3 1 coordinate systems and time seeber 2 1
Download
1 / 27

3.1. Coordinate-systems and time. Seeber 2.1. - PowerPoint PPT Presentation


  • 69 Views
  • Uploaded on

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.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' 3.1. Coordinate-systems and time. Seeber 2.1.' - rasha


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.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
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

  • 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 !


Kap 3 polar motion
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.


Ch 3 polbev gelsen
Ch. 3 POLBEVÆGELSEN

  • .


Kap 3 polar movement
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


Kap 3
Kap. 3

  • Polbevægelse, 1994-1997, Fuld linie : middel pol bevægelse, 1900-1996


Kap 3 international terrestrial reference system itrs
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".


Kap 3 itrs
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


Kap 31
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





Ch 3 transformation cis cts
Ch. 3, Transformation CIS - CTS

  • Precession

  • Nutation

  • Rotation+

  • Polar movement

Sun+Moon


Ch 3 precession
Ch. 3, Precession.

  • Example: t-t0=0.01 (2001-01-01)

  • .


Ch 3 nutation primarily related to the moon
Ch. 3, Nutation – primarily related to the Moon.

  • Movement takes place in Ecliptica




Ch 3 example for point on equator
Ch. 3, Example for point on Equator.

  • Suppose θ=0, xp=yp =1” (30 m)

  • .


Ch 3 exercise
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.


Ch 3 time requirement
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.


Ch 3 siderial time and ut see fig 2 13
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


Ch 3 ut
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



Ch 3 dynamic time
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


Ch 3 gps time
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


Ch 3 clocks and frequency standards
Ch. 3, Clocks and frequency standards.

  • With GPS we count cycles. Expect the fequency to be constant.


Ch 3 praxis see seeber fig 2 15
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.


ad