1 / 27

3.1. Coordinate-systems and time. Seeber 2.1.

3.1. Coordinate-systems and time. Seeber 2.1. Z. NON INERTIAL SYSTEM. Mean-rotationaxis 1900. Gravity-centre. Y- Rotates with the Earth. CTS : Conventional Terrestrial System. Greenwich. X. CIS.

rasha
Download Presentation

3.1. Coordinate-systems and time. Seeber 2.1.

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 3.1. Coordinate-systems and time. Seeber 2.1. Z NON INERTIAL SYSTEM Mean-rotationaxis 1900. Gravity-centre Y- Rotates with the Earth CTS: Conventional Terrestrial System Greenwich X

  2. CIS • Zero-meridian for Bureau Internationale de l’ Heure (BHI) determined so that star-catalogues agree in the mean with observations from astronomical observatories. • The connection to an Inertial System is determined using knowledge of the Z-axís (Polar motion), rotational velocity and the movement of the Earth Center. • We obtain an Quasi-Inertial system, CIS. • More correct to use the Sun or the centre of our galaxe !

  3. Kap. 3 POLAR MOTION • Approximatively circular • Period 430 days (Chandler period) • Main reason: Axis of Inertia does not co-inside with axis of rotation. • Rigid Earth: 305 days: Euler-period.

  4. Ch. 3 POLBEVÆGELSEN • .

  5. Kap. 3 POLAR MOVEMENT • Coordinates for the Polen and Rotational velocity • IERS (http://www.iers.org) • International Earth Rotation and Reference System service (IAG + IAU) • http://aiuws.unibe.ch/code/erp_pp.gif • Metods: VLBI (Radio astronomi) LLR (Laser ranging to the Moon) SLR (Satellite Laser ranging) GPS, DORIS

  6. Kap. 3 • Polbevægelse, 1994-1997, Fuld linie : middel pol bevægelse, 1900-1996

  7. Kap. 3. International Terrestrial Reference System (ITRS) • Defined, realised and controlled by IERS ITRS Center. http://www.iers.org/iers/products/itrs/ • Geocentric, mass-centre from total Earth inclusive oceans and atmosphere. • IERS Reference Pole (IRP) and Reference Meridian (IRM) konsist with BIH directions within +/- 0.005".

  8. Kap. 3, ITRS. • Time-wise change of the orientations secured through 0-rotation-condition taking into account horizontal tectonic movements for the whole Earth. • ITRS realised from estimate of coordinates for set of station with observations of VLBI, LLR, GPS, SLR, and DORIS. See: ftp://lareg.ensg.ign.fr/pub/itrf/old/itrf92.ssc

  9. Kap. 3 • Paris, 1 July 2003 Bulletin C 26 • INFORMATION ON UTC - TAI • NO positive leap second will be introduced at the end of December 2003. • The difference between UTC and the International Atomic Time TAI is : • from 1999 January 1, 0h UTC, until further notice : UTC-TAI = -32 s • Leap seconds can be introduced in UTC at the end of the months of December or June, depending on the evolution of UT1-TAI. Bulletin C is mailed every six months, either to announce a time step in UTC, or to confirm that there will be no time step at the next possible date. • http://www.iers.org/iers/products/eop/leap_second.html

  10. Kap. 3

  11. Kap. 3 Variationer jord-rotationen.

  12. Kap. 3

  13. Ch. 3, Transformation CIS - CTS • Precession • Nutation • Rotation+ • Polar movement Sun+Moon

  14. Ch. 3, Precession. • Example: t-t0=0.01 (2001-01-01) • .

  15. Ch. 3, Nutation – primarily related to the Moon. • Movement takes place in Ecliptica

  16. Ch. 3, Nutation: • .

  17. Ch. 3, Earth rotation and polar motion (ERP). • .

  18. Ch. 3, Example for point on Equator. • Suppose θ=0, xp=yp =1” (30 m) • .

  19. Ch. 3, Exercise. 2 May 1994: x”=0.1843”=0.000000893, y”=0.3309”=0.0000014651 (x,y,z)=(3513648.63m,778953.56m,5248202.81m) Compute changes to coordinates.

  20. Ch. 3, Time requirement • 1 cm at Equator is 2*10-5 s in rotation • 1 cm in satellite movement is 10-6 s • 1 cm in distance measurement is 3*10-11 s • We must measure better than these quantities. • Not absolute, but time-differences.

  21. Ch. 3, Siderial time and UT. (see fig. 2.13). • Siderial time: Hour-angle of vernal equinox in relationship to the observing instrument • LAST: Local apparent siderial time: true hour angle • GAST: LAST for Greenwich • LMST: Local hour angle of mean equinox • GMST: LMST for Greenwich • GMST-GAST=Δψcosε • LMST-GMST=LAST-GAST=Λ xp

  22. Ch. 3, UT • UT= 12 hours + Greenwich hourangle for the mean sun. Follows siderial time. • 1 mean siderial day = 1 mean solar day -3m55.909s. • UT0B is time at observation point B, must be referred to conventional pole • UT1= UT0B + ΔΛP

  23. Ch. 3, UT1, GMST and MJD • .

  24. Ch. 3, Dynamic time • ET: Ephemeis time (1952) to make equatins of motion OK. • TDB= Barycentric time – refers to the Sun • TDT=Terrestrial time • From general relativity: clock at the earth moving around the sun varies 0.0016 s due to change in potential of sun (Earth does not move with constant velocity). • TDB=ET on 1984-01-01

  25. Ch. 3, GPS Time • GPS time = UTC 1980-01-05 • Determined from Clocks in GPS satellites • GPS time – UTC = n * s-C0, • C0 about 300 ns

  26. Ch. 3, Clocks and frequency standards. • With GPS we count cycles. Expect the fequency to be constant.

  27. Ch. 3, Praxis, see Seeber, Fig. 2.15. • Precision quarts crystal: temperature dependent, aging • Rubidium: good stability, long term • Cesium: stable both on short term and long term – transportable, commercially available. • Hydrogen masers: 10-15 stability in periods of 102 to 105 s. • Pulsars: period e.g. 1.6 ms.

More Related