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Huey > NVD Manual Questions > Flashcards

NVD Manual Questions Flashcards

1
Q

What is the primary purpose of the I2 tube and what are the components?

A

Used to detect and intensify energy in the visible and near infrared region of the electro-magnetic spectrum.

  1. Photocathode
  2. MCP
  3. Phosphor screen
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2
Q

GEN-1 NVDs, date, gain, susceptibility

A

Introduced in 1950s, 3 stage night vision scope used by snipers in Vietnam, 40,000 times the gain of single stage tube, very susceptible to single light source blooming and almost a foot long requiring high voltage made it not very mobile.

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3
Q

GEN-2 date, description

A

1960s, could be head mounted, used the MCP, Use of MCP reduced blooming but did result in the halo effect around point light sources. No large advance in resolution or gain over GEN-1, just more mobile.

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4
Q

GEN-3, Description of two I2 advancements and what they do

A

Introduced Gallium Arsenide photocathode, which shifted the sensitivity to 400-950nm with peak sensitivity from 600 to 900nm, which more closely matches energy available in the night sky and improving LLL performance. Also introduced Aluminum oxide film on the MCP, which traps the IONs and prevents them from contaminating the photocathode.

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5
Q

How long can GEN-3 tubes last consistently

A

reliability greater than 10,000 hours

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6
Q

What is the consequence of the Aluminum oxide coating on the MCP

A

They had to increase the voltage between the PC and MCP. In order to prevent arching between the two, distance had to be increased, which resulted in increased halo size when viewing point light sources.

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7
Q

Generation vs Omnibus?

A

Generation describes the technology and components. Omnibus is the procurement lot contract under which the NVG or component was purchased.

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8
Q

Omnibus 5 Contact

A

Purchased by the army. Did not have the aluminum oxide film and used a power cycling to protect the photocathode from IONs. Required less voltage and therefore reduced halo size because the two could be closer together. Omnibus 5 have 0.8 mm Halo while 4 have 1.25mm

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9
Q

Omnibus 6 Contract, Halo Size, Spectral Sensitivity, Hours

A

Used a thinner film and was required to have smaller halo. Resulted in 0.7mm halo size, 425-900nm, 10,000 hours.

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10
Q

FLIR description

A

Forward looking Infrared: Allow aircrew to see farther into the infrared region by collecting and amplifying the energy emitted by objects that radiate heat energy.

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11
Q

What is high light level and 20/30 rule?

A

.0022 Lux or above = 20% of the moon disk at least 30% above the horizon.

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12
Q

What is sensor fusion? What is it used for?

A

It is the melding of data from different sensors to form a complete view of the scene.

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13
Q

What does ANVIS stand for

A

Aviator Night Vision Imaging System

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14
Q

Human eye sensitivity

A

.4-.7 microns

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15
Q

Near, Mid and Far IR region

A

0.7-3 microns: primarily reflected and scattered solar and lunar radiation.
3-5 microns: Combines the properties of reflection and radiation but past 4 microns mostly radiated sources of energy.
8-14 microns: Is where GEN-1 FLIR operates

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16
Q

Illumination or illuminance definition and units.

A

Amount of light generated from a source. (P)1lumen/m^2 = 1lux = 1 meter candle = .0929 ft-candle

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17
Q

Luminance definition and unit

A

reflected light (L) 1 lu/steradian/m^2=1c/m^2=.2919ft-lambert(ft-L)

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18
Q

Units for the EM spectrum

A

1nanmeter (nm) is one billionth of a meter and is commonly used to express wavelengths less than a micrometer.
1 micrometer or micron (mum) is one millionth of meter.

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19
Q

Thermal Theory

A

All objects above absolute 0 of (273 degrees C) emit energy and mostly in the mid or far IR regions in the form of radiation. Natural and fabricated thermal sources produce the thermal scene. FLIR’s use a thermally variable environment to create an image for the aircrew. Objects either radiate energy as a result of their own molecular vibration or reflect energy from another source.

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20
Q

Four principle sources of thermal energy

A
  1. Solar energy
  2. Fuel Combustion
  3. Friction heat
  4. Thermal reflection
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21
Q

Define emissivity

A 
The ability of any object to emit thermal energy compared to a black body at the same temperature.
Highly reflective (polished silver 0.02) objects will have low emissivity while objects with high absorption ability will have high (water 0.96) emissivity.  Radiated energy/reflected energy.
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22
Q

Define a black body

A

It is a perfect absorber and emitter of radiant energy used a theoretical tool for comparison and has E = 1.00

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23
Q

Two types of thermal radiation

A

Thermal source: like the sun with a large spectrum of emitted energy that has a maximum occurring at a particular wave-length
Selective source: have an output concentrated in a narrow wavelength intervals called line spectra.

24
Q

Thermal Mass

A

The ability of an object to store thermal energy. It is determined by an objects temperature, mass and composition.

25
Q

Thermal Inertia

A

The rate at which an object will change temperature. It is a combination of thermal mass and thermal resistivity.

26
Q

Three main factors that affect NVD performance

A
  1. Illumination and thermal scene factors
  2. Terrain Contrast
  3. Atmospheric Conditions
27
Q

Four factors affecting lunar illumination

A
  1. Lunar Cycle
  2. Moon angle
  3. Lunar Albedo
  4. Variation in Earth to Moon distance
28
Q

Full Moon, Quarter Moon, Star light

Star light over cast Illumination

A

Full Moon = 0.1 Lux
1/4 Moon = 0.01Lux
Clear sky Star light (airglow + star light)= .001 Lux
Moonless Overcast Star light = .0001 Lux

29
Q

What is Airglow and how much illumination does it provide on a clear sky night

A

It is emissions from atoms and molecules in the upper atmosphere that produces energy in the near IR region providing 40% of a moonless night’s illumination or .00178 Lux. Star light provides the significant source providing .00022 Lux.

30
Q

What are the three different twilights

A

Civil: 0-6 degrees
Nautical: 6-12 degrees
Astronomical: 12-18 degrees

31
Q

Define Albedo

A

Illumination reflected of terrain. The varying degrees of albedo gives us contrast allowing us to break out the different objects.

32
Q

What does texture provide

A

Provides recognition and depth perception cues and improves the comfort level of aircraft

33
Q

What is MRTD

A

Mean resolvable temperature difference is the smallest temperature difference a thermal sensor can differentiate between.

34
Q

What is the diurnal cycle

A

The rate at which individual targets heat and cool. Usually targets are warmer than their surrounding at night and colder than their surrounding during the daytime. Diurnal crossover happens twice a day. Once in the morning and once in the evening.

35
Q

Atmospheric Attenuation Factors

A

Absorption, scattering and refraction. Refraction is negligible.

36
Q

Three atmospheric molecules that most affect FLIR performance

A

Water(absolute humidity), carbon dioxide(relatively constant except higher in urban areas, ozone (generally not a factor and is 25-35km above earth surface)

37
Q

Two types of Scattering

A

Generally less significant than absorption.

  1. Molecular scattering occurs when energy is scattered by particles that are much smaller than the wavelength of the incident radiation. Generally is negligible for wavelengths one micron and bigger so not a huge factor for FLIR performance
  2. Aerosol Scattering involves large particles such as dust or smog. It scatters energy by reflection when the wavelength is less than or equal to the size of the diameter of the particle.
38
Q

Objective lens type used by H-1 pilots and focus range

A

Class B lens rejects wavelengths below 665nm. Class B identified by R stamped on the lens housing and the lens appears to have a blue green hue. 41cm to optical infinity

39
Q

What does LASER stand for? What are the two types? Which is more powerful?

A

Light Amplification by the Stimulated Emission of Radiation. There are continuous wave and pulsed. Pulsed is typically more powerful and damaging because the energy is condensed into small bullet like pulses.

40
Q

What does Nd: YAG stand for?

A

Neodymium: Yttrium Aluminum Garnet

41
Q

What is LIF and LEP

A

Light Interference Filter and Laser Eye Protection

42
Q

What is the purpose of the Photocathode? What chemical do we use on it? What is it sensitive to? Why?

A

Converts incoming visible and near-IR energy into electrical energy in the form of electrons. PC are grown by vaporizing several elements in a vacuum and depositing them on a transparent window. Gallium Arsenide PC is sensitive from 400-950nm with a peak between 600-900nm, which is significant because the night sky is 5-7 times more iridescent in the 800-900nm than it is in the visible region.

43
Q

Describe MCP

A

Micro Channel Plate us 1mm thin wafer of more than 6 million glass tubes at a 5 degree bias. For every electron that enters, more than a thousand will exit.

44
Q

What is the ion barrier film

A

On the MCP and traps positive ions that are created by the electrons impacting the MCP. The ion barrier film lengths the life of the I2 tube by 2,5 to 3 times.

45
Q

Phosphor Screen

A

Turns electrons into light. Is positively charged to pull the electrons to it. Uses P43 phosphor that exhibits primary output of 545nm, which closely matches the peak sensitivity of the eye.

46
Q

Define Luminous Gain

A

The gain of the output to the input. For the AN/AVS-9 it can range from 50,000 - 80,000.

47
Q

Define NVG system gain

A

The amount the total amount of change the NVG can create. NVG system gain can range from 6k-8k for the AN/AVS-9.

48
Q

ABC circuit

A

Automatic brightness control adjusts the voltage of the MCP to maintain the NVG image brightness at a preset output for a wide range of illumination down to .0022 lux. Bellow .0022 (starlight) the NVG can not increase the gain and the image will degrade brightness and contrast and scintillation will become visible. This circuit is for the user comfort. Also protects from sudden bright flashes like forward firing munitions.

49
Q

BSP circuit.

A

Bright Source Protection limits the number of electrons leaving the photocathode by reducing the voltage between the photocathode and the MCP. It is extremely important in conserving the length of life for the PC.

50
Q

What is the proper eye relief and FOV

A

Designed for 25mm eye relief and still have 40 degree FOV.

51
Q

Three ways to make aircraft lighting NVG compatible

A
  1. Spectral Separation (filters)
  2. Geometry (baffles, light location)
  3. Absorption (flat black instrument panel, anti-reflective console)
52
Q

FLIR: Types of Scanners

A

Serial Scanning: Scan horizontally
Parallel Scanning: Scan Vertically (AH-1W NTS uses this)
Focal Plane (Staring) Array: Checkerboard array that is stationary with respect to the visual field. Each detector has it’s own pixel thus allowing for continuous updates. Most popular being developed today. 640X480 image or better.

53
Q

FLIR: Level

A

Level control is used to position a selected span of temperatures relative to all temperatures within the scene. Any temps bellow are suppressed as black and any above are displayed as white (in white hot)

54
Q

FLIR: Gain

A

Determines the size of the temperature window. Ranges from high gain (one degree) to low gain (100 degrees).

55
Q

White hot vs Black hot

A

White hot used when searching for targets because targets are generally hotter than the background and you’ll be able to pick it out easier.
Black hot tends to produce a more natural image or scene for the pilot.

56
Q

Shades of Gray

A

Each darker shade of gray is determined by dividing the brightness by the square root of 2 until the background brightness becomes the limiting factor.

Huey (15 decks)

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