Peter L. Marasco

The impact of target luminance and radiance on night vision device visual performance testing

Visual performance through night-vision devices (NVDs) is a function of many parameters such as target contrast, objective and eyepiece lens focus, signal/noise of the image intensifier tube, quality of the image intensifier, night-vision goggle (NVG) gain, and NVG output luminance to the eye. The NVG output luminance depends on the NVG sensitive radiance emitted (or reflected) from the visual acuity target (usually a vision testing chart). The primary topic of this paper is the standardization (or lack thereof) of the radiance levels used for NVG visual acuity testing. The visual acuity chart light level might be determined in either photometric (luminance) units or radiometric (radiance) units. The light levels are often described as “starlight,” “quarter moon,” or “optimum” light levels and may not actually provide any quantitative photometric or radiometric information. While these terms may be useful to pilots and the users of night-vision devices, they are inadequate for accurate visual performance testing. This is because there is no widely accepted agreement in the night vision community as to the radiance or luminance level of the target that corresponds to the various named light levels. This paper examines the range of values for “starlight,” “quarter moon,” and “optimum” light commonly used by the night vision community and referenced in the literature. The impact on performance testing of variations in target luminance/radiance levels is also examined. Arguments for standardizing on NVG-weighted radiometric units for testing night-vision devices instead of photometric units are presented. In addition, the differences between theoretical weighted radiance and actual weighted radiance are also discussed.

Psychophysical measurement of night vision goggle noise

Pilots, developers, and other users of night-vision goggles (NVGs) have pointed out that different NVG image intensifier tubes have different subjective noise characteristics. Currently, no good model of the visual impact of NVG noise exists. Because it is very difficult to objectively measure the noise of a NVG, a method for assessing noise subjectively using simple psychophysical procedures was developed. This paper discusses the use of a computer program to generate noise images similar to what an observer sees through an NVG, based on filtered white noise. The images generated were based on 1/f (where f is frequency) filtered white noise with several adjustable parameters. Adjusting each of these parameters varied different characteristics of the noise. This paper discusses a study where observers compared the computer-generated noise images to true NVG noise and were asked to determine which computer-generated image was the best representation of the true noise. This method was repeated with different types of NVGs and at different luminance levels to study what NVG parameters cause variations in NVG noise.

An alternative to radiance limits for vision enhancement device cockpit integration

With the introduction of the night-vision goggle (NVG) into vehicle cockpits, the transfer of visual information to the observer became more complex. The problem emanated from the image intensifier tube photocathode spectral response. NVGs were capable of sensing and amplifying visible cockpit light, making observation of the scene outside of the cockpit, the primary use for NVGs, difficult. Over the years, several documents were published outlining night vision imaging system (NVIS) compatible lighting performance. These documents limited the permissible amount of light visible to image intensifier tubes that cockpit displays could emit, enhancing pilot visual performance. Recent advances in short wave infrared (SWIR) sensor technology make it a possible alternative to image intensifiers for night imaging application. However, while popular SWIR cameras are not particularly sensitive to visible light, they may be sensitive to other display emissions not attenuated by state-of-the-art NVIS filters. This paper examines the possibility of expanding the traditional treatment of vehicle cockpit compatibility to include new, novel vision enhancement devices yet to be designed and vehicle cockpit geometry.

Psychophysical measurement of night vision goggle noise using a binocular display

Users of night vision goggles (NVGs) have reported differences in perceived noise across various NVGs. To understand these differences, we need to measure NVG noise in a psychophysical context. In the precursory study, subjects attempted to characterize NVG noise by examining choices across different parameters of filtered white noise generated on a computer monitor. Subjects adjusted parameters of the filtered noise to match the noise for each combination of two goggles and two luminance levels. Significant differences were found between luminance levels, NVG type, and parameter relationships. Concerns from the previous experiment have yielded this study to better understand if this characterization process has merit. In the previous study, the parameter sequence was constant across trials. We increased the number of trials and subjects, and we included an accounting for parameter sequence. In addition, we used a modified Wheatstone stereoscope to simulate NVG tube independence. We discuss our results in terms of luminance levels, parameter sequence, subject variability, and relationships between parameters.

Effect on vision of light scatter from HMD visors and aircraft windscreens

The amount of scattered light, or haze, typically increases as transparent materials age, wear, become dirty, or become scratched from cleaning. Light scattered from scratched aircraft transparencies, such as windscreen, head-up-display combiners, and helmet visors, can potentially reduce pilot visual performance and reduce target detection range. Presented in this paper are the results of an investigation of light scattered from transparencies exhibiting different levels of wear and surface damage. Two methods of measuring scattered light are compared. Visual performance under conditions of white light scatter relevant to the use of helmet-mounted displays in the cockpit is also examined.

Current and future helmet-mounted displays for piloted systems

Scientists and Engineers in the Air Force Research Laboratory (AFRL) are constantly asked what are the new technologies and concepts that are being developed to significantly increase the warfighters capabilities. The warfighting communities have different opinions and priorities based on their platform capabilities and operational requirements that the Laboratory has to make trade-offs to maximize the payoff on investment for the Air Force operator community in this tighter budget era. This paper will discuss the current state of helmet mounted displays in rotorcraft and fast jets as well as the future technology advancements needed to increase warfighter productive and/or reduce life cycle costs.

Military display market: fourth comprehensive edition

The military display market is analyzed in terms of all fully electronic and many electro-mechanical displays used on combat platforms across all DoD Services. The military market for displays is defined by parameters such as active area, bezel-to-bezel measurement and technology. Other characteristics such as luminance, contrast ratio, gray levels, resolution, viewing angle, color, video capability, and night vision imaging system compatibility are noted. This study takes into account all displays that are either installed or funded for installation. In some few cases, it also includes planned displays. Display sizes having aggregate defense applications of 5,000 units or greater and having DoD applications across 10 or more platform fleets, are tabulated. The issue of size commonality is addressed where distribution of active area across platform fleets, individually, in groups of two through nine, and ten or more, is illustrated. Military displays are also analyzed by technology, where total quantities of such displays are broken out into CRT, LCD, AMLCD, EM, LED, Incandescent, Plasma and TFEL percentages. Custom, versus Ruggedized Commercial-Off-The-Shelf (RCOTS), versus Commercial Off-The-Shelf (COTS) designs are contrasted. High and low information content designs are identified. Displays for several high-profile military programs are discussed, to include both technical specifications and program history. Our defense-wide study as of February 2006 has documented 1,195 direct-view and 15 virtualview display sizes across 628 weapon system platforms for a total of 1,161,977 displays.

Measurement of visual performance through scattering visors and aerospace transparencies

Light scattered from helmet visors and aerospace transparencies is known to reduce visual performance. One popular measurement technique, maintained by the American Society for Testing and Materials, is ASTM D 1003. It is a standard procedure used to measure haze inherent in transparent materials, which is defined as the percent of the total transmitted light that is scattered. However, research has shown that visual acuity measured through several different types of helmet visors does not correlate well with visor haze. This is most likely due to the fact that the amount of light scattered from a transparent material depends heavily on the light illuminating the transparency and on the viewing geometry, behavior that ASTM D 1003 does not characterized. Scattered light causes transparent parts to appear luminescent and imparts a veiling luminance when superimposed over a target, reducing target contrast and inducing a visual performance loss. This paper describes an experiment in which threshold target background luminance, the luminance at which a target was barely visible, was measured for a number of observers viewing a Landolt C target through several levels of veiling luminance. Threshold luminance was examined for predictable behavior with respect to veiling luminance.

Increased Compactness of an Imaging Spectrometer Enabled by Freeform Surfaces

A freeform imaging spectrometer in the Offner-Chrisp geometry is demonstrated to be 5x more compact than one with traditional surfaces. Performance and manufacturability was analyzed using spectral full-field displays and a demonstration prototype was realized.

Gradient index eyepiece technology for head-mounted display applications

Eyepieces used in full color head-mounted displays require a high degree achromatization to exhibit the level of performance required by observers. Many times, this leads to the use of dense glass materials and multi-element systems. The advent of new gradient index material systems as part of the DARPA-sponsored Manufacturable Gradient Index Optics (M-GRIN) may yield new design degrees of freedom for eyepiece and HMD designers. New plastic material systems may be used to simplify eyepiece design and shorten the eyepiece overall length, pulling the entire HMD system closer to the observer’s head and improving systems center of gravity. This paper will examine the possibility of using large aperture GRIN optics to achromatize an eyepiece and reduce its overall mass. Assumptions about the material system (index of refraction (n) and delta n) and a candidate full color microdisplay will be clearly stated and may not reflect any commercially available system.