Showing papers on "GPS/INS published in 1998"

A low-cost GPS/inertial attitude heading reference system (AHRS) for general aviation applications

Abstract: An inexpensive Attitude Heading Reference System (AHRS) for general aviation applications is developed by fusing low cost ($20-$1000) automotive grade inertial sensors with GPS. The inertial sensor suit consists of three orthogonally mounted solid state rate gyros. GPS is used for attitude determination in a triple antenna ultra short baseline configuration. A complementary filter is used to combine the information from the inertial sensors with the attitude information derived from GPS. The inertial sensors provide attitude information at a sufficiently high bandwidth to drive an inexpensive glass-cockpit type display for pilot-in-the-loop control. The low bandwidth GPS attitude is used to calibrate the rate gyro biases on-line. Data collected during laboratory testing is used to construct error models for the inertial sensors. Analysis based on these models shows that the system can coast through momentary GPS outages lasting 2 minutes with attitude errors less than 6 degrees. Actual performance observed during ground and flight tests with GPS off was found to be substantially better than that predicted by manufacturer supplied specification sheets. Based on this, it is concluded that off-line calibration combined with GPS based in-flight calibration can dramatically improve the performance of inexpensive automotive grade inertial sensors. Data collected from flight tests indicate that some of the automotive grade inertial sensors (180 deg/hr) can perform near the low end of tactical grade (10 deg/hr) sensors for short periods of time after being calibrated on-line by GPS.

Method and apparatus for adaptively processing GPS signals in a GPS receiver

Abstract: A method and apparatus is disclosed for adaptively processing Global Positioning System (GPS) signals in a GPS receiver. An adaptive method of processing GPS signals optimizes the initial acquisition of GPS signals by performing the search using three separate parameters. These parameters include satellite number, Doppler information, and integration time. A block processing method of GPS signal processing is performed for particular in-view satellites over particular time intervals and for each of a set of hypothesized Doppler frequencies. Each parameter is optimized such that the GPS signal acquisition operation for a location fix is performed in a short period of time.

GPS error modeling and OTF ambiguity resolution for high-accuracy GPS/INS integrated system

Abstract: The Center for Mapping at The Ohio State University is currently developing a fully digital Airborne Integrated Mapping System (AIMS) for large-scale mapping and other precise positioning applications. AIMS, installed in an aerial platform, incorporates state-of-the-art positioning [differential Global Positioning System (GPS) integrated with an Inertial Navigation System (INS)] and imaging (Charge-Coupled Device) technologies. The project goal is to develop a low-cost hardware prototype that acquires position and orientation of an aerial platform with accuracy of 4–7 cm and below 10 arcsec, respectively, over long baselines, and performs essential processing of digital imagery in real-time and in post-processing mode. A tightly integrated GPS and high-accuracy INS provide orientation and position of the aerial platform. To the best of the authors' knowledge, AIMS is the first tightly integrated GPS/INS system whose existing prototype promises sub-decimeter accuracy in positioning, and below 10 arcsec in orientation, in the airborne scenario. However, the expected high performance still remains to be verified against the ground truth. The new GPS/INS tightly integrated system for high-precision airborne applications is described, with special emphasis on the GPS component of the system. The evaluation of the actual prototype and the airborne test results are discussed. A detailed description of the tight GPS/INS integration and Kalman filter implementation is presented elsewhere.

The role of dead reckoning and inertial sensors in future general aviation navigation

Abstract: Possible configurations for a general aviation autonomous navigation system are studied. Doubtless, an advanced GPS receiver is a "must have" system component. GPS has had some outages due to unintentional interference or even intentional jamming and aircraft should be able to navigate through such an event. Natural candidates for GPS backup are inertial sensors, magnetic compass, and air-speed sensors. All these sensors can be calibrated during GPS availability. Moreover, for dead reckoning systems, wind velocity can be estimated as well. This paper presents an original statistical model for wind variations that matches actual data very well. Using this model and a parametric family of inertial measurement sensors, horizontal position errors during a GPS outage are compared for a variety of configurations: a dead reckoning system, stand alone inertial sensors and inertial sensors integrated with the dead reckoning system.

Navigating Urban Areas by VISAT—A Mobile Mapping System Integrating GPS/INS/Digital Cameras for GIS Applications

Abstract: Following a brief system description of VISAT (Video, Inertial, and SATellite GPS), a mobile survey system for the establishment of geographic information systems (GIS) in urban centers, the quality control component of the system and results of a performance analysis are discussed. Data collected in test networks in Calgary, Denver, and Laval City are used to assess system performance in terms of accuracy and reliability, and to develop a real-time quality control algorithm for the navigation sensors. Special attention is given to detecting and fixing GPS cycle slips by applying independent inertial navigation system (INS) trajectory data. In urban centers where, because of tree coverage and shading by buildings, frequent cycle slips are the rule rather than the exception, the effectiveness of INS bridging is crucial for overall performance. Results show that system specifications have been met, and in many cases performance is better than specified.

A portable dead reckoning system for extending gps coverage

Abstract: This invention extends GPS coverage in an automotive environment without requiring direct interfaces (50) to the vehicle's sensors in a unique and cost effective way. Since it removes all required vehicle interfaces (50) (except power), it produces a virtually portable navigation system with no installation requirements beyond that of the GPS receiver (30) itself. It also removes the necessary 'customization' of the navigation system to each particular vehicle. Fundamentally, the position of a vehicle is obtained by GPS receiver (30) data augmented with a low cost gyro (35) whereby the gyro (35) accurately tracks the heading changes of the vehicle (in the absence of sufficient GPS information), and the GPS receiver includes an innovative algorithm for deriving speed information from Doppler measurements from just one or two GPS satellites.

Time transfer using the phase of the GPS carrier

Abstract: We have conducted several time-transfer experiments using the phase of the GPS carrier rather than the code as is done in current GPS based time-transfer systems. We connected atomic clocks to geodetic GPS receivers. We then used the GPS carrier-phase observations to estimate relative clock behavior at 6 minute intervals. GPS carrier-phase time transfer is more than an order of magnitude more precise than GPS common-view time transfer, and agrees within error with two-way time-transfer measurements. GPS carrier-phase time-transfer has an uncertainty of 100 psec and a frequency uncertainty of 2 parts in 10/sup 15/ for averaging times of a day.

Increased jamming immunity by optimizing processing gain for gps/ins systems

Abstract: A system and method for increasing jamming immunity in a GPS/INS system. The system includes a signal processor for receiving and down-converting GPS signals to a baseband frequency to provide I and Q (sine and cosine) signals. An integrate and dump operation is performed on the I and Q signals to provide GPS range and range rate residuals which are uncorrelated from sample to sample. A Kalman filter estimates navigation state corrections from the GPS range and range rate residuals. A NAV function, responsive to the output of the Kalman filter and range error and velocity errors signals, provides guidance information and signals for correcting at least one of earth centered earth fixed (ECEF) position, velocity, initial attitude and IMU alignment states which are dynamically calculated from the range and range rate measurements. A line of sight geometry function maps position and velocity vector information from the NAV function into geometric range and range rate scalar information and feeds the scalar information to the signal processor and circuitry to perform an integrate and dump operation.

On-the-fly accuracy enhancement for civil gps receivers

Abstract: Method and means for enhancing the position accuracy of a civil GPS receiver (21) by compensating for errors in its position solution with data derived from a military GPS receiver (12), wherein the civil GPS receiver may be disposed in a mobile expendable vehicle (20) and the military receiver in a mobile launch vehicle (10). The compensating data is obtained by a comparison of the pseudorange measurements of the military GPS set and another civil GPS set disposed with it in the launch vehicle and attached to the same antenna. Two embodiments are disclosed: 1) an On-the-Fly Relative Navigation technique, applicable when the expendable receiver (20) tracks the same satellites as the military and civil sets are tracking, and 2) an On-the-Fly Differential Navigation system, used when the expendable receiver (20) is not tracking the same satellites as the launch sets.

Gravity Modeling for High‐Accuracy GPS/INS Integration

Abstract: The feasibility of improving airborne GPS/INS integrated navigation by use of accurate deflection of the vertical (DOV) information is investigated in this paper. Based on the available 2 times 2 arcmin DOV grid, tests were run on GPS/INS navigation data, and the results were compared with the corresponding results where the DOV compensation was not used. The issue of stochastic modeling of the anomalous gravity field in the state vector of the integrated filter is also addressed. The tests were conducted using the Airborne Integrated Mapping System (AIMS™), whose positioning component is based on a tightly integrated GPS/INS. The system is designed to provide orientation and position of an aerial platform, with estimated accuracy of 4–7 cm in position and ∼ 10 arcsec in orientation in postmission mode. A brief overview of the system is also given, including a discussion of current error modeling and airborne test results.

Current position detecting device for vehicle

Abstract: PROBLEM TO BE SOLVED: To stably and accurately determine an azimuth variation quantity from an output of a gyro without making a device constitution complex even though a conversion gain of the gyro includes a gain error. SOLUTION: This detecting device is provided with a Kalman filter (error estimating portion 15) obtaining an error between a estimated navigation data (a car speed, an absolute azimuth, an absolute position) which a relative track calculating portion 13 and an absolute position calculating portion 14 calculates and a GPS (global positioning system) position-measured data from a GPS receiver 8 as an observed value based on a moving distance and an azimuth variation quantity calculated by a moving distance calculating portion 11 and an azimuth variation quantity calculating portion 12 from a detected value of a car speed sensor 4 and a gyro 6. As one of the condition quantity, an error of a conversion gain (gain error) from a gyro output to an angular velocity is set. The azimuth variation quantity calculated using the gyro output and the conversion gain is corrected by a presumption value of the gain error demanded by the Kalman filter. COPYRIGHT: (C)2000,JPO

GPS estimation algorithm using stochastic modeling

Abstract: The use of direct, or closed-form, solutions of the trilateration equations for obtaining the position fix in the GPS receiver is investigated. A new closed-form position determination algorithm that works in the presence of pseudorange measurement noise and for an arbitrary number of satellites n, where n/spl ges/4, using stochastic modeling is developed. The closed-form algorithm provides an estimate of the GPS solution, viz., user position and user clock bias, as well as the estimation error covariance. The direct algorithm is a two step procedure which, (1) entails the solution of a linear regression problem, and, (2) an update of the solution based on an additional nonlinear measurement equation. Realistic simulation experiments are performed and the direct algorithm's performance is discussed and compared to the iterative least squares algorithm currently used in GPS.

A complete GPS/INS integration technique using GPS carrier phase measurements

Abstract: For its synergistic relationship, the integrated GPS/INS system has been adopted in many navigation systems. In this paper, a complete GPS/INS integration technique utilizing GPS carrier phase measurements is proposed. A measurement model of double-differenced GPS carrier phase measurements is newly derived in order to be used with the INS error model. Also, an algorithm is suggested to resolve the integer ambiguities of GPS carrier phase measurements by employing MS information. From simulation results, performance of the suggested technique is verified.

GPS/INS Based Lateral and Longitudinal Control Demonstration: Final Report

Abstract: This report describes the results of a study focusing on implementing and analyzing the performance of a Differential Global Positioning System (DGPS) aided Inertial Navigation System (INS) for possible future application in Advanced Vehicle Control Systems (AVCS) The DGPS/INS system provided estimates of vehicle position, linear velocities, and angular rates Position accuracy at the centimeter level was achieved and demonstrated through two experiments

Inertial navigation accuracy enhancement

Abstract: Apparatus for the improvement of inertial navigation system (INS) position/velocity comprises frame stores for storing sequential images from a video camera and a comparator for comparing pixels in predicted images, derived from earlier stored images as modified by INS linear and angular velocity outputs, with pixels in actual later stored images, to derive a velocity error correction signal which is used to correct the INS output. The video processing correction system described is passive and hence does not reveal the aircraft's whereabouts as would be the case with other positional correction systems using radar, nor does it rely on systems outside the control of the INS, e.g., GPS, nor is it reliant on a vast terrain feature database.

Low dynamic IMU alignment

Abstract: IMU alignment is addressed by examining results from two different INS error modeling approaches using actual flight test data recorded from captive pod mounted IMU and reference INU. The emphasis of this paper is alignment during the aircraft's low dynamics ground operations before takeoff. The two MS error models used to produce the alignment results are based on computer frame and perturbation error models, and are formulated to use position observations in a transfer alignment Kalman filter algorithm. The use of position observations is consistent with other navigation aides such as GPS. Performance measures used to evaluate the two INS error models' results include: filter state convergence rates, IMU navigation solution heading compared to the reference MU heading, and post-alignment unaided navigation position error growth during manoeuvres after aircraft takeoff. For all three, the perturbation error model shows better results. The results suggest that alignment and aided navigation can be accomplished and sustained with a navigation filter algorithm which implements the perturbation error model without an alignment manoeuvre.

Ins alignment method using a doppler sensor and a GPS/HVINS

Abstract: Transfer/in-flight alignment technique using a Doppler velocity sensor. An aircraft navigation system (10 and/or 20), a Doppler velocity sensor (50) and an alignment filter (45) are used to align the inertial navigation system (4) of a slave vehicle. The velocity (and/or position) of the aircraft navigation system, the velocity (and/or position) of the slave vehicle's inertial navigation system (40) and the velocity measurement of a Doppler velocity sensor (50) are used to generate the measurements of the alignment filter (45). The DVS and aircraft navigation system are used simultaneously to align the inertial navigation system of the slave vehicle. A GPS receiver (60) with a GPS antenna (70), a Doppler velocity sensor (50) and an alignment filer (46) are used to align the inertial navigation system (40) of a flight vehicle. The velocity (and/or position) of a GPS receiver (60), the velocity (and/or position) of the inertial navigation system (40) of a flight vehicle and the velocity measurement of a Doppler velocity sensor (50) are used to generate the measurements of the in-flight alignment filter (46).

A fuzzy navigational state estimator for GPS/INS integration

Abstract: To achieve improved performance over a cascaded Kalman Global Positioning System (GPS)/Inertial Navigational System (INS) when biases are present, a fuzzy state estimator can be used. A Kalman filter assumes there is no bias in the measurement source, e.g., the GPS receiver. However, standard positioning system (SPS) GPS has selective availability (SA) and other satellite errors that translate into a bias associated with each satellite. This causes the GPS receiver position output to have a bias that is dependent upon which satellites are being used to determine the position. As the vehicle maneuvers, the GPS receiver uses different satellites, causing the bias to change. Another changing bias in a cascaded filter is the GPS receiver time lag. This time lag creates a bias that is dependent upon the vehicle's velocity and changes as the vehicle maneuvers. A standard Kalman filter will introduce errors into the filter's state velocities and positions as it tries to follow the GPS data with these changing biases. By using a fuzzy state estimator, which can incorporate heuristics into the filter that compensate for the changing biases, the errors in the state position and velocity due to these changing biases can be significantly reduced, providing a better performing state estimator for a SPS GPS/IRU system.

A Reduced-Order Model Integrated GPS/INS for

Abstract: The dominant factor in determining the computation time of the Kalman filter is the dimension n of the model state vector. The number of computations per iteration is on the order of n3. Any reduction in the number of states will benefit directly in terms of increased computation time. In this paper, a high order model in integrated GPS/INS is described first, then a reduced-order model based on the high-order model, is developed. Finally, a faster tracking approach for Kalman filters is discussed.

GPS-aided navigation and unaided navigation on the joint direct attack munition

Abstract: The Joint Direct Attack Munition (JDAM) provides a low-cost accuracy enhancement to existing MK-83, MK-84, and BLU-109 weapons. Low-cost has been achieved through the use of commercial standards and high-volume production techniques. Accuracy improvements are achieved with a GPS-aided Inertial Navigation System (INS), an adaptive optimal guidance algorithm, an autopilot featuring a robust servo structure, and a tail actuator subsystem. Flight testing has demonstrated an impact uncertainty considerably less than the 13 meter Circular Error Probable (CEP) requirement in CPS-aided missions. This paper focuses on the JDAM navigator and Kalman filter algorithms that support both GPS-aided and unaided missions. The GPS-aided navigator consists of a tightly-coupled GPS/INS integration that supports both conventional and relative GPS operation. During GPS-aided operation, the JDAM Kalman filter is configured to estimate the basic kinematics states, calibrate critical inertial sensors, estimate GPS receiver clock errors, and estimate line-of-sight biases between the weapon and each NAVSTAR satellite tracked during the mission. JDAM also includes an unaided navigation mode that is used if GPS is denied. Unaided navigation relies on a transfer alignment algorithm to align the weapon's navigator to the carrier aircraft's navigator and to calibrate critical inertial sensors before release. Transfer alignment enhancements include senescence error estimation and an adaptive Kalman filter tuning algorithm that modifies filter process noise based on the weapon's vibration environment.

A reduced-order model for integrated GPS/INS

Abstract: The dominant factor in determining the computation time of the Kalman filter is the dimension n of the model state vector. The number of computations per iteration is on the order of n/sup 3/. Any reduction in the number of states will benefit directly in terms of increased computation time. In this paper, a high order model in integrated GPS/INS is described first, then a reduced-order model based on the high-order model, is developed. Finally, a faster tracking approach for Kalman filters is discussed. A typical aircraft trajectory is designed for a complex high-dynamic aircraft flight experiment. A Monte Carlo analysis shows that the reduced order model presented in this paper provides satisfactory accuracy for aircraft navigation.

An integrated GPS/INS navigation system for small AUVs using an asynchronous Kalman filter

Abstract: A small AUV navigation system (SANS) is being developed at the Naval Postgraduate School. The SANS is an integrated GPS/INS navigation system composed of low-cost, small-size components. It is designed to demonstrate the feasibility of using a low-cost inertial measurement unit (IMU) to navigate between intermittent GPS fixes. The paper reports improvements to the SANS hardware, latest testing results after compensating heading-dependent derivations in the TCM-2 compass measurements, and development of an asynchronous Kalman filter for improved position estimation.

Methods for gyro bias estimation using gps

Abstract: Augmenting the GPS receiver (30) with some form of Dead Recknoning (DR), such as a gyros (35), fills in the gaps occurring as a result of loss of GPS coverage. The present invention permits reliable and automatic estimation and calibration of the gyro zero rate bias. In particular, three specific methods (FIGs. 2-4) are disclosed whereby one method (FIG. 2) makes use of a 'GPS gyro' for detecting vehicle heading change, another (FIG. 3) makes use of a 'GPS accelerometer' for detecting stationary periods, and another (FIG. 4) makes use of a Kalman filter model for open loop heading error and is used to extract the contribution of and so estimate the gyro bias.

Control of Flexible Structures Using GPS: Methods and Experimental Results

Abstract: Active control of the attitude and vibration of a e exible structure using the Global Positioning System (GPS) is demonstrated. Measurements of the carrier phase of the GPS signal at several antennas are used to estimate the deformation and orientation of the structure. This distributed measurement capability, combined with excellent zero-frequency performance, makes the GPS sensor an excellent choice for a wide range of applications, including space structures, suspension bridges, and skyscrapers. The control system developed around the GPS sensor is presented for a particular structure modeled after the Space Station. The results from several new experiments demonstrate that the GPS sensor provides rotational accuracies better than 0.1 deg for static tests. Measured spectra also demonstrate that the carrier-phase GPS techniques are sufe ciently accurate to resolve many of the modes of vibration. Several feedback control experiments are used to show that the sensor provides an accurate and robust measure of the structural deformations. These experiments culminate in a fast slew maneuver under feedback control, which providesa cleardemonstration oftheapplication of carrier-phaseGPS forboth alignment and vibration control. This work shows the potential for GPS as a high-precision, real-time structural sensor.

GPS/INS integration in a severe urban environment

Abstract: GPS satellite visibility data collected over a ground track in the "deep urban canyons" of lower Manhattan indicated that there were usually too few satellites being tracked to form a position solution. The present study investigates the augmentation of such limited GPS data with a low cost, low accuracy INS. The navigation system is assumed to be self-contained and unobtrusively attached to the host vehicle. Initial covariance matrix analyses produced errors far in excess of that deemed necessary for a remotely sited operator to locate the vehicle on the correct street, when the navigation data is projected onto a map display. A series of software upgrades were then shown to produce significant performance improvements. In the final phase of this effort, a simplified simulation program was used to display navigation data on a grid map of the area in question. It was then found that a revised navigation algorithm produced data that appears to greatly enhance the ability of an operator to correlate the navigation data with the correct streets on the map.

GPS/INS Integrated Navigation System In Support of Digital Image Georeferencing

Abstract: This paper discusses different aspects of the process of direct georeferencing of aerial digital images by GPS/INS. The emerging digital frame camera technology received significant attention over the past 3 years due to its cost effectiveness and on-line storage capability. However, due to some limiting geometrical characteristics, its use in aerial applications has not been favored by photogrammetrists. The problem of exterior orientation with such cameras becomes unstable when using GPS alone for georeferencing and, thus, full attitude resolution would help overcome the geometrical limitations of such cameras. In a joint research project between The University of Calgary and The University of California at Berkeley, a low-cost multi-sensor system for remote sensing applications is developed. It integrates GPS, INS, and a digital camera. The main objective of developing such a system is to acquire georeferenced digital imagery in remote areas where ground control is unavailable. 3D positioning accuracy of ground objects for airborne remote sensing applications is at the meter level. In the sequel, the concept of direct georeferencing of digital images without ground control is reviewed. The potential of a low-cost IMU is discussed. System development, calibration, and testing are presented in some detail. Besides photo ecometrics, the major system applications will be near real-time digital mapping at scales 1: 10 000 and smaller and the generation of digital elevation models for engineering applications.