NVD Manual Questions Flashcards
What is the primary purpose of the I2 tube and what are the components?
Used to detect and intensify energy in the visible and near infrared region of the electro-magnetic spectrum.
- Photocathode
- MCP
- Phosphor screen
GEN-1 NVDs, date, gain, susceptibility
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.
GEN-2 date, description
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.
GEN-3, Description of two I2 advancements and what they do
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.
How long can GEN-3 tubes last consistently
reliability greater than 10,000 hours
What is the consequence of the Aluminum oxide coating on the MCP
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.
Generation vs Omnibus?
Generation describes the technology and components. Omnibus is the procurement lot contract under which the NVG or component was purchased.
Omnibus 5 Contact
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
Omnibus 6 Contract, Halo Size, Spectral Sensitivity, Hours
Used a thinner film and was required to have smaller halo. Resulted in 0.7mm halo size, 425-900nm, 10,000 hours.
FLIR description
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.
What is high light level and 20/30 rule?
.0022 Lux or above = 20% of the moon disk at least 30% above the horizon.
What is sensor fusion? What is it used for?
It is the melding of data from different sensors to form a complete view of the scene.
What does ANVIS stand for
Aviator Night Vision Imaging System
Human eye sensitivity
.4-.7 microns
Near, Mid and Far IR region
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
Illumination or illuminance definition and units.
Amount of light generated from a source. (P)1lumen/m^2 = 1lux = 1 meter candle = .0929 ft-candle
Luminance definition and unit
reflected light (L) 1 lu/steradian/m^2=1c/m^2=.2919ft-lambert(ft-L)
Units for the EM spectrum
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.
Thermal Theory
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.
Four principle sources of thermal energy
- Solar energy
- Fuel Combustion
- Friction heat
- Thermal reflection
Define emissivity
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.
Define a black body
It is a perfect absorber and emitter of radiant energy used a theoretical tool for comparison and has E = 1.00
Two types of thermal radiation
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.
Thermal Mass
The ability of an object to store thermal energy. It is determined by an objects temperature, mass and composition.
Thermal Inertia
The rate at which an object will change temperature. It is a combination of thermal mass and thermal resistivity.
Three main factors that affect NVD performance
- Illumination and thermal scene factors
- Terrain Contrast
- Atmospheric Conditions
Four factors affecting lunar illumination
- Lunar Cycle
- Moon angle
- Lunar Albedo
- Variation in Earth to Moon distance
Full Moon, Quarter Moon, Star light
Star light over cast Illumination
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
What is Airglow and how much illumination does it provide on a clear sky night
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.
What are the three different twilights
Civil: 0-6 degrees
Nautical: 6-12 degrees
Astronomical: 12-18 degrees
Define Albedo
Illumination reflected of terrain. The varying degrees of albedo gives us contrast allowing us to break out the different objects.
What does texture provide
Provides recognition and depth perception cues and improves the comfort level of aircraft
What is MRTD
Mean resolvable temperature difference is the smallest temperature difference a thermal sensor can differentiate between.
What is the diurnal cycle
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.
Atmospheric Attenuation Factors
Absorption, scattering and refraction. Refraction is negligible.
Three atmospheric molecules that most affect FLIR performance
Water(absolute humidity), carbon dioxide(relatively constant except higher in urban areas, ozone (generally not a factor and is 25-35km above earth surface)
Two types of Scattering
Generally less significant than absorption.
- 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
- 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.
Objective lens type used by H-1 pilots and focus range
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
What does LASER stand for? What are the two types? Which is more powerful?
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.
What does Nd: YAG stand for?
Neodymium: Yttrium Aluminum Garnet
What is LIF and LEP
Light Interference Filter and Laser Eye Protection
What is the purpose of the Photocathode? What chemical do we use on it? What is it sensitive to? Why?
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.
Describe MCP
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.
What is the ion barrier film
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.
Phosphor Screen
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.
Define Luminous Gain
The gain of the output to the input. For the AN/AVS-9 it can range from 50,000 - 80,000.
Define NVG system gain
The amount the total amount of change the NVG can create. NVG system gain can range from 6k-8k for the AN/AVS-9.
ABC circuit
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.
BSP circuit.
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.
What is the proper eye relief and FOV
Designed for 25mm eye relief and still have 40 degree FOV.
Three ways to make aircraft lighting NVG compatible
- Spectral Separation (filters)
- Geometry (baffles, light location)
- Absorption (flat black instrument panel, anti-reflective console)
FLIR: Types of Scanners
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.
FLIR: Level
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)
FLIR: Gain
Determines the size of the temperature window. Ranges from high gain (one degree) to low gain (100 degrees).
White hot vs Black hot
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.
Shades of Gray
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.
