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Synthetic Vision Systems (SVS) provide pilots with a virtual visual depiction of the external environment. When using SVS for aircraft precision approach guidance systems accurate positioning relative to the runway with a high level of integrity is required. Precision approach guidance systems in use today require ground-based electronic navigation components with at least one installation at each airport, and in many cases multiple installations to service approaches to all qualifying runways. A terrain-referenced approach guidance system is envisioned to provide precision guidance to an aircraft without the use of ground-based electronic navigation components installed at the airport. This autonomy makes it a good candidate for integration with an SVS. At the Ohio University Avionics Engineering Center (AEC), work has been underway in the development of such a terrain referenced navigation system. When used in conjunction with an Inertial Measurement Unit (IMU) and a high accuracy/resolution terrain database, this terrain referenced navigation system can provide navigation and guidance information to the pilot on a SVS or conventional instruments.
The terrain referenced navigation system, under development at AEC, operates on similar principles as other terrain
navigation systems: a ground sensing sensor (in this case an airborne laser scanner) gathers range measurements to the
terrain; this data is then matched in some fashion with an onboard terrain database to find the most likely position
solution and used to update an inertial sensor-based navigator. AEC's system design differs from today's common
terrain navigators in its use of a high resolution terrain database (~1 meter post spacing) in conjunction with an airborne
laser scanner which is capable of providing tens of thousands independent terrain elevation measurements per second
with centimeter-level accuracies. When combined with data from an inertial navigator the high resolution terrain
database and laser scanner system is capable of providing near meter-level horizontal and vertical position estimates.
Furthermore, the system under development capitalizes on 1) The position and integrity benefits provided by the Wide
Area Augmentation System (WAAS) to reduce the initial search space size and; 2) The availability of high
accuracy/resolution databases. This paper presents results from flight tests where the terrain reference navigator is used
to provide guidance cues for a precision approach.
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