Ananth K. Vadlamani

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

Improved downward-looking terrain database integrity monitor and terrain navigation

Terrain database integrity monitors and terrain referenced navigation systems are both based on performing a comparison between stored terrain elevation data and data obtained from airborne sensors such as radar altimeters, inertial measurement units (IMUs), Global Positioning System (GPS) receivers etc. The concept of consistency checking as used for the integrity monitor function originated from terrain referenced navigation systems. This paper discusses the extension to a previously proposed method of improving the performance of a spatial integrity monitor for terrain elevation databases. Furthermore, this paper discusses an improvement of the terrain-referenced aircraft position estimation for aircraft navigation using only the information from downward-looking sensors, GPS and the terrain databases, and not the information from the IMU. Horizontal failures have been characterized based on the sensed terrain information. Kalman filter methods have been designed to achieve the integrity monitor and terrain navigation performance improvements. The performance of the proposed position estimator and integrity monitor is evaluated using flight test data from NASAs flight trials at Eagle/Vail (EGE), CO and Ohio Universitys flight trials at Albany (KUNI), OH, Asheville (AVL), NC, and Juneau (JNU), AK.

Dual Airborne Laser Scanners Aided Inertial for Improved Autonomous Navigation

A dead-reckoning terrain referenced navigation (TRN) system is presented that uses two airborne laser scanners (ALS) to aid an inertial navigation system (INS). The system uses aircraft autonomous sensors and is capable of performing the dual functions of mapping and navigation simultaneously. The proposed system can potentially serve as a backup to the Global Positioning System (GPS), increase the robustness of GPS or it can be used to coast for extended periods of time. Although the system has elements of a conventional TRN system, it does not require a terrain database since its in-flight mapping capability generates the terrain data for navigation. Hence, the system can be used in both non-GPS as well as unknown terrain environments. It is shown that the navigation system is dead-reckoning in nature since errors accumulate over time, unless the system can be reset periodically by the availability of geo-referenced terrain data or a position estimate from another navaid. Results of the algorithm using a combination of flight trajectory data and synthesized ALS data are presented.

Aerial vehicle navigation over unknown terrain environments using inertial measurements and dual airborne laser scanners or flash ladar

A precise navigation system for uninhabited or inhabited aerial vehicles is discussed in this paper. The navigational capability of an aerial vehicle must be robust and not easily influenced by external factors. Nowadays, many navigation systems rely somehow on the Global Positioning System (GPS), wherein the GPS signals may be rendered unusable due to unintentional interference caused by atmospheric effects, interference from communication equipment, as well as intentional jamming. The navigation method discussed in this paper integrates measurements from an Inertial Measurement Unit (IMU) with measurements from either two airborne laser scanners (ALS) or an airborne Flash LADAR (AFL) to provide autonomous navigational capability and a reliable alternative to GPS. The proposed system has applications in unknown or partially known terrain environments or it may also be used for autonomous landing systems in Lunar or Martian environments. Two approaches are described in this paper, one approach uses Dual Airborne Laser Scanners (DALS) (one pointing forward, the other pointing aft) and the other approach uses an AFL. Advantages and disadvantages of both approaches are discussed. The proposed navigation system uses strapdown IMU measurements to estimate the aerial vehicle position and attitude and to geo-reference the laser sensor data. It then uses the maps created from both the fore and aftpointing scanning LADARS or the consecutive Flash LADAR range-images to estimate systematic IMU errors such as position and velocity drifts. The proposed navigation algorithm is evaluated using flight test data from Ohio Universitys DC3 aircraft and synthesized ALS and AFL measurements. Initial results are observed to achieve meter level accuracies in the systems position drift performance.

Preliminary design and analysis of a lidar based obstacle detection system

This paper outlines the use of a high-resolution laser range scanner to detect terrain features and obstacles and the development of a test bed for the obstacle and terrain feature detection system. Results from tests conducted at Ohio University and simulations from data collected during flight tests in the vicinity of Braxton County Airport (K481), WV are presented.

Synthesis of Airborne Laser Measurements for Navigation Algorithms

Airborne laser scanners are widely used for remote sensing and mapping and they are recently being applied to navigation of aerial and ground vehicles. Evaluation of new navigation algorithms in the presence of varying platform, sensor, and environment parameters requires high-fidelity measurement models of the airborne laser sensor. We present a procedure for the synthesis of airborne laser scanner measurements using aircraft flight trajectory, the scanners mechanical and optical characteristics and the target environment model.

Flight Test Evaluation of Various Terrain Referenced Navigation Techniques for Aircraft Approach Guidance

This paper discusses the evaluation of two sets of terrain referenced navigators (TRN). The first set of TRN systems use radar altimeter measurements, baro-altimeter measurements, and inertial navigation system (INS) measurements, whereas, the second set uses an INS integrated with terrain observations from an Airborne Laser Scanner (ALS). The former set includes techniques such as Terrain Contour Matching (TERCOM), Sandia Inertial Terrain-Aided Navigation (SITAN), and Parallel SITAN. The latter set includes the Terrain Aided Inertial Navigator (TERRAIN), a TRN system that has recently been designed and implemented at Ohio University. The performance of all the aforementioned TRN schemes are evaluated for precision approach and landing using sets of data from two actual flight tests: (a) with NASA Langleys B757 in Eagle-Vail, CO, (b) and with Ohio Universitys DC-3 in Braxton, WV. The flight test data is unique in the sense that several types of radar altimeter and ALS systems were flown and that terrain databases from various sources are available for these areas. Furthermore, the flight test data include both en- route and approach path segments. The paper addresses various aspects of the TRN systems when used with conventional civil commercial aircraft sensors. These aspects include the sensitivity to the systems to sensor accuracy and operational performance, database resolution.

Flight test and simulation results of an integrated dual airborne laser scanner and inertial navigator for UAV applications

This paper discusses an integrated dual airborne laser scanner (DALS)/inertial (INS) navigator for Unmanned Aerial Vehicles (UAV). The discussed navigator enables UAV operations over environments for which no a priori terrain data is available and trajectories for which loop closure is not a possibility. The system was designed, implemented and, in the absence of a UAV platform with enough capacity to carry the airborne laser scanner systems, flight tested onboard Ohio Universitys DC-3 aircraft over Athens, Ohio, USA. The proposed DALS/INS systems can be used as an alternative means of navigation in GPS-denied and unknown terrain environments. In these environments the usual navigation solution based on the integration of GPS and INS is no longer available. This paper addresses both a feedforward and a feedback coupled implementation of DALS/INS. Furthermore, both simulation results and actual DC-3 flight test results are shown.

Terrain Elevation Data Integrity Monitor and Referenced Navigation

Synthetic vision systems provide a synthesized view of the outside world to pilots on displaysintheflightdeck.Terraindatabasesonboardaircraftareusedasthesourceofterrain elevation information on synthetic vision system displays. Because the primary function of thesedisplaysistoimproveflightsafety,itisimperativethattheterraindatausedtogenerate the imagery conform to a high level of integrity. Otherwise, instead of preventing accidents, the terrain database would be cause of more. Hence, it is necessary to include an integrity monitor function that ensures the terrain data are consistent with the real world. In this paper, we revisit previously proposed concepts and present the development of a 3D spatial data integrity monitor. The framework is also extended to a terrain referenced navigation scheme such that both operations can be performed simultaneously. Presented furthermore is a Kalman filter design and its associated tradeoffs for improving the performance of the integrity monitor and navigation functions. The performance of the integrity monitor and position estimator for navigation is evaluated using flight test data collected in the vicinity of Braxton County airport in West Virginia.

Flight test results of loose integration of dual airborne laser scanners (DALS)/INS

Aircraft positioning and navigation capability much be robust to ensure continuity of operation. Such navigation information is largely provided by an inertial navigation system (INS), which is a self-contained autonomous system. INS is usually integrated with GPS measurements to improve its accuracy and a GPS/INS package is a common feature of most navigation systems. However, these systems suffer degraded performance in non-GPS environments; such as when GPS is denied due to interference or jamming, or when GPS is unavailable as in Lunar or Martian scenarios. In recent years, the challenge of navigating in non-GPS environments has generated much interest. With this same objective, we investigate the use of dual airborne laser scanners (DALS), integrated with an INS for navigation in non-GPS and unknown terrain environments. In this paper, we present a proof-of-concept demonstration of the DALS/INS autonomous navigation system with flighttest data, collected onboard Ohio Universitypsilas DC-3 aircraft over Athens, OH.