degrading NVG performance, the crewmember
should minimize time spent looking at bright light sources
within the 40 degree FOV
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IV.Night Vision Sensors
D. Night Vision Devices
4. Operational Considerations
b)
Lights and Lighting (Cont)
•
When flying with the landing light, searchlight, or IR bandpass filter installed aircrew members should avoid
concentrating on the area illuminated by the light
•
The sky above the horizon tends to activate the ANVIS ABC
level to dim objects below the horizon when flying in the
direction of the setting sun before EENT or in direction of
rising sun BMNT.
•
Training flights during these periods are not recommended.
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IV.Night Vision Sensors
D. Night Vision Devices
4. Operational Considerations
c)
Depth Perception and Distance Estimation
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NVG’s distort depth perception and distance estimation
•
Quality of depth perception in given situation depends on
factors including ambient light, type and quality of NVGs,
degree of contrast, and experience
•
Aircrew must rely on monocular cues to accurately estimate
distance
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IV.Night Vision Sensors
D. Night Vision Devices
4. Operational Considerations
d.
Color Discrimination
•
NVGs are monochromatic, producing a green image
•
Green hue may cause crewmembers to experience a
pink, brown, or purple afterimage when the NVGs are
removed
•
This is called monochromatic adaptation and is a normal
physiological phenomenon
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IV.Night Vision Sensors
D. Night Vision Devices
4. Operational Considerations
e.
Aided Flight Scanning Techniques
•
Basic principles of scanning are same for aided and
unaided flight.
•
NVG’s improve ground reference but significantly reduce
FOV
•
Reduction of FOV requires crewmembers to use continual
scanning to compensate for loss of peripheral vision
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IV.Night Vision Sensors
D. Night Vision Devices
4. Operational Considerations
e.
Aided Flight Scanning Techniques (Cont)
•
Rapid head movement can induce spatial disorientation
•
Crewmembers should move eyes while turning their head
which will result in a 70-80 degree FOV with only 30-40
degree head turn.
•
NVGs are primary source for detailed visual information
•
Inside the cockpit, crewmembers can look under or around
the NVGs for information
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IV.Night Vision Sensors
D. Night Vision Devices
4. Operational Considerations
f.
g.
Obstruction Detection
•
Obstructions have poor reflective surfaces and are difficult to
detect
•
Best way to locate wires is by looking for support structures
Spatial Disorientation
•
Maneuvers requiring large bank angles or rapid attitude
changes tend to induce spatial disorientation
•
Aviators should avoid rapid attitude changes and use proper
scanning techniques
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IV.Night Vision Sensors
D. Night Vision Devices
4. Operational Considerations
h.
Airspeed and Ground Limitations
•
Aviators using NVGs tend to over fly their capability to see
•
Different light levels affect the distance at which objects are
identified and limit the ground speed flown at terrain flight
altitudes
•
Aviators should reduce ground speed to allow enough
reaction for detection and avoidance
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IV.Night Vision Sensors
D. Night Vision Devices
4. Operational Considerations
h.
Airspeed and Ground Limitations (Cont)
•
Object acquisition and identification are related to ambient
light levels, visibility, and contrast between the object and
its background
•
Variables affecting the ability to see through the NVGs
1. Type, age, condition of NVG
2. Cleanliness of windscreen
3. Moisture content in the air (humidity)
4. Individual/collective proficiency and capability
5. Weather conditions
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IV.Night Vision Sensors
D. Night Vision Devices
4. Operational Considerations
i.
Aircraft Lighting
•
Exposure to various sources of lighting not compatible with
NVGs may degrade an aircrew members ability to see
•
AN/AVS 6 is designed to be operated with blue-green cockpit
lighting. Red cockpit lighting is not authorized for use with
NVGs.
•
Blue-green cockpit lighting will not degrade performance, but
lights should be dimmed to a low readable level
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IV.Night Vision Sensors
D. Night Vision Devices
4. Operational Considerations
i.
Aircraft Lighting (Cont)
•
Aircraft external lights such as position lights, formation
lights, anti-collision lights, or electroluminescent light panels
should be turned off or subdued as appropriate
•
NVG operations are degraded by external lights unless
properly modified.
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IV.Night Vision Sensors
D. Night Vision Devices
4. Operational Considerations
j.
Weather
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When using NVGs, aircrew members may fail to detect
entry into or prescience of IMC.
•
NVGs enable crewmembers to see through obscurations
such as fog, rain, haze, dust, and smoke.
•
Loss of celestial lights, light intensity, or fading of moon
and stars should alert crewmembers of deteriorating
weather
•
Rain will not be detected on windscreen due to NVGs
depth of focus making the windscreen out of focus
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IV.Night Vision Sensors
D. Night Vision Devices
4. Operational Considerations
k.
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Weapons
•
During weapons fire, aircrew members may
briefly lose sight of the target due to the NVGs
momentarily shutting down
•
Recovery from bright flash illumination is more
rapid with NVGs than unaided.
QUESTIONS?
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