M. Uijt de Haag

Closed-Loop Sequential Signal Processing and Open-Loop Batch Processing Approaches for GNSS Receiver Design

Global navigation satellite system (GNSS) receiver design is considered in terms of closed-loop and open-loop receiver architectures that utilize sequential and batch processing techniques. The paper uses the Global Positioning System (GPS) as a case study to demonstrate that an open-loop approach that combines batch and sequential signal processing improves GNSS signal tracking characteristics as compared to the traditionally applied closed-loop sequential receiver design for a number of important application areas. Particularly, for flight test scenarios considered, it is demonstrated that open-loop batch/sequential processing improves the GPS tracking margin by 8 dB as compared to the closed-loop sequential tracking for the case of deep GPS/Inertial Navigation System (INS) integration mode that performs code and carrier phase tracking and data bit recovery.

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.

A shadow detection and extraction algorithm using digital elevation models and x¿band weather radar measurements

The aviation industry has been investigating the potential of synthetic and enhanced vision systems (SVS and EVS) to increase the situational awareness of pilots who are operating in low‐visibility weather conditions. Synthetic vision displays provide a real‐time depiction of a terrain model from the pilots perspective. To ensure the integrity of this terrain depiction, consistency checking using remote sensing of the terrain environment has been suggested. This requires the detection and extraction of terrain features from both the model and the sensor measurements. Further, the features must be represented in the same reference domain. Terrain shadowing occurs when areas are not in the line‐of‐sight of the observer. It is these shadowed regions and their morphological characteristics that are identified as the feature domain in which consistency can be assessed between two sources of terrain information. This paper describes an algorithm to extract shadow features from digital elevation models during flight to enable direct comparison with x‐band radar modus operandi. Results are presented using flight‐test data acquired from two platforms with different radar equipment. The proposed algorithm not only has application to the consistency‐checking problem, but also to terrain navigation, image fusion, and digital elevation model accuracy assessments.

Implementation of a Flash-LADAR aided inertial navigator

GPS aided inertial systems can provide high accuracy position and attitude information in many operational scenarios; however, their use is limited to environments where GPS signals are available. An alternative method can be based on the use of Flash-LADAR or other 3D imaging sensor data to navigate in the GPS-devoid environments or the integration of these 3D imaging sensors with an inertial measurement unit. Flash LADAR (laser radar) and 3D imaging technology consists of a laser or light transmission source that is being emitted over a relatively large aperture coupled with a focal plane array detector capable of creating an ldquoimagerdquo of the observed scene where each pixel not only has an associated intensity value but also an estimate of the range to the observed object. With the recent development of short-range low-cost (Lt

Evaluating the impact of sensor data uncertainty and maneuver uncertainty in a conflict probe

10 k) 3D imager technology, the use of such technology to aid a low-cost inertial measurement unit (IMU) has become practical and of great interest. Current low-cost 3D imager or Flash LADAR technology is capable of greater than 100 times 100 pixel resolution with 5 mm depth resolution at a 30 Hz frame rate. From this 3D range, features such as planar surfaces created by the walls, lines created where planes intersect, and points from the intersection of lines can be measured with high precision. In this paper we will focus the discussion on the 3D imager feature extraction performance aspects and lay the basis for the image and IMU-based feature association and integration architecture. Data from an indoor test will be utilized to illustrate some of the concepts explained in this paper..

Preliminary design and analysis of a lidar based obstacle detection system

A conflict probe estimates the future separation with other traffic, both for the current state of ownship and variations to this state, using assumptions on how traffic will maneuver. The separation margin between ownship and traffic used in the separation requirements accounts for i) sufficient spatial and temporal margin to restore separation in case it is lost and ii) uncertainty in the current and future position data. Uncertainty in the traffic state data can be attributed to sensor inaccuracies, datalink latency, limitations of the extrapolation models and pilot / automation actions that can not be taken into account in the extrapolation models. The goal of the research described in this paper is to use a priori and on-line sensor performance characteristics and knowledge regarding potential maneuvers of the other traffic to specify conflict probe and conflict resolution system parameters. As part of the approach to achieve this, a sensor simulation tool has been integrated with an experimental and configurable conflict probing implementation. This paper discusses the effects of uncertainty in traffic state data on conflict probing and the corresponding evasive maneuver strategy, based on simulation results for different sensor and probe settings and conflict geometries. Additionally, a demonstrator graphical user interface concept to provide information about the uncertainty and an integrated simulation setup are discussed.

Design and evaluation of taxi navigation displays [airports]

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.

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

The presentation of an electronic map of the airport relative to the position of ownship is regarded as a means to improve the safety and efficiency of surface operations. This paper discusses the design rationale behind a surface moving map display based on an analysis of the surface navigation task and the associated information requirements. It is illustrated how the various elements depicted in the display aim to support the pilot with information collection, integration and extrapolation. Implementation, testing and evaluation are briefly addressed.

Influence of oscillator variations on the observed frequency behavior in software-based navigation receivers

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.

The application of image analysis techniques to forward looking terrain database integrity monitoring

This letter discusses the effects of oscillator behavior such as phase and frequency offsets on the observed frequency behavior in software-based receivers. Frequency errors introduced by the front-end oscillators and sample clocks cause the observed frequency to differ from the actual frequency. Frequency errors directly affect the user velocity and position estimates in navigation receivers unless these errors are explicitly estimated and removed. This letter will show the derivation of a quantitative relationship between the observed frequency and the true frequency of the received signal in the presence of local oscillator and sample rate errors.