摘要:

ABSTRACTCaptain P. V. H. Weems was a graduate of the U.S. Naval Academy in the class of 1912 and cofounder of our Institute of Navigation. After his first retirement in the early 1930s, Weems continued his efforts in his own small business, called “The Weems System of Navigation.” Because of this, many pilots knew him best for the Weems Plotter, the E6B Computer, his textbooks on both marine and air navigation, and other piloting and dead reckoning instruments. His principal interest and thrust, however, was always the improvement of celestial navigation. The persistent devotion of Capt. Weems to the problem produced outstanding results. The Star Altitude Curves were his proudest achievement and were adopted by the Army Air Corps just prior to World War II. Weems' love of people and the force of his personality, together with his refusal ever to accept the answer “no,” gave us this Grand Old Man of Nav

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1993.tb02290.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTEarly man was an inveterate traveler, and he often encountered situations in which natural landmarks and directional references failed him. His first successful attempts to devise an artificial heading reference to aid him in his journeys are generally conceded to have been made in ancient China. References to these instruments in original texts are sparse and confusing, and are sometimes attributed to legend rather than to fact. The “south pointer” mentioned in these writings was thought by early researchers to refer to the magnetic compass, but modern scholars feel that there have been errors in interpretation, and that the magnetic compass was not invented until a much later era.This paper describes the design and construction of a working model of a south‐pointing carriage based upon a reasonable conjecture as to the working principles of the original instrument. Clues derived from ancient texts were used where appli

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1993.tb02291.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTThe main characteristics of both GPS (1.5 GHz) and Loran‐C (100kHz) navigation systems are reviewed, with emphasis on vehicular navigation applications. The effects of the GPS line‐of‐sight requirement and of Loran‐C signal attenuation in mountainous areas are illustrated using signal availability statistics collected for major roads located in British Columbia, Canada. The advantages of an integrated GPS/Loran‐C system are demonstrated using GPS and multichain digital Loran‐C receiver data collected along a 230 km road section. Signals sufficient for horizontal navigation (HDOP ≤ 5) are available approximately 60 percent of the distance in the case of GPS, 75 percent in the case of Loran‐C, and some 95 percent in the case of GPS/Loran‐C. The advantages of multichain versus single‐chain Loran‐C receiver operations in mountainous areas are also demonstrated. A performance analysis of the digital Loran‐C receivers used for

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1993.tb02292.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTIn Western Europe, the radionavigation system Loran‐C experiences serious interference problems from harmonic (HM) signals passed by the input bandpass filter. Since the influence of an HM signal on the performance of a Loran‐C system depends strongly on the signal's frequency, the frequency spectrum must be analyzed with high resolution for an optimal interference suppression strategy. Only the signals with a harmful influence on the operation of the Loran‐C system must be suppressed. The approach taken in this paper is to apply a special windowing function in the time domain, together with a nonstandard sampling pattern in the frequency domain, when performing spectrum analysis. The spectral weighting created in this way corresponds with the receiver's sensitivity for interference signals. Therefore, the signal detected as the most powerful will be equal to the most ha

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1993.tb02293.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTAnalytical and simulation models are described which can evaluate the use of automatic dependent surveillance (ADS) with precise navigation for intersecting track route structures. Although the analysis is applied for an area where Loran‐C is available, it is also relevant to GPS. It is shown that, by combining ADS and accurate navigation such as Loran‐C, it may be possible to raise the flow rates on intersecting tracks by as much as an order of magnitude over those possible using current over‐the‐ocean air traffic control (ATC) procedures. This new concept would provide for the same level of safety as current pro

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1993.tb02294.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTThis paper investigates the implementation of three variations of the Kalman filter—centralized, decentralized, and federated. The underlying theory for these designs is first overviewed, and the designs are then compared on the basis of accuracy, computational efficiency, and fault‐tolerance performance. Special attention is paid to the federated filter design and its potential use for fault detection and system recovery. Two numerical examples are included to illustrate the three different filters. The first is the simulated navigation of an object traveling in a straight‐line trajectory that is being positioned by two sensors, while the second is a GPS positioning problem using pseudorange and carrier phase observations. Blunders are purposely planted in these two data sets. The numerical results presented support the hypothesis that better fault‐tolerance performance can be achieved with a federated‐decentralized filter than with a centralized filter

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1993.tb02295.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTA receiver autonomous integrity monitoring (RAIM) algorithm is proposed, and used to analyze the integrity monitoring capabilities of potential sole‐means (or stand‐alone) systems based on integrated use of GPS and GLONASS, GPS supplemented with a geostationary overlay, and enhanced GPS constellations. As in the other RAIM algorithms, the idea is to take advantage of the redundant measurements. Our focus, however, is on the quality of the position estimate, rather than on diagnosing whether the system is working as intended.The proposed approach uses the redundant measurements to generate a position estimate and a measure of its quality. The latter, called integrity level, is denned as an upper bound on the position error. The estimation of the integrity level is the main innovation in the proposed scheme. The RAIM algorithm is tailored to an abundant redundancy of the measurements, and addresses the following issue: Given a snapshot of the pseudorange measurements, one of which may be in error, can we compute a position estimate that can be shown with high confidence to meet the user's accuracy requirem

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1993.tb02296.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1993.tb02297.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY