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149 Cards in this Set
- Front
- Back
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Describe the general effects of drugs on the crewmember
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Some over-the-counter drugs can have unpredictable or idiosyncratic effects in some individuals. The unpredictable effects could be very dangerous in flight. Many over-the-counter drugs have side effects like drowsiness, dizziness, visual impairments and some are diuretics and can cause dehydration. Some examples are:
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Describe the possible effects of antihistimines on aircrew
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Side effects include drowsiness, reduced coordination, reduced visual accommodation, dizziness and a rapid heart rate.
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Describe the possible effects of Decongestants on aircrew
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Can have a very strong stimulant effect that is magnified with caffeine use. The stimulant effect can interfere with sleep.
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Describe the possible effects of Phenylpropanolamine on aircrew
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Main ingredient in appetite suppressants. Can cause headaches, loss of appetite, interferes with sleep, nausea, rapid heart rate and dizziness
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Describe the possible effects of Cough Suppressants on aircrew
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Can cause drowsiness, blurred vision, difficulty with urination, and upset stomach. May also increase the sedative effects of other drugs.
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Describe the possible effects of Laxitives on aircrew
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Can cause stomach cramping, watery stool, unexpected bowel movement in flight!
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What is the issue between over-the-counter drugs and nutritional supplements?
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Some over-the-counter drugs can act synergistically with nutritional supplements, caffeine or certain foods to greatly increase their potency. This can also be dangerous.
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Describe the residual effects of alcohol on a crewmember in flight
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Alcohol can negatively affect the vestibular system for up to 48 hours after drinking. Alcohol increases the sensitivity of the semicircular canals causing exaggerated sensations. This leads to an increased incidence of vertigo in flight. NATOPS cautions that flight over water, at night and IMC conditions could be dangerous under these conditions. This effect might not be noticeable on the ground where your brain naturally suppresses inputs from the vestibular system (visual dominance). In a degraded visual environment, when you body relies on vestibular system input, severe vertigo can result. Alcohol also disrupts sleep quality by suppressing rapid eye movement (REM) sleep. REM sleep is absolutely necessary and even 8-10 hours of sleep after drinking might not be adequate. Trying to fly while hung over, dehydrated, fatigued due to a lack of REM sleep and with a compromised vestibular system certainly constitutes a notable “precondition for unsafe operations” according to the Human Factors Analysis and Classification System.
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Describe the hazards associated with smoking and chewing tobacco products
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Everyone knows that smoking is bad for your health. In addition to an increased risk of cancer, smokers are at a greater risk for strokes and heart attacks. Although physical fitness can help to mitigate this risk, smokers will always have an increased risk. In fact, according to the American College of Sports Medicine, a person would have to be more than 100 pounds overweight to have the same risk of heart disease as someone who smokes. As discussed in the Aviation Physiology brief, smokers can have a physiological altitude of 3-5K feet before leaving the ground. This makes them more susceptible to hypoxia. This also reduces the effectiveness of their night vision as the eyes are very sensitive to hypoxia. Smokers often begin to experience nicotine withdrawal symptoms as soon as 3-4 hours after their last cigarette. In a recent study on nicotine withdrawal in pilots the most frequent symptoms reported during nicotine deprivation were nervousness, craving for tobacco, tension-anxiety, fatigue, difficulty in concentration, decrease in alertness, disorders of fine adjustments, prolonged reaction times, anger-irritability, drowsiness, increase in appetite, and impairment of judgments. These nicotine withdrawals can impact performance and can be a serious distracter.
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Describe the physiological need for proper diet and nutrition
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Perhaps the greatest nutritional threat to aircrew is not eating for long periods of time before flight. NATOPS states that, “Failure to eat within 12 hours preceding the end of flight may impair performance and the ability to adequately control the aircraft.” Your brain relies exclusively on carbohydrates for energy. When blood sugar drops, information processing is compromised. At the very least, hunger can be a distracter. When was the last time you ate? Can you imagine a scenario in which you do not eat for 12 hours prior to flight? Do you always eat breakfast prior to a morning flight? If so, what do you eat? Do you carry snacks with you in flight? What are some good options? It is difficult to pack some types of foods in your flight suit pocket but you can carry items like power bars or even a candy bar if that is all you have. It is better to eat a candy bar than not eat for long periods of time and have your performance compromised by hypoglycemia and hunger. Low carbohydrate diets will adversely affect your athletic performance and they will slow physiological adaptations to exercise.
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Describe the adverse impact of dehydration on crewmember performance.
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Dehydration definitely affects physical performance. A 3% body weight loss due to dehydration can cause a reduction in cardiovascular endurance, a reduction in muscular endurance, reductions in muscular strength and a reduction in muscular power. The impact is greater with increased levels of dehydration. Dehydration can also cause a 30% reduction in Gz tolerance. Even small amounts of dehydration put you at a greater risk of a heat injury. A good rule of thumb for hydration prior to physical activity is to drink until you urinate clear before starting. This is especially true prior to exercise in the heat.
Thirst is generally a good indicator of hydration status, unless you are exercising vigorously or are exposed to a challenging thermal environment. In a hot environment you must drink proactively because under these conditions thirst lags behind hydration status. Because dehydration can affect your Gz tolerance and performance, you should treat a flight like an exercise session and ensure that you are well hydrated prior to flight. You should also consider options for in flight hydration. After a particularly challenging flight, you should rehydrate quickly, just as you would after a hard workout. Sports drinks are a good choice. So is water. If all you have is Coke, it is better than nothing. It is not true that you lose more water than you gain when you drink soft drinks. You can hydrate effectively with most water based beverages. Those with high sugar content will take longer to process and caffeinated beverages will result in a small amount of water. Neither issue is particularly significant and shouldn’t prevent you from drinking these beverages to rehydrate if they are all you have access to. |
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Describe the effects of caffeine on crewmember’s performance
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Research has shown that caffeine can increase confidence, energy levels, alertness, decrease sleepiness and improve mood in sleep deprived individuals. This effect can last for up to 12 hours after an appropriate dose. You should not shy away from using caffeine to manage fatigue for fear of becoming dehydrated. The dehydrating effect of caffeine has been greatly exaggerated. Caffeine is a diuretic but the effect is small. Caffeine is well tolerated and does not appear to result in negative health consequences if daily intake is reasonable (< 450 mg per day). Individuals with high blood pressure should consult with a flight surgeon prior to using caffeine as an alertness management aid. Caffeine can elevate blood pressure in those with high blood pressure. Habituation occurs over time resulting in a need for higher doses for the same effect. The ergogenic effects of caffeine are much less pronounced in habitual coffee drinkers. An effective dose is 100-600 mg (more is required in coffee drinkers). Higher doses can cause jitters. It takes about 20 minutes for caffeine effects to reach their peak. The effect can last up to 12 hours in sensitive individuals. You should consider this when planning sleeping periods. Beyond 48 hours of wakefulness, caffeine will have little impact on alertness.
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List examples of physiological stressors.
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Alcohol, smoking/tobacco, medicating/supplements, improper nutrition, improper sleep
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List examples of mission related stressors.
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Environmental – temperature, noise
Operational - Deployment pumps, new or unfamiliar mission type, change in airframe or equipment, cockpit Ergonomics, night operations, circadian desynchronosis |
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List examples of psychological stressors.
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• Death of someone close
• Divorce • Legal concerns • Injury or illness • Marriage • Pregnancy • Change in financial status • Increased workload • Change in living conditions • Arguments • Lower grades than expected • Change in sleep habits • Change in social activities • Change in eating habits |
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State the effects of nutritional supplements on performance.
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In 1994 congress passed the Dietary Supplement Health and Education Act. The purpose of the law was to make a wider variety of products available to the consumer. However, the law had two very undesirable consequences. Supplements are no longer tested for safety prior to sale. The FDA has no clinical trials type of process for supplement approval prior to sale. Several legally marketed supplements have been pulled from the market for serious safety concerns, but only after several adverse events, including several deaths. You should be very wary of new or exotic supplements. The second serious consequence of the DSHEA is that supplements are not tested for purity prior to sale. A recent study tested the purity of a number of over the counter nutritional supplements and found that 75% did not contain what the label said. In some cases, they had no active ingredient at all. Even if you find a supplement that is safe and effective, you may have a hard time finding a good source. U.S. Pharmacopeia (USP) is beginning to certify nutritional supplements. USP is a non-profit group that certifies safe manufacturing processes and content to ensure that the product was manufactured safely and contains what is on the label. Unfortunately, few nutritional supplements have USP certification yet.
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On average, night shift workers get how many hours less sleep per day than those who work during the day.
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1.5 - 2 hours
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List methods of combating stress in the flying environment
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• Keep you body healthy through proper nutrition, hydration and exercise.
• Manage Environmental stressors. • Manage psychological stress • Sleep strategies • Manage operational stressors |
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List the symptoms of excess stress
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• Insomnia
• Irritability • Angry outbursts • Difficulties making decisions • Forgetfulness • Low energy level • Constant worrying • Propensity for mistakes • Sweating • Digestive Problems • Migraines • Neck/Back Pain • Accident Proneness • Change in Appetite • Increased Smoking • Alcohol/Drug Use |
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What is circadian desynchronosis?
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Circadian desynchronosis refers to a situation in which the body’s circadian rhythms do not match a person’s daily activities or time zone. Serious circadian desynchronosis can result from shift work. Initially, the body can be 12 hours off. This can result in a person being sleepy at inappropriate times and alert at inappropriate times. This can compromise performance and prevent you from sleeping when you have the opportunity. Recall that sunlight is the primary signal that sets circadian rhythms. A person who works at night and sleeps during the day is always getting sunlight at a time that conflicts with their daily activities.
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Describe situations of inappropriate use of medications and nutritional supplements.
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Use of creatine to bulk up
Drinking red bull or rock star for energy Taking Sudafed or TheraFlu for a cold Using Afrin prior to flight |
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Describe circadian rhythms and how they predict alertness.
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Circa = about, dian = day. A circadian rhythm is a physiological event that occurs on a 24 hour cycle. This is the circadian rhythm of alertness as determined by a Mean Sleep Latency Test (MSLT). MSLT involves simply measuring how long it takes someone to fall asleep in a dark, quiet room. Alertness drops between 3-6 AM and 3-6 PM. The dip that occurs between 3-6 AM is very large. It is very difficult to maintain alertness during this time period. The afternoon dip between 3-6 PM can be significant, especially if you are sleep deprived. These periods of decreased alertness are set by the light and dark cycle. We will always experience decreased alertness during these times as long as we are exposed to sunlight during the day. People who work at night and attempt to sleep during the day can successfully move the period of decreased alertness earlier or later by an hour or so, but it never goes away. Circadian rhythms can override the sleep battery and can cause spikes in alertness and drowsiness.
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What are some strategies for dealing with night shift work and circadian desynchronosis?
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Some strategies that can help are maintaining a night schedule when off-duty. This prevents an individual from having to re-adapt to a night shift every Monday. Educating personnel and families about the implications of night shift work and the importance of maintaining a quiet sleep environment can be helpful. Sunlight automatically triggers alertness and can make it difficult to fall asleep after working all night. If shift workers can get home and get in bed before the sun comes up, they will be more successful in getting to sleep. Finally, night shift workers should monitor their performance and health more proactively. It is easy to get caught in the vicious cycle of excessive caffeine consumption, poor sleep and fatigue.
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Define sleep
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Sleep is defined as unconsciousness from which the person can be aroused by sensory or other stimuli and it has many stages
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What are the two categories most researchers divide sleep into?
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(1) slow wave sleep which is the majority of a night's sleep, is deep, restful sleep, and is characterized by its slow brain waves, dreams that aren't recalled upon waking and decreases in vegetative functions such as BP, resp rate and BMR; and (2) REM sleep which usually occurs after 80-100 min of sleep and then every 90 min throughout the night in 5-30 min periods (the duration will decrease or even cease to exist w/increased fatigue), is active sleep, and is characterized by its REM, active dreaming, irregular HR and resp, decreased muscle tone, and high brain activity.
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A person is less likely to be awaken during what type of sleep?
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A person is less likely to be awakened during REM sleep than slow wave sleep, even though people normally awake in the morning during REM sleep.
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Most sleep during each night is of the what variety?
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Slow-wave
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Do you dream during slow wave sleep?
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Although slow-wave sleep is frequently called “dreamless sleep”, dreams and sometimes even nightmares do occur during slow-wave sleep. The difference between the dreams that occur in slow-wave sleep and those that occur in REM sleep is that those of REM sleep are associated with more bodily muscle activity, and the dreams of slow-wave sleep usually are not remembered. That is, during slow-wave sleep, consolidation of the dreams in memory does not occur.
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Slow wave sleep is associated with what?
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This sleep is exceedingly restful and is associated with decrease in both peripheral vascular tone and many other vegetative functions of the body. For instance, there are 10 to 30 percent decreases in blood pressure, respiratory rate, and basal metabolic rate.
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How long does REM sleep last?
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REM sleep: in a normal night of sleep, bouts of REM sleep lasting 5 to 30 minutes usually appear on the average every 90 minutes. When the person is extremely sleepy, each bout of REM sleep is short, and it may even be absent. Conversely, as the person becomes more rested through the night, the durations of the REM bouts increase.
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Name 6 important characteristics of REM sleep:
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1. It is usually associated with active dreaming and active bodily muscle movements.
2. The person is even more difficult to arouse by sensory stimuli than during deep slow-wave sleep, and yet people usually awaken spontaneously in the morning during an episode of REM sleep. 3. Muscle tone throughout the body is exceedingly depressed, indicating strong inhibition of the spinal muscle control areas 4. Heart rate and respiratory rate usually become irregular, which is characteristic of the dream state. 5. Despite the extreme inhibition of the peripheral muscles, irregular muscle movements do occur. There are in addition to the rapid movements of the eyes. 6. The brain is highly active in REM sleep, and overall brain metabolism may be increased as much as 20 percent. The electroencephalogram (EEG) shows a patter of brain waves similar to those that occur during wakefulness. This type of sleep is also called paradoxical sleep because it is a paradox that a person can still be asleep despite marked activity of the brain. |
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Summarize REM sleep
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REM sleep is a type of sleep in which the brain is quite active. However, the brain activity is not channeled in the proper direction for the person to be fully aware of his or her surroundings, and therefore the person is truly asleep.
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Describe a typical sleep cycle.
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When we sleep we go through a series of stages. Stage 1 sleep is very light sleep. Stage 4 is very deep sleep. It typically takes about an hour to get into deep stage 4 sleep. Another type of sleep is rapid eye movement sleep or REM sleep. It is during this type of sleep that we do most of our dreaming. The graph shows a typical 7 ½ hour sleep period. During this sleep period the person goes through several sleep cycles with increasing amounts of REM sleep near morning. This is optimal. Anything that interrupts this pattern can result in fatigue upon waking. Frequent wakings, even if brief, can completely disrupt this pattern and can result in considerable fatigue and sleep debt. Frequent wakings can prevent a person from getting enough deep stage 3 and 4 sleep.
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Discuss napping and sleep inertia
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If a person is sleep deprived, nothing can completely restore performance except for sleep. Napping is one of the most affective alertness management strategies that you can use. Have you ever woken up from a nap feeling tired and groggy and less alert than before the nap? It is likely that you were suffering from sleep inertia. Recall that it takes about an hour to get into deep stage 4 sleep. If you wake someone up during stage 4 sleep, their alertness and performance can be compromised for the first 15-20 minutes. After that, alertness is generally improved as a result of the nap. If performance immediately after the nap is an issue, a one hour nap might not be a good idea. In this type of situation, a 30-40 minute nap would be preferred. It is long enough to help to restore some alertness and performance but short enough to keep you from getting into deep stage 4 sleep. If performance immediately post nap is not an issue, you should sleep as long as you want as long as it does not interfere with your normal bed time. Napping will be easiest between 3-6 AM and 3-6 PM. These are times of the day that our circadian rhythm of alertness is low and falling asleep would be easier.
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Describe the causes of acute fatigue.
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Acute fatigue is intense tiredness or exhaustion felt as a result of the natural build-up of metabolic wastes. This can be the result of intense physical exertion, a demanding flight, or a long workday. Acute fatigue is short-term and is characterized by a feeling of being "worn out" and will usually be relieved by rest.
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Describe the causes of chronic fatigue.
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Chronic fatigue is less intense than acute fatigue and is characterized as an accumulation of fatigue over time, usually days or even weeks. This can be the result of extended workweeks with little time off or failing to obtain adequate sleep (short duration or poor quality). Chronic fatigue is associated with a feeling of being "burned out." It takes the body longer than one night’s rest to recover normal energy levels. Studies indicate that cumulative fatigue results in an exponential increase in performance errors. For the night systems player, cumulative fatigue means that the second night of a cycle can be more tiring than the first and by the end of the cycle can be very obvious.
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State the effects of circadian dysynchronosis (jet lag) on performance.
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Desynchronosis usually occurs as a result of the body's internal rhythm being out of synch with the normal routine when shifting to a new work schedule. This is a problem that is encountered in rapid transmeridian travel where it is referred to as “jet lag." This also shifts the time of day for the physiological nadir. The body can physically readjust to crossing time zones at the rate of about 1-1.5 hours per 24-hour period. Since the natural body cycle is set for a longer day, it is normally easier to adjust to a new time schedule when traveling from east to west than vice versa. Aircrew starting a night training period will experience similar problems.
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Why is readjustment to jet lag more difficult?
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However readjustment to this type of desynchronosis will be more difficult because the activity pattern is out-of-synch with both circadian rhythms and the daily zeitgebers that would reset these rhythms. Studies and experience have demonstrated that it can take many days or weeks to readjust to changes in sleep/work cycles. The degree of adjustment to desynchronosis varies greatly among individuals. Some people adjust readily while some never can fully adjust, but everybody is affected to some extent. Some of the factors that affect adjustment to desynchronosis are personality, age, motivation, sleep quantity and quality, amount of physical exertion, and the extent of the desynchronosis. It is possible that some aircrew may never fully adjust during a normal night training cycle.
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State the effects of fatigue on performance
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Fatigue, especially cumulative fatigue associated with circadian disruption and sleep deprivation, poses a serious threat to night systems mission accomplishment. Many experts believe that performance will degrade anytime the circadian rhythm is disrupted. Many manufacturers who slow the assembly line during the second half of the late shift to compensate for reduced performance recognize this. The accidents at Three Mile Island, Chernobyl, and Bopal all occurred during the "graveyard shift." In many ways fatigue is very similar to hypoxia; it subtly erodes performance, is difficult to recognize, and fosters an unwillingness to do anything about it.
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State the effects of complacency on perfromance
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Complacency allows for acceptance of situations that would normally not be permitted, especially in the context of a night systems mission. Attention span and vigilance are reduced, important elements in a task series are overlooked, and scanning patterns that are essential for situational awareness break down (usually due to fixation on a single instrument, object, or task). Critical but routine tasks are often skipped because fatigue reduces overall willingness to respond.
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How does fatigue affect computational skills?
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Computational skills become degraded. The most difficult tasks for a fatigued aviator are those that require complex, swift decisions or planning. Fatigue typically results in errors caused by omission of a task as opposed to performing a task incorrectly. Uninteresting or complex tasks are more seriously affected by fatigue than interesting or simple tasks.
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How are communications affected by fatigue?
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Either neglecting to make appropriate calls or not responding to calls affects communications. This is because short-term memory is seriously affected. Communications from a fatigued aviator often trail off and there are a lot of “uhs." There is a tendency to inaccurately restructure conversations and the individual tends to hear what he expects to hear as opposed to what is actually transmitted. The desire to initiate action decreases with fatigue, including interactions with other people.
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How does fatigue affect decision making?
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Irrational decisions. The ability to assimilate information and form a rational solution is significantly degraded when fatigued. The decisions made may be different than what a well rested aviator would make in the same situation.
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What is the correlation between fatigue and irritability?
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Irritability. Fatigue makes people more irritable and less tolerant of others. This can significantly degrade crew communication and coordination, both of which are critical for successful night systems mission accomplishment.
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Define “LASER” and state the characteristics of a LASER beam
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Light Amplification of Stimulated Emission of Radiation. The characteristics of a LASER beam include mono-chromatic (very narrow wavelength band, compared to white land), coherent (in phase, amplitude consistent), and collimated.
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Describe the differences between pulsed and continuous wave LASERs and the implications for LASER eye damage, hazard distances, and protective devices.
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Continuous wave (CW) LASERs – beam is continuous unless chopped (strobe like affect – power output remains constant); beam is greater than .25 sec in length (aversion response time); measured in Watts; takes longer for the output to be as hazardous as pulsed LASERs; a LASER that can be operated in either CW or pulsed modes, will have less output power in the CW mode because the total amount of energy is spread out over time. Pulsed LASERs – beam is less than .25 sec in duration; energy is measured in joules concentrated in shorter time interval; shorter pulses are more hazardous; nanosecond (10-9) pulses are common; pulse is defined by the pulse width (or emission duration) and the number of pulses per second known as pulse repetition frequency (PRF); peak energy output is very high; Femtosecond (10-15) are now readily available.
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Which has greater possibility for eye damage, coninuous wave LASER or pulsed LASER and why?
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Because the pulse LASER does not allow for aversion response the possibility of eye damage is greater with a pulsed LASER. This also increases the hazard distance and also will require protective devices where a continuous wave LASER may not. Shorter pulses are more dangerous to humans because all of the energy must be absorbed and dissipated in a shorter time interval. Pulsed LASERs cannot be classified as Class II LASERs.
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Which class LASERs are considered eye safe and why?
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Class 1 and 2 are considered “eye safe” because the physiological reflex known as the aversion response is usually adequate protection against such low power LASERs. There are no documented injuries attributed to class 1 or 2 LASERs.
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State what wavelengths
comprise the following bands of the electromagnetic spectrum: UV, visible, near and far IR and what portion comprises the most significant optical hazard. |
UV C 100-280 nm
UV B 280-320 nm UV A 320-400 nm Visible 400-700 nm Near IR (IR A) 700-1400 nm Middle IR (IR B) 1500-1800 nm Far IR (IR C) 3000-1,000,000nm |
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Describe the Class 1 LASER systems classification as it pertains to LASER safety.
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Class 1: low power LASERS
Probably an embedded LASER Pulsed or CW No known hazards associated with their use with up to 5 cm optical aids No safety requirements Least powerful of all LASER classes By inherent design cannot emit radiation in excess of the MPE Only certification label is required |
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Describe the Class 2 LASER systems classification as it pertains to LASER safety.
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Class 2: Examples are bar code scanners
“eye safe” up to 5 cm because of their low power output No pulsed LASERs Only CW visible LASERs. Must be within aversion response time Yellow caution labels are used on all class 2 LASERs Emits power in excess of Class 1 but not in excess of 1 milliwatt. |
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Describe the Class 3a LASER systems classification as it pertains to LASER safety.
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Class 3a: Caution label is “eye safe” unless viewed with magnifying optics
Safe for unaided viewing for up to 0.25 seconds but they are not safe for aided viewing or emission durations longer than 0.25 seconds. Danger level means it exceeds the MPE Many of the newer diode pointers are class 3a LASERS but have red and black danger labels because the output power is high enough to cause injury to the unaided eye. Medium power LASERs. Class 3a between 400 and 700 nm having an accessible output power between 1 and 5 milliwatts. Irradiance less than 2.5 mw/cm2 will have caution label Irradiance more than 2.5 mw/cm2 will have danger label |
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Describe the Class 3b LASER systems classification as it pertains to LASER safety.
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Class 3b: Hazardous viewing under most conditions, some have diffuse reflections
Definitely not eye safe Require some engineering controls and require a danger label/sign Require LEPs Ex. Is the Green Beam Dazzler |
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Describe the Class 4 LASER systems classification as it pertains to LASER safety.
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Class 4: Most hazardous class
Not eye safe under all viewing conditions Most have a diffuse reflection hazard Because the more powerful LASERs are in this class, an LSSO must also be concerned about determining if there are skin hazards with a LASER in this class. Require many more safety devices and engineering controls. Most military range finders and designating LASERs are class 4 LASERs. |
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List the LASER classes according to the new ANSI standards
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Class 1 – remains the same
Class 1M – class 1 LASER under magnification Class 2 – remains the same Class 2M – class 2 LASER under magnification Class 3R – was class 3a Class 3B – changed from 3b, definition remains the same Class 4 – remains the same |
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Describe LASER eye protection requirements for personnel who may be exposed to LASER energy during military operations.
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LASER eye requirements for personnel are based on LSRB requirements for the system which is based on wavelengths and and the OD to reduce hazardous radiation levels below the MPE.
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Describe the relationship between optical density, Maximum Permissible Exposure, and Nominal Ocular Hazard Distance as they pertain to LASER eye protection and LASER safety.
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As MPE decreases the NOHD requirement increases and thus the OD increases to decrease the transmission of hazardous radiation to reduce the levels of radiation below the MPE. Therefore as MPE decreases the OD required for LEPs increases. Low MPE = high NOHD and likely high OD requirement
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State what wavelengths are
absorbed by the cornea, lens and retina and which are considered to be the most dangerous to the eye. |
Cornea 100-280nm (UV C), 280-320nm (UV B), 320-400nm (UV A), 1500-1800nm (IR B), 3000-1000000nm (IR C)
Aqueous Humor 1500-1800 (IR B) Lens 320-400nm (UV A), 1500-1800nm (IR B) Vitreous Humor 1500-1800nm (IR B) Retina 400-700nm (Visible), 700-1400 (IR A) |
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Describe specular reflective hazards as they relate to LASER range safety.
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Specular reflective hazards: any smooth, polished surfaces
Not just mirrors Jewelry and standing water Some surfaces not normally speculative become so when coated with rain or water Changes direction of beam only does not change the intensity or divergence It’s just like looking directly into the beam The angle at which a LASER beam strikes a reflector is known as the angle of incidence. The angle at which the reflected beam leaves a reflecting surface is called the angle of reflection and is equal to the angle of incidence. Does not alter the NOHD. If the LASER hits the specular reflector at 30m and the NOHD is 50m then you can consider it hazardous for another 30m from the reflector |
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Describe diffuse reflective hazards as they relate to LASER range safety.
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Diffuse reflective hazards: Rocks, trees, concrete
Scatter the beam reflection Rough pitted surfaces When LASER light hits the light reflected will not stay intact as it was in original beam Tends to break-up and spread in random directions Results in lower energy densities in the reflected beam Although the light may be breaking up and scattering, some LASERs are powerful enough that even the diffuse reflection is hazardous Diffuse may become specular if wet |
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What is the most dangerous range of wavelengths for eye injury in regard to LASERs? Why?
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Most dangerous is 400-1400nm because the retina is affected and you may not perceive pain or that you have been hit. Permanent damage to retina is likely
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State the typical peak spectral response (wavelength) range of 3rd Generation aviation
Night Vision Goggles using gallium arsenide photocathodes (example: AN/AVS-9). |
The AN/AVS-9 uses P43 phosphor with a spectral output that exhibits a primary peak output in the green (= 550nm) which closely matches peak of sensitivity of the eye.
All GEN 3 NVG photocathodes are made of gallium arsenide that is very sensitive to the near infrared part of the electromagnetic spectrum and closely matches theavailable night sky radiation |
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State the difference between the electromagnetic energy sources for FLIR and NVG sensor imaging.
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The AN/AVS-9 NVGs operate in both the visible and near IR spectrum. In addition, the AN/AVS-9 NVGs are dependent entirely on reflected energy emanating from the terrain. This means that, as with the eye, external scene illumination will be required for visual observation. For example, when a scene is illuminated by an external source such as the moon, the scene is observed primarily by reflected energy. Reflected light (luminance) is normally expressed in terms of foot-lamberts (ft-L), while the amount of light generated from a source (illuminance) is expressed in terms of the unit Lux or lumens per square meter (lm/m2). Below three microns the background is dominated by reflected and scattered solar (lunar) radiation. However, as we proceed into the IR spectrum beyond approximately 4.5 microns, the background becomes dominated by terrain self-emission. Terrain thermal self-emission relies on the temperature of the terrain objects and on the objects associated emissivity. FLIR systems operate in this portion of the EM spectrum. Based on the selective sensitivity and the environmental presence of different
energy forms, the two sensors, AN/AVS-9 and FLIR, operate at different but complementary regions of the EM spectrum. NVGs deal with reflected energy and FLIRS deal with radiant energy. The FLIR operates by processing differences in thermal energy in the 3-5 or 8-12 micron band and anything that attenuates these wavelengths will affect FLIR system image quality. AN/AVS-9 NVGs, on the other hand, operate by intensifying reflected light energy between 625-960 nanometers. |
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State the three major environmental factors influencing NVD performance
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The three major factors that influence NVD performance include: (1) illumination / thermal scene, (2) terrain contrast and (3) atmospheric conditions.
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State the three primary terrain factors that need to be examined for proper NVG mission planning
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The three primary terrain factors that need to be examined for proper NVG mission planning include: (1) terrain reflectivity (albedo), (2) terrain contrast and (3) terrain shadowing.
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What is the most important environmental factor controlling the performance of the FLIR and NVGs and why?
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The atmosphere is the most important environmental factor controlling the performance of the FLIR and NVGs. The atmosphere can attenuate light and thermal energy through refraction, absorption or scattering, reducing the level of energy reaching the NVGs or FLIR.
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Describe the effects on NVD performance during inadvertent IMC.
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Atmospheric conditions will impact each NVD sensor based upon their spectral sensitivity. This atmospheric attenuation will negatively impact intensified image quality. There are a great variety of particle sizes within individual as well as multiple cloud formations. Therefore, it is difficult to predict how much they will attenuate NVG and FLIR performance. The problem is exacerbated by the fact that water in low level clouds is found in the gaseous, liquid, and sometimes even solid forms. This means a varied and unpredictable effect on NVDs, so one must be attuned to noting degradation in each.
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What are the effects of water vapor on NVD performance?
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Water vapor exists at all temperatures. Because the amount of water vapor a cloud formation can hold increases with temperature, summer clouds generally have higher liquid water content than winter clouds. These liquid water particles are normally between 0.5-80 microns in diameter and are generally opaque to visible and near IR energy. For this reason, thick, dense clouds can be easily seen with NVGs, especially when silhouetted against the night sky. This also means that thick clouds can reduce the amount of illumination that strikes the ground, thereby reducing the available luminance to the NVGs. Thin and wispy clouds have greater space between particles, therefore a greater amount of the near IR radiation will be passed without scattering. Near IR wavelengths have a greater chance of passing through these clouds without being scattered than do the shorter visible wavelengths. It is possible for thin, wispy clouds to be seen by the naked eye (visible light or shorter wavelengths) but remain invisible when viewed through NVGs.
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The potential “invisibility” of thin clouds, fog or marine layers is possible given what three conditions?
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The clouds are thin and wispy, at least on the edges.
The clouds are low level and set in against the terrain. The ambient illumination is either very high or very low, degrading NVG performance. |
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What is the threat from thin clouds that progress into thicker clouds when you are on NVDs?
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The presence of thin clouds that progress into thicker ones can hide terrain features and creates a severe hazard for NVG operations. Low clouds lying upon and between hills present a particularly dangerous situation due to the inability of the aircrew to distinguish between the clouds and the terrain. In that regard, a common question occurs; “If the cloud is invisible, why can't the aircrew see the terrain behind it?” The answer is predictably complex. First, the cloud reduces visual and near IR contrasts and detail. This produces a false perception of distance, resulting in aircrew either not seeing the terrain, or thinking it is much farther away than it actually is. Second, the cloud may get progressively thicker, allowing the pilot to progress through the cloud without initially perceiving a “cloud wall.” If a cloud is detected, the perception may be that it is off at a distance. Clouds reduce illumination to an extent dependent on the amount of cloud coverage and cloud density or thickness. For example, a thick, overcast layer of clouds will reduce the ambient light to a much greater degree than will a thin, broken layer of clouds. The aircrew must be alert for a gradual reduction in light level and notice the obstruction of the moon and the stars. The less visible the moon and stars, the heavier the cloud coverage. If the NVG image becomes grainy and begins to scintillate (sparkle), this is an indication that weather may be causing a low ambient light condition. Also, shadows caused by broken or scattered cloud layers blocking the moon’s illumination can be seen on the terrain. Although clouds can decrease illumination and resulting luminance from the moon and stars, they can reflect enough cultural lighting to help offset the loss of lunar illumination. This will only occur in areas with significant cultural lighting and is only helpful if it is clear beneath the overcast.
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What are the effects of fog on NVD performance?
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The effects of fog are similar to those of clouds. Generally, fog is distinguishable from clouds only in regard to distance from the ground. Particle size varies from 2 to 20 microns, which is very similar to a cloud. Typically, fog has fewer particles and a smaller range of particle sizes than clouds. Fall is the most likely season and early morning the most likely time to encounter fog. Urban areas tend to have less fog (probably due to urban heat islands) than rural and mountainous areas tend to have more fog than sites nearer sea level. Chances of fog increase as temperatures decrease and the dew point spread approaches zero. Since fog tends to stay close to the ground it is more a navigation hazard to rotary wing aircraft than to fixed wing aircraft. However, fog can mask or partially mask ridgelines and other navigational features making it more difficult to navigate or use funneling techniques in the target area. One way to note an increase in the moisture content of the air while utilizing NVGs is to observe a decrease in the intensity of ground lights. This is especially obvious if you are flying at an altitude high enough to use as a comparison ground lights that might be out of the area of increased moisture content. Also, the halo effect noted around lights when viewed directly with NVGs will tend to get larger and more diffuse in an area of increased moisture. The enhanced contrast in an area illuminated by ground lights will also be lessened or absent.
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What is the effect of rain on NVD performance?
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Like clouds, the performance of AN/AVS-9 and FLIR in rain is difficult to predict as droplet size and densities are variable. All previous discussions on water vapor, clouds, fog, absorption and scattering are applicable here. Due to small droplet size and low density, light rains or mists cannot be readily seen with NVGs.
However, contrast, distance estimation and depth perception will be effected due to light scattering and the resulting reduction in light level. Heavier rains will be more discernible due to luminance blocking and more obvious signs such as rain on the windscreen. |
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What is the effect of snow on NVD performance?
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Snow occurs in a wide range of particle sizes and geometric shape. Snow crystals, while small in size, are generally large in comparison to the wavelength of visible, near and far IR radiation and will easily block or scatter those wavelengths. However, snow will not normally degrade thermal signatures as much as fog and rain due to its lower particle density. The density of the snowflakes will determine how much illumination and luminance is blocked and how much degradation occurs to the NVG image. Snow can reflect available light and thus enhance luminance when on the ground. Also, snow can add a slightly different texture that may aid in contrast discrimination. Due to the excellent reflectivity of snow, less illumination is required to give the same luminance for the subject without snow. Thus the NVGs can see the terrain under lower light level conditions.
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Sand or dust __ __ and____ will determinethe overall affect on NVD performance.
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Particle size and density
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What are the effects of obscurantes on NVD performance? Can obscurants be intentional or unintentional?
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Obscurants can be intentional or unintentional. An unintentional example is factory smoke, whereas intentional examples include such things as battlefield smoke from oil fires or other chemical sources. The effect of blowing sand or dust is similar to that created by snow except that the particles are far less reflective and much larger. This condition is significant since dust / sand particles completely block the near infrared light from striking and reflecting from the terrain. Since there is less luminance, the scene is darker. As with snow, during vertical operations or with strong winds, there can be an almost total block of IR radiation resulting in a “brown out”. Artillery and/or bomb impacts in the sandy terrain would put large amounts of sand or dust into the air. The impact of battlefield obscurants on NVG performance is similar to those mentioned above and depends on particle size and density. NVG visibility “inside” or through these obscurants would be poor.
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Describe the techniques used to reduce the likelihood of spatial disorientation when using NVGs.
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Constant vigilance and a good scan pattern, both inside and outside the cockpit, must be maintained to help prevent spatial disorientation
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Are Night Vision Goggles (NVGs) active or passive sensors and what do they utilize?
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Passive. Image intensifier tube technology.
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Describe an image intensifier tube.
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An image intensifier tube is an electronic device that amplifies available atmospheric illumination or light (i.e., moon, stars, sun, cultural lighting, etc.). NVGs rely upon this illumination reflected off the terrain or a target to form an image that is presented to the aircrew as a green monochromatic representation of the world.
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What principles do NVGs work under?
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NVGs operate using the same principles as the human eye (reflected energy), with the following two exceptions: (1) NVGs are exponentially more sensitive to illumination than the human eye and (2) NVGs are sensitive to a different portion of the electromagnetic spectrum than the human eye.
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What is the first optical component of the NVG?
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The first optical component of the NVG is the objective lens. The lens is actually a combination of optical elements that function to focus the incoming photons of light onto the I2 tube.
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What is the focal range of the objective lens on NVGs?
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The AN/AVS-9 objective lens possesses variable focus with a focal range spanning from 25 mm to beyond optical infinity. These shorter focal distances allow for NVG use in weapons systems trainers or simulators.
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Describe the objective lens filte on the AN/AVS-9 and discuss veiling glare.
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The AN/AVS-9 objective lens possesses a 665nm Class B "minus blue" objective lens filter, but also adds a "leaky green" notch filter. This "leaky green" notch filtering allows approximately 1% transmission of = 545 to 550nm) produced by an aircraft's HUD to a narrow band of energy ( reach the image intensifier (I2) tube's photocathode thereby entering the intensification process. This allows aircrew the ability to view HUD stroke symbology and raster FLIR imagery directly through the I2 tubes. Unfortunately, NVG compatible cockpit lighting also partially emanates in the 545-550nm range. When this enters the objective lens of the NVG, a low level “noise” is manifested as a haze that is called “veiling glare”. This haze does not generally impact NVG performance, but Veiling Glare can decrease visual acuity under low light conditions.
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What are the three primary internal components essential for creating an intensified image that GEN 3 I2 tubes possess?
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(1) Photocathode, (2) Microchannel Plate (MCP) and (3) Phosphor Screen. The photocathode is responsible for converting the incoming light energy into electrical energy in the form of electrons.
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Ultimately NVG image brightness is determined by what?
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Ultimately, NVG image brightness is determined by both the velocity and number of electrons striking the phosphor screen, all GEN 3 NVGs use a device known as a microchannel plate (MCP).
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Describe the micro channel plate.
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The MCP is a very thin (1-mm) wafer that consists of 1.5 million tiny glass tubes. The MCP is located next to the photocathode; therefore, electrons accelerating from the photocathode are channeled first through the MCP. The inside passages of these tubes are coated with a material that causes secondary electron emissions.
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The tiny glass tubes in the micro channel plate are tilted approximately ___ degrees. Why?
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8 degrees. so that the electrons passing through are sure to strike the tubes walls. As they do, more electrons are emitted from the wall, each of which will in turn strike the opposing wall, emitting more electrons, etc. As a result of this process, for each electron that enters the intensification process, 1,000 or more will exit. These electrons are in turn accelerated forward, maintaining their relative spatial position, until they strike and excite the phosphor screen.
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Describe the phosphor screen in the AN/AVS-9
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The phosphor screen is comprised of a very thin layer of phosphor deposited on the inside of the rear window (fiber optic). The basic function of the phosphor screen is to convert the electron beam energy to light. The screen is charged with a positive potential of several thousand volts with respect to the MCP to accelerate and attract the negatively charged electrons exiting the MCP. Phosphors emit light when electrons strike them and the output light wavelength is a function of the type of phosphor used.
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What phosphor does the AN/AVS-9 use and what is the primary peak output?
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P43 phosphor with a spectral output that exhibits a primary peak output in the green (wavelength= 550nm) which closely matches peak of sensitivity of the eye.
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Describe the fiber optic inverter in NVGs and why is it important.
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As the image is processed through the image intensifier tube (Photocathode, MCP and phosphor screen) of the AN/AVS-9, the resultant image is inverted as it emerges from the phosphor screen due to the inherent proximity focus system design. Ultimately, image inversion to proper orientation is accomplished by attaching the phosphor screen to a fiber optic inverter. This inverter is actually a bundle of millions of microscopic light transmitting fibers. During manufacturing, this fiber optic bundle is heated and given a 1800 twist providing the needed inversion to produce an upright image without requiring a second eyepiece lens The fiber optic inverter also collimates the image, making the image at the eyepiece lens appear to be at the appropriate distance from the viewer.
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Why is collimation in NVGs important?
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Without collimation, the eye's focus would be set for the distance to the eyepiece lens; a distance which would place severe strain on the eye and lead to significant human factor problems.
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What is the final optical component of the image intensifier tube? What is it's function?
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The eyepiece lens is the final optical component of the image intensifier tube. As with the objective lens, the eyepiece lens is a series of optical components. The function of the eyepiece lens is to focus the light from the phosphor screen via the fiber optic inverter onto the eye. The adjustment for this lens allows for some corrective lens wearers to use the NVGs without the aid of their spectacles However, the majority of personnel who use corrective lenses, such as for astigmatisms, will still need to use either their spectacles or contact lenses when operating with NVGs.
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What is the diopter adjustment range of the eyepiece in the NVG?
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Diopter adjustment range: +2 to -6.
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An image intensifier (I2) tube can perform its function satisfactorily only if it has a sufficient what?
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Gain
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Define luminous gain.
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The luminous gain is defined as the ratio of the NVG's output brightness to the input illumination.
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The image intensifier tube gain is set by who and why?
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I2 tube gain is set by the tube manufacturer based on the specifications delineated in the NVG procurement contract.
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Gain (in regard to NVGs) can also be described as what?
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Gain can be described as either I2 tube gain or NVG system gain.
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I2 gain is measured solely through what and that is the typical range?
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I2 tube gain is measured solely through the I2 tube and typically ranges from 45,000 - 65,000 for the AN/AVS-9. NVG system gain is measured with the I2 tube placed in the NVG (objective lens and eyepiece lens optics).
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What is NVG system gain?
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NVG system gain can range from 6,000 - 8,000 for the AN/AVS-9.
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What factors affect NVG tube gain?
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Several factors affect the tube gain and are important in the design process; including photocathode current, electron beam voltage, luminous efficiency of the phosphor screen and luminous sensitivity of the photocathode.
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Higher intensifier gain is obtained through what in NVGs?
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High intensifier gain is obtained through photoelectron multiplication within the MCP and acceleration of the output electrons. The kinetic energy of the accelerated electrons is converted to light at the phosphor screen.
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NVG system and I2 minimum gain was specified at what for the AN/AVS-9?
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5,500 (system) / 45,000 (I2 tube) for the AN/AVS-9.
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Essentially, gain will govern the NVG image brightness for what?
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Low light level inputs.
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NVG gain ____ as light levels approach approximately quarter moon illumination levels
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Increases.
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Does gain increase, decrease or remain the same below quarter moon illumination?
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Below approximately quarter moon, subsequent drops in illumination will not result in substantial increases in gain. This results in degradation of NVG system resolution, image contrast and image brightness.
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Does gain increase, decrease or remain the sameunder high light level conditions?
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Under high light level conditions, the NVGs become less sensitive (degain or shutdown) due to bright source protection (BSP) activation thereby degrading system resolution and image contrast as well
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The power supply of Generation lll tubes is designed with ___ gain control circuits. Name them.
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The power supply of Generation lll tubes is designed with two gain control circuits. These circuits provide protection to the user, extend NVG service life, and have a direct effect on the performance and resolution of the NVGs. Automatic Brightness Control and Bright Source Protection.
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What is Automatic Brightness Control (ABC)?
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The first circuit, the automatic brightness control (ABC), automatically adjusts MCP voltage to hold image brightness to a preset level for a full range of ambient illumination levels by controlling the number of electrons which exit the MCP. This protects the viewer from bright flashes and provides sufficient image quality to the viewer over a wide range of ambient light conditions. Since the output brightness is held within the preset range, as ambient illumination increases, it follows that the gain of the tube is actually decreasing. Therefore, the benefit derived from high gain intensifier tubes is realized only at low illumination levels since above a certain illumination level, the ABC holds image brightness constant. If the manufacturer does not set the gain and ABC correctly, the image the pilot views on the lens will overpower anything being viewed through the lens such as HUD symbology. Therefore, ABC is set to optimize viewing of the intensified image while allowing transmission of the HUD image at an acceptable HUD intensity level.
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Whis is Bright Source Protection?
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Image intensifier tube exposure to bright light sources, left unchecked, could result in damage to the photocathode, the MCP, and the eye. The second gain control circuit is the bright source protection (BSP) circuit, which limits the number of electrons leaving the Photocathode by reducing the cathode voltage at very high Photocathode illumination levels. This feature automatically activates when high input light levels cause excessive photocathode current to flow. The BSP circuit actually starts to take effect at fairly low light levels and has an increasing effect until the voltage drops to the point needed to ensure that electrons can penetrate the MCP ion barrier film. The intensifier tube would shut down completely if the voltage dropped lower. BSP is extremely important as the lifetime of a GEN 3 NVG is largely a function of the life span of the photocathode.
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Describe the impact NVDs have on visual performance and perception compared to normal daytime vision.
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NVDs DO NOT turn night into day.
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List some of the primary limitations of NVDs:
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Not an all weather system.
Absolute humidity and luminance levels define operating envelope. Limited target acquisition capability using system alone. Limited field-of-view (FOV). Limited system resolution and electromagnetic spectral response. |
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What is the greatest aeromedical concern of NVD operations?
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The greatest Aeromedical concern of NVD operations is the impact NVDs have on the visual system.
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One of the obvious limitations of NVDs is what?
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The reduced field of view (FOV).
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What is the field of view for the AN/AVS-9
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AN/AVS-9 FOV is 40 degrees.
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What is the field of view for the AV-8B NAVFLIR
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AV-8B NAVFLIR FOV is 20 degrees horizontal by 13.4 degrees vertical
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What is the field of view for the F/A-18C/D NAVFLIR
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F/A-18C/D NAVFLIR FOV is 20 degrees horizontal by 17.5 degrees vertical.
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Field of view is decreased by what percentage using NVGs?
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80%
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Which has a better field of regard, NVG or NAVFLIRs? Why?
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The ability to scan gives the AN/AVS-9 a significant advantage in field of regard over the NAVFLIR. The FOR for AN/AVS-9 is basically along the aircraft's wing but for the fixed forward NAVFLIR, the FOR is equal to the FOV. Exclusive fixed forward viewing will increase the potential for loss of situational awareness and reduces the aircrew’s ability to judge height and distance.
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The increased scan with NVGs must be balanced against what?
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Excessive head movement as the potential for disorientation and fatigue increases with increased head movement. Limitations on excessive flight maneuvering should also be considered during night systems missions.
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NVD field of view can be increased at the expense of what?
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Expense of resolution, weight/size, and cost. This monochromatic green, electro-optical image has visual limitations.
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Does NVDs provide direct viewing?
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Unlike binocular viewing, NVDs do not provide direct viewing of the scene. Instead, the electro-optical process within the system provides what amounts to a TV image.
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As with the eye, NVDs are impacted by what factors?
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Angular size, illumination, contrast, retinal adaptation, atmospheric conditions, relative motion, search patter and time. In flight, the physical limitations of the NVD and the reduction in ability to recognize and detect objects, terrain, and targets must always be considered. Although not as noticeable as FOV loss upon initial viewing, a reduction in visual acuity (resolution) and contrast also occurs with NVDs. This loss of resolution and contrast is usually very insidious, but is nonetheless very important to consider in night systems mission planning because it impacts almost all visual cues that are used for orientation and target/hazard detection.
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MIL-SPEC resolution for AN/AVS-9 visual acuity is what? Why is this okay?
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MIL-SPEC resolution for AN/AVS-9 is 20/40 in the central FOV and is allowed to drop off to 20/70 around the edges. NAVFLIR MIL-SPEC resolution is 20/70. These values would appear to make NVDs unacceptable for flight since 20/20 vision is prerequisite for flight status. However, the dark adapted, unaided eye provides 20/200 to 20/400 visual acuity. Therefore, while not meeting photopic eye capability, NVDs far exceed the eyes performance at night. NVD resolution is determined in a laboratory under ideal conditions and this level of resolution cannot always be expected when flying due to variables such as cockpit lighting, transparency properties and environmental conditions.
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What are some of the factors that determine whether an object is visible of not?
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The angular size of an object is the relative size of an object on the retina. A person who is 20/20 can distinguish an object that subtends 1 minute of arc on their retina at 20 feet. A person who is 20/40 has to either get twice as close (10 feet) or the object has to be doubled in size (2 minutes of arc) to see the same level of detail as the 20/20 individual. A well-illuminated object is easier to see than a poorly illuminated one. Vision exams are conducted under high illumination conditions. Illumination must be the optimum range to be seen. Too much or too little illumination can decrease visibility. Generally, detection and cueing improves with increased illumination. The higher the contrast, the easier an object is to see and the eye should be adapted for the ambient light level to see effectively. Again, vision is tested with 100% contrast targets, black letters on a white background.
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NVD system resolution is limited by what?
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NVD system resolution is limited by design constraints. Primarily, the number of channels in the microchannel plate (MCP), optics, and inherent video noise drive AN/AVS-9 resolution. Improvements in MCP technology revolve around increasing the number of channels, which is comparable to increasing the number of pixels in a computer monitor.
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What is is the sole reason for reduction in visual acuity as the contrast of the image is reduced.
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The video noise that is seen under a low light level condition.
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NAVFLIR resolution is determined by what?
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Detector size/number, scan rate, optics, display resolution, and inherent noise. Detector number, size and display resolution appear to be the promising areas for near term improvements
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Name 6 visual cues that are impacted by NVDs.
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FOV, contrast, resolution, depth perception, distance estimation, and static and dynamic cues.
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What is depth perception compared to distance estimation?
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Ddepth perception is primarily determining the relationship of objects in relation to each other, distance estimation is determining “how far away an object is."
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What are the 2 types of depth perception cues we use?
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Binocular and monocular.
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Describe binocular depth perception cues.
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The binocular factors of convergence and stereopsis are involved with depth perception. With NVDs, this type of depth perception appears to be limited, with monocular cues being primarily utilized for depth perception.
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What is stereopsis?
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Stereopsis, caused by the disparity of images on the retina of the two eyes, is the most important factor in judging the distance of near objects. The maximum practical limit of stereopsis is only 200 meters.
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Describe monocular depth perception cues.
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The monocular cues to depth perception (conscious and subconscious cues learned from experience) include relative size and height, overlapping contours, distribution of light and shadow, atmospheric/aerial perspective, texture gradients, convergence of parallel lines, and, perhaps most importantly, motion parallax. Although these monocular cues are less important than stereopsis in close, they become more dominant as the distance between the observer and the object in question increases. Keep in mind that anything that will adversely impact NVG resolution will also impact the perception of these cues.
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What happens to depth perception and distance estimation in lower illumination?
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As resolution decreases due to lower illumination or flower contrast scenes, the cues will be less discernible resulting in poorer depth perception and distance estimation capability.
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Why will objects appear farther away on NVGs?
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Distance estimation is significantly altered with NVGs for a variety of reasons. Objects will appear further away than they actually are due to a reduction in visual acuity. This is primarily a learned subconscious phenomenon as we expect objects that are less distinct in detail to be farther than ones which have sharp detail.
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What is minification?
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Another factor that degrades distance estimation is the phenomenon of instrument myopia (minification). Minification is a decrease in the perceived size of an object, or of its image, in relation to the object. Looking at a collimated "TV image" on a display such as the AN/AVS-9 eyepiece lens or the HUD causes objects to appear to be further away than they actually are.
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What are some operational examples of distance estimation problems on NVGs?
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Operational examples of distance estimation problems include overestimating altitude or the distance to an object in the flight path. Additionally, care must be taken to maintain adequate separation from other aircraft during rendezvous and formation flight.
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Dynamic visual cues are used to provide aircrew cues for what?
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Dynamic visual cues are used to provide aircrew cues for direction, altitude, and speed.
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What are the three primary dynamic cues?
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(1) static cue motion, (2) optical flow, and (3) peripheral vision motion.
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What is static cue motion?
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Static cue motion is the summed effect of the change in one or more of the static cues caused by aircraft movement. Static cues include elevation, known size, density, masking, and perspective. Central vision tracking is a method for seeing static cue motion and will be degraded by NVDs.
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What is optical flow?
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Optical flow is the angular rate and direction of movement of objects as a result of aircraft velocity measured relative to the aviators eye. This provides the visual perception system the information necessary to interpret speed and direction of motion. If there is no relative motion, there is no optical flow. We use central vision to obtain optical flow information.
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How is optical flow affected by NVGs?
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Since visual acuity is degraded with AN/AVS-9, the optical flow cues will be degraded as compared to daytime cues.
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What is peripheral vision motion?
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Peripheral vision motion, also known as motion parallax, is a subconscious method of detecting optical flow. It is dependent on a wide FOV and is the primary airspeed and altitude sensory input. With the significant reduction in FOV of AN/AVS-9 and the NAVFLIR, this cue is severely degraded and central vision tracking becomes the primary detection means. This leads to one of the most insidious dangers when flying low altitude profiles. Just as in the day, visual acuity will improve as the aircraft gets closer to the ground. However, because of the reduction in peripheral vision motion, the ensuing "speed rush" that would indicate close proximity to the ground is not available and controlled flight into the ground becomes a real possibility. The use of an aggressive scan will help "fill in the blanks." During high cockpit workloads or periods of fatigue, scanning is one of the first tasks to be impacted. A dedicated effort must be made to avoid fixation and to maintain the scan necessary to provide this vital cue. The radar altimeter becomes a crucial instrument to cross check when flying low-level profiles.
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Does the use of NVDs require dark adaptation?
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The use of NVDs does not require dark adaptation. The brightness (luminance) at the eyepiecelens and HUD is sufficient to partially activate the photopic visual system (cones) and leads to “mesopic” vision.
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Do NVDs influence dark adaptation?
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The use of AN/AVS-9 does influence dark adaptation, but not significantly because the peak output of the AN/AVS-9 P43 phosphor (560 nm) does not match the peak sensitivity of scotopic (night) vision (510 nm).
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How long does dark adaptation take?
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Army studies have shown that a dark-adapted individual reacquires dark adaptation within three minutes ofdegoggling. It is believed a non-dark adapted individual takes approximately 10 minutes to "dark adapt" or maximize unaided vision after removal of the AN/AVS-9. This is an important consideration for landing unaided after an NVG mission. Full dark adaptation never really occurs in the cockpit because of the light intensity provided by instrument lights.
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How do An/AVS-9's respond to bright lights such as weapons flash?
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The NVGs do "shut-down" as they degain from the input of bright light; however, it takes less than one second for the AN/AVS-9 to recover. Any lingering effect is physiological.
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Ones source of balance and perspective is largely due to what?
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Peripheral cueing, while central cueing is responsible for fine detail an interpretation.
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How is peripheral viewing affected on NVGs?
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Due to the design of AN/AVS-9 and the helmet, there is considerable unaided peripheral viewing capability. What can be seen in the periphery depends on many variables; illumination level, terrain type, artificial light sources, etc. Though the aircrew is not completely dark adapted, they are partially dark adapted and able to discern some features outside the NVG image. Flying over terrain where cultural lighting is generously scattered, many lights and the motion of these lights as they speed by can be detected in the periphery while looking into the NVD image. This adds to overall orientation (situational awareness) by feeding information that is familiar from unaided night operations.
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What can result in significanly enhanced spatial orientation on NVGs when flying in canyons?
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When flying in canyons during periods of good illumination, features and motion may be detected in the periphery outside the AN/AVS-9 FOV. When peripheral cueing is added to both the NVG and NAVFLIR image, good marriage of sensor and real world imagery can result in significantly enhanced spatial orientation.
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