SECTION V

GEODYNAMICS

GEODYNAMIQUE

President: M. Feissel (France)

Secretaries: C. Wilson (USA)

(Commission V) H.-G. Wenzel (Germany)

(Commission VII) T. Tanaka (Japan)

I- Terms of Reference

According to the by-laws of the IAG, the Section V "Geodynamics" deals with the following topics :

-  reference systems,

- monitoring and study of time-dependent phenomena, such as polar motion, Earth rotation, Earth tides, recent crustal movements, variations of gravity, sea surface topography including mean sea level,

- geodetic aspects of international geodynamic projects, such as the Lithosphere project,

- geophysical interpretation of gravity and related data.

The objectives of Section V are :

(a) to promote the study of all scientific problems mentionned above and encourage the research in these fields,

(b) to promote and coordinate international cooperation in this field,

(c) to provide, on an international basis, for discussion and exchange of the results of the studies, research and works indicated in paragraph (a) and (b) above,

(d) to involve as many active geodesists as possible in the program of the Section V and to make them enthousiastic supporters,

(e) to promote the cooperation with other international organizations workin in the field of geodynamics.

II- Structure

Commissions :

Commission V : Earth Tides

President: H.-G. Wenzel (Germany)

Commission VII : Recent Crustal Movements

President : T. Tanaka (Japan)

Special Commissions :

SC 3 : Fundamental Constants

President : E. Groten (Germany)

SC 8 : Sea Level and Ice Sheet Variations

President : W.E. Carter (USA)

Special Study Groups :

SSG 5.172 : Understanding Natural Hazards :

The geodetic contribution

Chairman : S. Okubo (Japan)

SSG 5.173 : Interaction of the Atmosphere and Oceans with the Earth's Rotational Dynamics

Chairman : C. Wilson (USA)

SSG 5.174 : Geophysical Interpretation of Temporal Variations of the Geopotential

Chairman : A. Cazenave (France)

SSG 5.175 : Interannual Variations of the Vertical and their Interpretations

Chairman : Z.X. Li (China)

International Services

International Centre of Earth Tides (ICET)

Director : B. Ducarme (Belgium)

International Earth Rotation Service (IERS)

Chairman of the DB : C. Reigber (Germany)

Director of the CB : M. Feissel (France)

Permanent Service for Mean Sea Level (PSMSL)

Director : P.L. Woodworth (UK)

Bureau International des Poids et Mesures (BIPM)

Time Section

Director Time Section : C. Thomas (France)

Commission V

Earth Tides

Marées Terrestres

President : H.-G. Wenzel (Germany)

Vice-President : S. Takemoto (Japan)

Secretary : O. Francis (Belgium)

1. Program of Activities

The objective of the Commission is to promote international cooperation and coordination of investigations related to the observation, pre-processing, 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 celestial bodies as the Moon, the Sun and the planets.

The Commission will collaborate with all international and national organizations concerned with the observation, pre-processing, analysis and interpretation of earth tides.

The Commission will make standard software for the prediction of earth tide phenomena available to the scientific community by an electronic information service, established at November 1st 1995 under :

address : gik.bau-verm.uni-karlsruhe.de

login : ftp

password : ftp

directory : pub/etc

The Commission will encourage and promote campaigns to develop, compare and calibrate instrumentation for earth tide observations, techniques of operation, procedures for data pre-processing and data analysis.

The Commission will organize the 13th International Symposium on Earth Tides at Brussels/Belgium in 1997.

2. Working Groups

- Working Group 1 : Theoretical tidal model

Chairwoman : V. Dehant (Belgium)

- Working Group 2 : High precision tidal data processing

Chairman : G. Jentzsch (Germany)

- Working Group 3 : Tidal measurements and geodynamic research

Chairman : R. Vieira (Spain)

- Working Group 4 : Calibration of gravimeters

Chairman : NN

- Working Group 5: Global gravity monitoring network

Chairman : B. Richter (Germany)

3. International Centre For Earth Tides (Icet)

The Commission supports the activities of the International Centre for Earth Tides (ICET) in collecting, analysing and distributing earth tide observations. The ICET is considered as the executive office of the Earth Tide Commission.

4. National Representatives

B. Ducarme (Belgium)

S. Pagiatakis (Canada)

H.T. Hsu (China)

Z. Simon (Czech Republic)

O.B. Andersen (Denmark)

J. Hinderer (France)

B. Richter (Germany)

S. Moldenski (Russia)

C.L. Merry (South Africa)

R. Vieira Diaz (Spain)

E. Klingele (Switzerland)

S. Hekimoglu (Turkey)

J. Wahr (USA)

Commission VII

Recent Crustal Movement

Mouvements récents

de l'écorce terrestre

President : T.Tanaka (Japan)

Secretary : W.Augath (Germany)

I- Objectives

- To promote the study of recent crustal movements.

- To promote and coordinate international cooperation in research of recent crustal movements.

- To support to exchange information and to publish the results of international studies.

II- Program of activities

1. Investigation of recent crustal movements by space techniques and conventional methods from the global viewpoint of geodynamics.

2. Improvement of methods for monitoring recent crustal movements of various scales as well as for data processing and analysis to develop modelling the dynamical process and to understand the mechanism of the movements.

3. Cooperation with CSTG and geophysical study groups in order to promote the above activities.

4. Cooperation with oceanic science research groups in order to understand the crustal movements under the ocean bottom.

The results from research activities in recent crustal movements will be presented and information will be exchanged at the Ninth International Symposium on Recent Crustal Movements in Cairo (1998), and IAG Regional Symposium on Deformations and Crustal Movement Investigations Using Geodetic Techniques in Szekesfehervar, Hungary (1996).

III- The internal organization

Bureau:

President : T.Tanaka (Japan)

Vice-President : P.Vanicek (Canada)

Vice-President : H.-G.Kahle (Switzerland)

Secretary : W.Augath (Germany)

Members of Bureau:

Yu.D.Boulanger (Russia)

P.Vyskocil (Czech)

Members of Executive Committee:

Chair of Sub-Commissions:

Europe :

Nordic :

North America :

Central and South America :

West Pacific :

South Asia :

Africa : A.Tealeb

IV- The list of members

National Representatives

B.Ducarme (Belgium)

G.Carrera (Canada)

K. Schmidt (Denmark)

A.Tealeb (Egypt)

K.Feigl (France)

J.Mierlo (Germany)

I.Joo (Hungary)

K.Heki (Japan)

J. Beavan (New Zealand)

J.Krynski (South Africa)

E.R.Pujol (Spain)

H.-G. Kahle (Switzerland)

J.B.Minster (USA)

Special Commission SC3

Fundamental Constants (SCFC)

President : E. Groten (Germany)

The SC3 will basically continue the work of SC3 in the past. The updating of fundamental reference systems is the principal aim. Therefore, the following objectives etc. do not differ from those of the earlier periods.

I- Objectives

To assemble the system of the primary geodetic parameters defining the geodetic reference systems such as GRS.

To review the current information on the numerical values of physical quantities which are fundamentally important in the fields of astronomy, geodesy, and geodynamics.

To combine this information into a uniform, compatible set.

To recommend to the XXIInd General Assembly (1999) of I.A.G. the publication of a set of most up-to-date representative values.

To consider and contact the status of the GRS 1980 in view of any necessary changes in this reference system, and to make a recommendation to the XXIInd I.A.G. General Assembly.

II- Membership

C. Boucher (France)

M. Bursa (Czech Republic)

B.H. Chovitz (USA)

A.H. Cook (United Kingdom)

J.O. Dickey, (USA)

R.J. Eanes (USA)

T. Fukushima (Japan)

A.M. Gontier (France)

E.W. Grafarend (Germany)

E. Groten (Germany)

Hsu Hotse (China)

D.D. McCarthy (USA)

H. Moritz (Austria)

E.C. Pavlis (USA)

G. Petit (France)

J.C. Ries (USA)

J.M. Rüeger (Australia)

A. Sidorov (Russia)

Z. Sima (Czech. Republic)

F.R. Stephenson, (United Kingdom)

C.C. Tscherning, (Denmark)

J.G. Williams (USA)

Ye Shuhua (China)

Additional members :

R. Vicente (Portugal)

M.I. Yurkina (Russia)

B. Guinot (France)

V.A. Brumberg (France)

Special Commission SC8

Sea Level and Ice Sheet Variations

President : W.E. Carter (USA)

1. Terms of Reference

- Promote, encourage, and assist international cooperation in studies and observing programs to apply advanced geodetic techniques to understanding the current rates and causes of changes in sea level and ice sheets.

- Foster interdisciplinary communication and cooperation among geodesists, geophysicists, glaciologists, oceanographers, and related earth scientists in the observation, study, interpretation, modelling and prediction of sea level and ice sheet temporal variations.

- Maintain close liaison with appropriate organizations such as Commissions and Special Study Groups of the International Association for Physical Sciences of the Ocean (IAPSO), the International Geosphere-Biosphere Program (IGBP) Land Ocean Interaction in the Coastal Zone (LOICZ) Projects, and national agencies with related responsibilities and programs, e.g., the US National Oceanic and Atmospheric Administration (NOAA).

Structure

- The President of SC8, the Presidents of Sub-Commissions formed by SC8, and the representatives of projects organized, coordinated, or endorsed by SC8 will serve as an ad hoc steering committee for SC8.

- Sub-Commissions and/or project teams will be organized by SC8 as deemed appropriate to carry out the work of Commission.

- Based on proposals submitted at General Assembly XXI, three Sub-Commissions will be established immediately upon approval of the SC8 plan by IAG :

. SSC8.1 Studies of the Baltic Sea, led by J. Kakkuri;

. SSC8.2 Vertical Crustal Deformation at the Edges of Continental Ice Masses, led by R. Dietrich.

. SSC8.3 Geodetic Methods for Ice-sheet Monitoring, led by Hans Werner Schenke.

3. Membership

G. Blewitt (UK)

T.S. James (Canada)

P. Morgan (Australia)

B. Douglas (USA)

S. Zerbini (Italy)

T. Yoshino (Japan)

A. Dodson (UK)

J. Wahr (USA)

E.R. Ivins (USA)

R. Peltier (Canada)

C. Bentley (USA)

W. Wiejak (Poland)

D.S. Robertson (USA)

A. R. de Mesquita (Brazil)

D. Pugh (UK)

J. Manning (Australia)

J. Kakkuri (Finland)

C. Lingle (USA)

H.W. Schenke (Germany)

R. Dietrich (Germany)

B. Engen (Norway)

J. Hannah (New Zealand)

B. Richter (Germany)

G. Maul (USA)

P. Woodworth (UK)

J.O. Dickey (USA)

K. Lambeck (Australia)

M. Bevis (USA)

Y. Takahashi (Japan)

M. Odamaki (Japan)

W.E. Carter (USA) - President

Sub-Commission SC 8.1

Vertical Crustal Deformation at the Edges

of Continental Ice Masses

1. OBJECTIVES

- Observe vertical crustal deformations with geodetic techniques in the marginal regions of continental ice masses (Greenland, Antarctica)

- Contribute with these observations to verify both ice load (historical and recent ice mass changes) and rebound models (viscoelastic response) in close interdisciplinary cooperation with modelling experts from glaciology and geophysics

2. Program of Activities

- Coordinate and initiate GPS observations of highest accuracy in ice free areas of Greenland and Antarctica (campaigns at remote sites in addition to permanent IGS stations)

- Promote use of other geodetic observations (gravimetry, tide gauge) for the purpose of SSC8.2

- Perform a consistent geodetic modelling of time variation of observed quantities (ellipsoidal heights, gravity, sea level) including periodical load changes due to ocean tides and seasonal ice mass variations

- Intercompare the observed geodetic effects with predictions of ice mass and rebound models, discuss the error budget of geodetic observations, ice mass balance models and viscoelastic modelling in interdisciplinary cooperation (glaciology, geophysics)

- Come out with conclusions on historical and recent ice mass changes in consistence of models and geodetic data. Compare these results with direct observations of recent ice mass changes (e.g. ice altimetry and INSAR, cooperation with SSC8.3)

Sub-Commission SC 8.2

"Vertical Crustal Deformation at the Edges of Continental Ice Masses"

Members :

R. Dietrich (Germany)

C. Boucher (France)

E. Dongchen (China)

R. Forsberg (Denmark)

G. Gendt (Germany)

P. Huybrechts (Germany)

F. Madsen (Denmark)

J. Maekinen (Finland)

D. McAdoo (USA)

K. Shibuya (Japan)

Sub-Commission SC 8.3

Geodetic Methods for Ice-sheet Monitoring

1. Rationale

Continental ice-sheets have great impact on the world climate, the global sea level and the weather patterns on all temporal and spatial scales. Therefore, precise geodetic methods and techniques must be evaluated and used for surveying and monitoring their size, extension and dynamic parameters.

2. Objectives

Observe horizontal and vertical movements and local strain rates, the surface topography, the structure and the margins of ice-sheets with geodetic methods.

Study the feasibility of advanced techniques (satellite radar altimetry, interferometric synthetic aperture radar, kinematic differential GPS, etc.) for surveying and monitoring ice-sheets and verify these observations with ground truth and geodetic fieldwork.

Monitor temporal variations of the ice-sheets extension and dynamics, in close interdisciplinary collaboration with glaciologists and geophysicists, in order to study the state (steady or unsteady) of the ice-sheets.

3. Work Program

- Study, by ground truthing in test areas, the accuracy of satellite radar altimetry for topographic mapping and for the observation of time dependent surface height changes.

- Investigate recent developments in interferometric synthetic aperture radar (INSAR) for monitoring height changes and structures of ice-sheets.

- Examine geodetic and geophysical methods of precisely measuring the vertical velocity of ice sheets with a maximum accuracy as this parameter is a direct indicator of ice mass balance.

- Organize interdisciplinary workshops and symposia together with glaciologists, geophysicists and others to foster interdisciplinary collaboration and communication and to harmonize the field activities.

- Observe and analyse the effect of ocean tides on ice-shelves in Antarctica.

Members :

G. Casassa (Chile)

M. Lange (Germany)

W. Niemeier (Germany)

N. Reeh (Denmark)

G. Seeber (Germany)

J. Sievers (Germany)

D. Vaughan (UK)

I. Whillans (USA)

D. Wingham (UK)

Special Study Group 5.172

Understanding Natural Hazards -

Geodetic Contribution

Chairman : S. Okubo (Japan),

I. Objectives

Applying theoretical, observational, and instrumental techniques to better understand natural hazards such as earthquake, volcanic eruption, and land slide.

II. Planned Activities

- Developing techniques to detect hidden seismic faults, premonitory signals of volcanic eruption/land slide from geodetic data.

Emphasis will be placed on air-borne precise gravimetry, SAR interferometry, Satellite altimetry, dense GPS monitoring network.

- Improving theory, which predicts changes of the geodetic observables : baseline change, elevation change, gravity change, strain and tilts changes and so on.

III. Membership

J. Brozena (U.S.A.)

G. Hein (Germany)

K. Hudnut (U.S.A.)

J. Kahar (Indonesia)

D. Massonnet (France)

M. Murakami (Japan)

T. Niebauer (U.S.A.)

S. Okubo (Japan) - Chairman

P. Pâquet (Belgium)

W. M. Welsch (Germany)

Zhao Shaorong (China)

Special Study Group 5.173

Interactions of the

Atmospheres and Oceans with the

Earth's Rotational Dynamics

Chairman : C.R. Wilson (USA)

I. Terms of Reference

International Association of Geodesy Special Study Group 5.173, 'Interaction of the Atmospheres and Oceans with the Earth's Rotational Dynamics' is established to coordinate studies related to understanding the causes of observed rotational variations arising from oceanic and atmospheric variability over the range of time scales from hours to decades. Understanding these rotational variations requires a combined effort of theory, observation, and numerical modelling of geodetic, oceanographic, and atmospheric processes

II. Program of Activities

Attention will be given to the following scientific problems and activities:

Analysis of global numerical models of the oceans and atmosphere, including wind contributions, torques, and angular momentum regional and global scale fluxes and budgets.

Polar motion, nutation and interactions of oceans and atmospheres with the earth at periods near 1 day and less.

Understanding the loss of correlation between atmospheric and earth rotation time series at periods shorter than about 2 weeks.

Earth rotation variability at periods longer than a year, as measures of climate, sea level change, and internal processes.

The SSG will communicate through electronic mail, and a WWW site will be maintained to post items of interest to the membership. The test version of the WWW site is located at :

http://www.utexas.edu/cons/geo/wilson/

This should prove to be an effective tool in developing the interdisciplinary communication that is required to address these problems.

Meetings of the SSG will be organized to coincide with other geophysical and geodetic conferences. Discussions concerning any special meeting activities of this SSG will be held electronically, and at the Fall meeting of the American Geophysical Union in San Francisco, in connection with a special Union Symposium on Earth Rotation.

III. Membership

Members

A. Brzezinski Poland)

S. Dickman (USA)

F. Bryan (USA)

B. Chao (USA)

S. Desai (USA)

O. de Viron (Belgium)

J.O. Dickey (USA)

M. Eubanks (USA)

M. Furuya (Japan)

T. Herring (USA)

D. Gambis (France)

H. Itoh (Japan)

K. Kuma (Japan)

R. Ponte (USA)

C. R. Wilson (USA) - Chairman

S. Yoshida (Japan)

D. Zheng (China)

Corresponding members

M. Bell (UK)

P. Brosche (Germany)

V. Dehant (Dehant)

R. Eanes (USA)

M. Feissel (France)

P. Gegout (France)

R. Gross (USA)

J. Hinderer (France)

T. Johnson (USA)

B. Kolaczek (Poland)

W. Kosek (Poland)

C. Ma (USA)

R. Madden (USA)

P. Mathews (Canada)

J. Merriam (Canada)

J.-F. Minster (France)

I. Naito (Japan)

J. Nastula (Poland)

D. Peltier (Canada)

J. Ray (USA)

R. Ray (USA)

R. Rosen (USA)

D. Salstein (USA)

J. Wahr (USA)

K. Weickmann (USA)

Special Study Group 5.174

Geophysical Interpretation of Temporal Variations

of the Geopotential

Chairman : A. Cazenave (France)

I- Terms of Reference

1. Current status on the determination of the temporal variations of the Earth's gravity field and expected improvments

2. Relationships with geophysical phenomena

- Subdecadal fluctuations : decadal, seasonal and intraseasonal time scales;

Constraints on surface mass redistributions within atmosphere and oceans,

Continental water storage, melting or accumulation of glaciers, etc.

- Long term ( larger than 10 years) and secular changes, with inference on :

Long period tides

sea level changes

mass balance of Antarctica and Greenland

Post glacial rebound and mantle viscosity structure

3. Complementary inputs from LOD and polar motion

Members

S. Bettadpur (USA)

R. Biancale (France)

A. Cazenave (France) - Chairman

M. Cheng (USA)

B.F. Chao (USA)

R. Eanes (USA)

P. Exertier (France)

P. Gegout (France)

T.S. James (Canada)

S. Klosko (USA)

J. Mitrovica (Canada)

S. Nerem (USA)

Y. Tamura (Japan)

J. Wahr (USA)

Special Study Group 5.175

Interannual Variations of

the Vertical and Their Interpretation

Chairman : Z.X. Li (China)

I. Objectives :

Further investigating the possibility of deriving the variations in the deflection of the vertical, including those in intraseasonal time scale if the Hipparcos Star Catalog is able to be used successfully in the near future from the optical astrometric observations; interpretations of these variations in examining the roles of atmosphere, ocean, and inner part of the terrestrial globe in causing these variations ; to search if abnormal deflection of the vertical could be used as a precursor to seismic events.

II. Program of activities :

- Selection of the continuous observational data of astrometric and gravimetric instruments performed in the past and still in operation, including stations distributed in seismic areas and low seismic areas ;

- Preparation of the atmospheric and oceanic data and other usable geophysical data; discussion in theory and data analysis ;

- Interpretation.

III. Members

M. Barlik (Poland)

M. Becker (Germany)

P. Gegout (France)

H.Li (China)

Z.-X. Li (China) - Chairman

H.-P. Sun (Belgium)

J. Vondrak (Czech Rep.)

International Center for Earth Tides

Centre International des

Marees Terrestres

(ICET)

(Federation of Astronomical and Geophysical Data Analysis Services, FAGS)

(World Data Center-C For Earth Tides)

Director : B. Ducarme (Belgium)

Vice-Director : Olivier Francis (Belgium)

Activities:

- Summary of Data Held: data from about 360 worldwide tidal gravity stations (hourly values, main tidal waves obtained by least squares analyses, residual vectors, oceanic attraction and loading vectors). The Data Bank contains also data from tiltmeters and extensometers.

- Data Products, Publications, Catalogues: a "Bulletin d'Informations Marees Terrestres" is published two or three times a year which contains a very great number of translations of Russian and some Chinese papers.

- A General Bibliography with 5027 references is also regurlaly kept up to date and published.

- User Services: the Center provides assistance for the setup of new stations, calibrations of the instruments, data processing as well as for tidal analysis. The assistance is accomplished either by a stay at the Centre or by providing FORTRAN programs.

- The ICET makes also available tidal predictions for any place and time, which are needed for field gravimetry, absolute gravity measurements and for tilt measurements. These predictions can be computed either on the basis of elastic Earth models and oceanic cotidal maps, or on basis of the results of direct measurements.

International Earth Rotation Service Service International de la

Rotation Terrestre

(IERS)

(Federation of Astronomical and Geophysical Data Analysis Services, FAGS)

Chairman of the Directing Board :

C. Reigber (Germany)

Director of the Central Bureau:

M. Feissel (France)

The International Earth Rotation Service (IERS) was established in 1987 by IAU and IUGG and it started operation on 1988 January 1st. It replaces the International Polar Motion Service (IPMS) and the earth-rotation section of the Bureau International de l'Heure (BIH) ; the activities of BIH on time are continued at Bureau International des Poids et Mesures (BIPM). IERS is a member of the Federation of Astronomical and Geophysical Data Analysis Services (FAGS).

I- Functions

IERS is responsible for :

- defining and maintaining the international terrestrial reference system recommended by the IUGG, based on observing stations that use the high-precision techniques in space geodesy ;

- defining and maintaining the international celestial reference system recommended by the IAU that is based on extragalactic radio sources, and relating it to other celestial reference systems ;

- determining the earth orientation parameters connecting these systems, the terrestrial and celestial coordinates of the pole and universal time ;

- organising operational activities for observation and data analysis, collecting and archiving appropriate data and results, and disseminating the results to meet the needs of users.

In 1996 it relies on five observing techniques: Very Long Baseline Interferometry (VLBI), Lunar Laser Ranging (LLR), Global Positioning System (GPS), Satellite Laser Ranging (SLR), and Doppler Orbit Radio-positioning Integrated on Satellite (DORIS).

II- Organisation

The main centres in IERS are the Central Bureau, Sub-bureaus, and Coordinating Centres for each of the observing techniques. It is supported by many other organisations that contribute to the tasks of observation and data processing.

The Coordinating Centres are responsible for organizing observations, objects to be observed, schedules, preprocessing of observational results, etc. and for the selection of models and procedures to be used in the analysis of observations. These centres are the following in 1995.

VLBI Coordinating Centre

National Earth Orientation Service

MS 926.9

Goddard Space Flight Center

Geodynamics Branch

Greenbelt, MD 20771, USA

Internet: CMA@GEMINI.GSFC.NASA.GOV

LLR Coordinating Centre

OCA/CERGA

Avenue Nicolas Copernic

06130 Grasse - France

Internet: veillet @ocar01.obs-azur.fr

GPS Coordinating Centre

Jet Propulsion Laboratory

MS 238-540

4800 Oak Grove Drive

Pasadena, CA 91109 - USA

Internet:BILL_MELBOURNE.

JPL#u#330#u#QMail@JPL-335-

SERVER.JPL.NASA.GOV

SLR Coordinating Centre

Center for Space Research 60605

The University of Texas at Austin

Austin, TX 78712-1085 - U S A

Internet: schutz@utcsr.ae.utexas.edu

DORIS Coordinating Centre

Institut Geographique National

B P 68

2 avenue Pasteur

94160 Saint-Mande - France

Internet: willis@ign.fr

The observations are organized in networks for each of the observing techniques, under the responsibility of the IERS Technique Coordinating Centres. They are archived in data centres and distributed to Analysis Centres. Some of the centres contribute, in operational mode, earth-orientation data to the Sub-Bureau for Rapid Service and Predictions (weekly bulletins) and to the Central Bureau (monthly bulletins). Most Analysis Centres produce global solutions based on many years of observations, including the determination of station positions and velocities, earth rotation and, in the case of VLBI, directions of extragalactic compact radio sources. The Central Bureau combines the various types of results to obtain the final results, which are disseminated to the user community in Annual Reports and electronically accessed data bases. Assessment of the accuracy and precision of the contributed solutions is also provided. Technical Notes are distributed; some describe the IERS Standards, while others contain the reports of the Analysis Centres and details of the final IERS results. The mailing list includes 780 institutes in 62 countries : space-geodesy and astronomical observatories, geodetic institutes, universities, time services, etc. The observational results of VLBI, LLR, GPS, SLR and DORIS are archived at several centres, subject to the agreement of the relevant Coordinating Centres. The results on earth rotation and reference frames are archived at the network and analysis centres which obtained them, as well as at the Central Bureau.

The atmospheric data related to earth-orientation variations from four major meteorological centres are collected, validated and made available by the Sub-Bureau for Atmospheric Angular Momentum. Currently, there are four participating centers contributing to the Sub-Bureau. It serves as a focal point for the collection of atmospheric measurements. The data is made available within the IERS and to the users community. Research is performed in order to assess the accuracy and completeness of the series derived by the participating meteorological centers.

The Central Bureau decides and disseminates the announcements of leap seconds in UTC and values of DUT1 to be transmitted with time signals.

The principal IERS centres are :

CENTRAL BUREAU

Observatoire de Paris

61, avenue de l'Observatoire

75014 Paris - France

Internet: iers@obspm.fr

Terrestrial Frame Section

Institut Geographique National

B.P. 68

94160 St Mande - France

Internet: boucher@ign.fr

Earth Orientation Section

Observatoire de Paris

61, avenue de l'Observatoire

F-75014 Paris - France

Internet: gambis@obspm.fr

Celestial Frame Section

Observatoire de Paris

61, avenue de l'Observatoire

F-75014 Paris - France

Internet: felicitas@fcaglp.edu.ar

- SUB-BUREAU FOR RAPID

SERVICE AND PREDICTIONS

National Earth Orientation Service

U.S. Naval Observatory

3450 Massachusetts Avenue, N.W.

Washington DC 20392-5420 - U S A

Internet: dmc@maia.usno.navy.mil

- SUB-BUREAU FOR ATMOSPHERIC

ANGULAR MOMENTUM

Climate Analysis Center

NOAA/National Weather Service

5200 Auth Road-Room 805

Washington, DC 20233 - U S A

Internet: salstein@aer.com

The Directing Board exercises general control over the activities of the service, including modifications to the organisation and participation that would be appropriate to maintain efficiency and reliability, while taking full advantage of the advances in technology and in theory. It is advised by a group of Corresponding Members, who are kept informed of the activity of the Directing Board and are encouraged to submit comments and suggestions. The secretary of the Board is provided by the Central Bureau.

The Members of the Board are, in 1996 :

C. Reigber International Union of Geodesy and Geophysics

B. Kolaczek International Astronomical Union

O.B. Andersen Federation of Astronomical and Geophysical Data

Analysis Services

C. Ma VLBI Coordinating Centre

C. Veillet LLR Coordinating Centre

W.G. Melbourne GPS Coordinating Centre

B.E. Schutz SLR Coordinating Centre

P. Willis DORIS Coordinating Centre

M. Feissel Central Bureau

with the permanent participation of :

D.D. McCarthy Sub-bureau for Rapid Service and Predictions

C. Boucher Terrestrial Reference Frame Section of the Central Bureau

F. Arias Celestial Reference Frame

Section of the Central Bureau

D. Gambis Earth orientation Section of the Central Bureau

D. Salstein Sub-bureau for Atmospheric Momentum

III- Publications

. Weekly Bulletin A Earth orientation parameters (x,y,UT1,dy,de) : Rapid Service, prediction. First issue covering observation dates in the last week in 1987.

. Monthly Bulletin B Earth orientation parameters (x,y,UT1,dy,de) combined solution and individual series. Information on UTC time scale. First issue covering observation dates in January 1988.

. Annual Report Earth-orientation parameters, terrestrial and celestial frames of the IERS Reference System: combined solutions and analysis of individual results. First issue, Report for 1988, published in July 1989.

. Special Bulletin C Announcement of the leap seconds in UTC.

. Special Bulletin D Announcement of the value of DUT1 to be transmitted with time signals.

. Technical Notes Reports and complementary information of relevance to the work of IERS on Earth orientation and the reference systems. The IERS Conventions (called earlier IERS Standards are published every three years in this series).

The precision of the published results depends on the delay of their availability. For the operational solutions of earth rotation (weekly and monthly bulletins) it is of the order of one millisecond of arc. The prediction accuracy is in the range of 0.005-0.020" for x,y, 0.002-0.015s for UT and 0.002" for dy, de (prediction lags of 10 and 90 days). For the scientific solution of reference frames and Earth orientation, the inaccuracy is lower than 0.0003" (1 cm).

The IERS publications are airmailed. Bulletin A is prepared and distributed by the sub-bureau for Rapid Service and Predictions;

The other publications are prepared and distributed by the Central Bureau. Bulletins A and Bulletin B are also distributed by e-mail and available on anonymous FTP (File Transfer Protocol) and World Wide Web.

The sub-bureau for Rapid Service and Predictions makes available various results on a Bulletin Board.

The Permanent Service For

Mean Sea Level

(PSMSL)

(Federation of Astronomical and Geophysical Data Analysis Services, FAGS)

Director : P.L.Woodworth (UK)

Introduction

Since 1933, the Permanent Service for Mean Sea Level (PSMSL) has been responsible for the collection, publication, analysis and interpretation of sea level data from the global network of tide gauges. It is based at the Proudman Oceanographic Laboratory, Bidston Observatory, United Kingdom and is a member of the Federation of Astronomical and Geophysical Data Analysis Services (FAGS) established by the International Council of Scientific Unions (ICSU). It is supported by FAGS, by the Intergovernmental Oceanographic Commission (IOC) and by the U.K. Natural Environment Research Council. Information on FAGS and its various services, including the PSMSL, can be found in FAGS (1989).

Description of PSMSL 'RLR' and 'metric' datasets

The database of the Permanent Service for Mean Sea Level (PSMSL) contains monthly and annual mean values of sea level from approximately 1600 tide gauge stations around the world.

The PSMSL receives monthly and annual mean values of sea level from approximately 110 national authorities, distributed around the world, responsible for sea level monitoring in each country or region. Data from each station are entered directly as received from the authority into the PSMSL raw data file for that station (usually called the METRIC file in PSMSL publications). The monthly and annual means so entered for any one year are necessarily required to be measured to a common datum, although, at this stage, datum continuity between years is not essential. While the PSMSL makes every attempt to spot inconsistent or erroneous data, the responsibility for the monthly and annual means entered into the METRIC files in this way is entirely that of the supplying authority. A description of data checks routinely made by the PSMSL is given in Woodworth, Spencer and Alcock (1990) and IOC (1992a).

In order to construct time series of sea level measurements at each station, the monthly and annual means have to be reduced to a common datum. This reduction is performed by the PSMSL making use of the tide gauge datum history provided by the supplying authority. To date, approximately two thirds of the stations in the PSMSL database have had their data adjusted in this way, forming the 'REVISED LOCAL REFERENCE' (or 'RLR') dataset. For scientific purposes, the RLR dataset is normally superior to the 'METRIC', although the latter, which contains the total PSMSL data holdings, can also be analysed bearing in mind the above datum continuity considerations.

The RLR datum at each station is defined to be approximately 7000mm below mean sea level, with this arbitrary choice made many years ago in order to avoid negative numbers in the resulting RLR monthly and annual mean values. The detailed relationships at each site between RLR datum, benchmark heights, tide gauge zero etc. are not normally required by analysts of the dataset, although they can be made available on request.

The contents of the PSMSL dataset have been described in a report 'Data Holdings of the PSMSL November 1993' (Spencer and Woodworth, 1993). This replaces similar reports from 1987 and 1991 and it is intended that further regular updates will be produced. Copies can be obtained on request from the address shown below. Further information about the PSMSL, together with maps and plots of the spatial and temporal distribution of PSMSL data, can be found in reports by Woodworth (1990, 1991) and Woodworth, Spencer and Alcock (1990).

Copies of the PSMSL dataset can be obtained over the Internet by Anonymous FTP. Alternatively, data can be obtained on a CDROM.

In special circumstances, subsets of the dataset can be provided on floppy disk or as computer printout.

The PSMSL will be pleased to provide data, information and advice to all organisations and individuals interested in measuring and analysing sea level changes.

Geocentric coordinates of tide gauge benchmarks

In 1988 a meeting of tide gauge experts and geodesists was held at the Woods Hole Oceanographic Institution under the auspices of the IAPSO Commission on Mean Sea Level and Tides. The conclusions of the meeting were published as Carter et al. (1989). A key recommendation of the meeting was that geocentric coordinates of tide gauge benchmarks, derived primarily from differential Global Positioning System (GPS) measurements relative to International Earth Rotation Service (IERS) `fundamental points' (but not exclusively e.g. DORIS), should be stored at the PSMSL alongside the sea level data.

A follow-up meeting was held in December 1993 at the Institute of Oceanographic Sciences Deacon Laboratory, Wormley, Surrey to review progress, with the conclusions and recommendations published as Carter (1994). Since the Woods Hole meeting, considerable developments have taken place with the GPS technique in particular and with the organization of centres to analyse such data, in particular with the development of the International GPS Service for Geodynamics (IGS). The PSMSL will work closely with the IGS and other organisations in order to provide time series of vertical land movements alongside the sea level time series.

Linkage to the IOC GLOSS programme and to woce sea level centres

The IOC-coordinated Global Sea Level Observing System (GLOSS) programme has as its aim the establishment of a high quality global core network of approximately 300 tide gauges to serve the various oceanographic and climate change related sea level research purposes of the next decades (Pugh, 1987; IOC, 1990a; Woodworth, 1991). The PSMSL took a major lead in the planning of GLOSS which in the long term will result in a significant improvement in the quantity and quality of data delivered to the PSMSL. Further information on the development of GLOSS from a PSMSL perspective can be found in IOC (1990b, 1991, 1992b) and Woodworth (1990, 1991), while the PSMSL can provide details of current status at any time.

Over the past couple of years many GLOSS Contacts at national sea level authorities have contributed detailed information about their tide gauge installations to the PSMSL in order to enable the compilation of a 'GLOSS Handbook'. This publication is the main source reference of information about the GLOSS network. The Handbook, edited by Dr.Lesley Rickards on behalf of the PSMSL and IOC, was first published in early 1991, with Version 2 in March 1994, and contains full cross-reference to the PSMSL data holdings from GLOSS sites. It is available on floppy disk together with a software package to interrogate it.

Anyone wishing to obtain a copy of the 'Handbook' can mail the PSMSL at any of the above addresses or mail Dr.Rickards directly at bodcmail@pol.ac.uk.

GLOSS has played a particularly important role in the provision of training courses and training materials. The reports IOC (1985, 1988) contain information on the operation of tide gauges to GLOSS standards.

The next decade will see major efforts to collect higher frequency (typically hourly) sea level data in order to provide an 'in-situ' World Ocean Circulation Experiment (WOCE) dataset, primarily for comparison to and validation of sea level data obtained from satellite radar altimetry (WOCE, 1988a, 1988b). The designated 'WOCE tide gauges' are mostly GLOSS island sites and pairs of gauges across straits and total about 100 stations. There are two WOCE Sea Level Centres (WSLC's): one at the British Oceanographic Data Centre at Bidston Observatory alongside the PSMSL (the so-called 'slow centre'), and the other at the University of Hawaii alongside the Tropical Ocean Global Atmosphere (TOGA) Sea Level Center (the so-called 'fast centre'), with the two centres working closely together. Eventually, the centres will be producing their own data holdings reports etc.

Any requests to the PSMSL for WOCE higher frequency data will be automatically passed to the WSLC's for servicing. Alternatively, they may be contacted directly via at :

bodcmail@pol.ac.uk (Internet) (Attn. Lesley Rickards)

for the Bidston WSLC and :

mitchum@lolo.soest.hawaii.edu (Internet) (Attn. Gary Mitchum)

for the Hawaii WSLC.

Address :

Permanent Service for Mean Sea Level

Bidston Observatory

Birkenhead, Merseyside L43 7RA

United Kingdom

Telephone: (44) 151-653-8633

Fax: (44) 151-653-6269

Telex: 628591 OCEANB G

Email: psmsl@pol.ac.uk

WWW: http://www.nbi.ac.uk/psmsl/sea_level.html

FTP : bisag.nbi.ac.uk and cd pub/psmsl

Time Section

Bureau International des

Poids et Mesures

(BIPM)

Director (Time Section ) : C. Thomas (France)

The Bureau International des Poids et Mesures (BIPM) has taken full responsability of the International Atomic Time (TAI), on 1988, January 1st. TAI was previsously established by the Bureau International de l'Heure (BIH).

Functions

The BIPM is in charge of :

- establishing TAI and also Coordinated Universal Time (UTC) (except for the UTC leap second occurence and announcement, in charge of IERS),

- providing the data making TAI and UTC available in the standard laboratories,

- participating to the worldwide coordination for time comparisons.

Activities and services

TAI is established on the basis of atomic clock data and atomic frequency standards data provided by 50 laboratories or national centers.

TAI and UTC are made available by the dissemination of corrections to be applied to the readings of the master clocks of the participating laboratories.

This activity requires accurate time comparisons between remote clocks, which are mostly based on the tracking of GPS satellites. The BIPM organizes these time comparisons by providing international GPS common-view tracking schedules and by checking differential calibration of GPS time receivers. The BIPM treats raw GPS data according to a unified procedure:

- Only strict GPS common views are used to minimize Selective Availability effects.

- The international network figures local stars on continental distances added to two long-distance links between the NIST (Boulder, Colorado, USA), the CRL (Tokyo, Japan) and the OP (Paris, France),

- Long-distance links are corrected for measured ionospheric delays on site and for precise satellite ephemerides.

The ultimate uncertainty is of a few nanoseconds for a tracking duration of 13 minutes.

In 1996, the stability of TAI is about 3x10-15 for averaging times of 2 months. The TAI scale unit differs from the SI second, on the rotating geoid, by an amount of +2x10-14 s. This shift, known with a relative uncertainty of 5x10-15, is due to the uniform application (following a decision of the Comité Consultatif pour la Définition de la Seconde in March 1996) of corrections compensating for the black-body radiation shift, to the results of primary frequency standards.

In addition to TAI, whose definitive issue is available every 2 months, the BIPM establishes a scientific time scale TT(BIPM) for applications requiring ultimate long-term stability. A new version of this time scale, based on data reprocessing, is available every year and covers several past years.

Availability of BIPM time data

(a) Publications

- Circular T (monthly)

Corrections to the readings of laboratory clocks, to get TAI and UTC. Data on time comparisons. Informations.

- Annual Report of Time Section of BIPM. Methods of evaluation of TAI. Data on the clocks and time comparisons. Data from the primary frequency standards, BIPM results on time scales.

- Schedules for GPS satellites tracking (for participating laboratories), issued about twice a year.

(b) BIPM Data Service

INTERNET Anonymous ftp (node 145.238.2.2.)

See the READ.ME file for complete description.

Address

Bureau International des Poids et Mesures

Pavillon de Breteuil

92312 Sèvres Cedex

France

Phone: + 33 1 45 07 70 72

Fax: + 33 1 45 07 70 59

E-mail: tai@bipm.fr