Different night vision goggle image intensification technologies were tested to compare goggle performance in low light
conditions. A total of four different night vision goggles were tested in a laboratory dark room. The laboratory tests
consisted of viewing Landolt acuity stimuli of different contrast levels with each set of goggles and without the goggles
in full light conditions (baseline performance). The results from the laboratory testing indicated that there were
significant differences in acuity between the NVGs, particularly for low contrast targets. These data suggest that NVG
standards developed using high contrast targets, even in low light conditions may not provide the full story of how the
NVG will perform in flight.
Expected temporal effects in a night vision goggle (NVG) include the fluorescence time constant, charge depletion at high signal levels, the response time of the automatic gain control (AGC) and other internal modulations in the NVG. There is also the possibility of physical damage or other non-reversible effects in response to large transient signals. To study the temporal behaviour of an NVG, a parametric Matlab model has been created. Of particular interest in the present work was the variation of NVG gain, induced by its automatic gain control (AGC), after a short, intense pulse of light. To verify the model, the reduction of gain after a strong pulse was investigated experimentally using a simple technique. Preliminary laboratory measurements were performed using this technique. The experimental methodology is described, along with preliminary validation data.
Helicopters are widely used in daytime forest fire suppression, conducting diverse tasks such as spotting, re-supply,
medical evacuation and airborne delivery. However, they are not used at night for forest fire suppression operations.
There would be many challenges when operating in the vicinity of forest fires at night, including scene obscuration from
smoke and dynamic changes in lighting conditions. There is little data on the use of Night Vision Goggles (NVGs) for
airborne forest fire suppression. The National Research Council of Canada (NRC), in collaboration with the Ontario
Ministry of Natural Resources (OMNR), performed a preliminary flight test to examine the use of NVGs while operating
near forest fires. The study also simulated limited aspects of night time water bucketing. The preliminary observations
from this study suggest that NVGs have potential to improve the safety and efficiency of airborne forest fire suppression,
including forest fire perimeter mapping and take-off and landing in the vicinity of open fires. NVG operations at some
distance from the fire pose minimal risk to flight, and provide an enhanced capability to identify areas of combustion at
greater distances and accuracy. Closer to the fire, NVG flight becomes more risk intensive as a consequence of a
reduction in visibility attributable to the adverse effects on NVG performance of the excess radiation and smoke emitted
by the fire. The preliminary results of this study suggest that water bucketing at night is a difficult operation with
elevated risk. Further research is necessary to clarify the operational limitations and implementation of these devices in
forest fire suppression.
Night vision devices (NVDs) or night-vision goggles (NVGs) based on image intensifiers improve nighttime visibility
and extend night operations for military and increasingly civil aviation. However, NVG imagery is not equivalent to
daytime vision and impaired depth and motion perception has been noted. One potential cause of impaired perceptions
of space and environmental layout is NVG halo, where bright light sources appear to be surrounded by a disc-like halo.
In this study we measured the characteristics of NVG halo psychophysically and objectively and then evaluated the
influence of halo on perceived environmental layout in a simulation experiment. Halos are generated in the device and
are not directly related to the spatial layout of the scene. We found that, when visible, halo image (i.e. angular) size was
only weakly dependent on both source intensity and distance although halo intensity did vary with effective source
intensity. The size of halo images surrounding lights sources are independent of the source distance and thus do not obey
the normal laws of perspective. In simulation experiments we investigated the effect of NVG halo on judgements of
observer attitude with respect to the ground during simulated flight. We discuss the results in terms of NVG design and
of the ability of human operators to compensate for perceptual distortions.
While anecdotal reports suggest that Night Vision Goggles influence spatial navigation and wayfinding (Braithwaite, Douglass, Durnford, and Lucas, 1998), few studies have systematically characterized the nature of these effects. To address this issue, the current study examined the impact of NVGs on navigation and wayfinding performance. One group of participants were required to navigate a walking maze and retrieve target objects while wearing NVGs (experimental condition), while a second control group navigated the maze without NVGs. We measured several performance metrics of navigation and wayfinding. Our results show that navigation and wayfinding with NVGs (experimental group) appeared to be harder, with longer navigation durations and more navigational errors compared to not using NVGs (control group). However, a significant decrease in navigation duration over the course of the wayfinding trials occurred earlier with NVGs, in addition to significant decreases in navigational steps compared to the control group. These results support the notion that NVGs directly affect spatial navigation and wayfinding performance. These degradations in performance should be considered in operational planning and NVG training programs. Further research is necessary to expand our understanding of the impact of NVGs on spatial cognition.
Perception of motion-defined form is important in operational tasks such as search and rescue and camouflage breaking. Previously, we used synthetic Aviator Night Vision Imaging System (ANVIS-9) imagery to demonstrate that the capacity to detect motion-defined form was degraded at low levels of illumination (see Macuda et al., 2004; Thomas et al., 2004). To validate our simulated NVG results, the current study evaluated observer’s ability to detect motion-defined form through a real ANVIS-9 system. The image sequences consisted of a target (square) that moved at a different speed than the background, or only depicted the moving background. For each trial, subjects were shown a pair of image sequences and required to indicate which sequence contained the target stimulus. Mean illumination and hence image noise level was varied by means of Neutral Density (ND) filters placed in front of the NVG objectives. At each noise level, we tested subjects at a series of target speeds. With both real and simulated NVG imagery, subjects had increased difficulty detecting the target with increased noise levels, at both slower and higher target speeds. These degradations in performance should be considered in operational planning. Further research is necessary to expand our understanding of the impact of NVG-produced noise on visual mechanisms.
Anecdotal reports by pilots flying with Night Vision Goggles (NVGs) in urban environments suggest that halos produced by bright light sources impact flight performance. The current study developed a methodology to examine the impact of viewing distance on perceived halo size. This was a first step in characterizing the subtle phenomenon of halo. Observers provided absolute size estimates of halos generated by a red LED at several viewing distances. Physical measurements of these halos were also recorded. The results indicated that the perceived halo linear size decreased as viewing distance was decreased. Further, the data showed that halos subtended a constant visual angle on the goggles (1°48’, ±7’) irrespective of distance up to 75’. This invariance with distance may impact pilot visual performance. For example, the counterintuitive apparent contraction of halo size with decreasing viewing distance may impact estimates of closure rates and of the spatial layout of light sources in the scene. Preliminary results suggest that halo is a dynamic phenomenon that requires further research to characterize the specific perceptual effects that it might have on pilot performance.
Proc. SPIE. 5800, Helmet- and Head-Mounted Displays X: Technologies and Applications
KEYWORDS: Defense and security, Goggles, Light sources, Visualization, Night vision, Light sources and illumination, Modulation transfer functions, Psychophysics, Night vision goggles, Standards development
Several methodologies have been used to determine resolution acuity through Night Vision Goggles. The present study compared NVG acuity estimates derived from the Hoffman ANV-126 and a standard psychophysical grating acuity task. For the grating acuity task, observers were required to discriminate between horizontal and vertical gratings according to a method of constant stimuli. Psychometric functions were generated from the performance data, and acuity thresholds were interpolated at a performance level of 70% correct. Acuity estimates were established at three different illumination levels (0.06-5X10-4 lux) for both procedures. These estimates were then converted to an equivalent Snellen value. The data indicate that grating acuity estimates were consistently better (i.e. lower scores) than acuity measures obtained from the Hoffman ANV-126. Furthermore significant differences in estimated acuity were observed using different tube technologies. In keeping with previous acuity investigations, although the Hoffman ANV-126 provides a rapid operational assessment of tube acuity, it is suggested that more rigorous psychophysical procedures such as the grating task described here be used to assess the real behavioural resolution of tube technologies.
When a bright light source is viewed through Night Vision Goggles (NVG), the image of the source can appear enveloped in a “halo” that is much larger than the “weak-signal” point spread function of the NVG. The halo phenomenon was investigated in order to produce an accurate model of NVG performance for use in psychophysical experiments. Halos were created and measured under controlled laboratory conditions using representative Generation III NVGs. To quantitatively measure halo characteristics, the NVG eyepiece was replaced by a CMOS imager. Halo size and intensity were determined from camera images as functions of point-source intensity and ambient scene illumination. Halo images were captured over a wide range of source radiances (7 orders of magnitude) and then processed with standard analysis tools to yield spot characteristics. The spot characteristics were analyzed to verify our proposed parametric model of NVG halo event formation. The model considered the potential effects of many subsystems of the NVG in the generation of halo: objective lens, photocathode, image intensifier, fluorescent screen and image guide. A description of the halo effects and the model parameters are contained in this work, along with a qualitative rationale for some of the parameter choices.
The influence of Night Vision Goggle-produced noise on the perception of motion-defined form was investigated using synthetic imagery and standard psychophysical procedures. Synthetic image sequences incorporating synthetic noise were generated using a software model developed by our research group. This model is based on the physical properties of the Aviator Night Vision Imaging System (ANVIS-9) image intensification tube. The image sequences either depicted a target that moved at a different speed than the background, or only depicted the background. For each trial, subjects were shown a pair of image sequences and required to indicate which sequence contained the target stimulus. We tested subjects at a series of target speeds at several realistic noise levels resulting from varying simulated illumination. The results showed that subjects had increased difficulty detecting the target with increased noise levels, particularly at slower target speeds. This study suggests that the capacity to detect motion-defined form is degraded at low levels of illumination. Our findings are consistent with anecdotal reports of impaired motion perception in NVGs. Perception of motion-defined form is important in operational tasks such as search and rescue and camouflage breaking. These degradations in performance should be considered in operational planning.
Night vision devices are important tools that extend the operational capability of military and civilian flight operations. Although these devices enhance some aspects of night vision, they distort or degrade other aspects. Scintillation of the NVG signal at low light levels is one of the parameters that may affect pilot performance. We have developed a parametric model of NVG image scintillation. Measurements were taken of the output of a representative NVG at low light levels to validate the model and refine the values of the embedded parameters. A simple test environment was created using a photomultiplier and an oscilloscope. The model was used to create sequences of simulated NVG imagery that were characterized numerically and compared with measured NVG signals. The sequences of imagery are intended for use in laboratory experiments on depth and motion-in-depth perception.