测绘外文文献.docx

1、测绘外文文献MODERN GEODETIC REFERENCE FRAMES FOR PRECISE SATELLITE POSITIONING AND NAVIGATION J. Kouba and J. Popelar Geodetic Survey Division, Geomatics Canada, Natural Resources Canada (NRCan) 615 Booth Street, Ottawa, Ontario, Canada K1A EO9 E-mail: *.ca; *.ca ABSTRACTThe NAD83 and WGS84 reference coor

2、dinate frames were established more than a decade ago to satisfy most mapping, charting, positioning and navigation applications. They are consistent at the 1-2 metre level on a continental and global scales respectively, reflecting the limitations of available data and techniques. With rapid improv

3、ements in positioning accuracy, mainly due to GPS, submetre navigation has become practical and reference frames at the cm to mm level are required by the most demanding users. The IERS Terrestrial Reference Frame (ITRF) was established in 1988 by the International Earth Rotation Service (IERS) to f

4、acilitate precise monitoring of the Earth Orientation Parameters (EOP) based on state-of-the-art techniques such as Very Long Baseline Interferometry (VLBI) and Satellite Laser Ranging (SLR). With the establishment of the International GPS Service for Geodynamics (IGS) in 1994, the ITRF is directly

5、accessible to users world-wide by means of precise global GPS satellite orbit/clock solutions and a large number of IGS monitoring stations. The most recent ITRF solutions, designated ITRF92 and ITRF93, are based on space geodetic observations including GPS up to the end of 1993 providing global con

6、sistency at the cm level. The Canadian Active Control System (CACS) facilitates access to ITRF through active participation in IGS and VLBI. Fiducial VLBI points included in NAD83 provide a direct link to ITRF and make it possible to upgrade NAD83 coordinates in order to satisfy positioning and navi

7、gation requirements with cm precision in the future. CACS facilitates the most efficient connections to the ITRF and NAD83 reference frames for high precision positioning by GPS as well as for general spatial referencing needs in Canada.1. INTRODUCTIONIn geodesy a reference coordinate frame implies

8、a scale, orientation and coordinate origin as part of a reference system which also includes Earth planetary models and constants necessary for satellite orbit determination, ge- odynamic and geophysical data analysis. Satellite navigation systems made it possible to establish a truly global geocent

9、ric reference system which was quickly adapted for precise geodetic positioning, especially over long distances. For the first time it was possible to determine distortions and misorientation of classical geodetic networks around the world. The U.S. Navy Navigation Satellite System (NNSS), also call

10、ed Transit or simply Doppler (Kershner and Newton, 1962) became the basis for the U.S. Department of Defense World Geodetic System 1972 (WGS72) and later WGS84 which define global geocentric reference frames consistent at about the 1-2 metre level. To upgrade and correct distortions of the classical

11、 North American Datum 1927 (NAD27), a readjustment of the geodetic networks in Canada, USA, Mexico and Greenland was jointly undertaken. This new datum, designated NAD83, was nominally made compatible with WGS84 by being geocentric and oriented according to transformed Doppler positions, but in addi

12、tion the NAD83 adjustment included VLBI (Very Long Baseline Interferometry) baselines. Thus both, WGS84 and NAD83, are consistent at about one metre, mainly due to the limitations of the Doppler techniques (Kouba, 1993). GPS and other space based techniques such as VLBI and Satellite Laser Ranging (

13、SLR) provide data with higher precisions to support studies of crustal dynamics and polar motion which require a more accurate global reference frame. The IERS Terrestrial Reference Frame (ITRF) was established in 1988 and is updated on an annual basis by the International Earth Rotation Service (IE

14、RS) to keep it current and to improve knowledge of station velocities which are necessary for maintaining the accuracy of this global reference frame. NAD83 can be related to ITRF precisely for a given epoch by a transformation based on common VLBI stations. The Canadian Active Control System (CACS)

15、 provides the most efficient method to upgrade NAD83 coordinates in Canada in order to meet positioning and navigation requirements with cm precision in the future.2. NORTH AMERICAN GEODETIC DATUM: NAD83The North American Datum 1927 (NAD27) was established at the beginning of this century using cont

16、inental triangulation with a centrally located datum point at Meades Ranch in Kansas, USA (Ross, 1936). Satellite geodesy in the 60s and 70s detected the approximately 100 m offset of the NAD27 origin with respect to the geocenter as well as distortions exceeding tens of meters in some parts of the geodetic control network (Mueller, 1974). A new reference frame wasrequired to facilitate use of efficient and precise satellite geodetic techniques