Showing papers on "Inertial navigation system published in 1991"

Application of Kalman filtering to the calibration and alignment of inertial navigation systems

Abstract: The development of Kalman filters for the calibration and alignment of complex inertial guidance systems is presented. The attitude error equation is augmented by gyro and accelerometer model parameters. The mechanization of the algorithm involves preprocessing the raw measurements to reduce the computational load. Results for simulated data show that preprocessing has very little effect on the performance of the filter. Other topics discussed include gyro and accelerometer models and a technique for generating parameter excitation trajectories. >

Integration of GPS and dead-reckoning navigation systems

Abstract: Recent developments of the second generation automotive navigation and route guidance systems have posed more restrictive requirements for vehicle positioning accuracy. Only after accurate current vehicle locations are available can appropriate maneuver instructions be generated from the route guidance algorithm. Dead-reckoning systems and GPS are two commonly used techniques for vehicle navigation systems. While both methods suffer from different drawbacks, superior performance can be obtained by combining these two techniques. In this paper we present a vehicle positioning system that integrates both the GPS and the dead-reckoning method. This system uses the GPS signals to adaptively calibrate the dead-reckoning sensors as well as to "rescue" the system from unexpected position errors. On the other hand, the dead-reckoning method, through the use of map-matching algorithm, provides feedbacks for calibrating the GPS position errors. Experimental results using the ZEXEL NavMate Navigation and Route Guidance System demonstrate the effectiveness of the integrated positioning system.

Apparatus and method for an aircraft navigation system having improved mission management and survivability capabilities

Abstract: An aircraft navigation system is disclosed for use in missions involving unfamiliar terrain and/or terrain having hostile forces. The navigation system includes an inertial navigation system, a map of the terrain with elevational information stored in a digitized format as function of location, a typical energy managed or narrow (radar or laser) beam altimeter, a display system, and a central processing unit for processing data according to preselected programs. The data processing system includes an operational mode (software program) for relating the continuing sequence of altimeter readings with the changing aircraft position on the digitized map. In this manner, the true position of the aircraft can be determined with respect to the digitized map and can be displayed on a plan view of the map. When the correct position of the aircraft with respect to the digitized map is known, a display of the map and the aircraft can provide presentations useful to the navigation of the aircraft, e.g., by displaying surface features that can provide potential danger for the aircraft. The correct position of the aircraft with respect to the digitized map can permit the aircraft to engage in terrain following procedures using only the relatively difficult to detect altitude range finding apparatus as a source of emitted electromagnetic radiation. The navigation system, in conjunction with information regarding hostile antiaircraft facilities, can provide a display permitting an operator to determine a reduced risk flight path.

Gravity aided inertial navigation system

Abstract: An autonomous covert Inertial Navigation System uniquely suited for underwater applications wherein Schuler and siderial errors are bounded without external navigation aids or active instrumentation of ground speed is achieved by integrating a conventional Inertial Navigation System with a gravity gradiometer capable of measuring gravity field components independently of platform accelerations.

Analysis of a Radome Air-Motion System on a Twin-Jet Aircraft for Boundary-Layer Research

Abstract: A “radome gust probe” system was installed on a twin-jet aircraft for the purpose of boundary-layer research. This system provided a useful relatively low-cost method for air motion and turbulence measurements on an aircraft already equipped with an inertial navigation system (INS) and a data acquisition system. An error analysis was made for the wind measurements and gave the limitations for the present system with an unmodified airliner-type INS, The major factors that limit the precision of the horizontal wind are the resolutions and accuracy of the aircraft ground speed components and the true heading. A simple method was devised to improve the heading resolution. From in-flight maneuvers, it was determined that the mean horizontal airspeed vector was accurate to <0.5 m s−1—limited by the long-term drift and oscillation errors from the INS-and that pitch and yaw contamination of the wind was less than 5%. The in-flight data indicate that there probably are unknown time lags within the INS, wh...

Ground collision avoidance system

Abstract: A method and system for avoiding ground collision through pilot warning messages which is implemented in aircraft having a plurality of sensors, onboard inertial navigation units, and altimeters for measuring aircraft performance or flight characteristics. Data is collected through a digital interface unit from data buses connected to these sources, transferred to one or more storage locations and a data validation unit for determining the validity of current altitude data. A series of data processing elements use the aircraft data to extrapolate an aircraft altitude path forward during a predetermined period of time as a function of the aircraft flight data. The extrapolated altitutde allows extrapolation of an aircraft flight path as a function of predicted terrain variations and changes in altitude in response to recovery from various aircraft maneuvers such as rolling, banking, diving, climbing, or accelerating. The extrapolated altitude, or changes in altitude, is compared to one or more predetermined safety limits, and one or more warning messages are provided if the extrapolated altitude is lower than an appropriate limit.

Modeling rugged terrain by mobile robots with multiple sensors

Abstract: Modeling the environment is an essential capability for autonomous robots. To navigate and manipulate without direct human control, autonomous robots must sense the environment, model the environment, and plan and execute actions based on information from the model. Perceiving and mapping rugged terrain from multiple sensor data is an important problem for autonomous navigation and manipulation on other planets, seafloors, hazardous waste sites, and mines. In this thesis, we develop 3-D vision techniques for incrementally building an accurate 3-D representation of rugged terrain using 3-D information acquired from multiple sensors. This thesis develops the locus method to model the rugged terrain. The locus method exploits sensor geometry to efficiently build a terrain representation from multiple sensor data. We apply the locus method to accurately convert a range image into an elevation map. We also use the locus method for sensor fusion, combining color and range data, and range and Digital Elevation Map (DEM) data. Incrementally modeling the terrain from a sequence of range images requires an accurate estimate of motion between successive images. In rugged terrain, estimating motion accurately is difficult because of occlusions and irregularity. We show how to extend the locus method to pixel-based terrain matching, called the iconic matching method, to solve these problems. To achieve the required accuracy in the motion estimate, our terrain matching method combines feature matching, iconic matching, and Inertial Navigation Sensor data. Over a long distance of robot motion, it is difficult to avoid error accumulation in a composite terrain map if only local observations are used. However, a prior DEM can reduce this error accumulation if we estimate the vehicle position in the DEM. We apply the locus method to estimate the vehicle position in the DEM by matching a sequence of range images with the DEM. Experimental results from large scale real and synthetic terrains demonstrate the feasibility and power of the 3-D mapping techniques for rugged terrain. In real world experiments, we built a composite terrain map by merging 125 real range images over a distance of 100 meters. Using synthetic range images we produced a composite map of 150 meters from 159 individual images. Autonomous navigation requires high-level scene descriptions as well as geometrical representation of the natural terrain environments. We present new algorithms for extracting topographic features (peaks, pits, ravines, and ridges) from contour maps which are obtained from elevation maps. Experimental results on a DEM supports our approach for extracting topographic features. In this work, we develop a 3-D vision system for modeling rugged terrain. With this system, mobile robots operating in rugged environments will be able to build accurate terrain models from multiple sensor data.

Velocity-plus-rate matching for improved tactical weapon rapid transfer alignment

Abstract: An improved rapid transfer alignment algorithm formulation is presented. This improvement takes advantage of angular rate data, available from strapdown aircraft Inertial Navigation Systems (INS), as measurements for updating a weapon strapdown INS via a Kalman filter based alignment algorithm. The two INS's are mounted to a common but flexible structure. The improved formulation overcomes limitations identified in a previous study, which used attitude measurements, to achieve rapid transfer alignment. Those limitations include a lack of weapon INS instrument calibration. The present formulation provides improved attitude and instrument calibration estimates as will be shown by monte carlo simulation results. These simulation results demonstrate attitude alignment errors less than 1.5 milliradians about the maneuver axis and less than 1 milliradian for the other axes, while providing gyro instrument calibration, These results are achieved using a 9 state Kalman filter, with combinations of 6 measurements, 3 velocity and 3 rate, operated at a 20 Hz measurement update cycle.

Expanding the Performance Envelope of GPS-Based Attitude Determination

Abstract: The advent of GPS-based attitude determination offers the potential for significant cost savings in applications where inertial guidance has traditionally been the standard approach We report new experimental results supporting advances in expanding the performance of attitude determination based on GPS Attitude is measured by differential measurements of GPS carrier phase between two or more antermas The performance envelope may be characterized in terms of accuracy and bandwidth, both functions of application-specific parameters such as antenna spacing and carrier-to-noise ratio The goals of the research reported here are to uantitatively identify the factors ultimately limiting performance ‘and to offer approaches and techniques through which the theoretical limits of the performance envelope may be reached Experimental results are included Factors limiting performance are multipath, carrier-to-noise ratio, and integer resolution Techniques are described for ameliorating multipath and increasing the bandwidth of differential carrier phase tracking A family of new ‘Eigenaxis” methods for resolving the integer ambiguities is presented Real time processing techniques are described which make possible survey-level accuracy attitude determination in high dynamic applications (such as high performance jet aircraft) based exclusively on GPS

Design and Flight Test of a Differential GPS/Inertial Navigation System for Approach/Landing Guidance

Abstract: NASA-Langley has conducted a flight test program evaluating a differential GPS/inertial navigation system's (DGPS/INS) utility as an approach/landing aid. The DGPS/INS airborne and ground components are based on off-the-shelf transport aircraft avionics, namely a global positioning/inertial reference unit (GPIRU) and two GPS sensor units (GPSSUs). Systematic GPS errors are measured by the ground GPSSU and transmitted to the aircraft GPIRU, allowing the errors to be eliminated or greatly reduced in the airborne equipment. Over 120 landings were flown; 36 of these were fully automatic DGPS/INS landings.

Strapdown inertial navigation system using high order

Abstract: Sculling error correction means, using third or higher order correction to correct for sculling errors in apparatus for converting angle measuring and acceleration measuring signals from a vehicle set of coordinates into a stabilized set of navigation coordinates

An integrated navigation system manager using federated Kalman filtering

Abstract: A federated Kalman filter architecture has been developed in which the Kalman filter processing is distributed among the navigation sensors to be integrated. Each navigation sensor with its Kalman filter can, in conjunction with the reference INS (Inertial Navigation System), be considered as a subsystem which functions as an independent manager. A central data fusion function is used to integrate the information from these navigators. Such a federated architecture can offer a number of advantages over one with a single central Kalman filter. These advantages include improved failure detection and correction, improved redundancy management, and lower costs for system integration. GEC Avionics has developed a system for the integration of INS with GPS (Global Positioning System) and TRN (Terrain Referenced Navigation), together with other navigation aids. Results are presented to demonstrate the performance and the benefits of using a federated approach. >

Gravity Aided Inertial Navigation System (GAINS)

Abstract: A new autonomous covert Inertial Navigation System (1X3) uniquely suited to underwater applications is described. Unlike the conventional INS, schuler and siderial errors ,are bounded without external navigation aids or active instrumentation of ground speed. As a result the system exhibits excellent long term navigation (both velocity and position) performance while maintaining the inherent covertness of an INS system. This new innovation in INS technology results by integrating a conventional INS with a gravity gradiometer capable of measuring gravity field components independently of platform accelerations. A number of integration schemes use gradiometer measurements to estimate gravity distrubance vector components which in turn are used to compensate INS accelerometer measurements. The resulting INS performance, although much improved, continue to exhibit random walk navigation errors. This new integration scheme goes further by taking advantage of navigation system velocity error observability. Velocity error is manifested in two ways. First. east velocity error results in vertical channel acceleration error through the coriolis term leading to detectable depth error. Second, gravity state estimates based mainly on gradiometer measurements are transitioned forward using estimated velocity. So errors in estimated velocity, both north and east, lead to disturbance vector solution errors and to gradient prediction errors. The vertical disturbance in turn leads to detectable depth error and gravity gradient prediction errors are observable with measured gradients. Parametric performance results are presented for GAINS, varying gyro, gravimeter, gradiometer, depth sensor quality and gravity field activity. If gravity maps are available (e.g. GEOSAT maps) GAINS can be used to implement gravity field based map matching navigation in order to further improve long term navigation performance. A significant added capability of a gradiometer based system is that these covert measurements along the vehicle track can be used to develop surrounding terrain estimates. So stealth enhancing terrain following terrain avoidance modes can be implemented.

INSIDE: a connectionist case-based diagnostic expert system that learns incrementally

Abstract: The authors describe a connectionist case-based diagnostic expert system that can learn while the system is being used. The system, called INSIDE (Inertial Navigation System Interactive Diagnostic Expert), was developed for Singapore Airlines to assist the technicians in diagnosing the inertial navigation system used by the airplanes. The system learns from past repair cases and adapts its knowledge base to newly solved cases without having to relearn all the old cases. >

System for aligning the inertial unit of a carried vehicle on that of a carrier vehicle

Abstract: The system may be used, for example, to initialize the inertial unit of a missile from the inertial unit of a vehicle carrying the missile. According to the invention, a servo-control circuit is provided for slaving data in the missile inertial unit on data from the carrier inertial unit, together with a Kalman filter connected in parallel with said servo-control circuit and designed to identify harmonization errors between the two inertial units.

An Application of Kalman Filtering to Airborne Wind Measurement

Abstract: Airborne wind measurement techniques currently being used onboard the National Aeronautical Establishment (NAE) Twin Otter Atmospheric Research Aircraft are described and their fundamental limitations are discussed In particular, a recently acquired LTN-90-100 strapdown Inertial Reference System (IRS) exhibits significant low frequency errors in its velocity components (primarily Schuler oscillation errors that can attain peak values of 2 to 3 m s−1), actually degrading wind computation accuracy compared with older techniques A new wind measurement technique, based on a Kalman filter integrated navigation approach, is shown to mitigate this problem and provide wind computation accuracy superior to previous methods Preliminary results, based on applying the Kalman filter to Twin Otter flight test data, indicate that inertial velocity accuracies of 03 m s−1 rms (per axis) are attainable under ideal conditions, with a corresponding improvement in the accuracy of earth-referenced wind components

Performance evaluation of six terrain stochastic linearization techniques for TAN

Abstract: Six terrain stochastic linearization techniques are discussed. Among them are three new ones which were developed for TAN (terrain-aided navigation). These three are the improved full-plane fit (IFPF), the mean tangent-line (MTL), and the two-subgroup fit (TSF) techniques. Performance evaluations for each technique are made and compared. The evaluation for each technique makes use of six measures. Each technique has its merits and demerits. On the whole, the TSF technique appears to be the best. >

Kalman filter mechanization for INS airstart

Abstract: A strapdown mechanization and associated Kalman filter were developed to provide both ground align and airstart capabilities for inertial navigation systems using Doppler velocity and position fixes, while not requiring an initial heading estimate. This is accomplished by use of a Doppler velocity sensor and a position source such as the global positioning system (GPS) manual fly-over update or target sighting systems. Filter transition from coarse to fine align mode is accomplished without disrupting the estimation of the inertial instrument or aiding sensor errors, by defining the azimuth error state as wander angle error, and using a simple, but effective, manipulation of the filter covariance matrix. >

Autonomous reconfigurable GPS/INS navigation and pointing system for rendezvous and docking

Abstract: This paper describes the results of an integrated navigation and pointing system software development effort sponsored by the NASA MSFC through a SBIR Phase 2 Program. The integrated Global Positioning System (GPS)/Inertial Navigation System (INS) implements an autonomous navigation filter that is reconfigurable in real-time to accommodate mission contingencies. An onboard expert system monitors the spacecraft status and reconfigures the navigation filter accordingly, to optimize the system performance. The navigation filter is a multi-mode Kalman filter to estimate the spacecraft position, velocity, and attitude. Three different GPS-based attitude determination techniques, namely, velocity vector matching, attitude vector matching, and interferometric processing, are implemented to encompass different mission contingencies. The integrated GPS/INS navigation filter will use any of these techniques depending on the mission phase and the state of the sensors. The first technique, velocity vector matching, uses the GPS velocity measurement to estimate the INS velocity errors and exploits the correlation between INS velocity and attitude errors to estimate the attitude. The second technique, attitude vector matching, uses INS gyro measurements and GPS carrier phase (integrated Doppler) measurements during a spacecraft rotation maneuver to determine the attitude. Both of these techniques require only one GPS antenna onboard to determine the spacecraft attitude. The third technique, interferometric processing, requires use of multiple GPS antennae. In order to determine 3-axis body attitude, three GPS antennae (2 no-coplanor baselines) are required.

GPS/INS integration for civil aviation

Abstract: The mechanization equations for generating the INS (inertial navigation system) solution in the proper coordinates are presented. Two different Kalman filter error models for integrating GPS (Global Positioning System) with INS are derived. The model which uses spheroidal component differences rather than Cartesian vector differences is preferable, since it uses error states which can be directly corrected in the INS mechanization equations. >

GPS Inertial Attitude Estimation via Carrier Accumulated-Phase Measurements

Abstract: This paper describes the design and simulation of an integrated GPS/INS that accomplishes space vehicle navigation and attitude estimation. The simulation contains models of an inertial measurement unit (IMU), a GPS receiver processing signals from an array of antennas placed on the spacecraft structure, and an integrated navigation filter. Interferometric equations are employed to process GPS carrier accumulated-phase measurements from precise antenna locations in the user vehicle. Vehicle orientation in inertial space is then obtained by relating baseline-difference phase measurements to orientations of antenna baselines relative to satellite line-of-sight vectors. The method of GPS-aided attitude estimation described herein is distinguished from other methods in that it does not employ search algorithms to resolve the carrier phase cycle ambiguity. Instead, the ambiguity is modeled as a random process and is included as an error state of a statistical filter. As a result, the attitude estimation time history evolves directly for any dynamic environment.

Graceful Degradation of GPS/INS Performance With Fewer Than Four Satellites

Abstract: Precision first pass weapon delivery with exceptionally accurate navigation are vital to the operational survivability of attack aircraft. Systems such as the Global Positioning System (GPS) are currently being fielded and integrated with inertial navigation systems (INS) to support such a capability. It offers the potential for less costly weapon targeting systems if target coordinates relative to the GPS reference can be provided. The current standard GPS receiver requires simultaneous signals from 4 satellites (with good geometry) to calculate and output useful position and velocity information. However, signals from 4 satellites may not always be available, especially in and around heavily defended target areas protected by high power jammers. These high power jammers, even when recognized and appropriately nulled out by adaptive array GPS antenna, can result in large sectors of the sky surrounding these jammers no longer being monitored for any GPS satellite signals. This paper recommends changes to the existing GPS equipment and new aircraft Kalman filter algorithms which provide graceful degradation of aircraft navigation performance when only one, two, three, or intermittent satellite signals are available, and quantifies the level of relative performance expected for these conditions. This paper also analyzes the relative performance of various Kalman filter mechanizations as a function of filter size.

Systematic methods for knowledge acquisition and expert system development (for combat aircraft)

Abstract: Nine cooperating rule-based systems, collectively called AUTOCREW which were designed to automate functions and decisions associated with a combat aircraft's subsystems, are discussed. The organization of tasks within each system is described; performance metrics were developed to evaluate the workload of each rule base and to assess the cooperation between the rule bases. Simulation and comparative workload results for two mission scenarios are given. The scenarios are inbound surface-to-air-missile attack on the aircraft and pilot incapacitation. The methodology used to develop the AUTOCREW knowledge bases is summarized. Issues involved in designing the navigation sensor selection expert in AUTOCREW's NAVIGATOR knowledge base are discussed in detail. The performance of seven navigation systems aiding a medium-accuracy inertial navigation system (INS) was investigated using Kalman filter covariance analyses. A navigation sensor management (NSM) expert system was formulated from covariance simulation data using the analysis of variance (ANOVA) method and the ID3 algorithm. >

Adaptive airborne MTI with two-dimensional motion compensation

Abstract: Clutter returns received by an airborne radar exhibit a Doppler bandwidth which depends on the platform speed, beamwidth and wavelength Echoes of slow targets may, therefore, be buried in the clutter band and are difficult to detect Perturbations of the flight path due to the flight dynamics of the aircraft and wind effects may cause further degradation of the MTI performance It has been shown in earlier papers of the author that space-time FIR filters applied to the output signals of a linear array antenna can be used to compensate adaptively for the flight path component of the platform motion so that a large improvement in signal-to-clutter-plus-noise ratio (SCNR) can be obtained Such filters are referred to as TASTE (techniques for airborne slow target extraction) methods In the paper these ideas are extended to the compensation of transversal velocity components by means of a planar array with horizontal orientation The influence of the system bandwidth is also investigated The results obtained can be generalised to compensate for three-dimensional perturbations of the flight path without using an inertial navigation device

Fault tolerant integrated inertial navigation/global positioning systems for next generation spacecraft

Abstract: The authors address the requirements, benefits, and mitigation of risks to adapt a commercial Hexad fault-tolerant inertial navigation/global positioning system (FT IN/GPS) for use in next-generation spacecraft. Next-generation requirements are examined to determine whether a high production base system can meet autonomous, reliable, and low-cost requirements for future spacecraft. The major benefits are the combining and replacement of functions, the reduction of unscheduled maintenance and operations costs, and a higher probability of mission success. The design, development, and production risks are mitigated by the long-term commercial production schedule for the Boeing 777 air data inertial reference unit (ADIRU) which begins in the mid-1990s. The conclusion is that a strapdown ring laser gyro (RLG) Hexad FT IN/GPS is the preferred integrated navigation and control system for next-generation vehicles. >

Robustness of structure from binocular known motion

Abstract: The paper analyses the important issues associated with structure computations through binocular motion when inertial navigation systems are used to find the sensor motion parameters. In particular, the authors study the conditions under which the relative error in environmental depth is reduced through the use of binocular motion over the separate use of monocular motion and static stereo. The results obtained give lower bounds on relative errors in depth. Examples on typical situations are included to illustrate their theoretical conclusions. >

A Discussion of GPS/INS Integration for Airborne Photogrammetric Applications

Abstract: The concept of using integrated GPS/INS for precise aircraft positioning is discussed and the integration algorithm is briefly reviewed. Airborne tests jointly conducted by the University of the Federal Armed Forces, Germany, The University of Calgary, and the Rheinbraun Company, Germany are used to assess the accuracy of the integrated system. Two Trimble 4000SX receivers, an LTN 90–100 strapdown inertial system and a Zeiss RMK 15a/23 photogrammetric camera were used in the experiment allowing for a comparison of perspective centers of the camera determined from traditional photogrammetric techniques and from GPS/INS integration. Results show that decimetre accuracy is achievable. The accuracy of the integrated system for attitude determination is also assessed but a conclusive result is not possible at this time. Relative angular velocities between the camera and the INS may have caused discrepancies in the respective attitudes.