This paper portrays the different Night vision techniques.' Night Vision' is referenced as innovation that gives us the supernatural occurrence of vision in all out dimness and the change of vision.
![]() « Previous: Summary: Findings and Recommendations ![]()
Suggested Citation:'Introduction.' National Research Council. 1987. Night Vision: Current Research and Future Directions, Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1037.
Suggested Citation:'Introduction.' National Research Council. 1987. Night Vision: Current Research and Future Directions, Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1037.
Suggested Citation:'Introduction.' National Research Council. 1987. Night Vision: Current Research and Future Directions, Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1037.
Suggested Citation:'Introduction.' National Research Council. 1987. Night Vision: Current Research and Future Directions, Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1037.
Suggested Citation:'Introduction.' National Research Council. 1987. Night Vision: Current Research and Future Directions, Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1037.
Suggested Citation:'Introduction.' National Research Council. 1987. Night Vision: Current Research and Future Directions, Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1037.
Suggested Citation:'Introduction.' National Research Council. 1987. Night Vision: Current Research and Future Directions, Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1037.
Suggested Citation:'Introduction.' National Research Council. 1987. Night Vision: Current Research and Future Directions, Symposium Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1037.
Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
![]()
INTRODUCTI ON
OPENING REMARKS-Brigadier General F. DoppeltUnited States Air Force School of Aerospace Medicine First, I'd like to thank you for inviting me. It's a great privi-lege to be here. Vision has been a very key part of all of our militaryoperations and has been a singular interest during my entire militarycareer. On behalf of Colonel Davis, USAF/SAM Commander, I'd like tocongratulate Colonel Tredici for doing an absolutely outstanding job inthe world of aviation vision. Participation with the National Research Council's Committee onVision has been a part of the activities of the Air Force and speci-fically the School of Aerospace Medicine for at least 40 years. TheArmed Forces Vision Tester participation on significant committees thathave worked on the use of drugs and their effect on vision, etc., arebut a few singular accomplishments. In fact, we're all aware that whenthe School of Aviation Medicine, a laboratory in Long Island circa 1917,was first formed as one of their key leaders, Dr. Wilmer, an ophthalmol-ogist, was associated very prominently with aviation vision. As I look at the Aerospace Medical Division's many and diversemissions from aircrew health aspects to human centered technology andresearch development, a tremendous amount of what we do involvesvision. Whether it's designing simulators, displays, night visiongoggles, or working specific target identification tasks, vision isthe key to almost everything the military operator does. We are visual animals for much of what we do is interpreted in thatprimary language of pictorial representations. If you shut your eyes,you can probably remember what this classroom looks like very, verywell, because it's imprinted in a very 'virtual' way in your mind. Asengineers, we go out and put that information on knobs and dials andtry to force the operator to relate the picture in his brain to somebutton, dial, or instrument. If you will, it goes through a doublelevel of 'virtual' information transformation. I remember back in 1965 when I first became associated with thespace program, astronaut Gordon Cooper made some interesting visualobservations in an early space flight which created some scientificcontroversy. As you may remember during a pass over Baja, he claimedto have seen a truck running down the center of the peninsula. Welooked at the optics of the situation and concluded that he could notpossibly have seen that truck running down the road. Well indeed,astronaut Cooper d id see the truck, for we later found out that there17
18was such a truck traveling about thirty or forty miles an hour on adirt road in the center of Baja. What astronaut Cooper saw was thecloud raised by the traveling vehicle. I'm sure he was able to computeits motion and properly concluded that it was a truck. So he used thisvisual process not only to see a piece of information but to interpretit and come up with what man does best--pattern recognition and inter-polation of that information into a meaningful identif ication We're in a world today where we know that our aircraft cannot oper-ate solely during the day. In fact, we understand very, very well thatour adversaries are capable of operating at night, as demonstrated inVietnam. We must develop technology which will make it difficult forour adversaries to assume that same nighttime safe harbor. We need tobetter understand how to marry sensor information, optics, man, and hismachine in a way that will give us the same kind of daytime effectivityof performance at night that our operations need. ~devoted to vision at night is really critical at this time.be busy at night, you need to keep us busy at night. We gain a tremen-dous advantage by being able to operate more credibly and more properlyat night. You need to deal with how well does the eye see at night,how well have we selected the right crew person, and how well have weoptimized the way in which he' s able to see and focus at night, throughp roper equ ipment design. I congratulate Colonel Tredici and all the f ine people that arehere today to put your best 'eyes' together to develop night visuals tandards and perhaps a new night vision tester .Alto nave a conferenceHe need to
AMBIENT ILLUMINANCE DURING TWILIGHT AND FROM THE MOONHerschel W. Leibowitz The geometry of twilight, the transition between night and daylightand daylight and night, has been precisely defined in terms of the posi-tion of the sun with respect to the horizon. Sunrise occurs when theupper limb of the sun becomes visible. Sunset occurs when the upperlimb of the sun becomes invisible. Twilight ends/begins when the cen-ter of the sun is 18 degrees below the horizon. During daylight, ambient illuminance is essentially independent ofsolar position until the sun falls to within 5 to 10 degrees of the hor-izon (Rozenberg, 1966~. The ambient illuminance at sunset/sunrise isabout 30 footcandJes,* which is near the maximum of contrast-dependentfunctions such as visual resolution, so that variations in illuminancebefore sunset and after sunrise would not be expected to have behav-ioral consequences. Figure 1 presents ambient illuminance betweensunrise/sunset and night as a function of the zenith distance of thecenter of the sun. During twilight ambient illuminance changes byalmost 6 orders of magnitude. Between sunset/sunrise and a zenithdistance of 103 degrees this function is approximately linear on asemi-logarithmic plot. Twilight is divided into three subperiods. Civil twilight is theperiod between sunset/sunrise and the time the center of the sun is 6degrees below the horizon. It is generally assumed that 'normal out-door activities' may be carried out during civil twilight. This is areasonable expectation at sunset and sunrise, when ambient illuminancevalues are 30 footcandles. However, in view of the low illuminancelevels encountered at the beginning of morning and the end of eveningcivil twilight, about 0.3 footcandle, one would expect significantSupported in part by grant EY 03276 from the National Eye Institute andby a grant from the U.S. Naval Development Center, Warminster, Pa.*All photometric values in this paper are given in terms of illumi-nance. The literature on visual performance is described in terms ofluminance units, which specify the light useful for activating the vis-ual system. Luminance is the product of illuminance and the percentreflectance (albedo) of the object in question.19
20degradation of visual resolution and other functions that are dependenton contrast sensitivity, as well as an increase in reaction time. How-ever, as a consequence of the selective degradation of recognition andorientation vision that occurs with a reduction in luminance, visualguidance and spatial orientation should be unaffected (Leibowitz andOwens, 1977~. Nautical twilight refers to the period when the center of the sunis between 6 and 12 degrees below the horizon. When the sun's centeris 12 degrees below the horizon, marking the beginning of morning andthe end of evening nautical twilight, ambient illuminance is scotopic,less than 0.003 footcandle. It is too dark to see the sea horizonprecisely enough for determination of altitudes for navigation, butvisually guided orientation should be possible under these conditionsas well as some form perception in the peripheral visual fields. m e period when the sun is between 12 and 18 degrees below the hor-izon defines astronomical twilight. The sky is still light but thereis very little ambient illuminance. When the sun is 18 degrees ormore below the horizon, the indirect light from the sun is less thanthat provided by stars (0.0001 footcandle) and about the same as fromairglow, zodiacal light, and the gegenschein. Illuminance levels areclose to the absolute scotopic threshold of the dark-adapted human eye.101,_ 'LitIn I I . ~w~ !Z l .. ok lo-2 lslow ' ._^ ,lll0~ 5~5eT. L =iCtVIL ~1 LIGHT _ j .I I I, 1 l NA~ L l MALI HT ~I ~ S=ONOMIC)U ! l . ~, , 900 950 of. lose ~ lo ZENITH DISTA`E ~ SUNFIGURE 1 Ambient illuminance during twilight, measured on a horizon-tal surface, as a function of the zenith distance of the sun. Dueto atmospheric refraction, the sun is visible at a zenith distanceg reater than 9 ~ deg rees. Source: Explanatory Supplement.
21TABLE 1 Estimated Illuminance from the MoonaE long at ion(degree s)180 (full moon)16014012090 (half-illuminated moon)604020Est imated I 1 luminance(footcandle)0.020.0130.0080.0050.0020.00060.00020.00002aBased on information from the Exploratory Supplement (1961~. Valuesoverestimate ambient illuminance when the moon approaches the horizon. As a consequence of the changing inclination of the sun's apparentpath through the sky and the horizon, the duration of twilight dependson both the latitude and the date. Near the equator, the sun's path isnearly perpendicular to the horizon. As a consequence, the sun's posi-tion changes rapidly with respect to the horizon and twilight is ofrelatively short duration. At 10 degrees north latitude (southernPhilippines, Costa Rica, central Ethiopia), the duration of civil twi-light is between 21 and 23 min. At 40 degrees north latitude (New York,Rome, northern Japan), the range is from 27 to 32 min. At 60 degreesnorth latitude (Stockholm; Leningrad; Juneau, Alaska), the durationranges from 40 to 106 min. The beginning and end of the various twi-light periods for any location on the earth's surface (altitude abovesea level must also be taken into account) (Exploratory Supplement,1961) can be interpolated to within 1-min accuracy by means of tablesin The Astronomical Almanac published annually and jointly by the U.S.and British governments (Washington, D.C.: U.S. Government PrintingOffice; London: Her Majesty's Stationery Office). It is of interestto note that at 40 degrees north latitude, ambient illuminance from thesky during civil and nautical twilights changes by a factor of 2 every4 to 5 min (depending on the date). Moonlight can have significant behavioral consequences duringnautical and astronomical twilight and at night. For a full moon atthe zenith, the illuminance on a horizontal surface is 0.02 footcandle,which approximates the ambient illuminance levels at the middle ofnautical twilight. After the full moon, the illuminance from the moonfalls off rapidly. Table 1 presents the estimated illuminance as afunction of elongation (angular distance from the sun) based on infor-mation from the Exploratory Supplement (1961~. Moon phase, rising, andsetting times can also be found In The Astronomical Almanac.-
22 Meteorological and atmospheric conditions can have a significanteffect on the quantity of light available during twilight and f rom themoon. Although the quantity of light f rom the sky during twilight andfrom the moon can be estimated accurately, the behavioral consequencesof the changes in ambient illuminance have not been systematically docu-mented in relation to the positions of the sun and the moon.REFERENCESExplanatory Supplement to the Astronomical Ephemeris and the American , .Ephemeris and Nautical Almanac.1961 London: Her Majesty' s Stationery Office, 1961.Leibowitz, H.W., and D.A. Owens1977 Science 197: 4302.Rozenberg, Georgii V 1966 Twilight..New York: Plenum.
Next: Photoreceptor Properties »![]() Comments are closed.
|
AuthorWrite something about yourself. No need to be fancy, just an overview. Archives
December 2022
Categories |