Greg Craig

Detection of motion-defined form using night vision goggles

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.

Hybrid enhanced and synthetic vision system architecture for rotorcraft operations

The ability to conduct rotorcraft search and rescue (SAR) operations can be limited by environmental conditions that affect visibility. Poor visibility compromises transit to the search area, the search for the target, descent to the site and departure from the search area. In a collaborative program funded by the Canadian Department of National Defence, CAE and CMC Electronics designed, and together with the Flight Research Laboratory of the National Research Council of Canada integrated and flight-tested an enhanced and synthetic vision system (ESVS) to examine the potential of the concept for SAR operations. The key element of the ESVS was a wide field-of-view helmet-mounted display which provided a continuous field-of-regard over a large range of pilot head movements. The central portion of the display consisted of a head-slaved sensor image, which was fused with a larger computer generated image of the terrain. The combination of sensor and synthetic imagery into a hybrid system allows the accurate detection of obstacles with the sensor while the synthetic image provides a continuous high-quality image, regardless of environmental conditions. This paper presents the architecture and component technologies of the ESVS 2000 TD, as well as lessons learned and future applications for the hybrid approach.

Physical modeling and characterization of the halo phenomenon in night vision goggles

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.

Comparison of Three Night Vision Intensification Tube Technologies on Resolution Acuity: Results from Grating and Hoffman ANV-126 Tasks

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.

Night Vision Goggle External Lighting Effects

The National Research Council of Canada, Transport Canada and the Federal Aviation Administration examined external lighting and night vision goggle interaction by quantifying the effects of incompatible lighting on visual acuity and recording pilot comments. Four observers and three sets of lights were tested using Landolt ring visual acuity charts created for distances of 15.2, 30.5 and 45.7 m. NVG compatible external lights provided consistent acuity scores in a symmetrically lit visual field. Acuity scores varied greatly with incompatible lights that caused an asymmetric viewing field. Implications for civil NVG operations are discussed.

Flight Manoeuvre and Spin Characteristics of the Harvard 4: Application to Human Factors Flight Research

The rear cockpit of the Harvard Mk IV aeroplane of the NRC Flight Research Laboratory has been re-equipped with a ‘glass’ cockpit, consisting of an LCD flat panel display screen, which is used as a head-down (HD) primary flight display (PFD), together with a data acquisition system and an advanced inertial measurement unit, the integration of which was conducted at the NRC. The PFD has been configured with a number of attitude-direction indicator (ADI) displays and a flight research programme conducted into the suitability of the displays for aiding unusual attitude (UA) recoveries. The UA recovery research programme used a range of UA entry techniques, which stimulated the vestibular system axes diversely – some sub-perceptible angular rates, some high angular accelerations and rates, coupled with a range of gravitoinertial force (GIF) vector orientations, which stimulated the vestibular and otolith organs variously. The entry techniques used the manoeuvre capability of the Harvard to the maximum extent. The general manoeuvre characteristics of the Harvard in pitch and roll are noted and idiosyncratic characteristics discussed. Of particular interest is the limitation placed upon roll-rate controllability by the propensity of the tapered wing to suffer wingtip/aileron uppersurface flow separation, which results in aileron overbalance (hinge moment reversal) and loss of roll damping. However, this wing-stall characteristic could possibly be a contributory reason why the NRC Harvard could be sustained in a low-α spin mode (almost like a ‘suspended’ spin recovery). The low-α spin mode is high rotation, most noticeably high rollrate (≈200°s -1 ). The spin mode was identified during a spin research flight programme, and has potential application to the simulation of sustained high roll rate tactical manoeuvring and post-rotation transition to hypergravity, for research into the physiological factors involved in spatial disorientation events.

In-flight evaluation of a fiber optic helmet-mounted display

The National Research Council of Canada (NRC), in conjunction with the Canadian Department of National Defence (DND), is investigating the use of helmet-mounted displays (HMD) to improve pilot situational awareness in all-weather search and rescue helicopter operations. The National Research Council has installed a visually coupled HMD system in the NRC Bell 205 Airborne Simulator. Equipped with a full authority fly-by-wire control system, the Bell 205 has variable stability characteristics, which makes the airborne simulator the ideal platform for the integrated flight testing of HMDs in a simulated operational environment. This paper presents preliminary results from flight test of the NRC HMD. These results are in the form of numerical head tracker data, and subjective handling qualities ratings. Flight test results showed that the HMD degraded handling qualities due to reduced acuity, limited field-of-view, time delays in the sensor platform, and fatigue caused by excessive helmet inertia. Some evidence was found to support the hypothesis of an opto-kinetic cervical reflex whereby a pilot pitches and rolls his head in response to aircraft movements to maintain a level horizon in their field-of- view.

Light source halos in night vision goggles : Psychophysical assessments

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.

Theoretical issues relevant to helmet-mounted display attitude symbology

This paper discusses theoretical issues that are relevant to Helmet-Mounted Display (HMD) attitude direction indicator (ADI) design. An ADI shows the relationship between the aircraft wings and the horizon and pilots use it to determine aircraft attitude (pitch and roll). The ADI is used for maintaining an aircraft attitude, capturing a precise attitude and recovering from an unusual attitude. An attitude indicator is an essential instrument because it provides pilots with orientation information that they do not normally have in instrument flight conditions. Recent work suggests that humans orient themselves within a fixed world-reference frame. We will discuss the relationship between the reference frames used by the human orientation system, the reference frames implemented in existing ADIs, and the reference frames available in a helmet-mounted display. A head tracked HMD system allows a system designer to implement symbology in many reference frames including the head, aircraft, and world reference frames. Traditional head down attitude symbology may not be appropriate for HMD use, and it may conflict with the reference frame used by human orientation systems. Based on the authors review of ADIs and frames of reference, research topics are discussed that examine the role of HMD ADI symbology.

Effects of image intensifier halo on perceived layout

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.