Jacob Campbell

Terrain database integrity monitoring for synthetic vision systems

A real-time terrain database integrity monitor for synthetic vision systems (SVS) that are to be used in civil aviation is presented. SVS provides pilots with advanced display technology including terrain information as well as other information about the external environment such as obstacles and traffic. The use of SVS to support strategic and tactical decision-making and the compelling nature of the terrain depiction may require terrain database server certification at the essential and flight-critical levels. SVS and terrain database characteristics are discussed and a failure model is identified. Real-time integrity monitors are proposed that check the consistency between terrain profiles described by the database and terrain profiles that are sensed in flight by either a downward-looking (DWL) sensor or a forward-looking (FWL) season A DWL sensor scheme is discussed in detail and it is shown that this scheme can provide the necessary integrity required for an essential certification of a terrain database server.

Application of laser range scanner based terrain referenced navigation systems for aircraft guidance

This paper discusses the various aspects of using airborne laser scanners (ALS) in terrain referenced navigation (TRN) systems. The paper addresses the system performance of these new ALS-based systems and compares their performance to traditional terrain referenced navigation systems based on radar altimeter and baro-altimeter sensors. The TRN system comparison also includes an inertial measurement unit (IMU) error sensitivity analysis and a discussion on the requirements imposed on the information content in the terrain elevation database by the remote sensor. The paper will use flight test data collected with Ohio Universitys DC-3Flying Laboratory in Braxton, WV to evaluate the various methodologies and analyses

Feature extraction and separation in airborne laser scanner terrain integrity monitors

This paper describes the methodology and algorithms used in an implementation of a downward-looking airborne laser scanner (ALS) based terrain and feature integrity monitor. Using a high accuracy and high resolution ALS sensor, the described integrity monitor can first separate features from the terrain and then use the extracted feature data to detect and observe systematic and blunder errors in a terrain feature database. Two applications are envisioned for such a system - the first is to check the quality and update a terrain feature database and the second is as a real-time monitor on all aircraft which have systems that use terrain feature databases. Real-time terrain database integrity monitors have been studied at the Ohio University Avionics Engineering Center (AEC) for nearly 10 years. The feature integrity monitor is different from previous research performed at Ohio University in that it extracts specific features, such as buildings, roads, and towers, and performs a consistency check between these objects and a stored feature database. To perform the consistency check between the feature database and the ALS data a four-part building extraction algorithm is used. Once the high-frequency building shapes are extracted, they can be compared to the onboard feature database to determine changes and errors. The four-part building extraction algorithm described in this paper has the following characteristics: it works on non-uniformly spaced point-cloud data, it is designed for integrity monitoring rather than complete scene reconstruction, and the automatic feature extraction is not dependent on (but may use if available) a-priori feature shape information. This paper outlines the four-part building extraction algorithm and provides insight into its operation by applying the algorithms to ALS data collected on NASAs DC-8 Airborne Laboratory over Reno, Nevada in 2003.

A terrain database integrity monitor for synthetic vision systems

This paper discusses a terrain database integrity monitor for Synthetic Vision Systems (SVS) in Civil Aviation applications. SVS provide the pilots with advanced display technology containing terrain information as well as other information about the external environment such as obstacles and traffic. SVS will improve situational awareness and thereby reduce the likelihood of Controlled Flight Into Terrain (CFIT). Safe utilization of the SVS for strategic and tactical applications may require a terrain database integrity check. The discussed integrity monitor checks the consistency between the sensed terrain profile as computed from DGPS and radar altimeter data and the terrain profile as given by the terrain databases. A case study to verify the integrity monitors performance is presented based on data collected during flight-testing performed by NASA at Asheville, NC.

Assessment of radar altimeter performance when used for integrity monitoring in a synthetic vision system

Synthetic Vision Systems (SVS) are being developed to support a wide variety of operations. These operations include tactical or critical applications of the SVS. To enable certification of an SVS as a flight-critical system several requirements must be met with regards to accuracy, integrity, availability, and continuity. Ohio University has been developing a prototype SVS as part of NASAs aviation safety program that includes a real-time terrain database integrity monitor to guarantee the required integrity. Ohio Universitys integrity monitor provides a consistency check between a terrain database profile and a synthesized terrain profile. The synthesized terrain profile is generated from information from Global Positioning System (GPS) and a radar altimeter. This paper explores the radar altimeter performance for use in a SVS terrain database integrity monitor. This data will be used in this paper to assess the various radar altimeters. Data from two different radar altimeters and highly accurate photogrammetry digital elevation models (DEM) are used to evaluate the performance of the radar altimeters. The effects of the terrain variation underneath the aircraft and the radar altimeter antenna beamwidth on the performance of the radar altimeter are discussed.

An X-band radar terrain feature detection method for low-altitude SVS operations and calibration using lidar

To enable safe use of Synthetic Vision Systems at low altitudes, real-time range-to-terrain measurements may be required to ensure the integrity of terrain models stored in the system. This paper reviews and extends previous work describing the application of x-band radar to terrain model integrity monitoring. A method of terrain feature extraction and a transformation of the features to a common reference domain are proposed. Expected error distributions for the extracted features are required to establish appropriate thresholds whereby a consistency-checking function can trigger an alert. A calibration-based approach is presented that can be used to obtain these distributions. To verify the approach, NASAs DC-8 airborne science platform was used to collect data from two mapping sensors. An Airborne Laser Terrain Mapping (ALTM) sensor was installed in the cargo bay of the DC-8. After processing, the ALTM produced a reference terrain model with a vertical accuracy of less than one meter. Also installed was a commercial-off-the-shelf x-band radar in the nose radome of the DC-8. Although primarily designed to measure precipitation, the radar also provides estimates of terrain reflectivity at low altitudes. Using the ALTM data as the reference, errors in features extracted from the radar are estimated. A method to estimate errors in features extracted from the terrain model is also presented.

Integration of a synthetic vision system with airborne laser range scanner-based terrain referenced navigation for precision approach guidance

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. AECs system design differs from todays 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.