Co-ordinates

GEODESY
Numerical simulations of the optimal
geodetic conditions with radioastron
The feasibility for the estimation of EOPs has been investigated, then appropriate number of stations and
epochs for the estimation of parameters have been analyzed
Erhu WEI
PhD, Professor, School of
Geodesy and Geomatics,
the Key Laboratory of
Geospace Environment
and Geodesy, Ministry
of Education, Wuhan
University, China
Sándor FREY
astronomer
PhD Institute of Geodesy,
Cartography and Remote
Sensing (FOMI), Satellite
Geodetic Observatory
Budapest, Hungary
Peilai ZHOU
engineer, Xiuzhou
District Branch, The
Bureau of Land and
Resources Jiaxing,
Jiaxing, Zhejiang, China
Jingnan LIU
professor, Academician
of CAE (P.R. China),
GNSS Center,Wuhan
University, China
Space Very Long Baseline
Interferometry (SVLBI) is the
unique space technology that can directly
interconnect the three reference systems,
which include the Conventional Inertial
System (CIS) fixed in space and defined
by radio sources, the Conventional
Terrestrial System (CTS) fixed to
the Earth and defined by a series of
observing stations on the ground, and
the dynamic reference system defined
by the movement of a satellite. In this
paper, the Space VLBI mathematical
model with notation parameters, and its
feasibility for estimation of EOPs are
discussed. Simulations have been done
for the SVLBI observations and related
parameters for RADIOASTRON. With
the results of the simulation, the feasibility
for the estimation of EOPs has been
investigated, then appropriate number
of stations and epochs for the estimation
of parameters have been analyzed.
Introduction
For all the three pillars of space geodesy
(the geometry of the Earth surface and its
displacements, the orientation of the Earth
Fig 1 Geometric Figure of Ground-Space Baseline
axis and its rotation speed, and the Earth’s
gravity field and its time variations), welldefined,
highly accurate and stable global
Earth-fixed and celestial reference frames
are of primary importance. Over the last
decade considerable changes took place
in space geodesy: the accuracy of the
space geodetic techniques has improved
dramatically up to 10 -9 for geometric
geodesy, Earth rotation and gravity field
measurement. Many new missions are
being prepared, planned, or on-going.
All these developments pose new and
demanding challenges concerning the
consistency and accuracy of the three
pillars and thus better-defined, more
accurate and stable global Earth-fixed
and celestial reference frames are crucial
to meet these challenges. As a new and
rapidly developing technique, SVLBI
has tremendous potentials in geodetic
research. SVLBI can not only directly
interconnect the above two reference
frames by determining the 5 Earth
orientation parameters (EOPs) which
include 3 Earth rotation parameters
(xp,yp,θk ) and 2 nutation parameters (ΔΨ,
Δε), but also it can be used to avoid or
examine the systematic errors made by
the other co-located multi-techniques.
Following the VLBI Space Observatory
Programme (VSOP) of Japan,
another Space VLBI mission, called
RADIOASTRON, is being planned by
Russia with international collaboration for
a launch as early as 2010. The two VLBI
observatories in Urumqi and Shanghai of
China may participate in the observations.
However the present and foreseeable
practical realizations of SVLBI are
driven by astrophysical goals. Also, with
VSOP observations, the geodetic test
result by Frey et al. (2002) showed that
it was difficult for VSOP to improve
Coordinates November 2010 | 27