摘要:

ABSTRACTAlthough the mathematical basis for rhumb lines on the ellipsoidal earth is well known, the earth's oblateness is usually neglected in dead‐reckoning sailing calculations. This leads to significant errors in the estimated position of a vessel over 1 day's sailing. This paper provides simple formulas that include the earth's oblateness, which can be readily applied to sailing calculations. The accuracy of these formulas is assessed, and they are shown to be good to about 10 m over ranges up to 1000 k

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1995.tb01893.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTFollowing the explosion at the Chernobyl nuclear plant, airborne cesium‐137 was transported into Sweden, the United Kingdom, Iceland, Greenland, and even the northeastern United States. Rainfall washed the radioactive material into the soil, where it was absorbed by the roots of plants. Sheep eating the affected plants threatened to transfer the radiation into the human food chain. Research into the correlation between levels of radioactivity and grass types has led to the need for an instrument that can monitor the positions of sheep at 1 min intervals, with an accuracy of 5 m.An unusual approach to postprocessed differential GPS (DGPS) has been shown to provide the optimal solution to the requirement. The design of the sheep‐borne unit has been optimized for minimal power consumption. Furthermore, a low‐cost GPS receiver has been shown to serve as a satisfactory reference station, providing the required accuracy without the need for a survey‐grade r

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1995.tb01894.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe merchant marine of the United States, like that of most other nations, comprises a wide range of commercial vessels with only loose links among the various sectors. The existence of a full constellation of GPS satellites, however, has produced a growing acceptance of GPS by the maritime end‐user community as a navigational standard. This process has been accelerated by a desire on the part of government and ship operators alike to reduce the likelihood of groundings resulting from navigational errors.The acceptance of this standard, however, has led to an unexpected consequence in that mariners may be too willing to over‐rely on the GPS‐generated information that has become available. In this paper we report observations concerning the training of maritime cadets in the use of GPS‐equipment. Furthermore, personal experience with the use of GPS in actual navigation situations is described. Through this experience we have been able to detect a broad range of simple equipment‐user mistakes. These mistakes, though easily prevented, are not easily detected unless some thought has been given ahead of time to constructing the piloting routine so that the navigator is automatically alerted to a problem. It is shown that a small adjustment in the way a marine GPS receiver is typically used will provide an automatic cross‐check with radar navigation techniques that are popular in the merc

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1995.tb01895.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTNavigation and positioning using the FAA's GPS Wide‐Area Augmentation System (WAAS) with single‐frequency receivers suffers potentially from the unknown spatial variability of ionospheric range delays (e.g., spatial gradients in ionospheric delays) between ground locations where dual‐frequency measurements from GPS satellites are being made. By deploying a sufficient number of dual‐frequency GPS code and/or codeless reference receivers, it is possible to correct for most of the ionospheric range delay in a given large region using WAAS real‐time prediction algorithms.The statistics of differences in range delay over station separations from approximately 350 km to over 1,600 km are presented, using ionospheric data collected from a number of stations in North America. The results illustrate large ionospheric gradients during periods of high magnetic activity. Fortunately, these events are infrequent. For the midlatitudes, the accuracy goal is to keep ionospheric range delays to only a few meters for at least 99 percent of the time so that WAAS can be used in precision approaches. To illustrate the possibility of achieving this goal, statistics of estimation errors in ionospheric range delay using this data set are also

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1995.tb01896.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThis paper describes an effective approach for ambiguity resolution on the fly (OTF)—the Fast Ambiguity Search Filter (FASF)—and presents comparative numerical results for this method and the least‐squares search approach. In the past, the search range of each ambiguity parameter was determined separately regardless of the assumed integers of the other ambiguities. In the new approach presented here, the search range is determined recursively for each ambiguity parameter. The effect of an assumed integer on other ambiguities is then fully taken into account when determining the uncertainty range of an ambiguity parameter. Another important characteristic is that all observations from the initial to the current epoch are taken into account through the use of a Kalman filter. An index of possible inability to fix the ambiguities is used. Therefore, a full search of all possible integer ambiguities is not required, and the computation is dramatically reduced. Computer memory is also saved since there is no need to retain all potential solutions. Test results show that both the computation time for ambiguity search and the observation period required for ambiguity resolution are significantly re

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1995.tb01897.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTTo determine the attitude of a moving vehicle in real time, GPS phase ambiguities should be instantaneously resolved. This paper presents an efficient technique for resolving phase ambiguities from data of one epoch, within the time interval between successive outputs. The technique employs a specific antenna configuration to limit significantly the range within which the integer ambiguities must be searched. The paper also investigates factors that can enhance the speed and robustness of ambiguity resolution.A number of static and kinematic tests have been conducted to evaluate the potential of the technique. Using a 486 DX computer with a 50 MHz clock rate, the success rate for finding the correct ambiguities from data of one epoch exceeds 99 percent. The computation time required is about 0.5 s. Results also show that the performance of the technique is the same for the static and kinematic modes.

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1995.tb01898.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThis paper investigates aspects of the geometrical arrangement of the receivers in a ground‐referenced aircraft geometric height measurement system. The system utilizes the replies transmitted by an aircraft in response to secondary surveillance radar (SSR) interrogations. The time differences of arrival (TDOAs) of the response signal at four receiving stations are measured and used to estimate the height of the aircraft. After a brief presentation of the system and the height computation algorithm, the paper focuses on the effects of the arrangement of the stations on system performance. It is shown that some arrangements result in situations under which no geometric height estimation is possibl

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1995.tb01899.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY