Visual acuity (resolution) and field of view are two significant parameters used to characterize night vision goggles (NVG5). Most users of NVGs surveyed within the US Air Force put these two parameters at the head of the list of characteristics that they would like to see improved. Unfortunately, it is well established that these two parameters are coupled together in an inverse relationship: an increase in field of view results in a reduction in visual acuity and vice versa. However, there are at least two ways to model the relationship between these two parameters: one based simply on geometric considerations and one based on the concept of the modulation transfer function (MTF) of the image intensifier tube and the contrast threshold function of the human visual system.To investigate these relationships, an experiment was conducted to determine how visual acuity through night vision goggles (NVGs) changes as a function of NVG field of view and ambient scene illumination level. A total of three trained observers were used for this study who ranged in age from 33 to 42 years of age. The NVGs used in the study had fields of view of 40, 47, and 52 degrees, respectively. Five levels of ambient scene illumination (corresponding to NVG output luminance levels of 0.01, 0.03, 0.08, 0.26, and 1.9 fL) were provided by a 2856K light source which ranged from overcast starlight to quarter moon. The targets used in the study were approximately 95+% contrast square wave targets ranging in size from 45 cycles! degree to 5 cycles per degree. The method of adjustment was employed by having the trained observer start at a distance of 30 feet and determine the highest spatial frequency target which was clearly discemable. The subject was then directed to walk back slowly from the target until it was just out of focus, and then walk forward until the target was barely discernable. The distance from the target was recorded and used to calculate the angular spatial frequency (and equivalent Snellen acuity).The results indicate that the simple geometric model of the inverse relationship between resolution and field of view is adequate for characterizing this design trade-off for the quality of image intensifier tubes currently available. INTRODUCTION AND BACKGROUNDTwo key parameters used to characterize night vision goggles (NVG5) are visual acuity (resolution) and field-of-view. An increase in field-of-view is accomplished by providing higher magnification of the image intensifier tube. However, since the image intensifier tube has a fixed linear resolution at its output screen, increased magnification means that the "picture elements" (pixels) will subtend a larger angle with respect to the O-8194-1522-7/94/$6.00 SPIE Vol. 2218 / 71 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/23/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx
Once considered too processing-intense for general utility, application of the third dimension to convey complex information is facilitated by the recent proliferation of technological advancements in computer processing, 3D displays, and 3D perspective (2.5D) renderings within a 2D medium. The profusion of complex and rapidly-changing dynamic information being conveyed in operational environments has elevated interest in possible military applications of 3D technologies. 3D can be a powerful mechanism for clearer information portrayal, facilitating rapid and accurate identification of key elements essential to mission performance and operator safety. However, implementation of 3D within legacy systems can be costly, making integration prohibitive. Therefore, identifying which tasks may benefit from 3D or 2.5D versus simple 2D visualizations is critical. Unfortunately, there is no "bible" of human factors guidelines for usability optimization of 2D, 2.5D, or 3D visualizations nor for determining which display best serves a particular application. Establishing such guidelines would provide an invaluable tool for designers and operators. Defining issues common to each will enhance design effectiveness. This paper presents the results of an extensive review of open source literature addressing 3D information displays, with particular emphasis on comparison of true 3D with 2D and 2.5D representations and their utility for military tasks. Seventy-five papers are summarized, highlighting militarily relevant applications of 3D visualizations and 2.5D perspective renderings. Based on these findings, human factors guidelines for when and how to use these visualizations, along with recommendations for further research are discussed.
Night Vision Goggles (NVGs) are being used increasingly by the military and law enforcement agencies for night operations. One critical issue in assessing the utility of an NVG is its resolving power or capability to make fine detail distinguishable. The resolution of Night Vision Goggles is typically assessed by measuring the visual acuity of an operator looking through the goggles. These methods can be time consuming. Further, inconsistencies associated with visual observations and judgement add to the variance associated with these measurements. NVG Modulation Transfer Function (MTF) was explored as a possible means of characterizing NVG image quality independent of a human observer. MTF maps the potential contrast output of the NVGs as a function of spatial frequency. The results of this MTF measurement were compared with a commonly used method of visual acuity assessment.
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