Articles in the Geodesy Category

Sep 2011 | No Comment

The Survey Department of Brunei Darussalam, with the collaboration of the Universiti Teknologi Malaysia (UTM), has carried out a study on the establishment of a new geodetic framework for the country. A new geocentric datum for Brunei Darussalam 2009 (GDBD2009) was established using GPS space geodetic technology based on the ITRF2005 reference frame. The GDBD2009 is related to ITRF2005 through the inclusion of the 8 GPS stations of the Brunei Darussalam Zero Order Network and have been processed together with more than fifty IGS stations around the world. The realization of GDBD2009 requires the determination of a new datum transformation and map projection scheme. A new set of transformation parameters to be use in converting from the existing local datum to the new GDBD2009 has been computed. The implication of this new datum on the existing cadastral and mapping practices, various GPS non-mapping applications, and the GIS/LIS related applications are taken into consideration.

Jun 2011 | No Comment

The use of a semi dynamic datum has been well accepted and its implementation and use have been relatively straight forward from a technical and geodetic perspective.

May 2011 | No Comment

Lennard Huisman, John Dawson and Peter J G Teunissen
The Asia-Pacific regional geodetic reference frame, presently characterized as a patchwork of national and regional datums, is below the standard that is now available, and expected, in other regions of the world such as Europe (Bruyninx et al, 2001), South America (Luz et al 2002) and North America (Henton et al 2007).

Nov 2010 | Comments Off on Numerical simulations of the optimal geodetic conditions with radioastron

For all the three pillars of space geodesy (the geometry of the Earth surface and its displacements, the orientation of the Earth axis and its rotation speed, and the Earth’s gravity field and its time variations), well-defined, highly accurate and stable global Earth-fixed and celestial reference frames are of primary importance. Over the last decade considerable changes took

Apr 2010 | No Comment

Space Very Long Baseline Interferometry (SVLBI) is an extension of the ground-based VLBI technology to space, which involves a simultaneous observation of the same radio source by two stations; one on the ground, the other being space-based. It could not only overcome the baseline length limitation problem specific to groundbased VLBI technology, with a great improvement on the observation resolution, but could also directly…

Jun 2008 | Comments Off on VLBI geodetic precision with different models

Very Long Baseline Interferometry (VLBI) is the unique space
geodetic technique which can provide the Celestial Reference Frame (CRF), the Terrestrial Reference Frame (TRF) and the relationship between the two frames — Earth Orientation Parameters (EOP) at the same time. VLBI has a widely usage in space geodetic, ground
geodetic, geophysical fields and so on. Presently, it can determine the position of the radio source outside the galaxy with 1mas precision, and determine several kilometers length of baseline on the earth’s surface with 1cm precision. Due to its high stability and high precision character, the Celestial Reference Frame outside the galaxy based on VLBI has been the best realization of the quasi-inertial referenceframe since 1980s. VLBI stations are the most important benchmarks in the International Terrestrial Reference Frame (ITRF), and VLBI is one main supporting technique which determines EOP. Till now, space and ground VLBI have accumulated more than 20 years’ data. They provide continuous and long-term data guarantee for space geodetic, ground
geodetic and geographical research.

Oct 2007 | Comments Off on The Potential of VSOP2

SVLBI (Space Very Long Baseline Interferometry) is an extension of the ground-based VLBI into the space. It has some important potential applications in geodesy and geodynamics, including the definition, practical realization, and the interconnection of different reference frames, determining the geocentric positions of VLBI stations, estimation of the gravity field of the Earth, and satellite orbit determination using the delay and delay rate observables.

Jun 2007 | Comments Off on The “Real” Definition of “ITRF”

To create no residual global rotation with regards to the crust in time evolution in orientation, IERS in the first ITRF88 retained the BIH Conventional Terrestrial System (CTS) and its Conventional Terrestrial Pole (CTP) 1984.0. Since then, it has realized the same “Pole”. However, IERS changed the name “CTP” to International Reference Pole (IRP).
Historical Start
The Earth’s first Terrestrial Reference Frame (TRF) was called Conventional International Origin (CIO) 1905 where the mean orientation of the Z-axis was defi ned by International Latitude Service from six years of observations between 1900 to 1905 (Note: There is NO other “CIO” ever defi ned). The records are not clear whether ILO ever provided a specifi c defi nition for the X-axis and/or the zero meridian.

Feb 2007 | Comments Off on The datum debate continues

In India, for topographical mapping, we are using an old Geodetic Datum (reference ellipsoid on which the coordinates: Latitude and Longitude are projected, and mapping is carried out), called Everest 1880, defined by the work of Col. George Everest (one of the greatest Geodesists, for whom the highest peak in the world is named). It is a local datum, best-fi tting for India (as in 1880), but not fi tting the Earth as a whole in the best possible manner.

Feb 2007 | Comments Off on Determination of local gravimetric geoid

The demand for a high resolution geoid model has grown substantially during the last few decades especially after inception of Global Positioning System (GPS). Many countries across the world have already developed their own geoidal model which serve as the means of deriving orthometric heights from GPS observations. The impact of GPS on surveying application is undeniable. More so, this revolution has not been confi ned to the surveying community, but has extended into mapping, navigation and Geographic information system (GIS) areas. During the last few years, we have been witnessing the wide spread adoption of GPS with an equivalently
vibrant range of accuracy requirement. Many of these applications require accurate vertical positions.
The task of transforming the ellipsoidal height obtained from GPS technique to the orthometric height has prompted geodesists around the world to determine the high precision geoid undulations, for their region of interest. In India the present day nation wide geoid was computed a long time back and based on astro geodetic observations with respect to Everest spheroid. It has various limitations and does not have any signifi cance as far as GPS solutions for orthometric height is concerned.