摘要:

ABSTRACTUnder the Selective Availability program the Department of Defense plans to provide the civil community with Standard Positioning Service (SPS), having an accuracy of 500 meters (2drms) when the NAVSTAR GPS becomes operational. Subsequent improvements in accuracy are expected to be instituted as national security considerations permit. However, provisions are also made to degrade accuracy to worse than 500 meters, if necessary. Depending on the type and level of Selective Availability imposed, different civil capabilities can be realized. These capabilities are described in this report. Differential operation, wherein a high‐quality, surveyed‐in receiver installation determines satellite pseudorange errors and communicates them to nearby users, offers a promising technique of improving SPS on a local scale. It can improve the accuracy of the GPS even when SPS is provided at full accuracy, i.e., when Selective Availability is removed. The type of corrections, the associated accuracy, and the update rate are discussed here. Differential system design alternatives and the advantages and disadvantages of each are also descri

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1983.tb00837.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTThe Microwave Landing System (MLS) is on the verge of implementation in the National Airspace System as a replacement for the Instrument Landing System (ILS). The present plan calls for the establishment of 1,250 systems by the year 2,000. The first ten years of MLS implementation will serve as a transition period in which both ILS and MLS will be extensively used. The MLS implementation strategy is based on the establishment of MLS networks of 4 to 7 facilities. Each network is centered on a major hub airport and the satellites are selected from regional airports that have commuter airline service with the hub. The MLS implementation program will take advantage of the increased reliability of digital electronics systems together with the reduced costs of those systems to provide the capability for all weather service at most MLS‐equipped airport

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1983.tb00838.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTAn airborne collision avoidance system, using the existing transponder equipment of the Secondary Surveillance Radar system as its basic cooperative element, has been under development since the mid 1970's. In June 1981, the FAA Administrator announced the FAA's commitment to implementing the Traffic Alert and Collision Avoidance System (TACS), with a low cost system for general aviation and a more sophisticated system for air carriers. This paper summarizes the status of the FAA's TCAS program.

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1983.tb00839.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1983.tb00840.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTPositional information in Loran‐C systems has traditionally been derived from two time differences measured between signals from a fixed triad of a master and two secondaries. In this limited mode of operation a station outage of the master means loss of all positional information. Loss of a secondary may require acquisition of a new secondary or, at least, suffering a shift in position resulting from a change in geometry and land paths. The introduction of master independence to a Loran‐C receiver eliminates the problem of master outage on all but the chains that have only three stations. A two chain Loran‐C receiver that computes position from various combinations of stations is basically immune to a single station outage in areas where two Loran‐C chains are receivable. In a master independent receiver that is tracking two chains with four stations each, there are 12 time differences being measured. Loss of any one station on either chain, even a master, reduces this number to 9. In fact, so long as any 4 stations are operational out of the eight positional information is available though accuracy may be diminished as the choice of geometry has been lost. A ranging capability provides a backup when only two stations are available.In order to avoid a shift in calculated position when forced to give up a prime station due to outage, positional information from the various pairs of stations is compared and reconciled continuously. When a single station is lost it does not change the calculated position because this possibility has been allowed for in the position calcu

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1983.tb00841.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTA greater degree of survivability is a significant requirement of future space systems. Toward this end, an important aspect is an autonomous navigation capability. For many space systems, an obvious choice is the use of the Navstar/Global Positioning System (GPS). With the operational 18‐satellite GPS constellation (plus three active spares), low altitude user satellites will have continuous tracking data available for navigation. On the other hand, with the current constellation of four satellites, there is less available data and, consequently, the accuracy of navigation varies a great deal throughout the user satellite orbit. This paper discusses the navigational performance that can be achieved with this constellation.Last summer, the Ladsat 4 satellite was placed into a near circular, sun synchronous, orbit at an altitude of 705 km, and at an inclination angle of 98.3 deg. This satellite contains a Navstar GPS receiver (called GPSPAC), and is the first user satellite to employ GPS. Using this satellite as an example, an error analysis was performed of the navigation accuracy that can be obtained for a low altitude satellite. During the course of a Landsat 4 orbit, it will be able to observe from none to four Navstar/GPS satellites. When four satellites are available, the three‐dimensional accuracy can be expected to be about 11 m.Since Landstat 4 is sun synchronous, i.e., its orbit plane rotates in longitude with the sun, there will be times during the year when this satellite and the GPS satellites simultaneously come together over the continental United States. This is where Landsat 4 is primarily used, and is the ideal geometric relationship between Landsat 4, the GPS satellites, and the earth. This favorable condition occurred last November. This paper discusses the use of Navstar/GPS to navigate Landsat 4 under this ideal geometric situation, as well as at other times during the year. The paper presents the results of a theoretical accuracy analysis. The actual on‐orbit experience with Landsat 4 is not covered

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1983.tb00842.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTThe first use of the Navstar Global Positioning System (GPS) by a spaceborne user occurred with the launch of NASA's Landsat 4 on July 16, 1982. One of the experimental packages onboard Landsat 4 is the Global Positioning System Package (GPSPAC). A brief description of the GPSPAC is presented and the operational history of the GPSPAC experiment onboard Landsat 4 is outlined.The responsibility for the control of the GPSPAC experiment and for the validation of its results resides at the Goddard Space Flight Center (GSFC). The role of the Naval Surface Weapons Center (NSWC) primarily is to aid GSFC in achieving the objectives of the GPSPAC experiment. Results of NSWC's evaluation of the GPSPAC performance are presented.

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1983.tb00843.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTThere are many geodetic datums in use throughout the world today. Each of these datums serves as a reference surface for the mapping, charting and geodetic work done in a specific geographical area. Each datum is defined by fitting a specific ellipsoid to the earth in such a manner as to minimize departures of this reference model from the geoid over the area of concern. Historically, these datums have been relatively oriented. Consequently, the position of the center of an ellipsoidal model relative to the center of mass of the earth is not known. The positions determined on one datum cannot be related directly to positions on another datum. The development of absolutely‐oriented datums incorporating satellite and gravity data has led to the development of datum transformations to relate positions on one datum to those on another.Sophisticated new electronic navigation and targeting technology requires highly precise input data to obtain output on the order of design accuracies. To obtain positions on the order of +/–1000 feet/300 meters, care should be taken by the users of such equipment that the datum to which positions are referred is taken into account. If positions are located on two different datums, then the user must know that one set of coordinates must be transformed into the other system prior to their input into the inertial navigation system as a point of departure and a destination.This paper reviews some basic practical and theoretical concepts of datum development and evaluates errors that may be encountered if a datum transformation is required but is not used. Hardware and software alone cannot minimize the occurrence of these errors. The user community must be educated in the basic concepts of position determination. Therefore, this work is presented in such a manner as to be readily adapted to teach users of varying backgrounds, education and expert

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1983.tb00844.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTThe three‐dimensional (3D) seismic survey is a relatively new technique used in the exploration and development of petroleum resources. It is well known that precise navigation (positioning) is required for the 3D seismic operation. However, it is not well understoodwhythis high level of precision is required. In addition, few, if any, attempts have been made to discuss actual positioning achievements while performing a 3D seismic survey. This paper attempts to fill both these voids.In this paper, the 3D seismic survey is simply explained from basic principles and the position accuracy requirements are developed. State‐of‐the‐art techniques and equipment are presented for positioning both the seismic vessel and the towed streamer containing an array of hydrophones.Results are presented for vessel positioning using the 450 MHz Syledis system in conjunction with a 2 MHz Argo system. A direct comparison of these two systems is given from data obtained during a 3D seismic survey. In addition, operational results are presented for the positioning of a towed hydrophone array.New techniques under development for positioning the seismic vessel and the towed hydrophone arrays are presented. The possible use of GPS technology for 3D seismic surveys is discussed and the system's impact for future work is evaluated.Conclusions are presented summarizing current 3D seismic accuracy requirements, the techniques and equipment required, results that can be expected, and what positioning technology can be expected in the

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1983.tb00845.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1983.tb00846.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY