External Evaluation of the Origin and Scale of the International Terrestrial Reference Frame
The International Terrestrial Reference Frame (ITRF) datum definition is of primary importance for many Earth Science Applications. While accurate origin information (Earth Center of Mass) is required for any precise satellite orbit determination, an accu
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External Evaluation of the Origin and Scale of the International Terrestrial Reference Frame X. Collilieux and Z. Altamimi
Abstract
The International Terrestrial Reference Frame (ITRF) datum definition is of primary importance for many Earth Science Applications. While accurate origin information (Earth Center of Mass) is required for any precise satellite orbit determination, an accurate scale is indispensable for various calibrations (altimeter absolute bias, GNSS satellite antenna phase center offsets). Studies involving vertical motion determination, such as mean sea level and Glacial Isostatic Adjustment (GIA) are also affected by the choice of the underlying Terrestrial Reference Frame. ITRF datum accuracy evaluation has been traditionally performed by comparing independent space geodetic technique performances and successive ITRF solutions. While the ITRF2005 to ITRF2000 comparison may lead to pessimistic evaluation of the ITRF datum accuracy, the question is raised whether the error budget deduced from the ITRF2008 to ITRF2005 comparison would be optimistic, especially for the time evolution of the origin. It is fundamental to explore external ways to evaluate the ITRF frame parameters and especially their time evolution which impacts the results of many climatic studies. The state of art of available methods is reviewed by stressing their advantages and drawbacks. Most of them have been already implemented and show that the ITRF2005 origin rate is probably reliable at the millimeter per year level. However these methods have been applied on different velocity field with different models and required assumptions which make their mutual comparison difficult. Thus, new analyses are required in the future. Keywords
Terrestrial reference system Terrestrial reference frame
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Introduction
A Terrestrial Reference System (TRS) is required from many Earth Science applications. It can be used to express positions at the Earth’s surface and deformations of the Earth, to compare independent measurements of the same phenomena and to represent the Earth in its rotational motion
X. Collilieux (*) Z. Altamimi IGN/LAREG and GRGS, Universite´ Paris Diderot, 35 rue He´le`ne Brion, 75013 Paris, France e-mail: [email protected]
in space. A TRS is a physical concept which is defined by the specifications of its origin, orientation and scale. As the axes of the system are inaccessible, a TRS is materialized by a Terrestrial Reference Frame (TRF), through the realization of its origin and scale, the orientation of its axes with respect to the crust, as well as their time evolution. This is usually achieved through the determination of a set of coordinates as a function of time of some points distributed at the Earth’s surface as illustrated by Fig. 5.1. The origin, orientation and scale information of the frame is inherent to its coordinates. But as these are the result of an estimation process, it is necessary to use a set of stations to mitigate as much as possible the random errors. A global
Z. Altamimi and
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