Head-Mounted Equipment [HMD/NVG/Glasses]

This category covers two types of head-mounted display: the Helmet Mounted Display (HMD) and Night Vision Goggle (NVG). A key distinction is that an NVG is a self-contained system whereas an HMD integrates with other systems of the platform supporting the user. An HMD provides functions similar to a Head Up Display but does so over a wide field of regard because the display turns with the user’s helmet. The simplest form of HMD is a Sight (such as that fitted to the Jaguar) which projects an LED reticle giving basic steering or weapon aiming data to one eye. More sophisticated systems are binocular and provide a full suite of symbology modes generated on twin CRT’s or, more recently, on solid state displays. In addition to this synthetic symbology the system can display a FLIR or LLTC video image from a steerable external sensor and there may even be head mounted IR Cameras as on the Eurofighter HMD. All these images can be programmed and overlaid. An accurate helmet tracking system is vital to ensure that the imagery presented is correct for the line of sight of the pilot. Since the helmet is now an integral part of the display system it is vital that it fits accurately and does not distort with high G manoeuvres or day-to-day handling. However the helmet must retain its basic role of protecting the pilot. Night Vision Goggles provide their user with a visible image of the night scene being viewed through them by amplifying the scene's luminance levels many times (>40,000 times). They do not work in zero light but faint starlight is sufficient. The image is produced on a screen and, since the device does not detect colour, this is a green P22 phosphor. Two such systems are used commonly joined to form a binocular system that may be fitted onto a clip on the user's protective helmet.