NVG Manual Read Flashcards
NVD provide the aircrew with what capabilities:
- Increased situational awareness.
- Enhanced navigational capabilities
- Enhanced Threat avoidance
- Enhanced threat detection
- Enhanced target acquisition
- Multi/mixed aircraft tactics
- Application of daytime air to GND tactics
- Expanded night air to air tactics
What are some of NVDs primary limitations:
- NVDs are NOT all weather systems
- Absolute humidity and illumination levels define the NVD operating envelopment
- NVDs possess a limitied target acquisition capability when used alone.
- NVDs possess a limited FOV
- NVDs possess limited system resolution and electromagnetic spectral response
Explain Gen 0 NVGs?
- Developed 1930s
- An Active sensor that required an accompanying infrared searchlight to illum the area of interest.
Explain Gen 1 NVGs?
- Introduced in the late 1950s with develop of Starlight Scope.
- Attained HLL gains by 3 stage configuration of solely a photocathode/phosphor screen stack.
- Provided gains in the range of 40,000x
- Downfalls
A. Extremely susceptible to bloomingB. Still extremely large.
What is blooming?
tendency for the tube to degain and shut down if a bright light enters the FOV
Explain Gen 2 NVGs?
- Developed late 1960s
- The first small enough to be placed into systems that could be head mounted.
- The introduction of MCP created mor eelectrons meaning less velocity needed.
- Still susceptible to blooming but more localized due to MCP
- Gain was only 10,000x vice 40,000x for Gen I
Explain Gen 3 NVGs?
Changes that defined Gen III were
Introduction of Gallium arsenide photocathode and the use of an aluminum oxide protective coating on the input side of the MCP
What did Gallium Arsenide provide in Gen 3 NVGs?
- Gallium Arsenide changed the spectral sensitivity of the NVG. Made it more sensitive in the near IR
A. Shift to the near IR better matches the energy in the night sky.
What is the spectral sensitivity of the NVGs?
Peak sensitivity?
400 to 950 nm (.4-.9 microns)
peak sensitivity being 600-900nm (.6-.9micron)
What does Aluminum Oxide in the MCP provide the GEN III NVG?
Negatives?
- Protects the photocathode from Ion bombardment created by MCP
- Consequence of the introduction is increase in voltage between MCP and photocathode. Therefore had to increase distance to prevent sparking.
A. Which in turn increases halo size
FLIR stands for?
Forward Looking Infrared
What are key features of a targeting FLIR?
The ability to slew and magnify.
What was the Go/No-Go for the AN/PVS -5? And why does it matter?
The Go/No-Go was at least 20% of the moon disc illumination at least 30 degrees in the sky. (I.e the 20/30 rule)
This rule is roughly equivalent to 0.0022 lux, which is the threshold for HLL.
What is sensor fusion?
The melding of data from different sensors to form a complete view of the scene.
3 noticeable improvements with the WP I2 tubes?
1.Reduction in Halo size
- Increased obstacle detection distances
- Reduced time for target correlation during ordnance employment
What is Illuminance? What is it expressed in?
The amount of light generated from a source. Expressed in Lux
The amount of light generated by a source is called what?
Illuminance
The amount an object reflects is called what? How is it expressed?
Luminance; (ft-L) foot lamberts
Define luminance?
The amount of light an object reflects
What is albedo?
The relationship/ratio between Illuminance(generated light) and luminance (or reflected light).
What are the factors that will determine how an object appears on the FLIR?
- Temperature
- Thermal history
- Emissivity
- Thermal mass
- Thermal inertia
What determines thermal energy?
An objects exposure to 1 of 3 principle sources of thermal energy:
a. Solar
b. Man Made
c. Thermal reflection
What is Emissivity? And Why does it matter?
The ability of an object to emit energy compared to a blackbody at the same temperature
Emissivity determines how much of the energy detected by a FLIR. Is from self emission and how much is reflected radiant energy
What is Thermal mass?
- The ability of an object to store heat
- Thermal mass is determined by temperature, mass, and type of material.
- Is reflected in a measurement called specific heat
What is Thermal Inertia?
- Is the rate at which objects change temperature and dependent upon combination of thermal mass and thermal resistance.
- Ultimately the thermal inertia that varies the heating and cooling cycle for different objects in the natural scene that allows for good contrast
What are the 3 major factors that influence NVD performance?
- Illumination/thermal scene
- Terrain contrast
- Atmospheric conditions
What factors affect the amount of Lunar Illumination?
- Lunar cycle
- Moon angle
- Lunar albedo
- Variation in earth to moon distance.
How long is a lunar month?
29.5 days
Which phase of the moon is brighter the waxing or waning moon?
The waxing portion
What is airglow?
- energy provided by emissions from atoms and molecules in the upper atmosphere
A. Approx 40% of energy provided on a moonless night.
How much light does starlight provide?
0.00022 lux
What are the three categories of twilight and how are they classified?
- Civil: 0 to -6 degrees below the horizon
- Nautical: -6 to -12 degrees below the horizon
- Astronomical: -12 to -18 degrees below the horizon
What is sky glow? When is it a factor.
The sun bouncing energy off the particles in the upper atmosphere. Is still a factor until after EENT.
What are the key factors to terrain contrast?
- Albedos
- Contrast
- Shadowing
Why is shadowing a greater factor at night then it is during the daytime?
At night, since the NVG require a source of illumination to function they will not be as much energy or any IOT see into the shadow
What are the 3 principle sources of thermal energy?
- Solar radiation
- Man made
- Thermal reflection
At what humidity does it become and effective wall for the FLIR?
Absolute humidity of 20 g/m3
What is relative humidity?
A ratio that expresses the amount of moisture in the air compared to the maximum amount at the same temperature.
What is absolute humidity?
Total amount of water vapor present in a given volume of air and is expressed in g/m3
What effects does humidity have on the NVGs?
Effects vary with particle size that plays more of a factor.
What are the two types of scattering?
Molecular and aerosol
What is molecular scattering?
When energy is scattered by particles that are much smaller than the wavelength of the incident radiation.
Not considered a major factor for predictions FLIR system performance.
What is aerosol scattering?
Involves large particles such as dust or smog and scatters energy by reflection when the wavelength is less than or equal to the diameter of the particle.
Causes a change in direction in all directions and it is equal to the diameter of the particle.
Little effect on the FLIR but significant effect on NVG.
Why can see through some some and haze.
How do NVGs differ from the human eye?
- NVGs are exponentially more sensitive to energy available in the night sky.
- NVGs respond to a different portion of the EM spectrum.
What is the range of adjustment on the vertical knob?
25 mm
What is the range for the tilt lever?
+- 5 degrees
What is the range of the fore and aft relief?
26mm
What is the designed eye relief for the AN/AVS-9?
25 mm
What are the 2 type of objective lens filtering?
Class B (minus blue) and Class C (leaky green)
What range does Class B objective lens filter out?
< 665 nm
Lens filtering that “rejects” energy below a specified wavelength of 665 nm.
Describe Class C Filtering objective Lens
“Leaky Green”
- Has a notch incorporated into the Class C filter to allow approx 1% transmission of a narrow band of energy (540 to 550 nm) to reach the I2 tube.
- The notch allows aircrew the ability to view the HUD symbology and raster FLIR image through the NVG
What are the three primary components of the GEN III I2 tube?
- Photocathode
- Microchannel Plate [MCP]
- Phosphor Screen
Describe the role Photocathode in the I2 tube.
- The responsibility if for converting the incoming visible and near-IR energy int electrical energy in the form of electrons.
What did the gallium arsenide photocathode provide?
The gallium arsenide photocathode was introduced with the GENIII I2 tube. Provided the following:
- More than 3 fold increase in sensitivity over GEN-I and GEN-II.
- Shifts the spectral response range toward the near infared spectrum
a. Response range: .4 -.9 microns (peak sensitivity between .6-.9 microns.)
b. This is significant because the night sky spectral irradiance is 5-7x greater in between .8-.9 micron range.
Describe the MicroChannel Plate [MCP]
- The MCP is a very thin (1mm) wafer comprised of more than 6 million tiny glass tubes or channels.
- Each tube is coated with a material that causes secondary electron emissions.
a. To ensure this happens ant the entrance of the tube the are canted that 5 degrees. - Because of this process for each electron that enters the MCP, 1,000 or more will exit.
- Increased electrons = increased gain
What did adding for tubes to the MCP do?
- Increased resolution
- Decreases distortion as they are closer together
- Increased gain.
What is the phosphor screen and what is its purpose?
- Comprised of a very thin layer of phosphor deposited on the inside of the rear window of a fiber optic bundle.
- The basic function of the phosphor screen is to convert the electrons into photons so the user can view the image.
What type of phosphor is used in the green and white NVGs?
Green= P43 @ wavelength of .545 microns
White = P45
What does the fiber optic converter do?
- Provides Image inversion, through the use of millions of microscopic light transmitting fibers that are heated and twisted 180 degrees.
What is collimigation? Where does it occur? Why is it important?
- Makes the image in the eye piece lens appear to be at the appropriate distance.
- Occurs because of the fiber optic inverter.
- Without it the eye’s focus would be set fro the distance to the eyepiece. =no depth perception.
Define Gain:
Gain is the comparison of the the system’s input with its output.
What are the two types of gain and define them?
- Luminous gain: is defined as the ratio of the NVGs output brightness to the input illumination.
- System gain: the brightness of the output image as compared with the input.
What is the difference???????
What is ABC?
Automatic Brightness Control:
- Is a circuit that automatically adjusts MCP voltage to maintain NVG image brightness at a preset output for a wide range of illumination levels by controlling the number of electrons that exit the MCP.
“THE DJ!!!!!!!”
At what light level is unable to keep the NVG brightness the same?
Tube gain increases from full moon to starlight illumination. As light levels pass below starlight, each subsequent drop in illumination does not result in an increase in I2 tube gain
What is BSP? How is it noticed?
- Circuit that limits the number of electrons leaving the photocathode by reducing the voltage between the photocathode and the input side of the MCP. If it didn’t could cause serve damage to photocathode.
- Aircrew will notice activation of BSP when an incompatible light source enters the NVG FOV and the I2 tube “shutdown” or “degain”
What is the function of the eyepiece?
To focus the light from the fiber optic inverter onto the eye.
