Twenty-first century demands on Top Gun pilots are so great that the relatively narrow field-of-view (FOV) of Head-Up Displays (HUD), approximately 20° in a fixed direction, is far too limiting and confining for all the tactical infor ation that is needed to be displayed for them to make split-second decisions based on sound judgement. This inadequacy has led, in part, to the development of Helmet-Mounted Displays (HMD), and thence, Helmet Integrated Systems (HIS). This paper gives the highlights from the patent description of a HIS that dates back to World War I, and which is a forerunner of the concept of those being developed today.

The design of an optical system for a helmet mounted display (HMD) is particularly demanding since the weight and center of gravity of the display is always critical. When major requirements include the ability to see through the display and to shape the package to wrap around the human head, the optical design becomes a challenge. Proven HMD optical design approaches and their relative merits are discussed.

Honeywell has developed a new helmet mounted display (HMD) with a 60° field of view (FOV) by using a unique Tilted Cat (Catadioptric) Combiner. The Tilted Cat display concept allows a wide FOV display to be designed: with a 3:1 display brightness improvement over the conventional folded catadioptric approach; provides a similar improvement in combiner see through transmissions; and only requires a small tilt on the optically powered combiner which minimizes the complexity of the optics. Large FOV HMD's with see through capability require tilted optically powered surfaces with complex optical systems for the display projection and relay. The optical performance of a tilted powered element becomes more asymetric as the tilt increases, and to maintain a resultant well resolved symmetric display image, additional non-symmetric, tilted, decentered lens elements are required. The Tilted Cat combiner permitted a practical display optical system to be defined for a 60° FOV. The high resolution performance levels of the smaller FOV displays was obtained, with the resolution limited only by the CRT's resolution. A summary of the design considerations, the development of, and the demonstrated performance data for the 60° Tilted Cat HMD will be presented.

Human engineering criteria applicable to the design of helmet mounted displays for use with night vision sensors, such as forward looking infra-red (FLIR) or low light level television (LLTV), are stated and reviewed. Systems requirements are presented which call for pilot operation at night that is as equivalent as practicable to flight under normal daytime visual rules. Requirements are developed that utilize head motion coupled to sensor movement to achieve the semblance of daytime pilotage while conducting operations at night under the cover of deep darkness. At the outset, salient factors are identified and prioritized which are applied to further design tradeoffs leading to helmet mounted visor displays. The prime design objectives being operational suitability, acceptability by the pilot community, reduced crew training requirements and minimal logistics support. In conclusion, alternate design configurations, computer analyses, operating experience, and pilot reaction are cited. Items to be addressed include: overall head supported weight, center-of-gravity, and other ergonomic factors affecting pilot acceptance: such as: comfort, eye-relief, total and instantaneous field of view, full or partial overlap of left-eye and right-eye fields of coverage, and head movement-to-sensor servo response. In addition, items of interest to the operating command: such as: training (ease or difficulty), maintenance of proficiency, and ease of viewing, will be discussed in light of data and operating experience from recently conducted flight trials. Finally, compatibility with nuclear biological and chemical (NBC) defense equipment and requirements, and laser eye protection will be discussed.

Visually Coupled Systems (VCS) involve the integration of Helmet Trackers, Helmet Displays, Helmets, Sensors, Weapons and Vehicles. A description of a VCS, its components, interfaces, and features will be described and a typical system concept with its functional features and performance is presented.

Helmet mounted displays (HMD) and auto-ground weapons delivery are as integral to attack rotorcraft today as bread is to a sandwich. Mission and system requirements have been studied extensively and design data available includes engineering analysis simulation studies flight testing, and combat results. However, very little design data, is available to establish HMD specifications for the emerging attack rotorcraft air-to-air mission requirements. Even cursory analysis of the air-to-air mission indicates several areas which differ from the air- missions studied in the past and these differences impact HMD and overall system requirements. The primary se of this paper is to examine the counterair mission for future attack rotors-raft and the implications for crew station design requirements, specifically regarding Heyes out', display and control technologies. The findings of research programs are discussed.

Digital image processing provides a means to manipulate an image and presents a user with a variety of display formats that are not available in the analog image processing environment. When performed in real time and presented on a Helmet Mounted Display, system capability and flexibility are greatly enhanced. The information content of a display can be increased by the addition of real time insets and static windows from secondary sensor sources, near real time 3-D imaging from a single sensor can be achieved, graphical information can be added, and enhancement techniques can be employed. Such increased functionality is generating a considerable amount of interest in the military and commercial markets. This paper discusses some of these image processing techniques and their applications.

The Visual Pisplay Research Tool includes a helmet mounted projector for the display of flight simulation Area-of-Interest imagery on a 10 foot radius dome. The imagery is transmitted to the helmet using two coherent fibre optic ribbons. Some improvements have been made to the fibre optic system and to the helmet fit. The imagery is head and eye slaved and the concepts for image positioning and stabilisation are described.

A two-channel Photography Based Image Generator system was developed to drive the Helmet Mounted Laser Projector at the Naval Training System Center at Orlando, Florida. This projector is a two-channel system that displays a wide field-of-view color image with a high-resolution inset to efficiently match the pilot's visual capability. The image generator is a derivative of the LTV-developed visual system installed in the A-7E Weapon System Trainer at NAS Cecil Field. The Photography Based Image Generator is based on patented LTV technology for high resolution, multi-channel, real world visual simulation. Special provisions were developed for driving the NTSC-developed and patented Helmet Mounted Laser Projector. These include a special 1023-line raster format, an electronic image blending technique, spherical lens mapping for dome projection, a special computer interface for head/eye tracking and flight parameters, special software, and a number of data bases. Good gaze angle tracking is critical to the use of the NTSC projector in a flight simulation environment. The Photography Based Image Generator provides superior dynamic response by performing a relatively simple perspective transformation on stored, high-detail photography instead of generating this detail by "brute force" computer image generation methods. With this approach, high detail can be displayed and updated at the television field rate (60 Hz).

The routine extravehicular activity (EVA) performed from the U.S. Space Station Freedom will require the astronaut to access large amounts of information during the EVA, especially for intensive EVA scenarios such as satellite servicing and emergency or contingent operations. As a result, NASA is presently designing a helmet mounted display (HMD) into the Freedom Station extravehicular mobility unit (EMU) to aid the EVA astronaut. The HMD allows the astronaut to view a virtual image behind a transparent combiner located conveniently above his or her primary field of view (FOV). This HMD system can be voice-driven for "hands-free" operation. NASA is currently exploring four HMD approaches. Two designs utilize cathode ray tubes (CRT's), while the other two use backlit liquid crystal displays (LCD's). Furthermore, two of these designs use purely conventional optics, while the other two employ conventional and holographic optics. A discussion of these designs and some key design issues, such as image source, FOV, exit pupil versus non-pupil-forming systems, monocular versus binocular and biocular viewing, degree of image overlap, and the use of holographic optical elements (HOE's), will be provided in this paper.

This paper presents a simple, inexpensive design of a helmet-mounted color display system. The sys-tem can be mounted on a variety of helmets, including a bicycle helmet. Color LCD displays are used. The optical decisions are discussed as well as limitations of the system. The entire helmet-mounted system cost about $1000 to build using off the shelf, readily available hardware, with the exception of the Polhemus tracking device. Issues of depth perception are discussed. Predictive tracking is implemented using a simple Kalman filter.

The Visual Display Research Tool (VDRT) is a visual research test bed designed for the evaluation of the feasibility of an eye-slaved area-of-interest display that features a helmet-mounted laser projector. The VDRT, located at the Navy's Visual Technology Research Simulator, has been evaluated by experienced Navy pilots and found to be a feasible solution to satisfying the demanding requirements for a flight simulator with a very large field-of-view and high scene fidelity.

The Fiber Optic Helmet Mounted Display (FOHMD) developed by CAE for the US Air Force Human Resources Laboratory (AFHRL), requires very large format, coherant fiber optic cables. These cables must support the FOHMD's demanding modulation transfer function (MTF) requirements in full color and be flexible, durable, lightweight, and up to six feet long. These requirements have so constrained glass technology that conventional approaches are not capable of delivering the requisite performance. The cables currently used on FOHMD systems have alternating layers of inactive material to buffer linear arrays of multifibers so that a lighter weight 25 by 19 mm end size is achieved with 5 micron core size individual fibers. This skip-layer, multifiber approach delivers reasonable performance when using spectral multiplexing across the inactive layers. However, residual fixed pattern noise, broken multifibers, and inadequate resolution have reduced system performance. Because of the critical influence of the fiber optic cables on overall system performance, an alternative, but riskier process, is being explored. Several smaller experimental cables have been assembled using leachable, fused, multifibers arrayed in a hexagonal pattern. The inconspicuous mating of hexagonal elements should be possible now because of an order of magnitude improvement in cable drawing technology. Fused/leached fiber optic cables have the potential to provide image transmission capability equal to ten channels of the best available computer image generators. When coupled with chromatic enhancement to mask fixed pattern and broken fiber noise, the resulting MTF of the FOHMD optics would deliver a resolution equal to 1.5 arc minutes per pixel.

To achieve the full potential of an area-of-interest (A0I) display requires that a high resolution area be accurately aligned with the direction of gaze. Two methods of eye position measurement with the Fiber Optic Helmet Mounted Display (FOHMD) have been developed and are described. This paper describes requirements necessary for successful eye tracking in aircraft simulators and introduces two approaches to monitoring eye position. In order to measure eye position over a wide field of view with sufficient accuracy, the oculometer must be able to measure various types of eye movements and also provide sufficient information to distinguish between eye movements and associated artifacts such as eye blinks and any anomalies introduced by spurious reflections or movement of the oculometer optics relative to the eye. In addition, the device must take into account variations in pupil size caused by changes in scene brightness and distinguish between pupil image displacements caused by actual eye movements or helmet slip. Under development are two oculometers that monitor both the center of the pupillary image and the corneal reflection and which possess both high temporal and spatial resolution.

Helmet mounted displays provide required field of regard, out of the cockpit visual imagery for tactical training while maintaining acceptable luminance and resolution levels. An important consideration for visual system designers is the horizontal and vertical dimensions of the instantaneous field of view. This study investigated the effect of various instantaneous field of view sizes on the performance of low level flight and 30 degree manual dive bomb tasks. An in-simulator transfer of training design allowed pilots to be trained in an instantaneous field of view condition and transferred to a wide FOV condition for testing. The selected instantaneous field of view sizes cover the range of current and proposed helmet mounted displays. The field of view sizes used were 127° H x 67° V, 140° H x 80° V, 160° H x 80° V, and 180° H x 80° V. The 300° H x 150° V size provided a full field of view control condition. An A-10 dodecahedron simulator configured with a color light valve display, computer generated imagery, and a Polhemus magnetic head tracker provided the cockpit and display apparatus. The Polhemus magnetic head tracker allowed the electronically masked field of view sizes to be moved on the seven window display of the dodecahedron. The dependent measures were: 1) Number of trials to reach criterion for low level flight tasks and dive bombs, 2) Performance measures of the low level flight route, 3) Performance measures of the dive bombing task, and 4) Subjective questionnaire data. Thirty male instructor pilots from Williams AFB, Arizona served as subjects for the study. The results revealed significant field of view effects for the number of trials required to reach criterion in the two smallest FOV conditions for right 180° turns and dive bomb training. The data also revealed pilots performed closer to the desired pitch angle for all but the two smallest conditions. The questionnaire data revealed that pilots felt their performance was degraded and they relied more on information from their instruments in the smaller field of view conditions. The conclusions of this study are that for tasks requiring close course adherence to a desired flight profile a minimum of 160° H X 80° V instantaneous field of view should be used for training. Future investigations into the instantaneous field of view size will be conducted to validate the results on other tactical tasks.

Helmet mounted sights and displays are becoming basic requirements for new aircraft designs, upgrade programs, special mission applications and simulators. The common objective in all these efforts is to increase the mission effectiveness and survivability of the ground/air/space vehicle crew. This presentation will focus on the human integration of the helmet, display and sight subsystem functions to meet this goal. The specific intent of this information will be to impart a higher level of sensitivity to the importance of helmet subsystem functionality as it applies to the interrelated issues of protection, comfort, pilot interface, aircraft interface and supportability. Design and field experiences relative to current helmet mounted sight/display (HMS/D) production and development programs will be presented. Emphasis will be placed on the evolution of specific helmet subsystems based on performance specifications, mission requirements analysis, user evaluation and the subsequent but inevitable tradeoff analysis. The performance potential of any HMS/D will ultimately be judged by the physical interface to the user. When a piecemeal, one-display-fits-all approach is taken, the results can be both ineffective and hazardous. When a thorough, functionally integrated approach is applied to the physical interaction of an HMS/D application, the vehicle crew capability will improve dramatically. Many fixed and rotary wing programs as well as land vehicle demonstrations have conclusively demonstrated this over the past twenty years. This can be safely achieved without compromising the current base line crew comfort and crew-to-vehicle interface.

Seventeen subjects were presented with stationary targets at random locations in an area 120 left and right and 90 deg upwards from straight ahead. Targets would change shape to indicate that they were threats. Using a head-coupled simulator with 5 different sized fields-of-view (FOVS), subjects had to search for the targets, monitor them for changes in shape, and shoot them. Occasionally, targets which had not changed shape would disappear and subjects had to indicate their last location. There were 9 target conditions which varied in complexity due to the number of targets presented, the number of threats, or the number of targets to be replaced. Decreasing the size of the FOV produced a significant decrement in the percentage of targets hit and a significant increase in the time for which the targets threatened the subjects. In addition, there were significant effects caused by target condition and significant interactions between these two main effects. The data suggest that the effect of FOV size was dependent on task difficulty. An easy task required a 20 deg FOV, whereas a more demanding task required a 60 deg FOV. Target replacement error was unaffected by FOV size, a finding that is consistent with an earlier experiment and which supports the hypothesis thit once the information is acquired, the size of the FOV does not affect its recall.

Helmet mounted displays have been advocated for use in high performance aircraft for several years. One such system uses a magnetic sensor embedded in a helmet to detect head movement and presents information tailored to the current head position on the helmet visor. A Helmet-Mounted Display and Sight (HMDS) system of this type, designed and developed by the Kaiser Electronics Company, was evaluated in piloted simulation at the McDonnell Aircraft Company in April and May of 1987. These studies were sponsored by the Human Engineering Division of The Armstrong Aeromedical Research Laboratory under their Vista Saber program. For these studies, four USAF pilots evaluated the HMDS in one hundred simulated air combat engagements. Approximately half the engagements were conducted using the HMDS and half with the display turned off. The simulated engagements were chosen to be representative of major types of Air Force missions and included air combat within as well as outside visual contact with the threat. These engagements were conducted against both armed and computer-controlled threats. The tactical utility of HMDS was evaluated using data collected during these simulated engagements. The data collected included subjective pilot workload data; performance data taken to indicate changes in weapons employment, sensor usage and mission success; and pilot comments. This paper will describe these tests and discuss the results obtained.

Ocular vergence and visual-accommodation data were collected. in a preliminary investigation involving simulated monocular and binocular helmet-mounted display (HMD) configurations with varying scenic backgrounds and attentional instructions. A binocular eyetracking system was used to objectively measure vergence and accommodation. Photographic slides aligned and positioned at optical infinity were used to simulate HMD symbology and out-of-the-cockpit scenery. The accuracy of ocular vergence and the relative distance of visual accommodation were affected by the HMD configuration (binocular, monocular, one-eye-occluded), the content of the scenic background (clouds or mountains), the focus of attention (symbology or background), and the ocular characteristics of the observer (distance of the dark-vergence and -focus).

This unclassified presentation discusses in detail the tactical applications of current technology helmet mounted display (HMD) systems in fighter aircraft such as the F-15 and F-16. Emphasis will be on potential uses of the system from an operator's viewpoint, with discussions involving the types of information desired by the pilot, basic human factors requirements, and the interfaces of an HMD into other on-board systems. The uses of a stroke symbology system are exclusively discussed because it is sensor-independent and has potential applications in most tactical aircraft. This paper is divided into three major operational sections: air-to-air, air-to-ground, and defense suppression. Each operational area is briefly outlined, and a generic profile of current capabilities is developed. The increased capabilities provided by an HMD system are discussed, as well as the requirements for an optimum system that interfaces with a digital intra/inter-flight data link and an on-board digital threat warning system. Based upon the criteria developed in the operational discussions, this paper lists a compendium of basic requirements for designers of operational HMD systems and outlines the merits and liabilities of each requirement.

Recent requirements have generated a demand for a computer model that can quickly produce spectral transmission curves and calculate the apparent contrast for night vision devices when viewing a target against a specified background. Since an operator might be looking through several optical elements that would act as filters it was necessary to have a capability to include multiple absorption filters. The contrast model is a Lotus 1-2-3 worksheet that retrieves the necessary data, calculates a relative intensity for both the target and the backbackground, spectrally displays these, then calculates the contrast. The target and background relative spectral intensity curves are then displayed on the screen allowing a quick, subjective analysis. The model will operate on virtually any MS-DOS computer. Each scenario is entered, processed and the relative spectral intensities and contrast calculated in just a few minutes, allowing the rapid analysis of many different scenarios in a short period of time.

Night imaging systems based on image intensification (I²) tubes are a major factor in the night operation capability of U.S. Army rotary-wing aircraft. A major problem associated with the use of these systems is the detrimental effect caused by internal cockpit lighting. Instrument lamps, caution lamps, utility lights, and other light sources inside the cockpit activate the bright source protection control circuits of the intensification tubes, thereby reducing their sensitivity to external natural and artificial illumination. In 1986, a Tri-Service specification, MIL-L-85762, "Lighting, aircraft, interior, night vision imaging system compatible," was adopted to resolve the cockpit lighting problems. MIL-L-85762 defines the measurement instrumentation and techniques required to certify lighting components as "ANVIS compatible." The specification does not address compatibility problems associated with AN/PVS-5 usage. Ongoing efforts related to MIL-L-85762 include characterization of lighting incompatibilities in current U.S. Army aircraft, implementation of programs to modify the lighting in incompatible cockpits, and certification of proposed lighting components for future aircraft systems. Additional work has been done to provide "near compatible" solutions to lighting problems associated with the use of AN/PVS-5 systems.

U.S. Army aviators use the AN/PVS-5 Night Vision Goggles (NVG) with a modified faceplate which enables wearing of corrective spectacles, when required. The next generation NVGs, the Aviator Night Vision Imaging System (ANVIS), permit spectacle wear by design. With only glass lenses available to the aviator requiring optical correction, there is a potential for eye injury from broken glass should the goggles be displaced accidentally. This paper discusses studies conducted at the U.S. Army Aeromedical Research Laboratory, Fort Rucker, Alabama to: (1) compare the impact resistance of glass, CR-39 (plastic), and polycarbonate lenses to simulated NVG tubes, (2) establish the approximate forces necessary to cause glass lens breakage by displaced NVG tubes, and (3) determine the performance of polycarbonate lenses in the aviation environment. Results demonstrate the significant improvement in impact-resistance afforded by polycarbonate ophthalmic lenses, verify the relatively low forces necessary to cause NVG displacement and subsequent glass lens breakage, and establish the feasibility of prescribing polycarbonate lenses for use by aviation personnel.

A theoretical model for characterizing the dynamic response of an electro-optical imaging system is developed. The model relates the spatial frequency degradations of an image display with the phosphor characteristics as well as with the relative velocity with which the object moves away from the sensor.

The performance of imaging systems is analyzed in terms of static and dynamic parameters. In particular, the degradation of image quality of electro-optical displays, caused by the relative motions between the target and the sensor and as predicted by the dynamic MTF and the temporal characteristics of the display, is analyzed. It is shown that the dynamic MTF of the imaging systems is primarily responsible for the smearing in the degraded images. Accordingly, real-time techniques are proposed for the restoration of motion-degraded displays.