The 1990s saw an increased emphasis on night operations within the Army. An integral part of this effort was research to improve the dismounted soldiers ability to see and hit targets at night. Today, night equipment, including night vision goggles (NVGs), aiming lights, and thermal sights, is becoming relatively common within the Infantry and other branches for the Army.
Commanders of dismounted forces emphasize the lethality of individual riflemen. Individual training focuses on maintaining high levels of marksmanship and successful tactics rely on getting proficient riflemen into the battle. With the Army's emphasis on night operations, commanders must be sure that riflemen are lethal at night as well as during the day. That lethality depends largely on whether riflemen can fire effectively with today's technology, NVGs, aiming lights and thermal weapon sights.
This appendix provides a better understanding of how your eyes are able to adapt to the night, as well as increased information on night devices and how they work. The information has been provided through continuous observation during operational testing by the test trainers, the Army Research Institute, and lessons learned by individual soldiers across the Army. Be it with the naked eye or with night devices you must learn what it takes to increase your ability not only to see better at night but also to increase your ability to "own the night."
Although operating at night has definite advantages, it is also difficult. Your eyes do not work as well as during the day, yet they are crucial to your performance. You need to be aware of constraints your eyes place upon you at night, because 80 percent of your sensory input comes through them. Some of these constraints are:
- Your ability to see crisp and clear images, your visual acuity, is reduced.
- Under certain conditions, you cannot distinguish one color from another.
- Your depth perception is reduced.
- You have "night blind spot," which makes it difficult to see objects at certain distances.
- Lights can cause you to lose your dark adaptation.
- Your eyes may seem to play tricks on you.
a. Normal Blind Spots. The "normal blind spot" is always present, day and night. It is caused by the lack of light receptors where the optic nerve inserts into the back of the eye. The "normal blind spot" occurs when you use just one eye. When you close the other eye, objects about 12 to 15 degrees away from where you are looking will disappear. When you uncover your eye, the objects will reappear.
b. Night Blind Spots and Viewing Techniques. When you stare at an object at night, under starlight or lower levels of illumination, it can disappear or fade away. This is a result of the "night blind spot," and you need to know what you can do to overcome it. It affects both eyes at the same time and occurs when using the central vision of both eyes. Consequently, larger and larger objects are missed as the distances increase. A hand grenade 2 meters away from your eyes might not be seen; an enemy soldier at 50 meters may be missed. An M1 tank at 300 meters can even be missed. So, if you are looking directly at something at night, you may miss it because of the "night blind spot."
(1) In order to avoid the "night blind spots," look to all sides of objects you are trying to find or follow. DO NOT STARE. This is the only way to maximize your night vision.
(2) A good technique for peripheral viewing is called "diamond viewing." It is similar to the off-center vision technique taught in rifle marksmanship. Diamond viewing means that you move your eyes just slightly, a few degrees, in a diamond pattern around the object you wish to see. You do not have to move your head-use your peripheral vision.
c. Stages Of Adaptation. There are three stages of dark adaptation that help to explain how the eye works at night.
(1) Daylight Vision. The first stage is daylight vision, which occurs under maximum lighting conditions such as when the sun is shining or in a well-lit room. Under these conditions, both your central and peripheral vision are used, which provides your best visual acuity-20/10, 20/15, and 20/20 vision. You also have your best color vision-colors look most vivid under daylight conditions. You also have your quickest reaction time.
(2) Twilight Vision. The next stage of adaptation is twilight vision. Twilight vision occurs during many military night operations and when driving around in a car at night. It occurs at dawn and dusk, down to full moonlight. It also occurs when there is artificial illumination and when snow is on the ground at night. It can occur in the daytime with several layers of jungle canopy.
(a) Because of the lower light levels at dawn, dusk, and full moon conditions, your visual acuity is poorer. Visual acuity can be as poor as 20/100. In fact, the best visual acuity you can hope to obtain under twilight conditions is between 20/50 and 20/100.
(b) You also have poorer color vision. You can still see colors but they won't be as vivid. You also have slower reaction times because of the reduced lighting levels.
(3) Night Vision. The final vision is night vision. Night vision occurs under starlight, as well as on moonless and cloudy nights when there are no stars or cultural lighting. Remember there is a "night blind spot" as discussed earlier.
(a) Under night conditions, everyone has the worst visual acuity-from 20/200 to 20/400 and possibly much worse. You can recognize silhouettes, but not the details of the objects. This is why knowing the silhouettes of vehicles and critical natural man-made objects is important.
(b) Under night vision conditions you cannot see colors-only various shades of gray can be seen. With night vision, the longer wavelengths of light, such as the reds and oranges, are hard to see and will appear dark. Unless a dark color is bordered by two lighter colors, it becomes totally invisible. Reds will be almost invisible at night. The reason red crosses are on white backgrounds on tents or vehicles are so they can be seen more easily at night. On the other hand, greens and blues will appear brighter, although you may not be able to determine their color.
d. Dark Adaptation. In order for your visual system to work efficiently at night, you need to dark-adapt. It takes about 30 to 45 minutes to fully dark-adapt or get your eyes used to seeing things under low light conditions, when going from a brightly lighted area into the dark. It takes longer to dark-adapt than many people think. It's similar to walking into a movie theater when it's very dark. You can't see things at first. Yours eyes will gradually adapt, enabling you to see more and more as time goes on. In addition, people dark-adapt at varying rates. People who are older, people who smoke, or people who may not be in great physical shape will take longer to dark-adapt or see things under low light conditions.
(1) Protecting (Before Operation). It is very important to protect your eyes before night operations so you can dark-adapt in an efficient manner. The following suggestions will help you dark-adapt more efficiently.
- Don't smoke before nighttime operations. Not smoking four to six hours before night operations will aid in dark adaptation.
- Wear sunglasses if you are going to spend time in the sun. Without sunglasses it will take longer to dark-adapt.
- Watch what you eat. Good nutrition is important in order to maintain adequate levels of Vitamin A.
- Use dim white lighting or red lighting before night operations.
(2) Protecting (During operation). Once you are dark-adapted, it is also important to maintain that dark adaptation.
- Minimize your use of unnecessary lighting to maintain your dark adaptation during operations at night.
- Close one eye before being flashed by flares and other bright lights to preserve your dark adaptation.
e. Illusion (Apparent Movement of Light). The illusion of movement, which a static light exhibits when stared at in the dark, is related to the loss of surrounding visual references that normally serve to stabilize visual perceptions. Consequently, very small eye movements are perceived by the brain as movement of the light. Under such conditions, the best thing to do is to begin a scan pattern and control the eye movement. Use large movements and scan to control illusions. Try to find another light and shift your gaze back and forth between the lights.
There are three devices available to dismounted soldiers that will help increase his lethality at night: night observation devices (NODs), aiming lasers, and thermal weapon sights. Each provides the dismounted soldier with different views of the infrared (IR) spectrum. Before soldiers are able to fully operate these devices they must receive training on how the systems work within the IR range and the electromagnetic (light) spectrum. The soldiers must also know what constraints and advantages each piece of equipment provides so that they can determine when to employ each device.
a. Electromagnetic (Light) Spectrum. The electromagnetic spectrum is simply energy (light). Within this spectrum of energy or light you can find x-rays, gamma rays, radio waves, cosmic rays, and ultra violet rays, to name a few. Also within this spectrum of light is visible light, visible light being what we are able to see with the naked eye. Just beyond red visible light is IR light, meaning just beyond. IR light is broken down into three different ranges: near IR, middle IR, and far IR. This is important for the soldier to know because it will give him an understanding of why some night devices cannot be used in conjunction with other night devices.
(1) There are two different types of night devices that will increase the soldier's vision into the IR range. The first one is image intensifiers (IČ), which rely on ambient light and energy within the near IR range emitted from natural and artificial light sources such as moonlight or starlight. Image intensifiers include the AN/PVS-4, PVS-5, PVS-7A/B/C/D, and PVS-14s. The Army also has devices that emit near IR energy in a colliminated beam, which are used as aiming devices such as the AN/PAQ-4B/C and the AN/PEQ-2A. Since both the image intensifiers and aiming lasers work within the same range of near IR energy they are able to work in conjunction with each other.
(2) The second device that uses IR light is the thermal sight. In the past thermal technology has been solely reserved for tanks, fighting vehicles, and antiarmor specialists such as TOW and Dragon gunners. These devices were very bulky, heavy and not very practical for the dismounted soldier. Now, the Army has a thermal device made for the dismounted soldier that can be mounted on his weapon or handheld. The TWS operates within the middle/far IR range. It is able to detect IR light emitted from friction, combustion, or from objects that are radiating natural thermal energy. Since the TWS and other thermal devices operate within the middle/far IR range they cannot be used in conjunction with image intensifiers or other IČ devices at this time.
b. Image Intensifiers (IČ) Devices. As the name implies, image intensification devices are designed to amplify light. To be effective, some degree of light must be available. When light enters the image intensifier tube, the light releases electrons, which the tube accelerates repeatedly until the light is much brighter. Under optimum conditions, second-generation devices, such as the PVS-5-series, intensifies ambient light up to about 1,500 times. Third-generation devices, such as the PVS-7/14-series NODS, doubles that level of intensification.
(1) Adjustments. Making the proper adjustments to your image intensification devices is crucial to your ability to acquire and engage a target at night. First, you must understand that you will not be able to obtain the same acuity level as you do during the day. Under optimum night conditions a soldier with 20/20 vision during daylight can expect no better than 20/50 with second generation NODs, and 20/40 with third generation NODs. But in order to approach these levels of acuity you must be able to adjust your NODs for optimum clarity.
During an Army Research Institute (ARI) study on night vision devises, they compared the hit probabilities for riflemen who used good NOD acuity settings (20/35 to 20/50) with the same riflemen who used poor NOD acuity settings (20/60 to 20/70). With good NOD acuity, soldiers had a hit probability at 75 meters of 76 percent; with poor acuity, the hit probability at 75 meters dropped to 47 percent.
(a) Mount the night observation device. Mount the head mount or helmet mount IAW the appropriate TM. If using the helmet mount, ensure that the tilt is adjusted until you have a comfortable viewing angle. The use of the nape strap is crucial to maintaining proper acuity with the NODs.
If the mounting bracket is permanently attached to the helmet, ensure that the nape strap rear bracket is also permanently attached (See TM 11-5855-306-10, AN/PVS-14). The use of the nape strap will prevent the weight of the NODs from pulling the helmet downward causing the NODs to rest on the bridge of your nose. The nape strap will allow for proper acuity of the sight and will allow you to engage targets with more ease and accuracy.
(b) Set eye-relief. Move the goggles so that the eyecups cover the eye but not so close that the eyepiece touches your eyelashes or glasses.
(c) Turn the goggles on.
(d) Set inner-pupillary distance (AN/PVS-7 series). Move each eyepiece until they are centered over each eye. Close one eye and make adjustments until the eye that is open is viewing a complete circle and not an oval. Continue to make adjustments to the other eye.
(e) Adjust the diopter ring. Adjust the diopter ring before adjusting the objective focus ring. The diopter adjustment ring focuses the display lens to your eye, while the objective lens focus ring focuses the target. You cannot focus the sight to the target without your eye being focused to the display first. Close one eye and with the eye that is open take the diopter ring and turn in one direction until the diopter is totally out of focus. Then turn the diopter ring back the opposite direction until the display is focused to your eye. Follow the same procedures for the other eye if using the AN/PVS-7 series. No further adjustment to the diopter adjustment ring should have to be made.
(f) Objective focus ring. While looking at an object, turn the objective focus ring until the objective lens is out of focus and then slowly turn the objective focus ring in the opposite direction until the object becomes as clear as possible. Adjustments will have to be made for targets at different ranges using the objective focus ring.
(g) Variable gain control (AN/PVS-14 only). The AN/PVS-14 has a variable gain control that controls the illumination input to the eye. Keeping the variable gain turned up will cause your brain to form two separate images, one darker and one very bright. With the variable gain turned down to the point that both eyes are almost receiving the same amount of light, the brain will produce one image making it seem like both eyes are looking through the same sight.
c. Aiming Lasers. Aiming lasers, AN/PAQ-4-series and the AN/PEQ-2A, also operate within the electromagnetic spectrum, specifically near IR range, and are seen through image intensification devices. The aiming lasers cannot be used in conjunction with the TWS since it operates within the middle/far IR spectrum. The aiming lasers emit a highly colliminated beam of IR energy that allows for quick "point and shoot" capability at night. Even though the aiming lasers provide a quick and easy means of engaging the enemy at night special attention must be given to the following:
- Proper adjustments to the image intensifiers.
- 10-meter boresight procedures or 25-meter zeroing procedures.
- IR discipline.
(1) Proper Adjustments to NVGs. Making the proper adjustments to the image intensifiers are crucial. It has been found, Army wide, that leaders and soldiers do not have a working knowledge of IČ devices and that the majority do not know how to make the proper adjustments in order to get the best possible picture. Since the aiming lasers cannot be seen with the unaided eye, and can only be seen with IČ devices, it is paramount that every soldier is made aware of how these devices work and how to maximize the quality of what is being viewed by making the proper adjustments to these devices.
(2) 10-Meter Boresight/25-Meter Zero. As aiming lights were being introduced to units, increasing attention was given to the difficulty in zeroing them to weapons, a problem identified in the initial Army tests. The basic problem with traditional 25-meter live-fire zeroing procedures is that the beam of an aiming light "blooms" when viewed through NVGs. Because this "bloom" covers up the silhouette in the center of the 25-meter target, a precise point of aim is almost impossible to achieve when zeroing.
(a) One solution to the 25-meter zeroing problem was the introduction of the bore light. The bore light allows you to zero your weapon system without the use of ammunition. A 25-meter zeroing allows the round to hit somewhere within a 19-inch circle at a 300-meter target, not center mass of the target. With the bore light, if boresighting procedures are done correctly and without human error, the strike of the round will impact a target at 300 meters very close to center mass. The other advantage to the use of the bore light is that a 25-meter zero is no longer necessary with aiming lights; if the boresighting procedures are done correctly, you will be able to engage targets out to 300 meters, dependant upon ambient light conditions.
(b) If a 25-meter zeroing is to be conducted, modifications to the M16A2 zero target must take place. A 3-centimeter circle is cut out of the center of the 300-meter zeroing silhouette. As you align the laser with the 3-centimeter cutout, the bloom will disappear ensuring that your point of aim is center mass of the 300-meter zero silhouette.
(3) Scanning. The night vision devices have a 40-degree field of view leaving the average shooter to miss easy targets of opportunity, more commonly the 50-meter left or right target. You must train to aggressively scan your sector of fire for targets. Target detection at night is only as good as you practice. Regular blinking during scanning, which must be reinforced during training, relieves some of the eyestrain from trying to spot far targets. After you have mastered the art of scanning, you will find that targets are easier to detect by acknowledging the flicker or movement of a target.
(4) Walking. Once a target has been located, you must be aware of the placement of the aiming laser. Laser awareness is a must. If you activate your laser and it is pointing over the target into the sky, you will waste valuable time trying to locate exactly where your laser is pointing. Also, it increases your chances of being detected and fired upon by the enemy. When engaging a target, aim the laser at the ground just in front of the target, walk the aiming laser along the ground and up the target until you are center mass, and then engage the target. Walking your laser to the target is a quick and operationally secure means of engaging the enemy with your aiming laser.
(5) IR Discipline. Once a target has been located and engaged with the aiming laser, the laser must be deactivated. While on the range IR discipline is active scanning with the laser off. Once a target is located, walk the laser to the target and engage. After the target has been engaged, the laser goes off.
d. Thermal Weapon Sight. Knowing about the electromagnetic spectrum and the range of IR in which the TWS operates will make it easier to understand how the TWS is able to take this energy and convert it into an image suitable for viewing. The TWS is able to absorb all available light into the lens, and then filters out all light except for middle/far IR (thermal light). The TWS then converts the thermal light into an image and creates a video that is displayed on the raster for viewing. The TWS is able to convert thermal energy that is reflected, radiated, or generated from an object. All objects, such as trees, metal, plastic, and living creatures, display a quality that allows them to be seen with the thermal technology. How well the objects display these qualities will determine how well they are seen.
- Absorption. During the day all inanimate objects absorb thermal energy from the sun to varying degrees. Metal objects have a much higher rate of absorption than wood, leaves, or grass; therefore, a metal object sitting in the sun will stand out more than the grass surrounding it when viewed through the TWS.
- Exposure. The amount of time an object is exposed to thermal energy determines how well that object will be seen. Naturally, an object with a long exposure time will have absorbed more thermal energy than an object exposed to the same thermal energy for a shorter period of time.
- Emissivity. Emissivity is the rate at which an object emits the thermal energy it has absorbed or generates. Usually, most objects that have a high absorption rate will have a high emissivity factor. Although the human body does not have a high absorption rate, it does have a high emissivity factor due to the fact that it generates a high amount of thermal energy. An object that has a high emissivity factor will be much hotter, and, therefore, when seen through the TWS, much easier to see and recognize.
- Reflection. Items such as glass and water have virtually no absorption rate. Instead they reflect the thermal energy, which makes it very difficult to see objects through glass and water. Snow and ice have the same effect, especially during the day with no clouds present. The snow or ice reflect most of the thermal energy from the sun, so it will be difficult to acquire a good thermal image on objects that are really close to the ground.
(1) Diurnal Cycle. There are two times during the day when motionless objects that do not generate their own thermal energy, such as trees, rocks, and man-made objects, become the same temperature as the surrounding air. This is known as the diurnal cycle. These times usually occur once in the morning and once in the evening. The specific times that this cycle will take effect is based on the time of the year, but it usually occurs shortly after sunrise and shortly after sunset. These two times during the day can be referred to as "crossover points." During the day, a motionless object will absorb thermal energy from the sun; the crossover point is the time when that object stops absorbing thermal energy and starts radiating thermal energy (night). As the night goes on, that same object will come to a point where it stops radiating thermal energy and will once again start absorbing thermal energy (day). During the diurnal cycle objects can be difficult to see, so adjustments must be made to the TWS in order to refine your thermal image.
(2) Adjustments. In order to maximize the use of the TWS, you must be able to make adjustments to the sight to obtain the optimal thermal image. Rain, snow, fog, smoke, and the diurnal cycle are just a few environmental or combat situations that may affect your thermal image. The TWS is equipped with a diopter focus ring, an objective focus ring, brightness knob, auto and manual contrast, and polarity switch that will allow you to maximize the capability of the sight.
(a) Diopter Focus Ring. When first making adjustments to the sight, start with the diopter focus ring. The diopter focus ring will focus the display screen (raster) to your eye. This is best done with the objective lens cover closed. Simply adjust the diopter focus ring until everything on the display screen is clear and easily read. Once you have adjusted the diopter focus to your eye, no other adjustments to the diopter focus ring should be necessary.
(b) Field of View (FOV). The TWS has two operating FOVs-wide and narrow. The wide field of view (WFOV) has the least magnification, but a greater FOV and is great for scanning. The narrow field of view (NFOV) has greater magnification, but less degrees of FOV. The soldier should be allowed to select the FOV that suits him best. Each soldier will learn, through use, which FOV to use under different combat situations.
When selecting a FOV, make sure that the FOV ring is turned completely to the left or to the right. If the FOV ring is turned only halfway, you will not be able to see through the sight.
(c) Objective Focus Ring. The objective focus ring will focus the sight to the target. Adjustments to the objective focus ring will be based on the range of the object being viewed. Make adjustments to the objective focus ring only after focusing the diopter focus ring.
Over-adjustment to the objective focus ring will lock the FOV ring to the point that the FOV cannot be changed.
(d) Brightness. The brightness knob is a dual-function knob that turns on the TWS and adjusts the brightness of the raster, and is used to refine the thermal image. Used in conjunction with the contrast knob, it helps combat the effects of the diurnal cycle, and other conditions that might require fine-tuned adjustment to the thermal image.
(e) Contrast. The contrast is a dual-function switch with an auto contrast and manual contrast mode. The auto contrast is used under normal operating conditions. The manual contrast is used under conditions other than normal such as during 10-meter boresighting during 25-meter zeroing; during rain, fog, smoke, or snow; during the diurnal cycle; or when trying to obtain as much detail of a target as possible. Used in conjunction with the brightness knob, the contrast allows you to obtain the best possible thermal image.
(f) Polarity. The polarity switch allows you to select between white-hot or black-hot. When in white-hot mode, the hotter objects will appear white while cooler objects will have shades of gray to black. When using black-hot, the hotter objects will be black while the cooler objects will be shades of gray to white. Use of the polarity switch is a users preference. Through continued use you will decide which polarity setting works best under different combat or environmental conditions.
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