[MP-3] Night Operations and NVG Considerations
Night Operations. Survivability and success in combat operations are a function of minimizing threat capabilities while maximizing one's own. One way to maximize our capabilities is through the use of night low-level operations which reduce the probability of detection by visual, electro-optic, or electronic means. Night operations increase the chance of surprise and decrease the chance of detection and weapons engagement by enemy forces. Night operations place increased emphasis on night imaging devices, which operate in the optical radiation portion of the electromagnetic spectrum. The use of these devices requires a thorough understanding of the night environment. This understanding includes the relationship between ambient illumination, the terrain, the night imaging device, and the human eye. Each of these are critical links in the night vision chain. This section presents techniques and considerations specifically for night operations. Special emphasis is placed on NVG operations since the use of NVGs is the safest means of conducting low-level night operations in the H-60. Detailed mission planning/preparation, alternate contingency planning in the event of mission changes, effective crew resource management, and situational awareness are all crucial elements to successful night operations.
Dark Adaptation. For the average human, it takes approximately 30 minutes for the retina to be fully dark adapted. Use of NVGs will lessen dark adaptation. Crews should remember this after removing their goggles as they will most likely be taxiing unaided and moving around a dark aircraft after shutdown.
Controlling exposure to bright sunlight is important. It may take your eyes up to five hours to recover from intense sunlight. If you are out on a bright, sunny day prior to a night flight, sunglasses are recommended. Additionally, your eyes need oxygen to maintain good night vision and smoking reduces oxygen intake and decreases night vision.
The most critical hours for night flying are morning and evening twilight. This is because some sunlight is visible during twilight, and the rods and cones in your retina haven't fully adapted. You're not getting full night vision or full day (color) vision. Consequently, objects on the ground and in the air won't be easy to see. Also, be aware that when you have full night vision, your best visual acuity is 20/200 (unaided), and you will have a blind spot in the center field of vision that you will have to "look-around" to see objects clearly. This blind spot will be reduced with a high moon illumination.
Dim cockpit lights to the lowest practical level. As the mission continues and your dark adaptation increases, dim the lights further. Use no more light in the cockpit than is necessary. H-60 cockpit instruments have back lighting, but the lower console radios are not lit. Keep all lights dim as possible to minimize reflections on the cockpit windows. Minimize use of lip/finger lights in threat areas. Dim other interior lights as much as possible to avoid detection.
NVG Planning Considerations.
Mission Planning. Thorough and detailed mission planning is absolutely critical to successful NVG operations. As a minimum, aircrews must consider the tactical environment, terrain, illumination, weather, crew capability and length of mission. Aircrews need to ensure they use the scale map(s) providing as much detail as necessary for mission accomplishment, and that all maps used are updated with the latest CHUM, with emphasis on any obstructions to their planned route of flight. Additionally, a thorough knowledge and understanding of some very specific terms is necessary to fully appreciate the NVG operations environment.
Illuminance vs. Luminance. The most common photometric terms used are illuminance (expressed as either lumens, lux, or foot-candles) and luminance (usually expressed as foot-lamberts).
Illuminance. Illuminance refers to the amount of light which strikes an object or surface. An example of illuminance is the amount of ambient light which strikes the ground from the moon.
Luminance. Luminance refers to the amount of light reflected from a surface. An example of luminance is moonlight which is reflected from certain aspects of the terrain which enables us to see those features. The moonlight striking the ground is illumination while the light reflected off the terrain which enables us to see the terrain is luminance. The relationship between illumination and luminance yields a ratio (incident light to reflected light) which is called albedo. While illumination from the moon may remain constant, luminance from different terrain varies. This is why the features of a blacktop road are more difficult to see than the features of a light colored concrete road. In summary, ambient light sources provide illumination or illuminance. However, what our eyes "see" and night imaging devices detect is the light reflected from objects and terrain or luminance. A high illuminance or lux means a large amount of light is striking an object or surface. Whereas a high luminance means a lot of light is being reflected by an object or surface.
Night Sky Illumination. There are many sources of ambient illumination which combine to light the night sky. Natural sources include the moon, stars, solar light, and other background illumination. There are also artificial sources, which are sometimes referred to as "cultural lighting". Some examples of artificial sources include lights from urban areas, automobiles, fires, weapons, searchlights and flares. Remember, illumination includes only light which strikes the object or terrain to be observed. It does not include the light reflected off the object or terrain; this is luminance.
Environmental Effects. The environment can have a major impact on the success or failure of NVG missions. Aircrews must consider available illumination, visual illusions, and weather conditions to be encountered during the planning and execution of any NVG mission. Any condition of the atmosphere which absorbs, scatters, or refracts the illumination, either before or after it strikes the terrain, will effectively reduce the usable light available. The exact amount of reduction is difficult to predict because a common factor cannot be applied to each condition of cloud or fog coverage. Make an estimation of light reduction by considering the basic illumination as a starting point and then knowing the particle size of the atmospheric condition (i.e., clouds or fog) and its density (lack of space between particles). Table 1 provides factors which affect luminance used by night vision goggles.
Table 1. Factors Affecting Luminance.
Atmospheric TransmissionWeather: clouds Fog, Rain, SnowObscurants: Dust (Brownout), Snow (Whiteout), Chemicals, Smoke |
TerrainContrast: Albedo, TextureShadows: Moon Angle |
AircraftHeading, Altitude, AttitudeCockpit LightingCockpit Structures |
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