5.3 Space-Time Reference Based on Newtonian Mechanics
293
ground stations is to determine its geometric formation (the stations’ coordinates)
and internal deformation (time-varying model). The connotation of the conventional
terrestrial reference system contains the theoretical methods and basic physical frame
to determine these parameters. The definitions and uses of the parameters and models
related to the terrestrial reference system are usually consistent with the international
convention, and so is the determination of the mean pole of the Earth.
The polar wander makes orientating of the terrestrial coordinate system change,
which brings much inconvenience in practice. Thereby, in 1967, the International
Astronomical Union (IAU) and the International Association of Geodesy (IAG)
proposed to use five International Latitude Service observing stations, including
Carloforte (in Italy), Kitab (in USSR/Russia), Mizusawa (in Japan), Gaithersburg
(in USA) and Ukaih (in USA), using the average latitudes between 1900 and 1905,
and to determine the position of the mean terrestrial pole, as a reference origin. That
is to say, the mean terrestrial pole is to use the average position of the Earth’s rotation
axis on the Earth’s surface during this period, commonly known as Conventional
International Origin (CIO), and the corresponding equatorial plane of the Earth is
called mean equatorial plane, or conventional equatorial plane. In practice, the
CIO is still widely used as the CTP. The terrestrial coordinate system established with
the CTP as the reference point is called Conventional Terrestrial System (CTS),
and the coordinate system corresponding to the instantaneous terrestrial pole is called
Instantaneous Terrestrial System (ITS), as shown in Fig. 5.4.
The International Terrestrial Reference System (ITRS) is an internationally recognized conventional terrestrial reference system with the best accuracy and stability.
In 1911, the International Union of Geodesy and Geophysics (IUGG) decided that
the IERS would take charge of the definition, realization and maintenance of the
ITRS. The basic definition of the ITRS is as follows:
(1) The coordinate origin is located at the center of mass of the whole Earth, in
which the mass of the whole Earth is the total sum of mass of the solid Earth,
ocean and atmosphere.
(2) The length of a meter defined in the SI units is used as the coordinate scale,
which is a local terrestrial reference frame scale defined based on the general
relativity. This coordinate scale is consistent with the timescale of Geocentric
Coordinate Time (TCG) defined by the IAG and IUGG, and it can be calculated
by the theoretical models of relativity.
(3) The orientation of coordinate system is consistent with the CTP and BIH Zero
Meridian at the 1984.0 epoch.
(4) The time evolution of the orientating parameters does not bring up residual
global rotation relative to the crust. In other words, there is not a whole residual
rotation for the horizontal motion of the reference system relative to the whole
Earth’s plates.
The ITRS is provided in the form of International Terrestrial Reference Frame
(ITRF) through the IERS ITRS Product Center, including the independent terrestrial
reference frames established by using space geodetic technologies, such as the VLBI,
Lunar Laser Ranging (LLR), SLR, GNSS and DORIS. The specific contents of
293
ground stations is to determine its geometric formation (the stations’ coordinates)
and internal deformation (time-varying model). The connotation of the conventional
terrestrial reference system contains the theoretical methods and basic physical frame
to determine these parameters. The definitions and uses of the parameters and models
related to the terrestrial reference system are usually consistent with the international
convention, and so is the determination of the mean pole of the Earth.
The polar wander makes orientating of the terrestrial coordinate system change,
which brings much inconvenience in practice. Thereby, in 1967, the International
Astronomical Union (IAU) and the International Association of Geodesy (IAG)
proposed to use five International Latitude Service observing stations, including
Carloforte (in Italy), Kitab (in USSR/Russia), Mizusawa (in Japan), Gaithersburg
(in USA) and Ukaih (in USA), using the average latitudes between 1900 and 1905,
and to determine the position of the mean terrestrial pole, as a reference origin. That
is to say, the mean terrestrial pole is to use the average position of the Earth’s rotation
axis on the Earth’s surface during this period, commonly known as Conventional
International Origin (CIO), and the corresponding equatorial plane of the Earth is
called mean equatorial plane, or conventional equatorial plane. In practice, the
CIO is still widely used as the CTP. The terrestrial coordinate system established with
the CTP as the reference point is called Conventional Terrestrial System (CTS),
and the coordinate system corresponding to the instantaneous terrestrial pole is called
Instantaneous Terrestrial System (ITS), as shown in Fig. 5.4.
The International Terrestrial Reference System (ITRS) is an internationally recognized conventional terrestrial reference system with the best accuracy and stability.
In 1911, the International Union of Geodesy and Geophysics (IUGG) decided that
the IERS would take charge of the definition, realization and maintenance of the
ITRS. The basic definition of the ITRS is as follows:
(1) The coordinate origin is located at the center of mass of the whole Earth, in
which the mass of the whole Earth is the total sum of mass of the solid Earth,
ocean and atmosphere.
(2) The length of a meter defined in the SI units is used as the coordinate scale,
which is a local terrestrial reference frame scale defined based on the general
relativity. This coordinate scale is consistent with the timescale of Geocentric
Coordinate Time (TCG) defined by the IAG and IUGG, and it can be calculated
by the theoretical models of relativity.
(3) The orientation of coordinate system is consistent with the CTP and BIH Zero
Meridian at the 1984.0 epoch.
(4) The time evolution of the orientating parameters does not bring up residual
global rotation relative to the crust. In other words, there is not a whole residual
rotation for the horizontal motion of the reference system relative to the whole
Earth’s plates.
The ITRS is provided in the form of International Terrestrial Reference Frame
(ITRF) through the IERS ITRS Product Center, including the independent terrestrial
reference frames established by using space geodetic technologies, such as the VLBI,
Lunar Laser Ranging (LLR), SLR, GNSS and DORIS. The specific contents of