IUGG Resolutions adopted

at the XXIth General Assembly in Boulder

and related to Geodesy


The International Union of Geodesy and Geophysics,

recognizing that:

a)since its establishment in 1988, the International Earth Rotation Service (IERS) has successfully developed a comprehensive observation and analysis system to realize the International Terrestrial Reference System (ITRS) and the International Celestial Reference System (ICRS), and to permanently link them by monitoring the Earth's orientation; and

b)IERS achievements are entirely due to the contributions of national agencies in terms of technical development, network operation, and data analysis;

noting that:

a)the IERS-published reference systems are of high quality and are used in a wide range of research and applications in geodesy and geophysics to provide quantities that the user would otherwise have to determine for himself and at his own expense;

b)the IERS Directing Board has published a strategy statement describing the optimal combination of the astronomical and space techniques to fulfill the IERS missions,

recommends that national agencies and institutions contribute to the operation of IERS by providing observations and products in compliance with the IERS Strategy.


The International Union of Geodesy and Geophysics,

referencing IUGG Resolution 4 of the XXth General Assembly in Vienna (1991) on the urgent need for an improved determination of the global gravity field of the Earth,

noting that several space agencies, such as ESA and NASA, have plans to realize a mission for the improvement of the Earth's gravity field and that such a mission will have important consequences for geodesy, solid earth physics and oceanography;

strongly recommends the implementation of a dedicated satellite gravity mission.


The International Union of Geodesy and Geophysics,

noting that Resolution C3 of the International Astronomical Union (IAU) at its XXIInd General Assembly in the Hague (1994) recommended rescinding Resolution 4 of its XVth General Assembly (1976) which established the Modified Julian Day (MJD) system, and using Julian Days as the only time scale for archiving and exchanging time-based astronomical phenomena,

recognizing that:

a)the Julian Day is not defined in terms of an internationally recognized time scale,

b)modified Julian Days are widely used in geodesy and geophysics, particularly for the slow changing parameters of the Earth Sciences, and that any change would cause confusion and risk of error,

c)Earth Sciences require the exchange of astronomical as well as geodetic and geophysical data,

requests the International Astronomical Union:

a)to reconsider its 1994 Resolution C3 regarding the use of Julian Days and to maintain the modified Julian Days scale wherever it is commonly used in geodesy and geophysics,

b)to prepare a joint IUGG/IAU recommendation for a precisely defined time scale including a continuous day-count convention suitable for archiving and exchanging time-based data used in the analysis of astronomical as well as geodetic and geophysical phenomena.