IAG Commission 3: Earth Rotation and Geodynamics
Sub-Commission 3.1: Earth Tides. 
Chair: Gerhard Jentzsch




Directing Board

G. Jentzsch (President), J. Hinderer (Vice-President), B. Ducarme (Director ICET), D. Crossley (GGP), S. Takemoto (Past-President), L. Manshina (WKG1), C. Kroner (WKG 2), Wu Bin (WKG3).

Terms of Reference 

The objective of the Sub-Commission is to promote international cooperation and coordination of investigations related to the observation, preprocessing, analysis and interpretation of earth tides. By earth tides, we understand all phenomena related to the variation of the Earth's gravity field and to the deformation of the Earth's body induced by the tide generating forces, i.e. the forces acting on the Earth due to differential gravitation of the celestial bodies as the Moon, the Sun and the nearby planets. The relation between earth tides and Earth rotation is certainly an important perspective of the work of the Sub-Commission. The Sub-Commission collaborates with all international and national organizations concerned with the observation, preprocessing, analysis and interpretation of earth tides. The Sub-Commission encourages and promotes campaigns to develop, compare and calibrate instrumentation for earth tide observations, techniques of operation, procedures for data preprocessing and data analysis. The Commission makes standard software for the prediction of earth tide phenomena and for the processing of earth tide observations available to the scientific community by the www. The Sub-Commission supports the activities of the International Center for Earth Tides (ICET) in collecting, analyzing and distributing earth tide observations. The ICET is considered as the executive office of the Earth Tide Sub-Commission. The Sub-Commission provides an Electronic Information Service with data and software files on its website. The Sub-Commission organizes yearly Earth Tides Symposia when the IAG or IUGG are not organizing general assemblies (next meeting is in Ottawa, 2-6 August 2004). The Sub-Commission creates WGs when necessary and adopts resolutions when necessary. The Sub-Commission has a medal that is delivered to a scientist for her/his outstanding contribution to international cooperation in earth tide research, on the occasion of the International Symposium on Earth Tides.

Working Groups

1. Working Group on “Gravitational Physics” chaired by Lalu Manshina, Montreal/Canada.

The general goal of the WG is to tackle among others the following scientific problems:

  • The Problem of Aberration: Modern tidal position catalogs assume that the true position of the tide causing body is responsible for the tidal forces, rather than the apparent position, as in optical astronomy. The problem may have consequences, as it may imply relative velocities between the gravity and optical signals. This is a case for experts in Celestial Mechanics and in Earth Tides.

  • The Gravitational Shielding: There is currently no accepted theory of gravity that incorporates or predicts gravitational shielding. The problem is possibly different from the absorption of gravitational radiation by matter. The Earth Tide community should think about, and search for, the consequences of shielding.


2. Working Group on “Earth Tides in Space Geodetic Techniques” chaired by Wu Bin (Instiute of Geodesy and Geophysics, Chinese Academy of Science, Wuhan, China).

The general goal of the WG is to strengthen the links between researchers of the tidal community and those who work in space geodetic techniques in both directions:

  • The tidal experts provide precise models for the displacements of observation sites on the Earths crust due to the tides and for the tidal variations to the gravitational field of the Earth;

  • The space geodetic techniques are used to validate and possibly to improve the tidal models, e.g. the tidal parameters.

The objectives or Terms of Reference are:

  • Cooperation with the analysis coordinators of the new IAG international services, e.g. IGS, IVS, ILRS, IDS, ... and the Working Groups which exist within these services,

  • Comparison of tidal parameters obtained from the different techniques,

  • Comparison of results obtained by space geodetic techniques and ground-based tidal measurements,

  • Exploring new satellites measurements (CHAMP and GRACE) for Earth tides,

  • Using GPS and ground-based gravimeter to study regional ocean tides.


The program of the WG is: 

  • Extension of the recommendations concerning the tidal influences given in the IERS Conventions (2000) to facilitate their practical use for space geodetic techniques; upgrade of 'supplements' to the IERS Conventions; establishment of subgroups of experts in order to help the IERS Convention Directing Board;

  • Evaluation and comparison of the potential of different space geodetic techniques to monitor tidal effects and to determine tidal parameters; Techniques such as VLBI, SLR, LLR, GPS and GLONASS, DORIS and PRARE, satellite altimetry will be covered; 

  • Determination of parameters of the tidal models by space geodetic techniques; This requires a priori corrections due to atmospheric and oceanic influences on the Earth's surface and on the geopotential and precise models for tidal influences on the Earth orientation parameters; The effect of pole-tide has also to be considered. 



3. Working Group on “Analysis of Environmental Data for the Interpretation of Gravity Measurements” chaired by Corinna Kroner, Jena/Germany.

The general goal of the WG is to identify the environmental parameters should be monitored and the procedure to monitor them, and to recommend the corrections and the related procedures that are necessary in the frame of tidal studies at all timescales.


The objectives of the WG are: 

  • Systematic investigation of effects of environmental parameters on the gravity vector, such as air pressure, air humidity, wind, seasonal effects of vegetation, ground water level variations, soil moisture; 

  • Understanding of the relation between the individual sources and their effects on the gravity vector, both in different periods, and different amplitudes; 

  • Development of models for the correction of environmental effects and recommendations for the recording of environmental parameters, and recommendations for the application of the corrections.


The program of the WG is: 

  • Exchange of information by meetings with printed papers in the Bulletin d'Information Marees Terrestres; 

  • Recommendations and proposals concerning the parameters to be recorded, their sampling and resolution; these parameters are temperature, humidity, precipitations (rain and snow), ground water table variations, snow accumulation, …

  • Identify efforts to realize a continuous monitoring of these parameters;

  • Identify correlation among these parameters;

  • Develop models for the correction of gravity and tilt measurements, and possibly for prediction of these corrections;

  • For this, special events could be studied and particular experiments (to be identified) could be done.