LIDAR Increases Aircraft Approach Precision

November 1, 2005 By: Jacob Campbell, Maarten Uijt de Haag

Ohio University researchers are testing a proof-of-concept precision-approach system that uses an airborne laser scanner in conjunction with a LIDAR terrain database — with a goal of safer landings

Students and professors at the Ohio University Avionics Engineering Center (AEC) recently had the opportunity to escape the classroom and participate in a flight test of their proof-of-concept terrain-referenced precision-approach guidance system. This flight test demonstrated for the first time that airborne laser scanners can guide an aircraft during landing in real time, with accuracies on the order of 1 meter. The system is based on estimating the aircraft's position by computing the best fit between airborne laser scanner data and a light detection and ranging (LIDAR)-generated terrain database.

Terrain-referenced navigation systems that compare sensed terrain with a known terrain database were first realized with the development of radar in World War II. Until recently, however, the performance characteristics of terrain-sensing radars and the limited level of detail and accuracy of terrain databases have restricted the reliability of such systems to tens of meters. Furthermore, their accuracy was dependent on the terrain traversed being relatively hilly. AEC's proof-of-concept guidance system demonstrates that positioning accuracies on the order of 1 meter are possible when using a high-accuracy, high-resolution LIDAR-generated database in conjunction with an airborne laser scanner.

Ohio University AEC's DC-3 flying laboratory.

Friendlier Flight. Ohio University has been researching aircraft navigation systems since the establishment of the AEC in 1963 by electrical engineering professor Dr. Richard McFarland. AEC has two missions: The first is to improve the safety and reliability of air transportation through application of new technology to aircraft navigation, guidance, communication, and control; the second is to provide high-quality education to the students who will advance the frontiers of aviation electronics. It is a unique facility for students and researchers due to the mix of basic theoretical research and the development and testing of new or improved electronic navigation systems. At the Ohio University Airport (KUNI) in Albany, Ohio, AEC operates a variety of aircraft to support its research. For the proof-of-concept approach guidance system, AEC used its DC-3 flying laboratory.

Positioning accuracies are achieved by using the technology developed to perform LIDAR mapping missions. LIDAR mapping technology is designed to create dense, accurate point-cloud models of the terrain and terrain features. The dense point clouds can be used to create terrain databases that have decimeter accuracy and 1-meter resolution or better. The high-accuracy, high-resolution terrain databases provide a spatially unique reference signal that is exploited by AEC's proof-of-concept approach guidance system in order to accurately estimate position.

The system is based on the TERrain Referenced Aided Inertial Navigator (TERRAIN) system developed at Ohio University. The multisensor TERRAIN system includes an airborne laser scanner, a navigation-grade inertial navigation system (INS), Wide Area Augmentation System (WAAS) GPS, and a LIDAR-generated terrain database (see Figure 1). Although it shares many of the same components, the TERRAIN system is fundamentally different in function from a LIDAR mapping system. LIDAR mapping systems are optimized to generate highly accurate spatial data that are used in products such as topographic or bathymetric maps. This optimization is achieved by postprocessing the airborne data, a method which conflicts with the TERRAIN system's goal to support real-time operation. Another difference in the TERRAIN system is the use ofa standalone (not GPS-aided) navigation-grade INS to provide attitude, instead of the tactical-gradeinertial measurement unit used in most LIDAR mapping systems.