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The advantages of NVGs in the military environment are:?
- a) Enhanced situational awareness at night;
- b) Enhanced manoeuvrability;
- c) Threat avoidance;
- d) Aggressive terrain masking;
- e) Use of unconventional night tactics;
- f) Enhanced safety in night multi?ship operations;
- g) Conduct of covert operations to maintain the tactical advantage; and
- h) Increased mission effectiveness in air to ground operations.
NVG related mishaps?
- -lack of appreciation of the limitations of NVGs,
- -failure to accommodate the known limitations
- -no device which will turn night into day
- -enhance an aviator's ability to operate visually during reduced illumination,
- -do not remove their susceptibility to visual illusions and spatial disorientation
Importance of Applied knowledge of the limitations of NVG?
- -enable adequate flight and mission planning
- -maximise the night vision operational capability without sacrificing flight safety.
The EMR Spectrum?
- Xrays 10-1 to 10-5
- Ultraviolet light
- Visible light 1-10-1microns
- Infrared light 1-103 microns
- microwaves 103-106
- - light, heat and radio waves are present in everyday life.
- -radio -receive specific frequencies
- -NVGs and the human eye are sensitive todifferent wavelength ranges of the EM spectrum
- -visible light is a relatively small portion of the entire EMR spectrum.
- -All EMR obeys the same laws of reflection, refraction, and diffraction; they differ from one another only in their
- frequency and wavelength.
- -Visible and near IR light are considered to be reflected energy
- -thermal bands in the mid and far-infrared are primarily radiated energy.
WHat is a Night Vision Device (NVD)?
- -Night Vision Goggles (NVGs)-operate in the visible and near IR spectrum, and depend mainly on reflected energy
- -Forward Looking InfraRed (FLIR) systems- operate below 3 microns
- -depend reflected and scattered solar radiation-sun/stars/moon/
NVG SCENE VARIABLES factors which will influence NVG performance?
- a) illumination,
- b) terrain considerations, and
- c) atmospheric conditions.
- - critical factor for NVG operations
- a) Natural Illumination:
- ? Lunar,
- ? (Moonless) Night Sky,
- ? Starlight, and
- ? Sky-glow.
- b) Artificial or "cultural lighting".
LUNAR ILLUMI NATION
- -primary source of natural illumination for NVG operations.
- -reflects about 7% of the sunlight which strikes it.
- a) Lunar Cycle-new, full, quarter, etc
- b) Moon Angle-brightest-overhead-less it rises or sets -quarter-moon overhead may provide more illumination than a low-angle full-moon.
- c) Lunar Albedo. Differences in the albedo (reflectance) of the illuminated portions of the moon's surface during the lunar cycle is the third factor.
- For example, the moon is about 20% brighter during the first quarter (waxing) than it is during the third quarter (waning) due to differences in the lunar surface.
- d) Earth-Moon Distance. The final and least significant factor is the variation in the earth?moon distance due to the elliptical nature of the lunar orbit around the earth.
- The changes in illumination resulting from this 26% change in distance are deemed insignificant for NVG purposes.
- Light Level Planning Programmes. Because of the cyclic trends in lunar illumination, computer programs have been developed to help NVG aircrew anticipate illumination conditions for their flight planning. However, the predictive reliability of the programmes has prevented their widespread adoption in the Australian Army Aviation.
NIGHT SKY ILLUMINATION?
- Moonless nights also have a significant amount of useable light for NVG operations.
- The EMR spectrum of the night sky has a large near
- -IR component, which matches the peak sensitivity of the NVGs
- It is possible to fly effectively with NVGs under these conditions with a good training program and proper flight planning.
- -Solar Influence.
- -Sky-glow. O
NVG TERRAIN CONSIDERATIONS?
- a) terrain reflectivity (albedo),
- b) terrain contrast, and
- c) terrain shadowing.
- -snow will reflect more light than surfaces like asphalt or dark rock.
- Terrain Contrast-reflectivity of two or more surfaces, contrast improves with illuminance up to about full moon
- and degrades as light levels decrease below quarter moon.
- water and desert-little contrast, can be troublesome to fly over in low light conditions.
- This problem is further compounded by a lack of terrain features or texture.
A shadow is cast whenever a light source (including moonlight) is obscured by an object or terrain feature.
EFFECT OF ATMOSPHERIC CONDITIONS ON NVG?
- The atmosphere is an important environmental factor determining NVG performance.
- It can attenuate light energy, reducing the level of energy reaching the NVGs, degrading the enhanced visual image.
- Atmospheric attenuation can occur by absorption or scattering.
VISUAL PERFORMANCE-NVG visual limitations include?
- a) Reduced field of view;
- b) Reduced visual acuity and resolution;
- c) Reduced contrast;
- d) Degraded depth perception;
- e) Impaired distance estimation; and f) Degraded static and dynamic cues.
- These visual parameters are usually subconsciously processed by the visual perception system. Subtle restrictions in
- visual performance or a degradation in the quality of visual cues may not be recognised until gross reduction in performance exists unless a conscious effort is made to remain aware of these limitations. Aircrew using NVGs must operate in an environment where normal day visual cues may be unavailable or easily misinterpreted.
FIELD OF VIEW (FOV)?
- One of the most obvious limitations of all NVDs is the reduced FOV.
- The FOV reduction with NVGs is dramatic and requires active compensation by the aircrew.