摘要:

ABSTRACTPiloting large vessels in increasingly congested waterways is no simple task. As in many scenarios involving decision making under uncertainty, masters, mates, and pilots engaged in piloting are inundated with much information and must make crucial decisions in real time. Piloting is also an inherently judgmental activity. Pilots and ship's captains invariably develop heuristics for transiting particular waterways. As vessels become larger, cargoes more hazardous, and the waterways more congested, decision aid technology is being considered to improve piloting decision making.This paper describes one approach to providing improved on‐board decision support to masters, mates on watch, and pilots navigating in restricted waters. We discuss (1) the use of cognitive decision aids in piloting, (2) the design of such a decision aid developed for New York harbor, and (3) the transition of the system from an off‐line prototype to an operational shipboard expert system for tankers transiting the Gulf of Ala

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1990.tb01531.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTFiber optic gyro technology has been developed to a point where these gyros are now being introduced into advanced engineering models of the next generation of inertial measurement units (IMUs). This paper covers the operating principles of the interferometric type of fiber optic gyroscopes, together with a brief comparison against ring‐laser gyroscopes. Recent flight test data of an IMU employing fiber optic gyro sensors are presented. Finally, the unique characteristics of the fiber optic gyro are discussed, with particular emphasis on the role they will play in future fault‐tolerant I

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1990.tb01532.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTThe newer Block II GPS satellites have the capability to control the accuracy of the Standard Positioning Service signals by a combination of dithering the satellite clock and manipulating the ephemeris data. This capability is called Selective Availability (SA). Differential GPS operation greatly reduces the effects of SA, in addition to the effects of ionospheric, tropospheric, and other slowly‐varying errors, for users in a local area around a reference station.A major technical issue in the design of reference stations has been the correction update rate. It has been assumed until recently that new differential GPS corrections are required about once every 10 s to maintain 5–10 m service accuracy. Until the recent launch of the new Block II satellites, there has been no firm evidence that this update rate would be adequate. This paper presents statistical analysis of recently obtained data sets from Block II satellites, specifically position and velocity variations and correlation times. Pseudorange corrections generated by differential reference station equipment using these signals are applied to the pseudoranges from a navigation receiver to obtain estimates of the effect of correction update rate on differential GPS performa

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1990.tb01533.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTThe concept of GPS semikinematic positioning is reviewed, with an emphasis on accuracies at the centimeter level. Details of the mathematical model used herein are given. A two‐step approach combines a Kalman filter to process kinematic carrier phase, phase rate, and pseudorange data, while a batch least‐squares adjustment processes static carrier phase data. A semikinematic test performed over a well‐controlled traverse in a mountainous region near Calgary is used to assess the performance of the algorithm. Several runs of the traverse were made with the station occupation time at 2–3 min. The analysis shows that centimeter‐level accuracies can be achieved when five satellites are observed in good geometery, even when frequent cycle slips occur. An accuracy improvement technique of reverse processing is also investigated. Recommendations for improving semi‐kinematic surveyi

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1990.tb01534.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTRecent advances in high‐precision differential GPS‐based satellite tracking can be applied to the more conventional GPS‐based direct tracking of low‐earth satellites. To properly evaluate the limiting accuracy of direct GPS‐based tracking (i.e., with no differential corrections provided from simultaneous ground observations), it is necessary to account for the correlations between the a priori errors in GPS states, Y‐bias (unmodeled forces on the GPS satellites), and GPS solar pressure parameters. These can be obtained only by careful analysis of the process by which the a priori GPS orbits have been determined. The analysis indicates that submeter real‐time accuracy can be readily achieved for a user above 700 km altitude, even when the user solution is based on a GPS ephemeris that is more than 12 h old. In the presence of Selective Availability, a user without access to the Precise Positioning Service will require a near‐real‐time correction to achieve met

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1990.tb01535.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTThe concept of employing simple, nonautonomous satellite repeaters on geostationary hosts for civil radionavigation has been recommended by a number of authors. This paper reviews the history of the geostationary repeater concept, especially for integrity broadcast and for coverage augmentation. It indicates how a worldwide geostationary overlay is likely to be more economical than launching additional autonomous navigation satellites. Also presented are recently developed technical considerations for the geostationary overlay concept, including design parameters for the navigation package, signal and data format considerations for augmentation and integrity, and ground network concepts for generating and timing the uplink signals.Early results of a test program being conducted with transmission of GPS‐like signals via an existing L‐band mobile communications satellite are reported. These results appear to validate the geostationary repeater overlay conc

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1990.tb01536.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTUser equipment that combines pseudoranges from GPS and Loran would be more reliable than an unaided GPS receiver or a Loran‐only receiver. It could remove coverage outages caused by satellite shutdowns and/or bad satellite geometry. Similarly, it could remove most of the coverage outages caused by Loran station shutdowns, high atmospheric noise levels, or precipitation static. A hybrid GPS/Loran receiver could also reliably provide self‐contained fault detection and isolation (otherwise known as receiver autonomous integrity monitoring, or RAIM).This paper treats position fixing, receiver autonomous fault detection, and receiver autonomous fault isolation as system services, and computes the probability of outage for these three services. Our analysis computes the outage probability for the level of service required for nonprecision approach and en route navigation in the National Airspace System. It assumes that GPS is configured in the Optimal 21 Satellite Constellation, and includes the effects of satellite as well as Loran station shutdowns. Finally, our analysis examines whether it is important to synchronize Loran transmissions to GPS t

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1990.tb01537.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1990.tb01538.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1990.tb01539.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1990.tb01540.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY