COMMISSION V:

“EARTH TIDES (1999-2003)”

 

S. Takemoto, President

 

During past four years the IAG Commission V organized the 14th International Symposium on Earth Tides in 2000 and the combined workshop of the ETC Working Group 7 and GGP in 2002.

 

The 14th International Symposium on Earth Tides (ETS2000)

 

The ETS2000 was held in Mizusawa, Iwate, Japan from August 28 to September 1, 2000. The Symposium sessions were: Tidal instrumentation; Results of ground based observations; Tidal observations using space techniques; Modeling of solid earth tides and related problems; Atmospheric and oceanic loading effects; Data processing; Superconducting gravimeters; Tidal studies in tectonic active regions; Tides on planet. 138 participants (including 10 accompanying persons) from 21 countries reported fully on their results of continuing researches on Earth tides and thus contributed to the progress of further research of Earth and Planetary Tides. Proceedings of scientific papers were published in the Journal of the Geodetic Society of Japan Vol. 47, No. 1, 2001. Other Reports on the ETS2000 including the list of participants were published in BIM (BULLETIN D'INFORMATIONS MAREES TERRESTRES). Following 11 resolutions were adopted at the closing session of the ETS2000.

 

ETS2000 Resolutions

 

  1. Recognising the importance of the observation of tidal effects and of the determination of tidal parameters by space geodetic techniques, the ETC recommends to continue this observational effort; to compare the results obtained by different space geodetic techniques between each other and with the results of ground based tidal measurements.

 

  1. Recognising the importance of the new international services on space geodetic techniques, the ETC recommends that WG6 establishes or intensifies the cooperation with the analysis coordinators of these international services concerning the tidal modelling.

 

  1. Considering the new fields of tidal research in lunar and planetary geodesy, the ETC recommends that the tidal community should take an active part in space missions related to lunar and planetary geodesy; requests a proper archiving of the data and metadata acquired during those missions and normal access to the world-wide geodetic community.

 

  1. Considering the increasing interest of the tidal community to lunar and planetary researches, the ETC recommends that a session on tides on the planets should be included in the future earth tides symposia.

 

  1. Recognising the importance of a global Earth coverage with superconducting gravimeters for the study of weak geophysical signals, for the determination of the liquid core resonance parameters, for the study of the polar motion effects on gravity, for the intercomparison of the load vectors derived from recent ocean tides models, for the study of global and regional gravity changes to validate the results of the dedicated satellite missions, the ETC recommends to extend the GGP observation period for an additional 6 year period starting July 2003, to maintain the existing sites and to encourage the installation of new GGP stations especially in the Southern hemisphere and in polar regions.

 

  1. Recognising the fact that presently the calibration of the superconducting gravimeters participating to the world-wide GGP project is not homogeneous, the ETC recommends that systematic calibration campaigns with absolute gravimeters should be planned and realised before the end of the current GGP observation period, through an international cooperative effort.

 

  1. Recognising the importance to keep in operation several calibration techniques for gravimeters to allow a mutual accuracy control, the ETC recommends that inertial calibration platforms and moving mass calibration devices should continue to be developed or maintained besides more usual calibration methods such as intercomparison with absolute or well-calibrated relative instruments.

 

  1. Recognising the importance of environmental data for the interpretation of tidal measurements, the ETC recommends:

a)       to record the following parameters:

·         The barometric pressure, temperature, precipitation, and ground water level. The sampling rate for the recording of environmental parameters should correspond to the sampling rate of the geodynamic data observed. A sufficient resolution and accuracy of the measurements of the environmental parameters should be granted.

·         Although the difficulties of monitoring soil moisture are recognised, its is recommended to undertake efforts to realize a continuous monitoring of this parameter.

·         The monitoring of wind is also recommended because wind might produce short-period noise as well as long-period modulations.

b)       to correct gravity data in long term studies for local (diameter 100km), regional (diameter 2000 km), and global atmospheric pressure signals as all three produce significant effects.

c)       to develop correction models for gravity, tilt, and strain related to:

·         ground water table variations

·         snow, rain and soil moisture

·         stress resulting from temperature variations

 

 

 

  1. Noting the importance for tidal measurements of accurate error estimates and appreciating that such estimates can be made only if the power spectral density of the noise is known, the ETC recommends to show noise spectra as Power Spectral Density expressed in unit 2/ frequency.

 

  1. On behalf of all participants of the 14th International Symposium on Earth Tides, the ETC thanks the Japanese National Committee for Geodesy, the Science Council of Japan, the Geodetic Society of Japan, the National Astronomical Observatory of Japan, the City of Mizusawa and the Iwate Prefecture for their generous support to the Symposium.

 

  1. ETC thanks the Local Organising Committee : Masatsugu Ooe (Chairman), Tadehiro Sato (Secretary) , Jiro Segawa (President of Geodetic Society of Japan) and the staff, for their wonderful welcome and their many efforts in making the 14th International Symposium on Earth Tides a great scientific success.

 

 

Combined Workshop of ETC-WG6 and GGP

 

A combined meeting of the ETC Working Group 7: Analysis of Environmental ata for the Interpretation of Gravity Measurements (Chairperson: Corinna Kroner) and the Global Geodynamics Project (Chairperson: David Crossley) was held in Jena, Germany during the period of March 11-15, 2002. The GGP Workshop concentrated on all issues surrounding superconducting gravimetry - instrumentation, site development, data processing, while at the meeting of the WG addressed topics on environmental effects on gravimeter, tilt, strain, and seismometer data. In all, 39 scientists from 16 countries participated. Proceedings of the Combined Workshop of ETC-WG6 and GGP were published in the Bulletin d'Informations des Marees Terrestres (BIM). Vols. 135 and 136, 2002.

 

 

Renewal of the ETC Homepage

 

The new ETC Homepage was opened at the following address:

http://www-geod.kugi.kyoto-u.ac.jp/iag-etc/ The standard software for the prediction of earth tide phenomena and for the processing of earth tide observations can be downloaded from the Electronic Information Service in ETC HP.

 

2nd ETC Medal

 

The ETC steering committee decided to award the 2nd ETC Medal (ETC Medal 2000) to the late Professor Hans-Georg Wenzel for his outstanding contribution to international cooperation in earth tide research. The ETC awarded the Medal to Ms Marion Wenzel at the Opening Session of ETS2000 on August 28 2000 at Mizusawa, Japan.

 

Next International Symposium on Earth Tides

 

The next (15th) International Symposium on Earth Tides will be held in Ottawa, Canada from 2-6 August 2004.