Synthetic vision combines GPS navigation system accuracy with digitized color displays depicting terrain and surface features on an intuitively presented 3D, flat-panel display. Several vendors have demonstrated the systems for safety and tactical enhancement. I see this technology as a remarkable and flexible leap for military and civil helicopter operations.
The first key advantage to synthetic vision is safety enhancement through visual reference to obstacles and terrain. To some it may seem more like a video game than aviating. But to those participating in the FAA’s Capstone experiment in Alaska, this portion of the Safe Flight 21 program allowed pilots to navigate below or in instrument meteorological conditions between mountainous terrain using a 3D “fly-through” map. The image is produced by combining a database called Digitized Terrain Elevation Data (DTED) in resolution levels from 0-5. The lowest resolution is 1 km, and the greatest is about 1 m. Synthetic vision offers aviators a perspective-rendered image of terrain relative to their position, altitude, attitude and heading. It doesn’t take a rocket scientist to see the safety benefit of developing a visual system for countering loss of visual cues in helicopters and airplanes using synthetic vision.
A second advantage is tactical enhancement for military ops. Today, only helicopters with terrain-following, terrain-avoidance radar can fly all weather at tactical altitudes. One can clearly see the advantage of flying with visual reference or autopilot link to intuitively projected terrain data. It unlocks the IMC low-altitude realm to many military operations. It also reduces your susceptibility. If you can get in enemy territory in lousy weather at tactical altitudes without having to transmit terrain-following radar signals, mission success dramatically increases because the enemy’s ability to detect and engage you decreases. Serious hurdles remain, though, to ensure flight safety in that tactical realm, not the least of which is avoiding man-made obstacles and ensuring an accurate altitude reference.
To fully understand the concept, one needs to understand the fundamentals. Most of Earth is mapped to Level 1 DTED (about 100 m). Level 2 is augmented by space-based synthetic aperture radar data to map the surface to 30-m resolution. Follow-on efforts have digitized large portions of the planet to tighter resolution, as small as 1 m in some areas.
Digital data by itself, though, doesn’t paint a very accurate view of the world. It’s all one color and doesn’t differentiate between water, dry lake beds, forests or meadows. Combining map, aerial and satellite images into an image of terrain is the tricky part. Some rudimentary military synthetic systems stretch map details over the terrain relief—words, lines, and all. The art of this science is blending the current map data with current,properly rendered imagery to give a composite image that closely mimics reality and provides essential mapping information. A tricky part is presenting that data with enough detail to allow low-altitude ops in which you’re not just flying over a brown, featureless blob representing land. Pilots must be able to sense closure and relative ground speed at low altitudes. In the absence of detailed features, programmers substitute wire frame over the terrain to allow better discernment and ground-passage detection.
The last great improvement is the inclusion of “highway-in-the-sky” boxes that can depict complex flight paths for instrument approaches or a tactically sound means to penetrate enemy airspace and avoid threats.
The astute reader will be thinking ahead to blending other applications with this awesome 3D tool. TCAS, ADS-B, Mode S and other FAA systems could easily be brought into the picture to display traffic in real time and build pilot-warning systems based on flight-path vector toward factor traffic. Military users can add tactical datalink tracks, radar contacts and threats received from national collection systems to avoid threats, engage targets or recovery personnel with greater flexibility and survivability.
The system requirements for implementing such technology are complex. You need a very powerful mission-processing computer than might be resident in a smart display or a separate, federated computer, a data bus with broadband capacity and speeds and a highly accurate navigation source with redundant internal accuracy checks. This system will require augmentation by differential GPS or Kalman-filtered 3D INS solutions to provide an accurate vertical altitude sufficient for ground avoidance. The displays will have to be daylight readable and NVG-compatible.
A side benefit of this capability is embedded recording. Instructors can easily imagine perfect maneuver reconstruction when we play back the 3D synthetic-vision video.
Safety, tactical advantage, and enhanced learning will all result from this technological innovation. We’ll have to train pilots to frequently crosscheck outside and avoid the “face-magnet” that this technology will invariably create in the cockpit.
The views expressed are the author’s and not an official position of the U.S. Air Force. This article has been approved for release by USAF Air Warfare Center Public Affairs.
Lt. Col. Steve Colby is commander of the USAF 34th Weapons Sqdn., based at Nellis AFB, Nev., which trains combat search-and-rescue helicopter instructor pilots. He can be reached at firstname.lastname@example.org.