摘要:

AbstractThe essential portion of a received Loran‐C signal of 100 kHz consists of groundwave only. The phase velocity of the groundwave which is related to TOA (time of arrival) and TD (time difference) values depends on various parameters, such as ground conductivity (or surface impedance), terrain variation, and the refractive index profile of the atmosphere. In order to calculate exactly the phase velocity, signal strength, etc., it is necessary to solve the electromagnetic wave equation, rigorously incorporating all of the above mentioned parameters. Since this is an impossible mathematical task, several approximate methods with various degrees of complexities had been sought by various authors in the past. Among these approximate methods or propagation models, the following are notable: (1) homogeneous flat earth model of Sommerfeld and Norton, (2) homogeneous spherical earth model of Watson, Van der Pol and Bremmer (the last two authors included also the effect of inhomogeneous atmosphere), (3) Millington's empirical model for an earth with mixed surface conductivities for computing signal strength, (4) Pressey and his associates' empirical model for earth with mixed surface conductivities for computing phase, (5) Wait's multisection spherical earth model, (6) Hufford's integral equation approach to the propagation over an irregular surface, and (7) Jollier's integral equation approach which is a generalization of Hufford's method with the aid of a computer. This paper presents a general overview of these methods and their limitations with a special emphasis directed towards Loran

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1979.tb01373.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractOmega is reviewed from the vantage point of several years operational experience with the system in nearly final configuration. After identification of some possible shortcomings or deficiencies, system design parameters are re‐examined with a view to determining possible investigations, modifications, or changes which might mitigate or lead to elimination of difficulties. Potential coverage limitations are identified in several areas while a coverage deficiency in central North America is to be expected. Significant reception difficulties have been noted in aircraft. Specific recommendations are made for investigations leading to improved receiver design and to mitigate reception problems in aircraft. Despite system maturity, a considerable and perhaps surprising latitude exists for modifications. Methods are presented by which one or more additional stations can be added without obsoleting existing equipments.This paper is an abridgment of an 80‐page report of the same title written with Mr. J. E. Britt and Mr. A. N. Smith.1This paper is intended to draw attention to, rather than substitute for, the longer work. A particular loss due to brevity is an adequate expression of appreciation to the many individuals who contributed advice or suggestions to the parent work and who are not individually acknowledged her

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1979.tb01374.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractIn the absence of torque, a gyroscope's spin axis will maintain a fixed angular orientation in space. This angular orientation is analogous to the fixed line of sight to a star. In principle then, one should be able to perform celestial navigation using gyroscopes as self‐contained stars.Unfortunately, most current inertial auto‐navigators apply torques to the gyroscopes. Ideally these torques are of just the right magnitude to cause the stable platform on which the gyros are mounted to stay locally level. In the case of strapdown inertial auto‐navigators, the gyroscopes are torqued to follow the host vehicle angular rates. This results in the gyroscope becoming just an angular rate sensor, and the only measure of true angular orientation rests within the system computer. These mechanizations lead to concepts unfamiliar to many navigators familiar with celestial navigation.Electrostatic gyroscope (ESG) inertial navigation systems are unique in that they are normally operated untorqued. As such, the orientation of their gyro spin axes remain fixed in inertial space. This makes it possible to consider their operation in terms of classical celestial navigation concepts. This paper will develop this similarity to the point where one familiar with celestial navigation will be able to understand the alinement problem and the fundamental error sources of ESG inertial systems.A specific type of ESG employed at Rockwell International in both gimbaled and strap‐down systems will be discussed. This will provide the basis for relating angle readout errors and drift rate to their counterparts in celestial navigation.The buzz words used in inertial navigation, such as Schuler tuning and Kalman filtering, will be related to concepts familiar to celestial navigators. The paper will be based on straightforward physical principles and the concepts presented without resorting to mathematical deve

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1979.tb01375.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1979.tb01376.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractThe principles of operation of the Relative Navigation (RELNAV) function of the Joint Tactical Information Distribution System (JTIDS), which are based on its highly accurate time‐of‐arrival measurement capability and on a specially structured architecture, are described. The system configuration for implementing the RELNAV function in the JTIDS Hughes Improved Terminal (HIT) is presented. The integration options for interfacing the LN‐31 Inertial Navigation Set with the HIT are discussed, and the selected interface is described. The RELNAV operational modes, control requirements and major software functions are discussed. A detailed description is given of the selected RELNAV algorithm and the associated timing and sequencing design. The filter state vector extrapolation and update formulation, the inertial processing and the source selection algorithms are presented. Some simulation results are pres

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1979.tb01377.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractCollisions at sea have been a problem to mariners since the earliest vessels engaged in commerce. The international and inland rules of the road developed in response to the problem are very helpful in preventing conflicts particularly in situations involving only two vessels. The advent of radar was thought by many to provide the ultimate solution but these thoughts were severely jarred by the Stockholm and Andrea Doria collision. Today, many are considering another technological breakthrough, the sophisticated computer, as the final solution but others question whether we will merely see computer assisted collisions in the future.This paper examines the issue of proposed requirements for collision avoidance equipment including the need for this equipment and the potential benefits to be gained from this equipment. The examination of the benefits consists of analysis of the results of two major research efforts conducted in the United States. The first of these is a study of recent collisions in U.S. coastal waters and the analysis of both the factors that caused these casualties and the methods that might have prevented these casualties. The second study involves a comparison of the actions taken by experienced navigators using visual, radar, non‐computerized and computerized aids. The results of these two studies are contrasted with results of studies done in the United Kingdom.With the study results as a background the United States efforts to encourage development of international standards for collision avoidance aids are addressed. The U.S. statutory requirement for shipboard carriage of this equipment is also discusse

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1979.tb01378.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractThe use and function of shipboard computer‐based collision‐avoidance automation devices with radar inputs are discussed. The fundamentals of the collision avoidance problem are presented in mathematical form. The relationships between the devices, the operators and the Rules of the Road are explored. Limitations of this type of automation fall in four interrelated categories which are analyzed. These categories are reliability, equipment complexity, ergonomics and non‐equipped vessels. The “Quilter Preplot” method of encounter evaluation for non‐equipped vessels is presented. It is concluded that ergonomics is the basic limitation in the effectiveness of computer‐based collision avoidance aids. This limitation is explored in depth. The ergonomic limitation is one of expecting operators who are not qualified on the devices or in the fundamentals of collision avoidance to use both effectively. It is a hidden limitation in that it has not yet been prope

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1979.tb01379.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1979.tb01380.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1979.tb01381.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1979.tb01382.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY