Quadriennal report 2003-2006

Michel Menvielle, Daniel Schertzer, Ioulia Tchiguirinskaia

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Michel Menvielle, Daniel Schertzer, Ioulia Tchiguirinskaia. Quadriennal report 2003-2006. Comité national français de géodésie et géophysique. 2007. hal-04784460

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Distributed under a Creative Commons Attribution 4.0 International License
COMITÉ NATIONAL FRANÇAIS
DE GÉODÉSIE ET GÉOPHYSIQUE

<figure><img src="image_2.png" /></figure>

Rapport Quadriennal 2003-2006

XXIVe Assemblée Générale
de l'Union Géodésique et Géophysique Internationale

<figure><img src="image_3.png" /></figure>

Perugia (Italie) 2-13 juillet 2007
Publié avec le concours de l'Académie des Sciences de Paris
CNFGG

Rapport Quadriennal 2003-2006

Édité par Daniel Schertzer & Ioulia Tchiguirinskaia

CEREVE, Ecole Nationale des Ponts et Chaussées

6-8 Avenue Blaise Pascal, Cité Descartes, 77455 Marne-la-Vallee Cedex 2

Disque compact réalisé par Eric Backelandt & Michel Buffet

CNRM/PAD, Météo-France

2, av. Rapp, 75340 Paris Cedex 07

Juin 2007
# Sommaire

PREAMBULE......................................................................................................................ix

COMITÉ NATIONAL FRANÇAIS DE GÉODÉSIE ET GÉOPHYSIQUE ...................... xiii

1. GÉODÉSIE .................................................................................................................... XIV

2. SISMOLOGIE ET PHYSIQUE DE L'INTÉRIEUR DE LA TERRE ................................................. XIX

3. VOLCANOLOGIE ET CHIMIE DE L'INTÉRIEUR DE LA TERRE ................................................. XV

4. GÉOMAGNÉTISME ET AÉRONOMIE.................................................................................... XVI

5. MÉTÉOROLOGIE ET PHYSIQUE DE L'ATMOSPHÈRE ............................................................ XVII

6. SCIENCES HYDROLOGIQUES ............................................................................................ XVII

7. SCIENCES PHYSIQUES DE L'OCÉAN.................................................................................... XVIII

STATUTS DU COMITÉ NATIONAL FRANÇAIS DE GÉODÉSIE ET

GÉOPHYSIQUE...................................................................................................................... XIX

ARTICLE 1 - MISSION .................................................................................................................... XIX

ARTICLE 2 - SIÈGE SOCIAL ............................................................................................................ XX

ARTICLE 3 - MEMBRES .................................................................................................................... XX

ARTICLE 4 - SECTIONS.................................................................................................................... XXI

ARTICLE 5 - (DISPONIBLE) ............................................................................................................ XXI

ARTICLE 6 - ASSEMBLÉE GÉNÉRALE.................................................................................... XXI

ARTICLE 7 - CONSEIL.................................................................................................................... XXII

ARTICLE 8 - BUREAU .................................................................................................................... XXII

ARTICLE 9 - DIVERS .................................................................................................................... XXIV

HISTORIQUE DU COMITÉ NATIONAL FRANÇAIS DE GÉODÉSIE ET

GÉOPHYSIQUE.................................................................................................................... XXV

1. GÉODÉSIE.................................................................................................................... 1

GEODETIC REFERENCE FRAMES IN FRANCE: HIGHLIGHTS 2004-2007, C. BOUCHER, Z.

ALTAMIMI, X. COLLILIEUX, F. DUQUENNE, B. GARAYT & J. LEGRAND.................................................... 3

I. INTRODUCTION .................................................................................................................... 4

II. OVERVIEW.................................................................................................................... 4

III. GEODETIC REFERENCE FRAMES; THE IGN/SGN ACTIVITIES .................................................... 7

III.1 The GPS network RBF ........................................................................................................ 8

III.2 The GPS permanent Network RGP .................................................................................... 9
<table><tr><td>III.3 Scientific levelling</td><td>11</td></tr><tr><td>III.4 Maintenance of NGF (French levelling network)</td><td>13</td></tr><tr><td>III.5 Contribution to international networks</td><td>14</td></tr><tr><td>IV. ITRF2005</td><td>15</td></tr><tr><td>IV.1 ITRF2005 Input Data</td><td>16</td></tr><tr><td>IV.2 ITRF2005 computation strategy</td><td>18</td></tr><tr><td>IV.3 ITRF2005 main results</td><td>20</td></tr><tr><td>V. REFERENCES</td><td>22</td></tr></table>

## MODELISATION DU CHAMP DE GRAVITE GLOBAL DE LA TERRE ET DE SES VARIATIONS TEMPORELLES, NOUVELLES MISSIONS SATELLITAIRES DE GRAVIMETRIE,

### APPLICATIONS, R. BIANCALE AND P. EXERTIER 25

I. LA DÉCENNIE DE LA GRAVIMÉTRIE SPATIALE 26

II. LES MISSIONS DE GRAVIMÉTRIE SPATIALE 26

III. LA MODÉLISATION 29

IV. LES MODÈLES DÉCADAIRES DE GÉOÏDE 30

V. LAGEOS 32

VI. RÉFÉRENCES 33

### DORIS APPLICATIONS FOR EARTH AND ATMOSPHERIC SCIENCES, P. WILLIS, L. SOUDARIN,

#### C. JAYLES, L. ROLLAND 35

I. INTRODUCTION 36

II. THE INTERNATIONAL DORIS SERVICE (IDS) 39

III. RECENT IMPROVEMENT IN DORIS DATA ANALYSIS 40

III.1 Increase in DORIS data availability 40

III.2 Availability of improved GRACE-derived gravity field models 44

III.3 Better handling of problems related to the South Atlantic Anomaly 45

III.4 Antenna correction models 45

III.5 Improvement data analysis during geomagnetic storms 46

III.6 DORIS for precise orbit determination 48

IV. DORIS FOR REAL-TIME ORBIT DETERMINATION 50

V. DORIS AND THE MAINTENANCE OF THE TERRESTRIAL REFERENCE FRAME 52

VI. GEOPHYSICAL APPLICATIONS OF THE DORIS SYSTEM 55

VII. IONOSPHERIC SOUNDING USING DORIS DATA 57

VIII. TROPOSPHERIC SOUNDING USING DORIS DATA 57

IX. CONCLUSIONS 57

X. DORIS BIBLIOGRAPHY (2003-2007) 58

### FRENCH ACTIVITIES IN GROUND GRAVIMETRY DURING THE PERIOD 2003~2006,

M.AMALVICT, R. BAYER, S. BONVALOT, N. DEBEGLIA, M. DIAMENT, F. DUQUENNE, H. DUQUENNE,

G. GABALDA, J. HINDERER, M.F. LALANCETTE, N. LEMOIGNE, B. LUCK, G. MARTELET, D. REMY, M.

SARRAILH & G. WOPPELMANN 65
<table><tr><td>I. MEASURE, REPRESENTATION AND MODELING OF THE GRAVITY FIELD</td><td>67</td></tr><tr><td>II. LOCAL STUDIES</td><td>70</td></tr><tr><td>II.1 The static field</td><td>70</td></tr><tr><td>II.2 The marine geoid</td><td>72</td></tr><tr><td>II.3 Time dependant gravity</td><td>72</td></tr><tr><td>III. IMPROVEMENT OF THE NATIONAL GRAVITY NETWORK AND COVERAGE</td><td>73</td></tr><tr><td>III.1 The integrated geodetic and gravimetric network</td><td>73</td></tr><tr><td>III.2 Quality control of the French gravity map and network</td><td>75</td></tr><tr><td>III.3 Quality control of geoid models</td><td>77</td></tr><tr><td>IV. ABSOLUTE GRAVITY (AG) ACTIVITIES</td><td>77</td></tr><tr><td>IV.1 Introduction</td><td>77</td></tr><tr><td>IV.2 The new portable A10 absolute meter</td><td>78</td></tr><tr><td>IV.3 Home sites and secondary sites</td><td>80</td></tr><tr><td>IV.4 Intercomparisons</td><td>81</td></tr><tr><td>IV.5 Dedicated campaigns of measurements</td><td>83</td></tr><tr><td>IV.6 Hydrology</td><td>87</td></tr><tr><td>V. ACKNOWLEDGMENTS</td><td>89</td></tr><tr><td>VI. REFERENCES</td><td>89</td></tr></table>

## TIME-VARYING GRAVITY WITH SUPERCONDUCTING GRAVIMETERS, J. HINDERER, J.-P.

BOY, S. ROSAT, Y. ROGISTER, M. AMALVICT, P. GEGOUT & C. DE LINAGE 97

<table><tr><td>I. INTRODUCTION</td><td>98</td></tr><tr><td>II. NORMAL MODES</td><td>99</td></tr><tr><td>III. ATMOSPHERIC AND HYDROLOGIC EFFECTS</td><td>101</td></tr><tr><td>IV. EARTH AND OCEAN TIDES</td><td>102</td></tr><tr><td>V. NON-TIDAL OCEAN EFFECTS</td><td>105</td></tr><tr><td>VI. EARTH ROTATION</td><td>105</td></tr><tr><td>VII. TECTONICS</td><td>106</td></tr><tr><td>VIII. GROUND/ORBIT VALIDATION</td><td>107</td></tr><tr><td>IX. CONCLUSION</td><td>109</td></tr><tr><td>X. REFERENCES</td><td>109</td></tr></table>

## 2. SISMOLOGIE ET PHYSIQUE DE L'INTÉRIEUR DE LA TERRE 115

IONOSPHERIC SEISMOLOGY, P. LOGNONNÉ, G. OCCHIPINTI, A. KHERANI, P.E. GODET, J. ARTRU, R. GARCIA, T. FARGES, H. HÉBERT, V. BAZIN, F. CRESPON, G. MOREAUX, J. HELBERT & E.JEANSOU 117

<table><tr><td>I. INTRODUCTION</td><td>118</td></tr><tr><td>II. THEORETICAL AND HISTORICAL BACKGROUND</td><td>120</td></tr><tr><td>III. TOWARD REMOTE SENSING SEISMOLOGY?</td><td>121</td></tr><tr><td>IV. IONOSPHERIC TSUNAMIS WARNING</td><td>123</td></tr></table>
V. EXPORTING REMOTE SENSING SEISMOLOGY ON VENUS? 125

VI. CONCLUSION 126

VII. REFERENCES 126

PLAQUES PLONGEANTES ET PANACHES DANS LE MANTEAU INFERIEUR, E. STUTZMANN,

J.BESSE, A. DAVAILLE & Y. REN 129

I. INTRODUCTION 132

II. LA CONVECTION MANTELLIQUE 135

III. LES PLAQUES PLONGEANTES SOUS LES AMERIQUES 138

III.1 Les données 138

III.2 La Tomographie 138

III.3 Identification des plaques dans le modèle tomographique 139

IV. LES PANACHES MANTELLIQUES 142

IV.1. les observations de surface 145

IV.2 Cinématique des plaques et des continents 146

IV.3 Les modèles tomographiques 147

IV.4 Modélisation de la convection 149

IV.5 Convection du manteau dans la boîte-Indo-Atlantique 149

V. CONCLUSIONS 150

VI. BIBLIOGRAPHIE 152

SEISMIC IMAGING USING AMBIENT NOISE, L. STEHLY, F. BRENGUIER, P. ROUX, M. CAMPILLO

& Y. COLIN DE VERDIERE 155

I. INTRODUCTION 157

II. BACKGROUND AND THEORETICAL APPROACH 158

III. SEISMIC NOISE ORIGIN IN THE 5-20 SECONDS PERIOD BAND 161

III.1 Using asymmetry of cross-correlation to study the origin of the seismic noise 164

III.2 Data processing and results 166

III.3 Comparison of the origin of the 10-20 s noise map with ocean wave height map 167

IV. TRAVEL TIME MEASUREMENTS FROM NOISE CORRELATION: 168

STABILITY AND DETECTION OF INSTRUMENTAL ERRORS USING THE PRINCIPLE OF TIME

SYMMETRY 168

IV.1 Data and measurements 169

IV.2 Stability of the travel time measurements between 1999 and 2005 170

IV.3 Evidence of instrumental errors between 1992 and 1996 173

IV.4 Correction of the instrumental errors 173

V. APPLICATION TO IMAGING 175

V.1 Surface wave tomography of Europe 177

V.2 3-D S-wave tomography of the Piton de la Fournaise volcano 178

VI. P-WAVES EXTRACTION FROM SEISMIC NOISE CROSS-CORRELATION 179

VII. REFERENCES 181
3. VOLCANOLOGIE ET CHIMIE DE L'INTÉRIEUR DE LA TERRE 183

4. GÉOMAGNÉTISME ET AÉRONOMIE 185

NEW PERSPECTIVES ON MARS' CRUSTAL MAGNETIC FIELD, B. LANGLAIS & Y. QUESNEL 187

I. INTRODUCTION 188

II. A GLOBAL MAP THE MARTIAN MAGNETIC FIELD 190

III. LOCAL STUDIES 193

III.1 Semi-inverse approach 194

III.2 Equivalent Sources 196

IV. IMPLICATIONS FOR EARLY MARS 198

IV.1 Polar wander 198

IV.2 Magnetic mineralogy and geological processes 200

V. CONCLUSIONS – THE CASE FOR LOWER ALTITUDE MEASUREMENTS 201

VI. ACKNOWLEDGEMENTS 203

VIII. REFERENCES 203

DAYSIDE MAGNETIC RECONNECTION: PROPERTIES AND IMPACT ON THE

MAGNETOSPHERE-IONOSPHERE SYSTEM, A. MARCHAUDON, J.-C. CERISIER, J.-M. BOSQUED,

Y.V. BOGDANOVA & C. J. OWEN 209

I. INTRODUCTION 212

II. INSTRUMENTATION 215

III. MAGNETOPAUSE RECONNECTION 216

III.1 IMF Clock-Angle And Solar Wind Pressure Effects On Magnetopause Reconnection 217

III.2 Formation of the stagnant exterior cusp during northward IMF 219

IV. MAGNETOSPHERE-IONOSPHERE COUPLING DURING RECONNECTION EVENTS 222

IV.1 Efficiency And Time Scales 224

IV.2 Spatio-Temporal Dynamics 225

V. ELECTRODYNAMICS OF RECONNECTED FLUX TUBES 226

V.1 Field-Aligned Currents Distribution 227

V.2 Ionospheric Current Closure 228

VI. SUMMARY AND CONCLUSION 229

VII. REFERENCES 230

5. MÉTÉOROLOGIE ET PHYSIQUE DE L'ATMOSPHÈRE 239

6. SCIENCES HYDROLOGIQUES 241

TELEDETECTION ET ETATS DE SURFACE, C. OTTLE, S. LEHEGARAT & M. ZRIBI 243

I. INTRODUCTION 243

II. OBSERVATIONS UTILES POUR L'HYDROLOGIE 245
<table><tr><td>III.3 Integration Of Altimetric Data In Hydrodynamical Models</td><td>298</td></tr><tr><td>III.4 Estimation Of The Water Volume Stored In River And Inundation Plain</td><td>301</td></tr><tr><td>III.5 Some Tools For Spatial Hydrology</td><td>302</td></tr><tr><td>IV. DISCUSSION</td><td>303</td></tr><tr><td>V. CONCLUSION</td><td>305</td></tr><tr><td>VI. ACKNOWLEDGEMENTS</td><td>307</td></tr><tr><td>VII. REFERENCES</td><td>307</td></tr></table>

TELEDETECTION RADAR DES PRECIPITATIONS INTENSES EN REGION

<table><tr><td>MEDITERRANEENNE, G. DELRIEU</td><td>311</td></tr><tr><td>I. INTRODUCTION</td><td>312</td></tr><tr><td>II. PHYSIQUE DE LA MESURE DES PRECIPITATIONS PAR RADAR METEOROLOGIQUE</td><td>312</td></tr><tr><td>III. « VISIBILITE HYDROLOGIQUE » DU RESEAU ARAMIS EN MEDITERRANEE</td><td>316</td></tr><tr><td>IV. TRAITEMENTS REGIONALISES ET ADAPTATIFS DES DONNEES RADAR POUR L'HYDROLOGIE</td><td>317</td></tr><tr><td>V. QUALITE DES ESTIMATIONS DE PLUIE PAR RADAR</td><td>323</td></tr><tr><td>VI. CONCLUSIONS ET OUVERTURES</td><td>325</td></tr><tr><td>VII. REMERCIEMENTS</td><td>326</td></tr><tr><td>VIII. REFERENCES</td><td>326</td></tr></table>

HYDROLOGIE ET TELEDETECTION : ALTIMETRIE, GEODESIE ET GRAVIMETRIE

<table><tr><td>APPLIQUEES A L'HYDROLOGIE, P. KOSUTH</td><td>329</td></tr><tr><td>I. LES ENJEUX DE LA TELEDETECTION SPATIALE APPLIQUEE A L'HYDROLOGIE</td><td>330</td></tr><tr><td>II. ALTIMETRIE ET MESURE DE NIVEAU DES EAUX CONTINENTALES</td><td>337</td></tr><tr><td>II.1 Le Principe de l'Altimetrie Satellitaire Radar</td><td>338</td></tr><tr><td>II.2 Application à la Mesure de Niveau des Eaux Continentales</td><td>340</td></tr><tr><td>III. GRAVIMETRIE ET MESURE DES VARIATIONS TEMPORELLES DES STOCKS D'EAU CONTINENTALE</td><td>347</td></tr><tr><td>IV. CONCLUSION : LES PROGRES TECHNOLOGIQUES ATTENDUS EN TELEDETECTION APPLIQUEE A L'HYDROLOGIE</td><td>349</td></tr><tr><td>V. REFERENCES</td><td>350</td></tr></table>

7. SCIENCES PHYSIQUES DE L'OCÉAN 353

RECENT OBSERVED VARIABILITY IN THE NORTH ATLANTIC SUBPOLAR GYRE

<table><tr><td>CIRCULATION, G. REVERDIN, P. LHERMINIER, V. THIERRY & H. MERCIER</td><td>355</td></tr><tr><td>I. INTRODUCTION</td><td>355</td></tr><tr><td>II. SHIPS OF OPPORTUNITY</td><td>357</td></tr><tr><td>III. OVIDE REPEATED HYDROGRAPHY</td><td>360</td></tr><tr><td>IV. SUBPOLAR MODE WATERS</td><td>362</td></tr><tr><td>V. CONCLUSIONS</td><td>363</td></tr></table>
VI. ACKNOWLEDGEMENTS.................................................................................................................. 364

VII. REFERENCES........................................................................................................................................ 364

THE DYNAMICS OF VORTEX PAIRS NEAR A TIME-VARYING UPWELLING, X. CARTON &

X. PERROT.................................................................................................................................................. 367

I. INTRODUCTION........................................................................................................................................ 367

II. OCEANIC RESPONSE TO A TIME VARYING WIND........................................................................ 368

III. MOTION OF A POINT VORTEX PAIR IN A TIME-VARYING BETA EFFECT........................................ 370

IV. CONCLUSIONS........................................................................................................................................ 372

V. REFERENCES........................................................................................................................................ 373
# Préambule

L'Union Géodésique et Géophysique Internationale rassemble sept Associations internationales spécialisées : Géodésie, Sismologie et physique de l'intérieur de la Terre, Volcanologie et chimie de l'intérieur de la Terre, Géomagnétisme et aéronomie, Météorologie et physique de l'atmosphère, Sciences hydrologiques, et Sciences physiques de l'océan. L'activité scientifique des géodésiens et géophysiciens rassemblés au sein de l'UGGI est essentiellement orientée vers l'étude scientifique de la Terre et ses applications aux besoins de notre société contemporaine, afin de mieux comprendre notre planète, en prévoir l'évolution et la protéger. Membre du Conseil International des Unions Scientifiques (CIUS), l'UGGI apporte à cet organisme, qui inspire la politique scientifique à l'échelle mondiale, le point de vue et la sensibilité des géodésiens et des géophysiciens.

Chacune des Associations qui composent l'Union constitue, dans son domaine, la seule association scientifique spécialisée à vocation planétaire; elle a pour mission :

* d'encourager, dans ses domaines de compétence, la recherche par des pays, institutions ou personnes individuels et de faciliter la coordination internationale de ces recherches;

* de fournir au niveau international un cadre pour la discussion et la publication des résultats des recherches ainsi effectuées.

Ces objectifs sont ambitieux, et tous ceux qui se sont un jour impliqués dans la vie des Associations – ou dans celle de l'Union – mesurent l'ampleur du défi qu'ils représentent. Ils nécessitent en particulier que nous réussissions à organiser des Assemblées de très haut niveau scientifique qui soient
attractives et ouvertes à tous, et notamment à nos collègues des pays en voie
de développement.

En 2007, l'Assemblée générale de l'Union géodésique et géophysique internationale (UGGI) se tient à Perugia, en Italie. Les Assemblées générales de l'UGGI sont des événements scientifiques d'un excellent niveau qui, malgré la multiplication des manifestations scientifiques internationales, attirent un vaste public. Elles revêtent aussi une dimension administrative importante : toutes les instances de l'Union et des Associations qui la composent sont en effet renouvelées lors de chacune de ses Assemblées générales, dont la tenue régulière rythme ainsi la vie de l'Union et de ses Associations.

L'UGGI et les Associations qui la composent sont dirigés par une assemblée de Comités nationaux, qui sont eux mêmes composés de la réunion de sept Comités nationaux spécialisés dirigeant les associations internationales correspondantes. Le Comité National Français de Géodésie et Géophysique (CNFGG) y représente la France, directement en ce qui concerne l'Union et via ses sept sections en ce qui concerne les Associations. A l'occasion de chaque Assemblée générale, le CNFGG – en sa qualité de Correspondant national français – doit publier et diffuser un Rapport quadriennal, qui a pour mission de présenter à l'ensemble de l'UGGI l'activité des géodésiens et géophysiciens qu'il représente.

Nous avons voulu que notre Rapport quadriennal s'inscrive dans la démarche
scientifique de l'Union, en contribuant à la diffusion de résultats récents et
remarquables. Nous avons donc choisi qu'il rassemble des articles
scientifiques qui dressent un panorama de la recherche et des réalisations
françaises dans les domaines de la géodésie et de la géophysique, durant les
quatre dernières années. L'objectif est de jeter des coups de projecteur sur des
domaines où les équipes françaises ont obtenu des résultats importants, en les replaçant dans leur contexte international. Les articles ainsi publiés sont regroupés selon les thématiques des sept associations internationales spécialisées qui composent l'Union.

La contrepartie de notre choix est l'effort demandé à ceux qui acceptent de contribuer, aux bureaux de section qui ont supervisé la rédaction des articles, à Daniel Schertzer et Ioulia Tchiguirinskaia qui ont assuré l'édition du Rapport, et à Eric Backelandt et Michel Buffet qui ont realisé le disque compact. Que chacun d'entre eux trouve ici l'expression des mes remerciements les plus chaleureux.

Michel Menvielle

Président du CNFGG
# COMITÉ NATIONAL FRANÇAIS DE GÉODÉSIE ET GÉOPHYSIQUE

## PRÉSIDENTS, SECRÉTAIRES GÉNÉRAUX ET TRÉSORIERS DU CNFGG

D'une façon générale, les membres des Bureaux entrent en fonction en janvier ou février, dès que l'Assemblée générale a approuvé leur nomination. L'astérisque portée après la date de 1923 signifie que nous n'avons pas pu consulter de documents plus anciens que cette date. Jusqu'à l'Assemblée générale de l'UGGI de Grenoble (1975), les sections étaient présentées dans l'ordre suivant : 1. Géodésie ; 2. Sismologie ; 3. Météorologie ; 4. Géomagnétisme / Aéronomie ; 5. Océanographie physique ; 6. Volcanologie ; 7. Hydrologie.

### Présidents

<table><tr><td>A. Lacroix</td><td>1920-1945</td></tr><tr><td>G<sup>al</sup> G. Perrier</td><td>1946</td></tr><tr><td>Ch. Maurain</td><td>1946-1950</td></tr><tr><td>R.P. Lejay</td><td>1951-1956</td></tr><tr><td>P. Tardi</td><td>1957-1961</td></tr><tr><td>J. Coulomb</td><td>1962-1964</td></tr><tr><td>A. Gougenheim</td><td>1965-1969</td></tr><tr><td>G. Laclavère</td><td>1970-1977</td></tr><tr><td>J. Goguel</td><td>1978-1981</td></tr><tr><td>M. Eyriès</td><td>1982-1985</td></tr><tr><td>M<sup>me</sup> M.L. Chanin</td><td>1986-1989</td></tr><tr><td>G. Grau</td><td>1990-1993</td></tr><tr><td>F. Barlier</td><td>1994-1997</td></tr><tr><td>P. Hubert</td><td>1998-1999</td></tr><tr><td>J.L. Cheminée</td><td>1999-2003</td></tr><tr><td>M. Menvielle</td><td>2004-</td></tr></table>

### Secrétaires généraux

<table><tr><td>G<sup>al</sup> Ferrié</td><td>1920-1926</td></tr><tr><td>G<sup>al</sup> G. Perrier</td><td>1926-1945</td></tr><tr><td>P. Tardi</td><td>1946-1952</td></tr><tr><td>A. Gougenheim</td><td>1953-1961</td></tr><tr><td>L. Cahierre</td><td>1962-1969</td></tr><tr><td>A. Couzy</td><td>1970-1977</td></tr><tr><td>J. de Beauregard</td><td>1978-1989</td></tr><tr><td>M<sup>me</sup> S. Perraut</td><td>1990-1997</td></tr><tr><td>J.P. Barriot</td><td>1998-2006</td></tr></table>

### Trésoriers

<table><tr><td>L. Cahierre</td><td>1962-1969</td></tr><tr><td>R. Schlich</td><td>1970-</td></tr></table>
# PRÉSIDENTS ET SECRÉTAIRES DES SECTIONS DU CNFGG

## 1. GÉODÉSIE

De 1952 à 1965, la section a été subdivisée en deux sous-sections, respectivement de triangulation (1a), et de gravimétrie (1b).

<table><thead><tr><th colspan="2">Présidents</th><th colspan="2">Secrétaires</th></tr></thead><tbody><tr><td>E. Fichot</td><td>1923*-1932</td><td>G<sup>al</sup> G. Perrier</td><td>1923*-1933</td></tr><tr><td>G<sup>al</sup> G. Perrier</td><td>1934-1946</td><td>P. Tardi</td><td>1934-1946</td></tr><tr><td>N...</td><td>1947-1950</td><td>G. Laclavère</td><td>1947-1950</td></tr><tr><td>P. Jacquinet</td><td>1951-1960(1a)</td><td>G. Laclavère</td><td>1951-1953(1a)</td></tr><tr><td>R.P. P. Lejay</td><td>1951-1958(1b)</td><td>G. Bonifacj</td><td>1954-1963(1a)</td></tr><tr><td>A. Brunel</td><td>1961-1965(1a)</td><td>H.M. Dufour</td><td>1964-1965(1a)</td></tr><tr><td>J. Goguel</td><td>1959-1965(1b)</td><td>M<sup>elle</sup> S. Coron</td><td>1951-1965(1b)</td></tr><tr><td>P. Tardi</td><td>1966-1968</td><td>H.M. Dufour</td><td>1966-1974</td></tr><tr><td>J.J. Levallois</td><td>1969-1974</td><td>J. Rechenmann</td><td>1975-1984</td></tr><tr><td>H.M. Dufour</td><td>1975-1984</td><td>C. Boucher</td><td>1985-1991</td></tr><tr><td>F. Barlier</td><td>1985-1989</td><td>H. Duquenne</td><td>1992-1996</td></tr><tr><td>A. Comolet-Tirman</td><td>1990-1992</td><td>J.P. Barriot</td><td>1997-2001</td></tr><tr><td>M<sup>me</sup> M. Feissel</td><td>1993-1996</td><td>N. Florsch</td><td>2002-2003</td></tr><tr><td>C. Boucher</td><td>1997-2003</td><td>G. Woppelmann</td><td>2004-2006</td></tr><tr><td>N. Florsch</td><td>2004-2006</td><td>S. Durand</td><td>2007-</td></tr><tr><td>R. Biancale</td><td>2007-</td><td></td><td></td></tr></tbody></table>

## 2. SISMOLOGIE ET PHYSIQUE DE L'INTÉRIEUR DE LA TERRE

Avant l'Assemblée générale de l'UGGI de Bruxelles (1951), la section portait le nom de section de sismologie (ou séismologie). À partir de 1932 et jusqu'en 1948, les sections de sismologie et de volcanologie ont été réunies sous la présidence d'A.Lacroix.
## Présidents

<table><tr><td>G. Bigourdan</td><td>1923*-1932</td></tr><tr><td>A. Lacroix</td><td>1932-1948</td></tr><tr><td>M<sup>me</sup> Y. Labrouste</td><td>1949-1960</td></tr><tr><td>L. Migaux</td><td>1961-1965</td></tr><tr><td>J.P. Rothé</td><td>1966-1972</td></tr><tr><td>P. Bernard</td><td>1973-1980</td></tr><tr><td>P. Mechler</td><td>1981-1984</td></tr><tr><td>M. Cara</td><td>1985-1988</td></tr><tr><td>G. Perrier</td><td>1989-1992</td></tr><tr><td>M<sup>me</sup> A. Deschamps</td><td>1993-1996</td></tr><tr><td>P. Richet</td><td>1997-2004</td></tr><tr><td>T. Monfret</td><td>2005-</td></tr></table>

## Secrétaires

<table><tr><td>E. Rothé</td><td>1923*-1942</td></tr><tr><td>H. Labrouste</td><td>1943-1944</td></tr><tr><td>J.P. Rothé</td><td>1945-1965</td></tr><tr><td>M<sup>me</sup> N. Jobert</td><td>1966-1968</td></tr><tr><td>M. Choudhury</td><td>1969-1972</td></tr><tr><td>J. Aubrat</td><td>1973-1980</td></tr><tr><td>B. Massinon</td><td>1981-1984</td></tr><tr><td>C. Weber</td><td>1985-1986</td></tr><tr><td>J.C. Ruegg</td><td>1987-1988</td></tr><tr><td>J.P. Montagner</td><td>1989-1990</td></tr><tr><td>M<sup>me</sup> H. Lyon-Caen</td><td>1991-1994</td></tr><tr><td>D. Andrault</td><td>1995-1997</td></tr><tr><td>M<sup>me</sup> N. Bethoux</td><td>1998-2001</td></tr><tr><td>E. Clévédé</td><td>2002-2004</td></tr><tr><td>M<sup>me</sup> M. Laigle-Marchand</td><td>2005-</td></tr></table>

# 3. VOLCANOLOGIE ET CHIMIE DE L'INTÉRIEUR DE LA TERRE

*Section de volcanologie (ou vulcanologie) jusqu'à l'Assemblée générale de l'UGGI de Moscou (1971).*

## Présidents

<table><tr><td>A. Lacroix</td><td>1923*- 1948</td></tr><tr><td>A. Michel-Lévy</td><td>1949-1955</td></tr><tr><td>L. Glangeaud</td><td>1956-1960</td></tr><tr><td>B. Gèze</td><td>1961-1966</td></tr><tr><td>P. Bordet</td><td>1967-1972</td></tr><tr><td>J. Goguel</td><td>1973-1977</td></tr><tr><td>P. Vincent</td><td>1978-1982</td></tr></table>

## Secrétaires

<table><tr><td>L. Gentil</td><td>1923*-1927?</td></tr><tr><td>A. Michel-Lévy</td><td>1927-1947</td></tr><tr><td>B. Gèze</td><td>1948-1953</td></tr><tr><td>P. Bordet</td><td>1954-1966</td></tr><tr><td>J.L. Cheminée</td><td>1967-1972</td></tr><tr><td>M. Girod et J. Varet</td><td>1973-1977</td></tr><tr><td>M<sup>me</sup> N. Vatin-</td><td></td></tr></table>
<table><tr><td>M. Treuil</td><td>1983-1988</td><td>Pérignon</td><td>1978-1982</td></tr><tr><td>J. Dubois</td><td>1989-1994</td><td>J. Hernandez</td><td>1983-1988</td></tr><tr><td>J.L. Cheminée</td><td>1995-1997</td><td>J.L. Cheminée</td><td>1989-1994</td></tr><tr><td>J.F. Lénat</td><td>1998-2001</td><td>M<sup>me</sup> N. Métrich</td><td>1995-1997</td></tr><tr><td>P. Allard</td><td>2002-</td><td>G. Boudon</td><td>1998-2001</td></tr><tr><td></td><td></td><td>P. Briole</td><td>2002-</td></tr></table>

## 4. GÉOMAGNÉTISME ET AÉRONOMIE

D'abord section de magnétisme et électricité atmosphérique, s'appela ensuite section de magnétisme et électricité terrestres jusqu'à l'Assemblée générale de l'UGGI de Rome (1954).

<table><thead><tr><th>Présidents</th><th></th><th>Secrétaires</th><th></th></tr></thead><tbody><tr><td>D. Berthelot</td><td>1923*-1927</td><td>É. Mathias</td><td>1923-1936</td></tr><tr><td>G<sup>al</sup> Ferrié</td><td>1928-1932</td><td>M.L. Éblé</td><td>1937-1943</td></tr><tr><td>Ch. Maurain</td><td>1933-1946</td><td>É. Thellier</td><td>1944-1954</td></tr><tr><td>J. Coulomb</td><td>1947-1955</td><td>M<sup>me</sup> A. Vassy</td><td>1955-1960</td></tr><tr><td>É. Thellier</td><td>1956-1960</td><td>A. Lebeau</td><td>1961-1963</td></tr><tr><td>L. Cagniard</td><td>1961-1966</td><td>G. Weill</td><td>1964-1965</td></tr><tr><td>É. Vassy</td><td>1967-1968</td><td>A. Haubert</td><td>1966</td></tr><tr><td>É. Selzer</td><td>1969-1973</td><td>J.L. Bureau</td><td>1967-1969</td></tr><tr><td>M. Petit</td><td>1974-1979</td><td>M<sup>me</sup> J. Christophe-<br>Glaume</td><td>1969</td></tr><tr><td>M<sup>me</sup> M.L. Chanin</td><td>1980-1985</td><td>J. Meunier</td><td>1970-1972</td></tr><tr><td>M. Blanc</td><td>1986-1988</td><td>J.J. Berthelier</td><td>1973-1974</td></tr><tr><td>M. Menvielle</td><td>1989-1995</td><td>M<sup>elle</sup> F. Rimbert</td><td>1975</td></tr><tr><td>A. Hauchecorne</td><td>1996-2001</td><td>J. Barat</td><td>1976-1978</td></tr><tr><td>M<sup>me</sup> M. Mandéa</td><td>2002-2006</td><td>M<sup>me</sup> M.L. Chanin</td><td>1978-1979</td></tr><tr><td>B. Langlais</td><td>2007-</td><td>J. Lavergnat</td><td>1980-1982</td></tr><tr><td></td><td></td><td>M. Blanc</td><td>1983-1985</td></tr><tr><td></td><td></td><td>G. Clerc</td><td>1986-1988</td></tr><tr><td></td><td></td><td>M<sup>me</sup> A. Berthelier</td><td>1989-1995</td></tr><tr><td></td><td></td><td>F. Bertin</td><td>1996-2001</td></tr></tbody></table>
M. Bitterly 2002-2002

J. Dyment 2003-2006

E. Thebault 2007-

## 5. MÉTÉOROLOGIE ET PHYSIQUE DE L'ATMOSPHÈRE

Section de météorologie jusqu'à l'Assemblée générale de l'UGGI de Toronto (1957).

<table><thead><tr><th colspan="2">Présidents</th><th colspan="2">Secrétaires</th></tr></thead><tbody><tr><td>H. Deslandres</td><td>1923*-1932</td><td>A. Baldit</td><td>1923*-1929</td></tr><tr><td>N...</td><td>1933-1937</td><td>G<sup>al</sup> Delcambre</td><td>1930</td></tr><tr><td>Ch. Maurain</td><td>1938-1946</td><td>L. Gain</td><td>1930-1938</td></tr><tr><td>A. Viaut</td><td>1947-1960</td><td>J. Sanson</td><td>1939-1946</td></tr><tr><td>J. Roulleau</td><td>1961-1963</td><td>R. Arléry</td><td>1947-1968</td></tr><tr><td>P. Queney</td><td>1964-1967</td><td>J. Pradel</td><td>1969-1970</td></tr><tr><td>J. Bricard</td><td>1968-1972</td><td>J. Blanchet</td><td>1971-1972</td></tr><tr><td>J. Bessemoulin</td><td>1973-1976</td><td>P.Y. Turpin</td><td>1973-1976</td></tr><tr><td>G. Soulage</td><td>1977-1980</td><td>M<sup>me</sup> D. Cruette</td><td>1977-1983</td></tr><tr><td>A. Villevieille</td><td>1981-1990</td><td>M<sup>elle</sup> H.L. Pham</td><td>1984-1991</td></tr><tr><td>P. de Félice</td><td>1991-1994</td><td>P. Aimedieu</td><td>1992-1996</td></tr><tr><td>J.L. Fellous</td><td>1995-2001</td><td>S. Janicot</td><td>1997-2001</td></tr><tr><td>J.P. Issartel</td><td>2002-</td><td>A. Jejcic</td><td>2002-</td></tr></tbody></table>

## 6. SCIENCES HYDROLOGIQUES

Appelée section d'hydrologie scientifique à sa création en 1923, la section a pris son nom actuel à l'Assemblée de Moscou (1971).

<table><thead><tr><th colspan="2">Présidents</th><th colspan="2">Secrétaires</th></tr></thead><tbody><tr><td>A. Rateau</td><td>1923-1929</td><td>A. Genthial</td><td>1923-1929</td></tr><tr><td>E.A. Martel</td><td>1930-1938</td><td>J. Aubert</td><td>1930</td></tr><tr><td>F. Diénert</td><td>1939-1948</td><td>A. Guillerd</td><td>1931-1937</td></tr><tr><td>A. Coutagne</td><td>1948-1951</td><td>A. Vibert</td><td>1938-1945</td></tr></tbody></table>
<table><tr><td>J. Aubert</td><td>1952-1960</td><td>A. Le Strat</td><td>1946-1951</td></tr><tr><td>A. Vibert</td><td>1961-1965</td><td>L. Serra</td><td>1952-1971</td></tr><tr><td>M. Gosselin</td><td>1966-1968</td><td>M. Roche</td><td>1972-1980</td></tr><tr><td>H. Schoeller</td><td>1969-1971</td><td>J. Sircoulon</td><td>1981-2001</td></tr><tr><td>L. Serra</td><td>1972-1976</td><td>P. Le Goulven</td><td>2002-2005</td></tr><tr><td>G. Castany</td><td>1977-1980</td><td>M. Lointier</td><td>2006-</td></tr><tr><td>M. Roche</td><td>1981-1989</td><td></td><td></td></tr><tr><td>P. Hubert</td><td>1990-1997</td><td></td><td></td></tr><tr><td>J.C. Olivry</td><td>1998-2005</td><td></td><td></td></tr><tr><td>P. Givone</td><td>2006-</td><td></td><td></td></tr></table>

## 7. SCIENCES PHYSIQUES DE L'OCÉAN

Section d'océanographie physique jusqu'à l'Assemblée générale de Zurich (1967).

<table><thead><tr><th colspan="2">Présidents</th><th colspan="2">Secrétaires</th></tr></thead><tbody><tr><td>M. Rollet de l'Isle</td><td>1923*-1929</td><td>A. Berget</td><td>1923*-1925</td></tr><tr><td>E. Fichot</td><td>1930-1939</td><td>C. Vallaux</td><td>1926-1934</td></tr><tr><td>D. Cot</td><td>1939-1945 (par intérim)</td><td>D. Cot</td><td>1934-1935</td></tr><tr><td>D. Cot</td><td>1945-1959</td><td>L. Pélissier</td><td>1936-1950</td></tr><tr><td>J. Rouch</td><td>1960-1963</td><td>A. Gougenheim</td><td>1951-1953</td></tr><tr><td>A. Gougenheim</td><td>1964-1970</td><td>G. Châtel</td><td>1954-1955</td></tr><tr><td>H. Lacombe</td><td>1971-1976</td><td>H. Lacombe</td><td>1956-1963</td></tr><tr><td>M. Eyriès</td><td>1977-1980</td><td>G. Peluchon</td><td>1964-1965</td></tr><tr><td>J. Bourgoin</td><td>1981-1984</td><td>J. Bourgoin</td><td>1966-1980</td></tr><tr><td>B. Saint-Guily</td><td>1985-1988</td><td>F. Madelain</td><td>1981-1986</td></tr><tr><td>M. Crépon</td><td>1989-2005</td><td>F. Gérard</td><td>1987-1989</td></tr><tr><td>A. Colin de Verdière</td><td>2006</td><td>B. Schrumpf</td><td>1990-1995</td></tr><tr><td></td><td></td><td>L. Mortier</td><td>1996-2005</td></tr><tr><td></td><td></td><td>Mme M-N. Houssais</td><td>2006-</td></tr></tbody></table>

Mise à jour le 13 mars 2007
# STATUTS DU COMITÉ NATIONAL FRANÇAIS
DE GÉODÉSIE ET GÉOPHYSIQUE

(2 février 1984)

## Article 1 - MISSION

1.1. Le Comité National Français de Géodésie et Géophysique (CNFGG) est constitué par l'Académie des sciences pour assurer, sous son égide et suivant ses directives, la participation française aux activités de l'Union Géodésique et Géophysique Internationale (UGGI).

1.2. En outre, et en raison de la compétence scientifique de ses membres (Art. 3), le CNFGG peut :

- provoquer et coordonner des études et des recherches relatives à la géodésie et à la géophysique,

- recevoir des demandes d'avis ou d'expertises et émettre des recommandations sur toute affaire relevant du domaine de sa compétence, y compris l'organisation de la recherche et de ses structures permanentes ou conjoncturelles.

1.3. Le CNFGG, régi par la loi du 1er juillet 1901, peut solliciter et recevoir de l'Etat ou d'organismes privés les concours de toute nature nécessaires à l'accomplissement de sa mission. Il s'interdit toute activité commerciale.
## Article 2 - SIÈGE SOCIAL

2.1. Le siège social du CNFGG est à l'Académie des sciences, 23 quai de Conti, 75006 Paris.

2.2. Le CNFGG est régi par les présents statuts à compter du 4 février 1992, date de l'Assemblée générale les ayant adoptés.

## Article 3 - MEMBRES

3.1. Les membres du CNFGG sont des personnes physiques, cooptées par l'Assemblée générale du CNFGG (Art. 6). Ils sont :

- soit membres "titulaires", admis sur proposition d'une section (Art. 4) en raison de leur compétence scientifique,

- soit membres "ès qualités", inscrits en raison de leur fonction sur une liste arrêtée par l'Assemblée générale.

3.2. Les membres du CNFGG sont normalement de nationalité française. Cependant, des personnalités étrangères peuvent, exceptionnellement et sur proposition du Conseil (Art. 7), être nommées membres à condition :

- soit que leur activité scientifique s'exerce essentiellement en France,

- soit qu'ils ressortissent d'un pays francophone n'ayant pas constitué de comité analogue au CNFGG.

3.3. La qualité de membre titulaire est perdue :

- soit par radiation, proposée par une section et décidée par le Conseil, avec appel suspensif possible devant l'Assemblée générale,

- soit par démission explicite,

- soit par démission implicite, concrétisant un défaut d'intérêt pour l'activité du CNFGG, constaté par le Conseil.
## Article 4 - SECTIONS

4.1. Le CNFGG est divisé en sections dont le nombre, les dénominations et les domaines de compétence scientifique correspondent respectivement à ceux des Associations internationales constitutives de l'UGGI.

4.2. Chaque section est administrée par un bureau de section comportant au moins un président et un secrétaire. Elle est régie par un règlement intérieur qui lui est propre, mais qui n'est opposable ni aux présents statuts ni au règlement intérieur du CNFGG (Art. 9).

4.3. Tout membre du CNFGG appartenant au comité exécutif d'une Association de l'Union Géodésique et Géophysique Internationale (UGGI) est membre de droit du bureau de la section correspondante du CNFGG.

4.4. Le bureau de chaque section est responsable de la liaison du CNFGG avec le bureau de l'Association correspondant à sa section. Il n'est cependant habilité à engager que la responsabilité de sa section, et non celle du CNFGG dans son ensemble. Le président de la section, ou son mandataire, est le représentant de la France dans les instances de l'Association internationale correspondante.

## Article 5 - (disponible)

## Article 6 - ASSEMBLÉE GÉNÉRALE

6.1. Le président du CNFGG (Art. 8) convoque les membres en Assemblée générale au moins une fois par an. L'ordre du jour, proposé par le Bureau, adopté par le Conseil, est communiqué à tous les membres au moins quinze jours à l'avance. Il est éventuellement amendé, puis adopté par l'Assemblée générale dès l'ouverture de la séance.
**6.2.** Le procès-verbal de l'Assemblée générale est adressé à l'Académie des sciences à titre de compte rendu.

## Article 7 - CONSEIL

**7.1.** Le Conseil du CNFGG est constitué par :

- les membres du Bureau (Art. 8) du CNFGG,

- le président (ou, en son absence, son mandataire) et le secrétaire de chaque section,

- le président sortant du CNFGG et de chacune des sections,

- les membres du CNFGG appartenant au comité exécutif de l'UGGI.

Il a pour président et secrétaire ceux du CNFGG.

**7.2.** Le Conseil se réunit sur convocation de son président, au moins une fois avant chaque Assemblée générale. Il prend toutes décisions nécessaires au fonctionnement du CNFGG, hormis celles :

- qui appartiennent statutairement à l'Assemblée générale,

- que le président estime devoir demander à cette Assemblée en raison de leur importance.

En particulier, le Conseil propose à l'Académie des sciences la délégation française à l'Assemblée générale de l'UGGI et aux Assemblées générales des Associations internationales constitutives de l'UGGI.

Il est rendu compte à l'Assemblée générale de l'activité du Conseil.

## Article 8 - BUREAU

**8.1.** Le Bureau du CNFGG comprend :

- le président du CNFGG,

- le premier vice-président,

- le second vice-président,
- le secrétaire général,

- le trésorier.

Le président du CNFGG ne peut avoir de fonction dans les bureaux des sections ni dans les bureaux de l'UGGI ou de ses Associations constitutives.

**8.2.** Le Bureau est renouvelé et prend ses fonctions dès avant l'issue de la dernière Assemblée générale du CNFGG tenue l'année qui précède celle où se réunit une Assemblée générale de l'UGGI.

Au cours de ce renouvellement :

- le premier vice-président devient, de droit, président,

- deux nouveaux vice-présidents sont élus par l'Assemblée générale,

- le secrétaire général et le trésorier sont élus par le Conseil réuni à cet effet dès avant l'Assemblée générale.

**8.3.** En cas d'empêchement ou de démission du président, ses fonctions sont assurées à titre intérimaire par le premier vice-président.

En cas d'empêchement définitif ou de démission du premier vice-président, le second vice-président devient premier vice-président en titre.

En cas d'empêchement définitif ou de démission du second vice-président ou de son accession à la première vice-présidence, un nouveau vice-président est élu par le Conseil.

**8.4.** Le Bureau est chargé d'administrer le CNFGG ; il peut prendre toutes décisions à cet effet hormis celles :

- qui appartiennent statutairement à l'Assemblée générale ou au Conseil,

- que le président estime devoir demander au Conseil ou à l'Assemblée générale en raison de leur importance.
En particulier, le Bureau décide de l'attribution, sur les fonds du CNFGG, de
subventions aux frais de voyage des congressistes.

Il est rendu compte au Conseil de l'activité du Bureau.

8.5. Le Bureau est seul habilité à engager la responsabilité du CNFGG, notamment dans ses relations avec le Bureau de l'UGGI. Le président du CNFGG est le représentant de la France au Conseil de l'UGGI.

## Article 9 - DIVERS

9.1. Les modifications aux présents statuts sont décidées par l'Assemblée générale sur proposition du Conseil. Elles deviennent valides après approbation par l'Académie des sciences.

9.2. Le fonctionnement du CNFGG est régi par un règlement intérieur. Ce règlement est préparé par le Conseil, et soumis pour approbation à l'Assemblée générale.

9.3. Le CNFGG peut être dissout par décision de son Assemblée générale. La décision devient valide après approbation par l'Académie des sciences, à qui l'actif est alors remis.

Statuts adoptés le 2 février 1984, amendés en 1985, 1986 et 1992
# COMITÉ NATIONAL FRANÇAIS DE GÉODÉSIE ET GÉOPHYSIQUE

## HISTORIQUE

À la fin de la guerre de 1914-1918, les académies des pays alliés se préoccupèrent de réorganiser les organismes internationaux de coordination des recherches. Les initiatives les plus marquantes prises alors furent la création de l'Union de géodésie et géophysique (UGGI / IUGG) en novembre 1918 et la mise en place du Conseil international de recherches en juillet 1919, ce dernier devenant en 1931 le Conseil international des unions scientifiques (CIUS / UCSI). C'est à la suite d'une proposition de Ch. Lallemand, directeur du nivellement général de la France, que l'UGGI prit naissance, regroupant géodésie et géophysique. Les Associations internationales de géodésie et de sismologie furent alors remplacées par des sections de l'UGGI. De plus, on créa des sections de météorologie, de magnétisme et d'électricité terrestres, d'océanographie physique et de volcanologie.

Les statuts de l'Union géodésique et géophysique internationale adoptés en 1919 stipulaient : « Un Comité national est constitué dans chacun des pays adhérents [sic] à l'Union. Il est créé sur l'initiative, soit de son Académie nationale, soit de son Conseil national de Recherches [...], soit de son Gouvernement. Les Comités nationaux ont pour attributions de faciliter et de coordonner, sur leurs territoires respectifs, l'étude des diverses branches de la Géodésie et de la Géophysique, envisagées principalement au point de vue international. [...] Les Comités nationaux désignent les délégués chargés de les représenter aux Assemblées de l'Union. »

En conséquence, l'Académie des sciences de Paris, qui avait adhéré à l'UGGI au nom de la France, décida le 1er décembre 1919 de créer une association nommée
« Comité national français de géodésie et géophysique ». Une première liste de membres du Comité fut établie par l'Académie des sciences en attendant que d'autres personnalités scientifiques puissent être désignées par un vote du Comité. Faisaient de droit partie de la liste les académiciens des sections de géographie et navigation, de physique et de minéralogie... Les autres membres étaient délégués par les administrations et sociétés savantes intéressées, ou désignés pour leur compétence particulière. Le premier président du CNFGG était A. Lacroix, secrétaire perpétuel de l'Académie ; son premier secrétaire général, le Général Ferrié.

Le CNFGG ne comportait donc initialement que six sections. La section internationale d'hydrologie scientifique ne fut créée qu'au cours de la réunion de l'Assemblée générale de l'UGGI tenue à Rome en mai 1922, « sous réserve expresse qu'elle se tirerait d'affaire sans rien coûter à l'Union ». Sa création permettait d'englober la Commision internationale sur les glaciers (CIG), qui avait été créée en 1894, mais dont les activités s'étaient ralenties depuis la guerre. La section française correspondante fut constituée au sein du CNFGG en novembre 1923.

Dès sa création, le CNFGG joua un rôle important non seulement sur le plan international, mais aussi sur le plan national. De nombreux programmes scientifiques français étaient élaborés et discutés dans les sections. Ce fut le cas, par exemple, de l'établissement du nouveau réseau magnétique de la France au 1er janvier 1924, de la détermination de la pesanteur dans les différentes régions françaises et dans les Colonies, du projet d'installation d'observatoires de physique du globe à Dakar et à la Martinique, du projet de mesure de la pesanteur en sous-marin selon la méthode de Vening Meinesz, de l'étude du pendule inversé Holweck-Lejay, etc. C'est ainsi également que la section de volcanologie se préoccupa dès sa création de favoriser les observations concernant la Montagne Pelée et le Piton de la Fournaise, efforts qui n'aboutirent que beaucoup plus tard (en 1981) à la mise en route d'un observatoire sur le volcan de la Réunion. L'établissement de ces divers programmes conduisit les membres du Bureau à entreprendre de nombreuses démarches, tant auprès de l'Académie des sciences que du ministère de l'Instruction
publique ou de celui des Colonies, afin d'obtenir les crédits nécessaires à leur
réalisation.

Peu de temps après la création du CNFGG, la section de magnétisme et électricité terrestres dirigea la préparation et la publication, en 1924, d'un ouvrage collectif intitulé Traité d'électricités atmosphérique et tellurique. Cette même section de magnétisme et électricité terrestres joua également, au début des années trente, un rôle important dans l'organisation de la participation française à la deuxième Année polaire internationale de 1932-1933. Si les travaux réalisés à cette occasion furent finalement d'ampleur réduite du fait de la crise financière qui sévissait alors dans le monde, ils n'en étaient pas moins importants par la concertation qu'ils avaient requise entre les différents pays développés et par l'emploi de nouveaux moyens d'investigation, comme les radiosondages.

Après que le CNRS eût été créé en 1939, le centre de décision concernant les projets scientifiques se déplaça progressivement vers cet organisme. Ce ne fut cependant pas le cas pour la météorologie, du fait de l'existence de l'Office national de météorologie (ONM) qui assurait déjà depuis près de vingt ans l'élaboration et la conduite des programmes scientifiques dans ce domaine d'étude.

L'activité du Comité national et de ses sections fut très réduite pendant la seconde guerre mondiale, du fait de l'occupation allemande. À la fin de la guerre, l'activité des sections reprit peu à peu.

À partir de 1952, la préparation de la participation française à l'Année géophysique internationale (AGI, 1957-1958), coïncidant avec un maximum de taches solaires, fut à l'ordre du jour. Le CNFGG s'était préoccupé dès son Assemblée générale de décembre 1953 de recommander l'attribution de crédits adéquats pour l'acquisition des matériels et la formation des personnels. Toutefois, il n'eut que peu à intervenir dans l'organisation de la recherche, car un Comité spécial, le Comité national français de l'AGI, fut créé à cet effet dans le cadre du CNRS. C'est tout naturellement au P. Lejay, alors président du CNFGG, que fut confiée en 1952 la présidence du Comité de l'AGI, le secrétaire général en étant J. Coulomb, alors
président de la section de magnétisme. Un Comité central des expéditions scientifiques présidé par le P. Lejay fut constitué dans le cadre du CNRS de façon à préparer la participation française, un sous-comité antarctique étant confié à G. Laclavère. J. Coulomb, G. Laclavère et P. Tardi firent partie du Comité spécial de l'AGI (CSAGI) que le Conseil international des Unions scientifiques créa pour organiser cette vaste entreprise à laquelle participèrent au total soixante-sept pays. Le souci de participer à des programmes internationaux se manifeste encore en 1958 par la création par le CNFGG de l'Association française de séismologie expérimentale, laquelle se livra à des tirs et des observations de sismique avec de nombreux pays voisins.

Le succès de l'Année géophysique fut tel qu'il parut opportun de la prolonger par une Année internationale du Soleil calme (1964-1967), pour l'étude de la physique des relations Soleil-Terre. L'organisation de la participation française à cette Année internationale du Soleil calme fut confiée à différents organismes de recherche à qui il revenait de prendre les décisions, et qui avaient accès aux sources de financement public. Cela marque la fin du rôle directeur du CNFGG sur les activités géophysiques françaises.

Le financement des activités propres du CNFGG a par ailleurs évolué de manière significative. Dans les premiers temps de son existence, le Comité recevait une subvention du ministère de l'Instruction publique qui était destinée à lui permettre de publier son compte rendu annuel. Puis, de 1930 à 1939, la Caisse des recherches scientifiques versa une subvention supplémentaire au Comité. À partir de sa création (1939), le CNRS fut chargé d'assurer le versement des deux subventions par l'intermédiaire de l'Académie des sciences. En 1952 et 1953, le ministère de l'Air et le Service hydrographique de la Marine accordèrent des subventions annuelles. Toutefois, en 1958, certaines de ces subventions diminuèrent et, même, furent supprimées. Le Comité dut demander à ses membres une cotisation annuelle à partir de 1966, laquelle permet actuellement de subvenir aux besoins courants du Comité. Il reçoit, d'autre part, des subventions du ministère de la Recherche via le Comité
français pour les unions scientifiques (COFUSI) et surtout, depuis 1976, du ministère
des Affaires étrangères, qui sont affectées aux voyages nécessités par la participation
des membres aux réunions scientifiques internationales.

Ne dirigeant plus la recherche, le Comité n'en reste pas moins très actif en
tant que forum où ses membres se rencontrent, font le bilan de leurs travaux et
élaborent les recommandations qu'il leur paraît nécessaire de présenter aux
autorités. Sa mission actuelle consiste à provoquer et à coordonner les recherches
dans son domaine d'action, à assurer la représentation française aux activités de
l'UGGI, et à émettre des avis sur les questions scientifiques de son ressort afin de les
soumettre aux autorités compétentes. Le recrutement se fait assez largement parmi
les personnes qui, possédant une compétence scientifique reconnue, font acte de
candidature. Il fut un temps cependant où le nombre des membres de chaque section
était strictement limité, encore que les statuts ne l'aient jamais imposé. Cette
conception n'a pas prévalu, ce qui fait que le Comité regroupe actuellement la
plupart des chercheurs français ayant une spécialité de géodésien ou de
géophysicien. Il compte plus de six cents membres, cooptés par l'Assemblée générale
sur proposition des sections compétentes. Cependant, la représentation des
ingénieurs des services et des entreprises industrielles reste malheureusement assez
faible.

Les moyens d'action du CNFGG pour favoriser l'information et la
concertation de ses membres sont d'une part les réunions des sections, avec leurs
exposés scientifiques, et d'autre part l'Assemblée générale annuelle du Comité, avec
les rapports des présidents de section et une importante conférence scientifique.
C'est lors de ces Assemblées générales que sont adoptées les recommandations
concernant les opérations scientifiques et les structures de la recherche. Le président
les porte ensuite à l'attention des ministres et des directeurs des grands
établissements de l'État et des institutions internationales.

Les domaines des sections ont évidemment suivi l'évolution des sciences et
les modifications du champ couvert par les Associations internationales. En 1965, les
sous-sections de triangulation et de gravimétrie de la section de géodésie, qui avaient été créées en 1952, furent rassemblées pour fournir un cadre propice à l'accueil des spécialistes de l'exploitation des satellites artificiels à des fins géodésiques. La section de magnétisme et d'électricité terrestres prit le nom de section de géomagnétisme et d'aéronomie en 1954, afin de suivre l'exemple donné à l'Assemblée générale de l'UGGI de Rome par l'Association internationale correspondante (AIGA/IAGA). À partir de 1971, la section d'hydrologie scientifique prit le nom de section des sciences hydrologiques.

Les réunions scientifiques des sections sont assez fréquemment organisées conjointement par plusieurs d'entre elles. Ainsi, les spécialistes d'une discipline ont-ils l'occasion de rencontrer ceux de la discipline voisine, ce qui élargit leur champ de vision et leur fournit d'utiles comparaisons. Cela est particulièrement utile aux chercheurs qui s'intéressent à un objet terrestre particulier, dont l'étude ne peut être conduite qu'en faisant appel aux ressources de nombreuses spécialités. Cependant, les domaines couverts par les différentes sections étant les mêmes que ceux des Associations internationales, le CNFGG souffre du même défaut que l'UGGI. La frontière avec la géologie, en particulier, est relativement arbitraire. La volcanologie, l'étude de la lithosphère appartiennent à la fois à la géophysique et à la géologie. La sismogenèse fait traditionnellement partie de la sismologie, mais les tectonophysiciens n'ont pas de place au sein de l'Union. De même, il n'existe aucun cadre officiel dans lequel les planétologues puissent se regrouper. Les contacts du CNFGG avec le Comité national de géologie sont donc essentiels au plan national et activement développés. C'est ainsi que, dès 1971, il fut créé un Comité national de géodynamique comprenant des membres désignés de nos deux Comités, afin de favoriser la participation française au projet géodynamique international.

Les phénomènes géophysiques ne connaissent pas les frontières des États. Aussi, la coopération internationale est-elle nécessaire. Le Comité assure la participation française aux Assemblées générales de l'UGGI et des Associations internationales qui en font partie, ainsi qu'aux divers commissions et groupes de
travail qui se réunissent à la même occasion. Outre leur contribution aux travaux scientifiques, les délégués envoyés par le Comité sont chargés de veiller avec leurs collègues des autres pays de langue française à la correction des versions françaises de tous les textes officiels de l'Union. Le président du CNFGG représente la France au Conseil de l'UGGI.

Le Comité édite son rapport quadriennal à l'occasion de chacune des Assemblées générales de l'UGGI. Cette publication prend la suite de ce qui s'appelait autrefois Rapport national. Créé en 1966, c'était une compilation, en principe exhaustive, de comptes rendus des travaux exécutés par les Français dans les différents domaines couverts par les sections. Depuis l'Assemblée de Vienne de 1991, ce rapport est rédigé différemment. Il contient des mises au point concernant un nombre limité de sujets. Ainsi obtient-on un panorama, peut-être un peu lacunaire, mais que l'on espère néanmoins équilibré, de la recherche française replacée dans son contexte international.

D'autre part, le Comité attribue depuis 1987 un prix à un étudiant ayant soutenu une thèse de géophysique ou de géodésie lors de l'année écoulée. Ce prix a acquis une grande importance dans nos disciplines, car il apporte une première consécration à de jeunes chercheurs ayant fait un travail novateur et ayant su en exposer les résultats avec clarté.

Dans une association comme le CNFGG, qui rassemble des hommes de science de spécialités aussi diverses, il est essentiel, pour que chacun s'y trouve chez soi, qu'un strict équilibre soit préservé entre les disciplines. C'est dans ce souci que les sujets des conférences scientifiques des assemblées générales du Comité sont choisis, de telle manière qu'ils couvrent tout l'éventail des sujets. De la même façon, le choix du lauréat du prix de thèse et la répartition des subventions de voyage confiées au CNFGG par le ministère des Affaires étrangères sont faits en visant à la plus grande impartialité.

Les statuts du CNFGG, dans la dernière version adoptée en 1984, prévoient que le renouvellement du Bureau s'effectue l'année qui précède l'Assemblée
générale de l'UGGI et que le premier vice-président élu quatre ans auparavant
devienne alors automatiquement président pour les quatre années suivantes. Le
président sortant reste membre du Bureau pendant encore quatre ans. Ainsi est-on
assuré que l'expérience se transmet et que la politique du Comité jouit d'une grande
continuité.

Gérard GRAU

Institut océanographique, 195, rue Saint-Jacques, 75005 Paris

Jean-Pierre LEGRAND

3 bis, rue des Glycines, 92700 Colombes
# Géodésie
# Geodetic Reference Frames In France:
## Highlights 2004-2007

C. BOUCHER<fnref n="1" />, Z. ALTAMIMI<fnref n="2" />, X. COLLILIEUX<fnref n="2" />, F. DUQUENNE<fnref n="3" />,

B. GARAYT<fnref n="2" /> & J. LEGRAND<fnref n="2" />

**Abstract** Several French institutions take part in research or service activities in the domain of geodetic reference frames. The “Service de géodésie et nivellement” (Geodesy and Levelling Department, SGN) of the Institut Géographique National (IGN) is in charge of the realization and maintenance of the national geodetic and height references in France. In order to increase data accuracy and availability, the SGN is improving its geodetic networks, especially by densifying the permanent GPS network, which has doubled in number since four years, and by maintaining the levelling network using a combination of precise levelling and GPS techniques. Furthermore the SGN is involved in working-out global networks (DORIS, IGS, ITRF). The ITRF product center, also hosted by IGN, is in charge of the primary realization of the ITRS on behalf of the international community. The last one, ITRF2005, is so presented.

**Key words** geodetic reference frame, geodetic network, ITRF2005, France

## Repères de Référence Géodésiques en France

**Résumé** Divers organismes français participent à des activités de recherche ou de service dans le domaine des repères de référence géodésiques. Le Service de Géodésie et Nivellement (SGN) de l'Institut Géographique National est le responsable en

<footnote n="1">¹ Conseil général des ponts et chaussées, tour Pascal B, 92055 La Défense, France</footnote>

<footnote n="2">² Laboratoire de Recherche en Géodésie, Institut Géographique National, ENSG, 6-8 Avenue Blaise Pascal, 77455 Champs-sur-Marne, France</footnote>

<footnote n="3">³ Institut Géographique National, 2 avenue Pasteur, 94165 Saint-Mandé, France
claude.boucher@recherche.gouv.fr</footnote>
France de la réalisation et maintenance des références nationales de géodésie et
nivellement. Afin de permettre un accès toujours plus facile et plus précis, le SGN
améliore ses réseaux géodésiques en particulier avec une densificaion du réseau GPS
permanent dont le nombre de stations a doublé en 4 ans, un entretien du réseau de
nivellement par techniques combinées de nivellement précis et GPS. Le SGN
participe aussi à l'élaboration de réseaux mondiaux (DORIS, IGS, ITRF). Le Centre
de produit ITRF, également hébergé par l'IGN, est chargé de déterminer la réalisation
primaire de l'ITRS pour le compte de la communauté internationale. La dernière en
date, ITRF2005, est ainsi présentée.

***Mots-clefs*** *Repère de référence géodésique, réseau géodésique, ITRF2005, France*

I. INTRODUCTION

This paper intends to provide informations
about activities occured in France or
performed by French organizations or
individual scientists, and linked to
Geodetic Reference Frames (GRF). After a
synthetic overview of these activities, the
two major contributions are described with
more details and illustrative data:

a) the activities of the French
mapping agency (Institut Géographique

National/IGN) for national reference
frames and contributions to global ones,

b) the newest solution for the
realization of the International Terrestrial
Reference System (ITRS), ITRF2005,
produced by IGN again, acting as ITRF
Product center for the International Earth
Rotation and Reference System Service
(IERS).

II. OVERVIEW

For a variety of reasons, the topic of
Geodetic Reference Frame is presently
strongly publicized by the geodetic
community. The most illustrative example
is maybe that the International Association
of Geodesy (IAG) has selected this topic
as their proposal as a new task force for
GEO, to which IAG belongs as an
international organization.

In parallel, works on concepts and
terminology has been reactivated,
specifically in the frame of the IAG Sub-
Commission SC 1.2 on Global Reference
Frames, in association with IERS and IAU
[1].

The designation of Geodetic
Reference Frame will be understood here
as any crust-based reference frame of
geodetic interest. In other words, this
means **networks** of physical points on
solid earth topographic surface for which
numerical values of coordinates are
estimated, having conventionally choosen

the coordinate system together with the
underlying reference system, designated
hereafter as Geodetic Reference System
(GRS).

<figure><img src="image_4.png" /><figcaption>**Figure 1:** The French GPS permanent network RGP.</figcaption></figure>

This implies that, besides the
tridimensional coordinate system, or
Terrestrial Reference System (TRS), we
also consider for example height systems.

We can identify three major
purposes for the use of such a GRF:

* A metrological approach: as a physical
realization of a Geodetic Reference

System, like standards realize units.

* A user oriented approach: the points
can be used to determine other points
(densification or expansion). This is a
major role of networks for
applications.

* A geophysical approach: the points are
deformation sensors of the solid earth
surface. This has the dual interest to provide data for geophysical knowledge and to improve the estimation strategy of positions by using better geophysical models.

Networks can be named as global if they cover more or less sparsely the whole Earth, or regional if they cover a region of the Earth, such as a continent or a country. They can also be considered according to their type of coordinate system and are then specifically qualified by:

* **horizontal** if using plane coordinates or geographical latitude/longitude,

* **vertical** if using heights,

* **tridimensional** if using cartesian or geographical (with ellipsoidal heights),

* **astronomical**, if using astronomical latitudes and longitudes.

* An other interesting criterium is the nature of the physical points:

* **Classical network**: passive markers or benchmarks, available either as standpoint or target for user's measurements.

* **Permanent network**: beacons or receivers operating permanently and providing data suitable for precise determination of their position. This is the typical case for Space geodetic ground tracking systems.

* **Active networks**: permanent station providing additional information (to their precise position) enabling users to

determine position of other points in the same TRS. Such current additional data are the raw measurements performed by the station, or derived differential corrections such as DGPS. Such data are available in real time or not, following various communication media.

Beside national activities described in the next paragraph, a noticeable aspect is a wide and long term involvment of several French organizations into international or european organizations relative to GRS. The major ones are shortly described now.

The first group includes international services under the umbrella of IAG, although some are under multiple umbrellas. They are involved into several major tasks :

* establishment and operation of observation systems,

* data (and products) collection, archival and dissemination,

* data analysis for determination of various products.

Another general specificity of these organizations is their status of non governmental scientific body, using the so called best effort scheme. In particular their success and perennity is only based on national contributions in kinds. In this context, this paper specifically describes a significant part of the present day contribution of French organizations (other
domains are not considered here, such as
gravimetry, astrometry...).

The services so concerned are:

* the International GNSS (formerly GPS) Service (IGS) [2],

* the International DORIS Service (IDS) [3],

* the International Laser Ranging Service (ILRS),

* the International Earth Rotation and Reference System Service (IERS).

The second group is for regional
organizations, and here mostly European
ones. The main one is EUREF, also under
IAG umbrella, but closely linked to other
European initiatives (Eurogeographics,
INSPIRE...) [4].

<figure><img src="image_5.png" /><figcaption>**Figure 2:** Quality control of the RGP: an example of lacking data.</figcaption></figure>

III. GEODETIC REFERENCE FRAMES; THE IGN/SGN ACTIVITIES

The SGN (Service de Géodésie et
Nivellement) of the IGN (Institut
Géographique National) is responsible of
the realization and maintenance of the
geodetic and levelling references in

France. In order to provide users with the
access of these references SGN has
established and maintained several
networks as described above.
### III.1 The GPS network RBF

The RBF (Réseau de Base Français) network was observed between 1994 and 1996. 1019 points were observed by GPS, in France and Corsica. Since this time the condition of each marker is verified every two years and in case of destruction built and observed again, the next year.

The first determination in ETRS89 was performed with the Ashtech software GPPS and the Geolab software in 1997. This is the realization of the EUREF French component named RGF93. Every station of the GPS permanent network (RGP) were connected to the nearest (2-3) RBF points. By comparison with the

weekly solutions of the RGP (GPS permanent network) the accuracy of about 2-3 cm in position can be confirmed for RBF.

In 2003, all the RBF observations were computed again using the Bernese software. Otherwise the baselines between RGP and RBF were observed during the operations of linkage of the RGP and levelling aided by GPS. The aim is for 2008 to combine all the determinations, and to fit to a EUREF solution of the RGP which will provide users with an access to the national reference with an accuracy better than 5 mm.

<figure><img src="image_6.png" /><figcaption>**Figure 3:** Quality control of the RGP: mountain mask.</figcaption></figure>
<figure><img src="image_7.png" /><figcaption>Figure 4: IGN/SGN computed network for E-GVAP.</figcaption></figure>

### III.2 The GPS permanent Network RGP

The RGP network was composed of 43 GPS permanent stations in 2003 and has increased to 85 stations at the end 2006. The GPS stations were installed by IGN and many partners (universities, research laboratories, district services, private organization). The network is developed in a large public and private partnership. Especially among the private partners, there are the real time providers (Exagone (OGE), S@t-info, D3E, Lél@). The real time service is with an admission charge, but the observations are transferred to the RGP for deferred and free of charge applications.

* 75 stations (20 IGN, 54 partners) deliver observations files every hour, with a one second sampling rate,

* 10 stations (1 IGN, 9 partners) deliver observations files every 24 hours, with a thirty seconds sampling rate,

* 17 stations are also EPN (EUREF Permanent Network) stations,

* 8 stations are also IGS (International GNSS Service).

* Two operational centres, one in Marne-La-Vallée, the other in Saint Mandé:

* collect data,

* check data quality,

* deliver data on the Internet,

* process hourly, daily and weekly solution,

* deliver products on the Internet.
<figure><img src="image_8.png" /><figcaption>**Figure 5:** E-GVAP: comparison between IGN/SGN and LPT ZTD and HL22 model.</figcaption></figure>

Data are public (free of charge).

The website (http://rgp.ign.fr/) is the interface with users. In real time a map shows if the data are arrived or not (Fig.1). Every station is described and diagrams give a view of the data quality (Fig.2 & 3).

Depending on the data flow, successive processes are carried out.

Along with the 1-hour data associated with IGS predicted orbits (IGU), hourly solutions are performed in

3-hour moving computation. Expected results are i) controlling data quality immediately, ii) providing near real time sub-products as atmospheric behavior parameters. The IGN contributes to E-GVAP (EUMETNET GPS water Vapour Programm) as a computation center (Fig. 4-5).

Through the availability of rapid orbits IGS products (i.e. after 28 hours), a daily solution is processed. The involved
products are intended to refine a reference control assessment and provide more accurate atmospheric models.

Finally, weekly solutions from precise IGS orbits and up to date EOP are made available. The IGN EUREF LAC (Local Analysis Center) contribution is included in these activities.

Regarding the maintenance of French national reference, several combinations are routinely performed:

* A daily 7-day moving combination is an efficient tool to recover large errors and to deal with any “instantaneous

stability defect” of RGP stations.

* Weekly precise solution is itself a combination.

In turn, all solutions (combinations) are re-combined in pluri-annual one, in order to provide users with the more accurate coordinate product.

The RGP observations between 1998-2006 are being reprocessed with the new Bernese Software version 5 with the new recommended specifications. This reprocess will provide the new RGF93 realization usable up to 5 millimeters accuracy requirements.

<figure><img src="image_9.png" /><figcaption>Figure 6: Motorized levelling.</figcaption></figure>

### III.3 Scientific levelling

For six years IGN has started to measure levelling lines (about 5000 km) with a great accuracy using the motorized levelling method (Fig. 6) and ZEISS NI002 level (Fig. 7). The levelling lines are linked to several tide gauges on French

coast and the first order network of Great-Britain (through the Channel Tunnel), Belgium, Germany and Spain (Fig. 8). This will be a french contribution to EVRS2007 (European Vertical Reference System).
<figure><img src="image_10.png" /><figcaption>**Figure 7:** Surveyor operating a Zeiss NI002 level for scientific levelling.</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>**Figure 8:** Scientific levelling lines.</figcaption></figure>
<figure><img src="image_12.png" /><figcaption>**Figure 9:** Observation scheme of levelling aided by GPS.</figcaption></figure>

<figure><img src="image_13.png" /><figcaption>**Figure 10:** The DORIS network: 57 stations, 33 countries.</figcaption></figure>

### III.4 Maintenance of NGF (French levelling network)

The maintenance of the French National Levelling Network is performed with levelling aided by GPS. The aim is to equip every town of more than 200 inhabitants with at least three levelling benchmarks. The distance between

benchmarks is less than one kilometre, and less than five kilometres between two sets of three benchmarks. A pivot is observed with GPS, and linked to the RBF and RGP networks and with levelling observations to NGF levelling network (Fig. 9). The
pivot is used for GPS determination of
village points, for 3 or 4 villages and
linked in height by precise levelling to
benchmarks. The 3 benchmarks are also
linked with each other by precise levelling.

The normal height is computed
with GPS and the RAF98 conversion grid,
and if one old benchmark exists it is
compared with the normal height from
precise levelling.

<figure><img src="image_14.png" /><figcaption>Figure 11: Ny-Alesund Doris station.</figcaption></figure>

### III.5 Contribution to international networks

**DORIS Network**

In collaboration with the CNES (the
French Spatial Agency), the IGN is in
charge of the building and maintenance of
the DORIS network (Fig. 10 and 11). IGN
is also a data center of the IDS
(International Doris Service). Between
2003 and 2006 9 new stations were

installed and 20 restored.

**ITRF**

Between 2003 and 2006, IGN has
determined precise geodetic ties between
spatial instruments (VLBI, Satellite Laser,
GPS, DORIS, see Fig. 12) of three ITRF
sites in China (Jiufeng, Sheshan) and
South Africa (Hartebeesthoek).
<figure><img src="image_15.png" /><figcaption>**Figure 12:** Laser and VLBI linking.</figcaption></figure>

<table><caption>**Table 1:** Summary of Submitted Solutions to ITRF2005</caption><thead><tr><td>TC - AC</td><td>Time span</td><td>Type of constraints/solution</td><td>EOPs</td></tr></thead><tbody><tr><td>IVS</td><td>1980.0-2006.0</td><td>Normal Equation</td><td><b>Polar Motion, rates, UT1, LOD</b></td></tr><tr><td>ILRS</td><td>1992.9-2005.9</td><td>Loose; variance-covariance</td><td><b>Polar Motion, LOD</b></td></tr><tr><td>IGS</td><td>1996.0-2006.0</td><td>Minimum; variance-covariance</td><td><b>Polar Motion, rates, LOD</b></td></tr><tr><td>IDS - IGN-JPL</td><td>1993.0-2006.0</td><td>Loose; variance-covariance</td><td><b>Polar Motion, rates, LOD</b></td></tr><tr><td>IDS - LCA</td><td>1993.0-2005.8</td><td>Loose; variance-covariance</td><td><b>Polar Motion, rates, LOD</b></td></tr></tbody></table>

## IV. ITRF2005

The ITRF Product Center hosted by the Institut Geographique National, France, together with the contribution of the ITRF combination centers (DGFI and NRCan)

released the ITRF2005 solution in october 2006. Contrary to previous ITRF versions, the ITRF2005 integrates time series of station positions and daily Earth
Orientation Parameters (EOP's). The time series solutions are now provided in a weekly basis by the Services of the International Association of Geodesy (IAG): International services of satellite techniques (IGS, ILRS, IDS) and in a daily (VLBI session-wise) basis by the IVS. Reasons for which it was decided to use time series of station positions and EOP as

input to ITRF2005 include:

* monitoring of non-linear station motions and all kinds of discontinuities in the time series: Earthquake related ruptures, site instability, seasonal loading effects, etc.

* rigorously and consistently including EOPs in the combination and ensuring their alignment to the combined frame.

<figure><img src="image_16.png" /><figcaption>**Figure 13:** ITRF2005 Sites with Co-located Techniques.</figcaption></figure>

## IV.1 ITRF2005 Input Data

### Space Geodesy Solutions

One set of time series per space geodesy technique was considered as input to the ITRF2005 combination. These solutions are the official time series provided by the international services of the 4 techniques, known as Technique Centers (TC) by the IERS. Note that these official TC's solutions result from a combination at the weekly (daily) basis of the corresponding

individual solutions provided by the analysis centers participating to the activities of each TC. Official time series were submitted to the ITRF2005 by the International VLBI Service (IVS), the International Laser Ranging Service (ILRS), and the The International GNSS Service (IGS). At the time of the ITRF2005 release, official weekly combined solutions from the International
DORIS Service (IDS) were not available, so that individual solutions were submitted by two DORIS analysis centers (AC), namely the Institut Géographique National (IGN) in cooperation with Jet Propulsion Laboratory (JPL) and the Laboratoire d'Etudes en Geophysique et Océographie Spatiale (LEGOS) in cooperation with Collecte Localisation par Satellite

(CLS), designated hereafter by (LCA). A specific analysis of DORIS solutions submitted to the ITRF2005 was performed prior to the ITRF2005 release. Table 1 summarizes the submitted solutions to ITRF2005, specifying the data-span, their type, the originally applied constraints and the nature of the included EOPs.

<figure><img src="image_17.png" /><figcaption>Figure 14: ILRS SLR Weekly translation and scale parameters with respect to ITRF2000.</figcaption></figure>

## Local Ties in co-location Sites

The very existence of the ITRF relies on the availability and quality of local ties in co-location sites as well as the number and distribution of these sites over the globe. The usual procedure adopted for the ITRF combination is to use the local ties as independent measurements with proper

weighting. This is achieved either by (1) introducing directly in the combination all implied tie vectors with their uncertainties, or by (2) using a SINEX file per co-location site. The reader may refer to [5] for more detail regarding the inclusion of local ties in the ITRF computations. For the ITRF2005, about 45% of the available
local ties are provided in SINEX files with
full variance-covariance information: all
the Australian sites [6]; three Italian sites:
Medicina, Noto [7] and Matera (Bianco,
personal communication); Wettzell and
Concepcion [8 and 9]); and all the DORIS
co-location sites were re-adjusted by the
ITRF Product Center in order to generate
full SINEX files. As illustrated by Figure
13, there are in total 95 co-location sites
implying about 175 tie vectors, distributed
as follows: 52 sites with two techniques,
36 with 3 techniques and 6 sites with 4

techniques. Note that, unfortunately, not
all these co-located instruments are
currently operating. For instance, among
the 6 sites having 4 techniques, only two
of them are currently operating:
Hartebeesthoek, South Africa and
Greenbelt, MD, USA. The ITRF2005 is
composed of 608 stations located in 338
sites as illustrated in Figure 13, with an
imbalanced distribution between the
northern hemisphere (268 sites) and the
southern hemisphere (70 sites).

<figure><img src="image_18.png" /><figcaption>**Figure 15:** ILRS SLR Weekly translation and scale parameters with respect to its own cumulative solution.</figcaption></figure>

IV.2 ITRF2005 computation strategy

The strategy adopted for the ITRF2005
computation consists on two steps:

**Step 1:**

Combination (rigorously stacking) of each
technique time series. This first steps
implies the following sub-steps:

* Apply minimum constraints equally to all loosely constrained solutions. This is the case of SLR and DORIS solutions where minimum constraints were applied to each weekly solution before their stacking. The minimum constraints application here amounts to adding the reference frame effect into the variance-covariance matrix without

altering the estimates;

* Apply minimum constraints over the origin and orientation parameters to the VLBI daily solutions provided under the form of normal equation. The addition of minimum constraints on origin and orientation to the free normal equation allows its inversion and preserves its physical scale parameter;

<figure><img src="image_19.png" /><figcaption>Figure 16: Intrinsic IVS VLBI Scale (in mm), with fitted annual signal superimposed.</figcaption></figure>

* Use as they are minimally constrained solutions. This is the case of GPS weekly time series;

* Form per-technique combinations by rigourously stacking the time series. Here we used the internal constraint approach of datum definition in order to preserve the intrinsic origin and scale embedded in the SLR weekly solutions and the scale of VLBI daily solutions;

* Identify and properly reject or down-weight outliers, properly handle discontinuities using piece-wise approach and iterate as necessary.

Nearby stations within the same site and multiple segments (in case of discontinuities) are constrained to have the same velocity, except for sites where geophysical events as earthquakes occur. The stacking yields for each solution/technique a global long-term
solution containing positions and
velocities and daily EOPs. Note that for
DORIS, we first stacked separately the
two AC solutions (IGN and LCA) and then
combined together the resulting two long-
term solutions.

**Step 2:**

Combination of the per-technique
combinations as results from the first step

analysis, adding the local ties. Note that
station positions of the per-technique long-
term solutions are propagated to their
epochs of minimum variances (as
described in [5]) prior to the combination.
This last step yields the final ITRF2005
solution containing station positions,
velocities and daily EOPs with full
variance-covariance information.

<figure><img src="image_20.png" /><figcaption>Figure 17: IVS VLBI and ILRS SLR Scales (in mm), with respect to ITRF2005.</figcaption></figure>

IV.3 ITRF2005 main results

**Results of time series analysis**

From the first step of the ITRF2005
computation (i.e. the time series stacking),
we focus here more specifically on the
temporal behavior of the SLR origin and
scale as well as the scale of VLBI time
series. Figure 14 illustrates the weekly
translation and scale parameters of the
ILRS SLR time series with respect to
ITRF2000. Figure 15 shows the same
parameters as determined using the

dynamically internal constraints approach
[10] that preserve the intrinsic datum
parameters of our choice, the origin and
scale in this case. From the two figures 14
and 15, it is more than clear that the Z-
translation and the scale have both non-
linear, but rather piece-wise behavior over
time. For the scale in particular we
distinguish three different drifts : from
1993 to 1996 (positive drift), from 1996 to
2001 (almost zero drift) and from 2001 to
2006 (negative drift). In order to test for the impact of the correlation between the Z-translation and the scale due to the poor SLR geometry, we stacked the ILRS SLR time series without estimating the scale (all weekly scale factors were set to zero). The results of this stacking show that (1) the temporal behavior from week to week of the Z-translation does not change and (2) the Z drift was insignificantly decreased by 0.1 mm/yr only and (3) the WRMS computed over the residual time series increased by 25%. This leads to the conclusion that the weekly translation and scale parameters are all significant and should be estimated when stacking the time series. Figure 16 displays the intrinsic

scale of the VLBI time series over which we superimposed an annual sinusoidal fit to show the amplitude and phase of the scale variation. These annual variations are most probably and partly attributed to the thermal expansion of the VLBI radio-telescopes which is not taken into account in the VLBI analysis, where the impact on the scale is may be of the order of 1.5 mm in amplitude [11]. Analogously to the 2.5 years minimum time-span necessary to minimize the effect of annual signals on the estimated linear station velocity as pointed out by [12], the annual variations of the VLBI scale have neglected effect on its linear behavior.

<figure><img src="image_21.png" /><figcaption>**Figure 18:** Temporal Translation and Scale Parameters of IGN and LCA DORIS Solutions with Respect to ITRF2005.</figcaption></figure>
**Results of the Global ITRF2005 Combination**

All the ITRF2005 results: station positions, velocities, Earth Orientation Parameters and other information are available at the ITRF2005 WEB site (http://www.itrf.ensg.ign.fr).

The ITRF2005 multi-technique combination involving the long-term solutions of the four techniques as well as the local ties in co-location sites revealed a relative scale bias between VLBI and SLR solutions of 1.0 ppb at epoch 2000.0 and a scale rate of 0.08 ppb/yr. In order to illustrate more the inconsistency between the two scales, Figure 17 displays both scales with respect to ITRF2005, showing

a clear bias both in the offset and the linear trend.

Regarding the DORIS contribution to ITRF2005, a detailed article was published [13] giving all the details of the DORIS solutions submitted to ITRF2005. In order to be complete here, Figure 18 displays the temporal translation and scale parameters for the two used solutions (IGN and LCA) with respect to ITRF2005. We selected to refer these parameters to ITRF2005 in order to show that the scale of IGN solution is very close to VLBI and SLR scales. It can also be seen that there is a significantly large scale difference between the two solutions, up to almost 10 ppb.

V. REFERENCES

[1] Boucher C. (2007). Report of the IAG SC 1.2 on Global Reference Frames. IUGG/IAG General Assembly, Perugia.

[2] Beutler G., Rothacher M., Schaer S., Springer T.A., Kouba J., Neilan R.E. (1999). The International GPS Service (IGS): an interdisciplinary service in support of earth sciences. Advances in Space Research 23 (4), 631-653.

[3] Tavernier G., Fagard H., Feissel-Vernier M., Le Bail K., Lemoine F., Noll C., Noomen R., Ries J.C., Soudarin L., Valette J.J., Willis P. (2006). The International DORIS Service: genesis

and early achievements, Journal of Geodesy 80 (8-11), 403-417.

[4] Torres J., (2005). EUREF, the infrastructure for geo-referencing in Europe: definition, realization and maintenance of European reference systems. Geoinformatics, 8 (6), 18-21

[5] Altamimi, Z., P. Sillard, and C. Boucher (2002). ITRF2000: A New Release of the International Terrestrial Reference Frame for Earth Science Applications. J. Geophys. Res., 107(B10), 2214, doi: 10.1029/2001JB000561.

[6] Johnston, G. and J. Dawson (2004). The 2003 Yarragadee (Moblas 5) Local
Tie Survey. Geoscience Australia
Record 2004/19, ftp://ftp.ga.gov.au
/sgac/sinex/ties/AUSYARR0311GA
.pdf

[7] Sarti, P., P. Sillard and L. Vittuari (2004).
Surveying co-located space-geodetic
instruments for ITRF computation.
Journal of Geodesy, doi: 10.1007
/s00190-004-0387-0.

[8] Schlüter, W., R. Zernecke, S. Becker, Th. Klügel, D. Thaller (2004). Local Ties between the Reference Points at the Fundamentalstation Wettzell. In: Richter B., W.R. Dick and W. Schwegmann (Eds.), IERS Technical Note 33, Verlag des Bundesamts für Kartographie und Geodäsie Frankfurt am Main, Germany.

[9] Schlüter, W., H. Hase, R. Zernecke, S. Becker, Th. Klügel, D. Thaller (2004). Local Ties between the Reference Points at the Transportable Integrated Geodetic Observatory (TIGO). In: Richter B., W.R. Dick and W. Schwegmann (Eds.), IERS Technical Note 33, Verlag des Bundesamts für Kartographie und Geodäsie, Frankfurt am Main, Germany.

[10] Altamimi, Z., X. Collilieux, C. Boucher (2006). Accuracy assessment of the ITRF datum definition. VI Hotine-Marussi Symposium of Theoretical and Computational Geodesy: Challenge and Role of Modern Geodesy, International Association of Geodesy, submitted.

[11] Collilieux X., Z. Altamimi, J. Ray (2005).

Impact of the thermal expansion of
VLBI radio-telescopes on the scale of
the Terrestrial Reference Frame.
Abstract AGU Fall Meeting.

[12] Blewitt, G., and D. Lavalée (2002). Effect of annual signals on geodetic velocity. J. Geophys. Res., 107(B7), doi: 10.1029/2001JB000570.

[13] Altamimi, Z., X. Collilieux, C. Boucher (2006). DORIS Contribution to ITRF2005. Journal of Geodesy, 80:8-11, doi: 10.1007/s00190-006-0065-5.

[14] Altamimi, Z., P. Sillard, and C. Boucher (2003). The impact of a No-Net-Rotation Condition on ITRF2000. Geophys. Res. Lett., 30 (2), 1064, doi: 10.1029/2002GL016279.

[15] Altamimi Z, Sillard P, Boucher C, (2004). ITRF2000: From Theory to Implementation. In: Sanso F (ed) V Hotine-Marussi Symposium on Mathematical Geodesy, IAG symp., vol. 127, Springer, Berlin Heidelberg New York, pp 157-163.

[16] Altamimi, Z., C. Boucher, and D. Gambis (2005). Long-term stability of the terrestrial reference frame. Adv. Space. Res., 36 342-349, doi: 10.1016/j.asr.2005.03.068.

[17] Altamimi, Z., C. Boucher and P. Willis (2005). Terrestrial Reference Frame Requirements within GGOS Perspective. Journal of Geodynamics, 40(4-5), 363-374, doi: 10.1016/j.jog.2005.06.002
# Modélisation du Champ de Gravité Global de la Terre et de ses Variations Temporelles, Nouvelles Missions Satellitaires de Gravimétrie, Applications

R. BIANCALE<fnref n="1" /> AND P. EXERTIER<fnref n="2" />,<fnref n="1" />

**Résumé** Les nouvelles missions spatiales dédiées à la gravité, telles CHAMP et GRACE, ont fait progresser considérablement notre connaissance du champ de gravité global. En particulier la mission GRACE nous a permis (en combinaison avec les missions laser LAGEOS pour une meilleure obtention du terme C20) de restituer un modèle de champ de gravité moyen : EIGEN-GL04S, dont la représentation en terme de géoïde atteint dorénavant la précision du centimètre sur l'ensemble du spectre grandes longueurs d'onde jusqu'à 200 km de résolution. De plus, les grandes variations temporelles de masses sont désormais cartographiables à des intervalles décadaires et procurent ainsi une information pertinente pour les études interprétatives en géophysique, glaciologie, hydrologie ou océanographie.

***Mots clefs*** Géodésie spatiale, champ de gravité, accélérométrie

## Modelling of the Global Earth Gravity Field and of its Temporal Variations, New Satellite Gravity Missions, Applications

**Abstract** From the new space gravity missions such CHAMP and GRACE our knowledge of the global gravity field of the Earth has improved considerably. In particular the GRACE twin satellites mission enable us (still in combination with the LAGEOS SLR missions in order to better recover the C20 term) to adjust a mean

<footnote n="1">¹CNES/GRGS (18 avenue Edouard Belin, 31401 Toulouse Cedex9, France
richard.biancale@cnes.fr</footnote>

<footnote n="2">²OCA/GRGS (avenue Copernic, 06130 Grasse, France
pierre.exertier@obs-azur.fr</footnote>
gravity field model EIGEN-GL04S whose geoid representation reaches the 1 cm accuracy over the whole spectrum down to 200 km resolution. Moreover large temporal variations of surface mass distribution become now available at 10-day intervals since mid-2002 and procure pertinent input for geophysic, glaciologic, hydrologic or oceanographic interpretation studies.

***Key words*** Space geodesy, gravity field, accelerometry

# I. LA DÉCENNIE DE LA GRAVIMÉTRIE SPATIALE

La modélisation du champ de gravité de la Terre aura connu d'importantes évolutions en cette première moitié de décennie, notamment avec l'arrivée des nouvelles missions de gravimétrie spatiale : CHAMP en 2000 puis GRACE en 2002. En quelques années ces missions, à travers les modèles EIGEN (pour « European Improved Gravity model of the Earth by New techniques ») établis en coopération entre le GRGS et le GFZ de Potsdam, ont amélioré drastiquement notre connaissance du champ global d'un facteur 100 à 1000 suivant les longueurs d'onde. De plus, la précision micrométrique des mesures inter-satellites GRACE a permis pour la première fois d'avoir accès aux variations de la gravité à des échelles temporelles mensuelles, voire décadaires et jusqu'à une résolution spatiale de l'ordre de 600 km.

En parallèle, les travaux de préparation à la prochaine mission GOCE de gradiométrie spatiale se sont poursuivis. Ce satellite de l'Agence Spatiale Européenne devrait permettre d'ici la fin de la décennie d'étendre notre connaissance du géoïde de façon homogène jusqu'à la résolution de 100 km.

Par gradations techniques et précisions croissantes cette trilogie de missions apporte une nouvelle façon gravifique d'ausculter la planète et ouvre la voie à de nombreuses études interprétatives en géophysique, en hydrologie, en océanographie, en glaciologie. Ce rapport fait succinctement état des missions, des modélisations et de leurs interprétations réalisées en France sur la période 2003-2006.

# II. LES MISSIONS DE GRAVIMÉTRIE SPATIALE

Des missions de gravimétrie spatiale, CHAMP (CHallenging Mini-satellite Payload for geophysical research and

application) fut la première a être programmée par l'agence spatiale allemande (DARA) et le GFZ. Elle est
réalisée par un satellite allemand dédiée à
la mesure globale des champs de gravité et
magnétique terrestres équipé d'une charge
utile internationale : la NASA/JPL a
délivré le récepteur GPS Blackjack et les
rétro-réflecteurs laser, le CNES le micro-
accéléromètre STAR de l'ONERA, le
LETI/CEA le magnétomètre scalaire,
l'Université Technique du Danemark le
magnétomètre vectoriel. Les instruments
spécifiques à la détermination du champ de
gravité sont le récepteur GPS qui donne la
trajectoire par le suivi des satellites de la
constellation GPS, les réflecteurs laser
ainsi que le micro-accéléromètre (de
précision 3 10⁻⁹ ms⁻² dans la bande de
fréquence de 10⁻⁴ à 10⁻¹ Hz) qui permet de
séparer les forces gravitationnelles des
forces de surface s'exerçant sur le satellite
(freinage atmosphérique, radiations solaire
et terrestre, thermique). Le satellite, lancé
le 15 juillet 2000 sur une orbite à 87°
d'inclinaison et 460 km d'altitude par une
fusée Cosmos depuis la base septentrionale
russe de Plesetsk a perdu en 6 ans plus de
100 km malgré trois manœuvres de
rehaussement. Quant à la technique
d'extraction des paramètres du potentiel
gravitationnel terrestre, elle se fait
classiquement par inversion des
perturbations orbitales déduites du suivi de
la trajectoire par les satellites de la
constellation GPS et par le réseau
international laser coordonné par l'ILRS.

Le CNES ayant fourni au projet
(allemand) l'accéléromètre STAR fabriqué
par l'ONERA, l'Equipe CNES de
Géodésie Spatiale a eu la responsabilité de
l'étalonnage de cet accéléromètre pendant
la phase d'évaluation et d'étalonnage qui
aura duré 8 mois après le lancement. Elle
est également co-responsable avec le
partenaire allemand GFZ, de la production
des modèles du champ de gravité EIGEN
dérivés des données de Champ. La
précision visée avec CHAMP : erreur
cumulée de 10 cm sur le géoïde moyen
pour une échelle de 400 km à sa surface, a
été atteinte en 2003 avec le modèle
EIGEN-CHAMP03S développé en
harmoniques sphériques au degré 150.

Depuis, cette mission, du moins en
ce qui concerne l'objectif gravitationnel, a
été supplantée par la mission suivante :
GRACE (Gravity Recovery and Climate
Experiment), réalisée en coopération
NASA-JPL/DLR par un couple de
satellites identiques co-orbitant à 200 km
de distance environ et muni d'un nouveau
système de mesure inter-satellites. Ce
système dénommé KBR (pour K-band
ranging) mesure (quoiqu'avec un biais)
cette distance par émissions croisées
micro-ondes en bandes K (à 24 GHz) et Ka
(à 32 GHz) avec une précision d'ordre
micrométrique dans la bande de fréquence
de 10⁻⁴ à 10⁻¹ Hz. Chacun des satellites est
muni en outre d'un récepteur GPS
Blackjack du JPL, de réflecteurs laser et d'un micro-accéléromètre Super-STAR de l'ONERA (de performance 3 10⁻¹⁰ ms⁻² dans la même bande de fréquence). Les satellites jumeaux GRACE ont été placés sur une orbite quasi polaire (à 89° d'inclinaison) à 480 km d'altitude le 17 mars 2002 avec une fusée Rockot, également depuis la base de Plesetsk.

La mise à disposition régulière des données de GRACE n'a cependant été effective que depuis l'été 2005. Dès lors, l'Equipe de Géodésie Spatiale du CNES/GRGS s'est investi dans un traitement systématique des données (GPS, laser, accélérométriques, inter-satellites KBR); elle produit dorénavant des modèles de géoïde décadaires à une résolution effective de l'ordre de 600 km. Ces modèles qui servent d'ores et déjà à de nombreuses études interprétatives sont disponibles sur les sites web du BGI comme de l'ICGEM. Ils sont également à la base des modèles statiques développés en coefficients harmoniques sphériques jusqu'au degré 150 tel EIGEN-GL04S (2005) ou jusqu'au degré 360 (par combinaison avec des grilles de données issues de la gravimétrie terrestre ou aéroportée et de l'altimétrie spatiale) tel EIGEN-GL04C (2006) réalisé en coopération avec le GFZ. Ce dernier modèle a été adopté comme standard pour le calcul opérationnel des orbites des

satellites altimétriques Jason1 et ENVISAT.

En complément, la mission GOCE (Gravity field and steady-state Ocean Circulation Explorer) du programme « Earth Explorer » de l'ESA, est destinée à cartographier les longueurs d'onde plus courtes du champ de gravité. Son lancement est prévu pour fin 2007, voire 2008. Le principe consiste à mesurer au moins trois des six composantes du tenseur gradient de gravité terrestre dans un satellite à l'aide d'un instrument nouveau : un gradiomètre. Celui-ci est constitué de six micro-accéléromètres triaxiaux (de sensibilité ~10⁻¹² ms⁻²) qui fournissent par différentiation l'information à petite longueur d'onde du géopotentiel. Ces données seront complémentées par celles du suivi continu de la trajectoire (avec un récepteur GPS européen embarqué) pour l'accès aux plus grandes longueurs d'onde. La sensibilité requise nécessite de faire voler le satellite à une altitude exceptionnellement basse (vers 260 km), ce qui nécessite un système sophistiqué de compensation des forces de surface par éjection de gaz froid (système « drag free » asservi aux accéléromètres) pour obtenir une durée de vie d'au moins deux ans. Ainsi, GOCE cartographiera le champ de gravité terrestre globalement avec une résolution de 100 km pour une précision restituée au sol de 1 mgal (10⁻⁵ms⁻²), soit
de moins de 2 cm sur le géoïde. Cette
précision bénéficiera notamment à
l'océanographie (circulation moyenne
absolue, transports de chaleur,
climatologie, etc.), à la géophysique
(meilleure connaissance de la croûte
continentale) et à la géodésie.

L'activité de préparation du
traitement des données de GOCE se fait au
sein du « European GOCE Gravity
Consortium » (EGGC) constitué de 10
équipes européennes. Le rôle confié à

l'Equipe de Géodésie Spatiale du CNES/GRGS est central : elle a la responsabilité de traiter les données de la mission et de produire un modèle global par la méthode dite directe, la plus lourde, mais aussi la plus rigoureuse. Comme pour les autres missions, cette activité est partagée entre le GRGS et le GFZ. Sa préparation consiste à mettre au point les standards de traitement, à mettre à niveau les logiciels et à les valider par simulation.

<figure><img src="image_22.png" /><figcaption>**Figure 1:** Historique des modèles européens en différences spectrales cumulées de géoïde par rapport au modèle EIGEN-GL04S (2005).</figcaption></figure>

III. LA MODÉLISATION

La modélisation du champ de gravité
global repose sur les fonctions
harmoniques sphériques développées sous

forme normalisée. La troncature de ces
modèles dépend à la fois de l'altitude des
orbites utilisées dans la modélisation et de
la précision des mesures. C'est pourquoi les séries des anciens modèles franco-allemand GRIM basés sur l'analyse des perturbations d'orbites (en général à plus de 800 km d'altitude) à travers les mesures de poursuite optique, Doppler ou laser précises au mieux au centimètre, ont été développés en deçà du degré 100. Ce n'est plus le cas de la nouvelle génération de modèles EIGEN issus de l'analyse des perturbations des nouvelles missions, d'une part d'altitudes plus basses et d'autre part suivies continûment par GPS. En outre l'amélioration des modèles GRACE jusqu'à EIGEN-GL04S (voir figure 1)

provient principalement de l'analyse des perturbations relatives entre les deux satellites GRACE à l'aide des mesures inter-satellites KBR. En fait, ces mesures sont utilisées dans leur forme dérivée temporelle, c'est-à-dire en terme de vitesse relative inter-satellites (dénommée KBRR). Toutes longueurs d'onde confondues jusqu'au degré 100, soit à 200 km de résolution, la précision désormais atteinte avec le dernier modèle EIGEN-GL04S approche le centimètre, alors qu'elle n'était que du mètre au début de la décennie.

<figure><img src="image_23.png" /><figcaption>**Figure 2:** Spectres des modèles décadaires (en hauteur d'eau équivalente).</figcaption></figure>

# IV. LES MODÈLES DÉCADAIRES DE GÉOÏDE

A regarder l'historique de la progression de la qualité des modèles européens de géoïde, il s'avère que les missions de ces

dernières années ont permis des progrès fulgurants. L'innovation principale apportée par la mission GRACE fut sans
conteste la réalisation de modèles
temporels qui démontrent désormais que
les grandes variations de masse deviennent
décelables depuis l'espace, qu'elles soient
liées au cycle hydrologique annuel, à la
fonte des glaces polaires ou encore à des
événements tectoniques majeurs. Ainsi, il
devient possible à travers les modèles
décadaires de géoïde, tels ceux restitués
par l'Equipe de Géodésie Spatiale du
CNES/GRGS, de mettre en évidence les
fluctuations saisonnières des grands
bassins hydrologiques. Les signaux
annuels bruts apparaissant en déformation
de géoïde peuvent atteindre jusqu'à 15 mm

avec une précision du dixième, ce qui
correspond par exemple, à des fluctuations
annuelles d'eau dans le bassin de
l'Amazone de l'ordre de 800 km³ en
accord avec différents modèles
hydrologiques. Exprimés en hauteur d'eau
équivalente, les spectres d'amplitude
montrent bien des variations moyennes
autour du cm par degré harmonique
sphérique (voir figure 2). Ce graphique
montre également qu'une stabilisation
croissante vers le modèle moyen a été
appliquée au-delà du degré 30 qui évite les
artefacts liés à la perte de sensibilité.

<figure><img src="image_24.png" /><figcaption>Figure 3: Séries temporelles issues des modèles décadaires en mer d'Andaman.</figcaption></figure>

Une autre application concerne les
phénomènes de déglaciation qui ont pu
être mis en évidence à partir de 3 ans de
mesures. Les modèles décadaires montrent

nettement un enfoncement du géoïde de
plus de 10 mm par an – soit une perte de
masse – sur les bords ouest de
l'Antarctique comme sud-est du Groenland
ou sud de l'Alaska. Là, des études interprétatives conduites au laboratoire LEGOS de l'Observatoire Midi-Pyrénées ont conclu à des pertes de plus de 100 km³ de glace par an qui sont naturellement à rapprocher du réchauffement climatique.

Enfin, comme autre exemple d'application, cette fois à caractère géophysique, il est à mentionner l'affaissement du fond de la mer d'Andaman suite au séisme de Sumatra du

26 décembre 2004. En quel-ques tours d'orbite, GRACE a pu détecter cette rupture brutale qui a engendré un enfoncement de 8 mm du géoïde (voir figure 3) ainsi qu'une élévation en arc de cercle à l'est de Sumatra. Plus curieux est le phénomène de relaxation qui perdure et qui donne lieu à des études interprétatives sur la rhéologie de la zone, comme celles conduites au LAREG/IGN ou à l'EOST/Strasbourg.

<figure><img src="image_25.png" /><figcaption>**Figure 4:** Série temporelle du terme d'aplatissement dynamique C20.</figcaption></figure>

## V. LAGEOS

Ces nouvelles missions gravimétriques ont grandement amélioré l'acuité de nos connaissances sur les transferts de masse à grande échelle. Reste qu'elles sont récentes et ne peuvent encore concurrencer plus de 20 ans d'observation laser sur les satellites LAGEOS par exemple pour

étudier sur le long terme le comportement de l'aplatissement dynamique de la Terre. Une étude réalisée en 2004 sur 19 ans de données laser des satellites LAGEOS a mis en évidence les anomalies (non modélisées) de variation de masse à l'échelle des hémisphères (sur le
coefficient C20) qu’un simple modèle incorporant les effets de dérive, périodiques de marées à 18,6 et 9,3 ans ainsi que les effets annuels et semi-annuels a pu résorber (voir figure 4). D’ailleurs, les modèles décadaires comme

le modèle moyen EIGEN-GL04S s’appuient également sur les données LAGEOS pour améliorer la restitution du terme C20, d’où le sigle GL pour GRACE-LAGEOS.

# VI. RÉFÉRENCES

Reigber Ch., P. Schwintzer, K.-H. Neumayer, F. Barthelmes, R. König, Ch. Förste, G. Balmino, R. Biancale, J.-M. Lemoine, S. Loyer, S. Bruinsma, F. Perosanz, T. Fayard: The CHAMP-only Earth gravity field model EIGEN-2, Adv. Space Res., vol. 31, n° 8, pp 1883-1888, 2003.

Reigber Ch., G. Balmino, P. Schwintzer, R. Biancale, A. Bode, J.-M. Lemoine, R. Koenig, S. Loyer, H. Neumayer, J.-C. Marty, F. Barthelmes, F. Perosanz, S. Y. Zhu: Global gravity field recovery using solely GPS tracking and accelerometer data from CHAMP, Space Science, 108, pp 55-66, 2003.

Deleflie F., P. Exertier, P. Berio, G. Métris, O. Laurain, J.-M. Lemoine, S. Loyer, A First Analysis of the Mean Motion of CHAMP, Adv. Geosciences, 1, 95-101, 2003.

Deleflie F., P. Exertier, P. Berio, G. Métris, O. Laurain, J.-M. Lemoine, and S. Loyer, Why the 18.6 year tide cannot explain the change of sign observed in J2dot, Adv. in Geosciences, 1, 103-108, 2003.

Reigber Ch., H. Jochmann, J. Wünsch, S.

Petrovic, P. Schwintzer, F. Barthelmes, K.-H. Neumayer, R. König., Ch. Förste, G. Balmino, R. Biancale, J.-M. Lemoine, S. Loyer, F. Perosanz: Earth Gravity Field and Seasonal Variability from CHAMP, in: Reigber Ch., Lühr H., Schwintzer P., Wickert J. (eds.), Earth Observation with CHAMP - Results from Three Years in Orbit, Springer, Berlin, 25-30, 2005.

Reigber Ch., P. Schwintzer, R. Stubenvoll, R. Schmidt, F. Flechtner, U. Meyer, R. König, H. Neumayer, C. Förste, F. Barthelmes, S.Y. Zhu, G. Balmino, R. Biancale, J.-M. Lemoine, H. Meixner, J.-C. Raimondo: A High Resolution Global Gravity Field Model Combining CHAMP and GRACE Satellite Mission and Surface Data: EIGEN-CG01C; Scientific Technical Report STR06/07, GeoForschungsZentrum Potsdam, 2006.

Biancale R., J-M Lemoine, G Balmino, S Bruinsma, F Perosanz, J-C Marty, S Loyer, P Gégout: 4 years of geoid variations from GRACE and
LAGEOS data at 10-day intervals.
http://bgi.cnes.fr:8110/geoid-
variations /README.html.

Ramillien G., A. Lombard, A. Cazenave, E. R. Ivins, M. Llubes, F. Remy, R. Biancale: Interannual variations of the mass balance of the Antarctica and Greenland ice sheets from GRACE,

Global and Planetary Change,
Elsevier, 53, 198-208, 2006.

Lemoine J.-M., S. Bruinsma, S. Loyer, R. Biancale, J.-C. Marty, F. Perosanz, G. Balmino: Static and temporal gravity field models inferred from GRACE data, submitted to Adv. Space Res, 2006.
# DORIS Applications for Earth and Atmospheric Sciences

P. WILLIS<fnref n="1" />,<fnref n="2" />, L. SOUDARIN<fnref n="3" />, C. JAYLES<fnref n="4" />, L. ROLLAND<fnref n="2" />

pascal.willis@ign.fr

rolland@ipgp.jussieu.fr

laurent.soudarin@cls.fr, christian.jayles@cls.fr

**Abstract** DORIS is a French precise orbit determination system. However, in the past 4 years, through the creation of the International DORIS Service, a larger cooperation was involved. Furthermore, the precision of its scientific applications (geodesy, geophysics) gradually improved and expanded to new fields (atmospheric sciences), leading for example to the publication of a Special Issue in the Journal of Geodesy. The goal of this manuscript is to present and explain these changes, as part as the French national report to the International Association of Geodesy, presented at the general assembly of the International Union of Geodesy and Geophysics in Perugia, Italy in July 2007.

**Key words** DORIS, orbit determination, geodesy, terrestrial reference frame, geodynamics

## Applications du système DORIS aux sciences de la Terre et de l'atmosphère

**Résumé** DORIS est un système d'orbitographie précise. Toutefois, au cours des 4 dernières années, grâce à la création de l'International DORIS Service, une

<footnote n="1">¹ Institut Géographique National, Direction Technique, 2, avenue Pasteur, BP 68,
94160 Saint-Mandé, France</footnote>

<footnote n="2">² Institut de Physique du Globe de Paris, Laboratoire d'Etudes Spatiales et de Planétologie, 4 place Jussieu, 75252 Paris, France</footnote>

<footnote n="3">³ Collecte Localisation Satellite, 8-10 rue Hermes, Parc technologique du canal,
31526 Ramonville, France</footnote>

<footnote n="4">⁴ Centre National d'Etudes Spatiales, DCT/PO/AL, 18, avenue Edouard Belin, 31401
Toulouse Cedex 4, France</footnote>
coopération internationale plus large a été mise en place. De plus, la précision pour ses applications scientifiques (géodésie, géophysique) s'est progressivement améliorée et étendue à de nouveaux champs d'applications dans le domaine des sciences de l'atmosphère, conduisant par exemple à la publication d'un numéro spécial DORIS dans le *Journal of Geodesy*. Le but de cet article est de présenter et d'expliquer ces changements, comme partie du rapport national français à l'Association Internationale de Géodésie, présenté à l'Assemblée générale de l'Union Géodésique et Géophysique Internationale à Pérouge, Italie en juillet 2007.

***Mots clefs*** DORIS, *determination d'orbite*, *géodésie*, *système de reference terrestre*,
*géodynamique*

# I. INTRODUCTION

DORIS (Doppler Orbit Determination and Radiopositioning by Satellite) is a French tracking system developed by CNES (French Space Agency) in cooperation with IGN (French mapping agency) and the GRGS (French Research group on satellite geodesy). This system is based on a

permanent network of dedicated beacons (Figure 1), fully automated and transmitting a radio-electrical signal on 2 frequencies (2 GHz and 400 MHz) using omni-directional antennas (Barlier et al. 2005; Willis et al., 2006b). These instruments can work in all type of environment.

<figure><img src="image_26.png" /><figcaption>**Figure 1:** DORIS permanent tracking station in Rikitea (French Polynesia). From H. Fagard (IGN/SIMB).</figcaption></figure>
<figure><img src="image_27.png" /><figcaption>**Figure 2:** DORIS Permanent tracking network (as November 28, 2006). From H. Fagard (IGN/SIMB).</figcaption></figure>

<figure><img src="image_28.png" /><figcaption>**Figure 3:** Improvement of the estimated DORIS antenna stability. From H. Fagard, J. Geod., 2006.</figcaption></figure>

The DORIS permanent network is composed of about 50 stations, geographically well distributed (Figure 2). This network was installed by IGN before the launch of the first DORIS satellite (SPOT2 in January 1990) and is still maintained by IGN, in close cooperation with CNES. About half of the DORIS

tracking equipments are located at close range with other fundamental geodetic systems (VLBI, Laser, GPS).

In the recent years, a rejuvenation of the network was undertaken by IGN. Major steps were taken to improve the geodetic stability of the beacons in order to allow sub-centimeter accuracy for the most
demanding applications such as reference frame determination. The geodetic stability of the DORIS beacons is now almost fully satisfactory (see Figure 3). The integrity of

the DORIS data is operationally controlled by CNES to insure that the best data are delivered to the scientific users (Jayles et al., 2006).

<figure><img src="image_29.png" /><figcaption>**Figure 4:** DORIS observations available at the IDS Data Centers (as at January 2006). From Tavernier et al., J. Geod., 2006.</figcaption></figure>

<table><caption>**Table 1:** SINEX time-series of DORIS station coordinates available at the IDS Data Center. As at February 2006. FromTavernier et al., J. Geod., 2006.</caption><thead><tr><th>Group</th><th>Software</th><th>Solution</th><th>Start</th><th>End</th><th>Files</th><th>Geocenter</th><th>EOP</th></tr></thead><tbody><tr><td rowspan="2">GSC</td><td rowspan="2">GEODYN</td><td>WD01</td><td>Jan-2004</td><td>Dec-2004</td><td>52</td><td rowspan="2"></td><td rowspan="2"></td></tr><tr><td>WD02</td><td>Jan-2004</td><td>Dec-2004</td><td>52</td></tr><tr><td rowspan="2">IGN</td><td rowspan="2">GIPSY/OASIS</td><td>WD05</td><td>Jan-1993</td><td>Oct-2005</td><td>668</td><td rowspan="2">X</td><td rowspan="2">X</td></tr><tr><td>MD03</td><td>Jan-1993</td><td>Oct-2002</td><td>118</td></tr><tr><td>INA</td><td>GIPSY/OASIS</td><td>WD05</td><td>Jan-1993</td><td>Dec-2005</td><td>1355</td><td></td><td></td></tr><tr><td rowspan="2">LCA</td><td rowspan="2">GINS/DYNAMO</td><td>WD13</td><td>Jan-1993</td><td>Sep-2005</td><td>664</td><td rowspan="2"></td><td rowspan="2"></td></tr><tr><td>MD02</td><td>Jan-2003</td><td>Dec-2002</td><td>120</td></tr><tr><td>SOD</td><td>ZOOM</td><td>WD01</td><td>Jun-2001</td><td>Jun-2001</td><td>3</td><td></td><td></td></tr><tr><td rowspan="2">SSA</td><td rowspan="2">ZOOM</td><td>WD01</td><td>Jan-2000</td><td>Jan-2005</td><td>209</td><td rowspan="2"></td><td rowspan="2"></td></tr><tr><td>MD01</td><td>Feb-2001</td><td>Apr-2002</td><td>16</td></tr></tbody></table>
II. THE INTERNATIONAL DORIS SERVICE (IDS)

In 2003, at the General Assembly of the
International Union of Geodesy and
Geophysics (IUGG) in Sapporo, Japan, the
IDS (International DORIS Service) was
created and officially recognized by the
International Association of Geodesy (IAG)
(Tavernier et al., 2005, 2006), following an
initial phase of a DORIS Pilot Project
(Willis et al., 2004b). A complete
organization was set up to collect and
archive DORIS data at 2 data centers:
NASA/CDDIS in the US and IGN in France
(Noll and Soudarin, 2006). Figure 4

summarizes the amount of DORIS data
currently available at these centers. Except
for the very earlier SPOT2 data (between
1990.0 and 1993.0) all data from all
satellites carrying a DORIS receiver on-
board are properly archived. This includes
satellites for earth observations (French
SPOT-2, SPOT-3, SPOT-4 and SPOT-5
from CNES), the US-French altimeter
mission satellites (TOPEX/Poseidon and
Jason) and the ESA mission for
environment and altimetry (ENVISAT).

<figure><img src="image_30.png" /><figcaption>**Figure 5:** Monthly accesses to IDS Web site. (http://ids.cls.fr). Dashed columns indicate incomplete system log files. From Noll and Soudarin, J. Geod., 2006.</figcaption></figure>

Several analysis groups have used
these data to estimate weekly or monthly
coordinates of DORIS stations (see Table 1)

and have submitted their results to these
IDS data centers: cddis.gsfc.nasa.gov for
NASA/CDDIS in the US and
doris.ensg.ign.fr for IGN in France. It must be noted that 2 groups in France (IGN/JPL and LEGOS/CLS) still submit such geodetic solutions on a regular basis. The IGN/JPL group submits their results every weeks, while the LEGOS/CLS groups currently prefer to submit their own results every 3 to 6 months. Furthermore, 2 other groups, Geoscience Australia/GSFC and Pecny Observatory/University of Bern

(Stepanek et al., 2006), have also computed geodetic solutions more recently. The International DORIS Service developed a Web site maintained in Toulouse by CLS at (http://ids.cls.fr), providing information on DORIS data and products. Figure 5 demonstrates that the number of connections to this Web site is still growing with time, showing interest from a larger community.

### III. RECENT IMPROVEMENT IN DORIS DATA ANALYSIS

In the past 4 years, a significant improvement was obtained for DORIS geodetic results (station coordinates). Let

us try to understand the reasons for this improvement.

#### III.1 Increase in DORIS data availability

First of all, the precision of the DORIS-derived station position is clearly dependent on the number of DORIS data available for this station and hence from the number of satellites equipped with DORIS receiver and providing their data to the IDS for scientific applications. Figure 6 shows that an increase of 1 to 3 satellites basically improve the precision of the results by a factor of 2, while an increase from 3 to 5 satellites improves the precision of the results by another factor of 2.

The number of DORIS satellites available at the time of observations is then a critical parameter. While only 2 DORIS satellites were available at the early

beginning of the system (1990-1993), 5 satellites were available since 2002 (SPOT-2, SPOT-4, Jason, ENVISAT, and SPOT-5). Best results are obtained using a proper combination of DORIS data from multiple satellites (Willis et al., 2003).

Figure 7 shows a comparison of the WRMS of all station coordinates, when compared to cumulative solution (positions and velocities estimated using the full DORIS data span, from 1993 to 2006). The changes in precision due to modification of the DORIS constellation (number of available DORIS satellites) are clearly visible on this figure as well.
<figure><img src="image_31.png" /></figure>

<figure><img src="image_32.png" /></figure>

<figure><img src="image_33.png" /></figure>

**Figure 6:** DORIS positioning precision with regards to number of available satellites (a) in latitude, (b) in longitude, (c) in height). Single week results (February 1-7, 2004). All possible choices for satellites selection were considered. From Willis et al., C.R. Geosci., 2005.
As the number of available DORIS satellites is critical for IDS, a recent study (Willis, 2007) investigated the consequences of future possible loss of

current satellites, before the launch of the already planned missions in 2008 and 2009 (Cryosat-2, Jason-2 and AltiKA).

<figure><img src="image_34.png" /></figure>

**Figure 7:** IGN/JPL (a), INASAN (b), LEGOS/CLS (c) weekly weighted root mean scatter (WRMS) with respect to their own cumulative solutions. Numbers in between the vertical lines superimposed over the plots indicate the number of satellites available for each time-span. From Altamimi et al., J. Geod., 2006.
<figure><img src="image_35.png" /></figure>

<figure><img src="image_36.png" /></figure>

<figure><img src="image_37.png" /></figure>

**Figure 8:** WRMS comparisons for all 43 DORIS stations in collocation with GPS using the EGM96 or the GGM01C gravity field (in North, East and Vertical). Units are in mm. Source Willis and Heflin, GRL, 2004.
<figure><img src="image_38.png" /><figcaption>**Figure 9:** Apparent velocities derived from DORIS/Jason data (from January 2002 to April 2003). From Willis et al., CR Geosci., 2004</figcaption></figure>

<figure><img src="image_39.png" /><figcaption>**Figure 10:** Plot of the relative SAA dose exposure in 2002-2005 at the 1300 km altitude of Jason-1 (dimensionless units). From Lemoine and Capdeville, J. Geod., 2006.</figcaption></figure>

### III.2 Availability of improved GRACE-derived gravity field models

Furthermore, improvements in the accuracy (external precision) were also obtained by using more sophisticated analysis strategies or better model. Figures 8 show a

comparison of 2 DORIS solutions (one computed using the older EGM96 gravity field and the other one computed using a more recent gravity field obtained using
GRACE data). DORIS coordinates were
compared over the 1990-2005 time span to
an external reference, obtained using GPS
coordinates of a close-by GPS tracking

station and the vector of the geodetic local
ties between the GPS and the DORIS
instruments in collocation, using terrestrial
surveying techniques.

### III.3 Better handling of problems related to the South Atlantic Anomaly

Some satellite-specific problems were also
detected and corrected. For example, intial
computations showed that using
DORIS/Jason data produced erroneous
results for station positions and station
velocities (Willis et al., 2003). For example,
station velocities around Brazil (Figure 9)
were totally corrupted by several tens of
centimeters. This artifact of computation
was later explained (Willis et al., 2004a) to
be related to successive radiation doses of
the satellite on-board quartz oscillator over
the South Atlantic Anomaly (SAA) region.

Over this region (see Figure 10), the
magnetic field is much weaker and energy
particles are naturally trapped, affecting
behavior of several satellite equipments, in
particular the on-board clocks. Using
DORIS data from the TOPEX/Poseidon
mission (orbit at the same altitude, and
satellite flying in close formation with
Jason), the LEGOS group (Lemoine and
Capdeville, 2006, and Figure 11) was
recently able to propose an empirical
correction model for the DORIS/Jason data.

### III.4 Antenna correction models

Some authors tried to apply GPS-derived
techniques to DORIS data analysis. For
example, Willis et al. 2005 try to estimate
phase center variation (PCV) maps for
DORIS data. Figure 12 shows an example
of such results. Each pixel of this map
corresponds to the mean value of the
DORIS residuals over one complete year, as
seen by the satellite, in this specific
direction in the satellite frame (North is in
the direction of the satellite velocity).

The adoption of such maps did not
show a drastic improvement in the geodetic

results (see also Willis et al., in press) but at
least they show some specific problems
related to the DORIS data or to the DORIS
data analysis. For example, on Figure 12,
the blue region at North (front of the
satellite) and the red region at south (back
of the satellite) can be seen on almost all
SPOTs maps and is equivalent to a time
tagging error in TAI of about 5 micro-
seconds (see also Zelensky et al., 2006).

Simpler approaches were also
investigated estimating only an empirical
parameter to correct the vector between the
center of mass of the satellite and the center
of phase of the antenna (Willis et al., 2007a;

Willis et al., 2007b).

### III.5 Improvement data analysis during geomagnetic storms

A close verification of the quality of the DORIS weekly geodetic results (station coordinates) showed that period of larger solar activity (geomagnetic storms for example) were of poorer quality. This can be explained by the fact that the atmospheric density models used to estimate the atmospheric drag applied on the satellite do not represent as well the actual physics of the atmosphere during these periods.

Tests have shown (Table 2) that a different estimation strategies, involving a more frequent determination of drag

empirical parameters using some proper time constrain (Willis et al., 2005c), can provide geodetic results that are less degraded and that are almost at the same accuracy level as periods during unperturbed atmosphere.

It must also be noted that the DORIS-derived empirical drag parameter seem to contain some valuable information on the physics of the atmosphere, as the estimated parameter shows a high correlation with atmospheric coefficient, such as Ap (Figure 13).

<figure><img src="image_40.png" /><figcaption>**Figure 11:** Geographical plot of the time derivative of Jason-1 frequency offset (Jason-1 frequency change rate) for cycle 26 (2002/09/20 to 2002/09/30). From Lemoine and Capdville, J. Geod., 2006.</figcaption></figure>
SPOT2 2002

<figure><img src="image_41.png" /></figure>

(a)

SPOT4 2002

<figure><img src="image_42.png" /></figure>

(b)
<figure><img src="image_43.png" /><figcaption>**Figure 12:** DORIS/SPOT antenna map corrections (2002). Source Willis et al., Adv. Space Res., 2005a.</figcaption></figure>

### III.6 DORIS for precise orbit determination

As said before, the main goal of the DORIS system is the determination of precise orbit of low earth orbiting (LEO) satellites. Table 3 provides the list of all satellites equipped with DORIS receiver and sharing their data through the IDS data centers. The most recent satellites are equipped with a second generation of receiver, allowing simultaneous tracking of ground beacons, thanks to a new multi-channel technology inside the receiver and the possibility of shifted frequency for the transmitting ground antennas (Tavernier et al., 2003).

Analysis of long-term time series of

DORIS residuals from different analysis centers have shown some common systematic errors and also some differences due to the analysis strategies (Figure 14).

On Figure 14, DORIS residuals for Jason satellites are quite different around the South Atlantic Anomaly region, because IGN/JPL throw away all data within this area in a pre-processing phase, while TU/Delft use a regular data processing and while UT/CSR uses a more refined analysis strategy, estimating an additional clock parameter (frequency drift equivalent to a clock acceleration) per ground station.
<table><caption>**Table 2:** Weekly RMS of DORIS station coordinates compared to cumulative solution (IGN03D02) using different processing strategies: (A) standard processing, 1 drag coefficient reset every 6 hours for SPOTs and ENVISAT, (B) 1 drag coefficient reset for all satellites, white noise, (C) 1 drag coefficient reset for all satellites, random walk. Weekly solutions from October 26 to November 29, 2003. Source Willis et al., Adv. Space Res., 2005.</caption><thead><tr><th rowspan="2">Week</th><th colspan="3">North (mm)</th><th colspan="3">East (mm)</th><th colspan="3">Vertical (mm)</th></tr><tr><th>A</th><th>B</th><th>C</th><th>A</th><th>B</th><th>C</th><th>A</th><th>B</th><th>C</th></tr></thead><tbody><tr><td>Oct 26 – Nov 1, 2003</td><td>38.5</td><td>12.5</td><td>11.2</td><td>28.8</td><td>15.9</td><td>17.2</td><td>28.7</td><td>15.3</td><td>14.4</td></tr><tr><td>Nov 2 – 8, 2003</td><td>15.4</td><td>12.5</td><td>11.6</td><td>12.6</td><td>10.8</td><td>11.8</td><td>12.2</td><td>12.5</td><td>12.8</td></tr><tr><td>Nov 9 – 15, 2003</td><td>10.6</td><td>10.4</td><td>9.2</td><td>11.6</td><td>10.0</td><td>11.6</td><td>10.0</td><td>9.8</td><td>10.3</td></tr><tr><td>Nov 16 – 22, 2003</td><td>22.7</td><td>9.7</td><td>9.7</td><td>20.3</td><td>10.7</td><td>10.8</td><td>27.8</td><td>11.7</td><td>12.1</td></tr><tr><td>Nov 23 – 29, 2003</td><td>13.4</td><td>10.4</td><td>11.9</td><td>11.4</td><td>11.0</td><td>10.3</td><td>13.5</td><td>12.8</td><td>14.4</td></tr></tbody></table>

<figure><img src="image_44.png" /><figcaption>**Figure 13:** Rapid determination (one per minute) of drag coefficient estimated independently for each DORIS satellite and Ap/2 values (every 3 hours). October 29 to 31, 2003. Source Willis et al., Adv. Space Res., 2005.</figcaption></figure>

Current post-processing accuracy of 2 cm (in the radial component) or better can now be obtained for higher satellites

such as TOPEX/Posiedon and Jason, while 3-4 cm accuracy are achievable for SPOT and ENVISAT satellites at a lower altitude
(Zandbergen et al., 2003). Best results are obtained for Jason in post-processing mode, using simultaneously all available tracking data on-board the satellite: GPS, SLR and DORIS (Luthcke et al., 2003; Haines et al., 2003; Choi et al., 2004; Haines et al., 2004).

The consequences of errors in the adoption of station coordinates on orbit

solution and hence of sea level derived from altimeter data was also analyzed (Morel and Willis, 2005). Some transfer function were obtained to better quantify this effect and to estimate the error due to the mis-modelling of the terrestrial reference frame (station coordinates and velocities) or geophysical products, typical global mean sea level.

<table><caption>**Table 3:** Past and current satellite missions carrying an on-board DORIS receiver and Precise Orbit Determination performances (1G = first generation, 2G = second generation, 2GM = second generation miniaturized). From Willis et al., CR Geosci., 2005.</caption><thead><tr><td>Satellite</td><td>Launch</td><td>Receiver Generation</td><td>Other tracking System</td><td>Altitude (km)</td><td>Orbit precision (radial RMS in cm)</td></tr></thead><tbody><tr><td>SPOT-2</td><td>January 1990</td><td>1G</td><td>-</td><td>830</td><td>3</td></tr><tr><td>TOPEX/Poseidon</td><td>August 1992</td><td>1G</td><td>SLR+GPS</td><td>1330</td><td>2</td></tr><tr><td>SPOT-3</td><td>1994</td><td>1G</td><td>-</td><td>830</td><td>3</td></tr><tr><td>SPOT-4</td><td>1998</td><td>1G</td><td>-</td><td>830</td><td>3</td></tr><tr><td>Jason</td><td>December 2001</td><td>2GM</td><td>SLR+GPS</td><td>1330</td><td>1</td></tr><tr><td>ENVISAT</td><td>March 2002</td><td>2G</td><td>SLR</td><td>800</td><td>2</td></tr><tr><td>SPOT-5</td><td>2002</td><td>2GM</td><td>-</td><td>830</td><td>3</td></tr></tbody></table>

## IV. DORIS FOR REAL-TIME ORBIT DETERMINATION

As the DORIS data are performed directly on-board the satellite, CNES has developed a specific software (DIODE, Jayles and Costes, 2004), processing DORIS data in real time and predicting the satellite orbit with a very good integrity and accuracy

performances. Figure 15 and Table 4 show an example of recent results. Currently a 5 cm orbit can be obtained in real-time when all models can be properly uploaded on board of the satellite.
<figure><img src="image_45.png" /></figure>

**Figure 14:** RMS values of DORIS residuals over multiple repeat cycles, binned by satellite pass. Data used is from January 15, 2002 to January 1, 2004 for TOPEX (left column) and Jason (centre) and from October 4 2002 to January 1, 2004 for ENVISAT (right). POD residuals were supplied by UT/CSR or ESOC (top row), IGN/JPL (centre) and TU Delft/DEOS (bottom). From Doornbos and Willis, 2007.

<figure><img src="image_46.png" /></figure>

**Figure 15:** Expected position accuracy for the coming DIODE version using actual TOPEX DORIS data in a post-processing mode (September 11 to September 22, 2004). Source Willis et al., CR Geosci., 2005.
<table><caption>**Table 4:** Overall comparison statistics (DIODE – POE) from DORIS/TOPEX data. September 11 to September 22, 2004. All units are in mm for position and mm/s for velocity.</caption><thead><tr><th></th><th>Minimum</th><th>Maximum</th><th>Mean</th><th>Std Dev.</th></tr></thead><tbody><tr><td>Radial</td><td>-154</td><td>122</td><td>-6</td><td>44</td></tr><tr><td>Tangential</td><td>-801</td><td>406</td><td>-73</td><td>137</td></tr><tr><td>Normal</td><td>-783</td><td>734</td><td>11</td><td>252</td></tr><tr><td>3-D Error</td><td>8</td><td>832</td><td>266</td><td>138</td></tr><tr><td>Radial velocity</td><td>-0.34</td><td>0.67</td><td>0.007</td><td>0.12</td></tr><tr><td>Tangential velocity</td><td>-0.12</td><td>0.12</td><td>0.00</td><td>0.04</td></tr><tr><td>Normal velocity</td><td>-0.80</td><td>0.69</td><td>0.00</td><td>0.23</td></tr><tr><td>3-D velocity error</td><td>0.001</td><td>0.82</td><td>0.24</td><td>0.13</td></tr></tbody></table>

<figure><img src="image_47.png" /><figcaption>**Figure 16:** DORIS collocation sites in the ITRF2005. From Altamimi et al., J. Geod., 2006.</figcaption></figure>

## V. DORIS AND THE MAINTENANCE OF THE TERRESTRIAL REFERENCE FRAME

Due to the good geographical distribution of the DORIS permanent tracking network, to its long-term time series of observations and to its numerous collocations with other

geodetic space techniques (Figure 16), DORIS is a rather attractive system for terrestrial reference frame maintenance (Willis et al., 2005a; Altamimi et al., 2006).
DORIS was a significant contributor to the ITRF2005, based on an approach using time

series of station coordinates (Altamimi et al., 2005a, 2005b; Meisel et al., 2005).

<figure><img src="image_48.png" /><figcaption>**Figure 17:** Weekly variations in origin and scale from the IGN (IGN/JPL), INA (INASAN) and LCA (LEGOS/CLS) solutions. From Altamimi et al., J. Geod., 2006.</figcaption></figure>

Different studies tried to assess the nature of the noise included in the DORIS-derived time series of station coordinates: white noise, colored noise (Williams and Willis, 2006; Le Bail et al., 2006, Nocquet et al., 2006). All analysis noted the presence of some systematic error, showing future ways of improvement, if analysis centers could be able to better understand these errors and to correct them. In particular, a clear signal at 118 days was demonstrated in several DORIS time series (Le Bail et al.,

2006).

In 2006, three different long-term times series of solutions could be analyzed: IGN/JPL INASAN (both using GIPSY/OASIS software), LEGOS/CLS using the GINS/DYNAMO software. Figure 17 shows the comparison of these individual weekly DORIS solutions with a combined long-term cumulative DORIS solution obtained by combination using the CATREF software. IGN/JPL and INASAN, using the same software and a very close
analysis strategy obtain almost indistinguishable results. The LEGOS/CLS solution present more differences as the software used and the analysis strategy is quite different. However, a lot of similarities can be seen in the results, even

in geocenter variation determination (see also Feissel-Vernier et al., 2006). The difference seen in the scale (definition of the unit of length) is still under investigation between those groups.

<figure><img src="image_49.png" /><figcaption>**Figure 18:** Weekly geocenter variations estimated using preprocessed DORIS/SPOT-4 data. (mm). From Willis et al., J. Geod., 2006.</figcaption></figure>

<table><caption>**Table 5:** DORIS and GPS detected post-seismic displacement at Fairbanks after the November 3, 2002 Denali Fault Earthquake. From Willis et al., J. Geodyn., 2004.</caption><thead><tr><th></th><th>Latitude offset<br>(in mm)</th><th>Longitude offset<br>(in mm)</th><th>Altitude offset<br>(in mm)</th></tr></thead><tbody><tr><td>GPS (Bock, 2003)</td><td>-53.5 ± 4</td><td>+15.1 ± 4</td><td>0</td></tr><tr><td>DORIS</td><td>-50 ± 4</td><td>+20 ± 7</td><td>0</td></tr></tbody></table>

Previous larger problems in the determination of the DORIS-derived geocenter (Figure 18) are now solved and fully understood. Previous results were obtained using an incorrect vector between the center of mass of the SPOT4 satellite in 1998 and the center of phase of the antenna (Willis et al., 2006a).

Finally other parameters, such as the daily position of the intersection of the axis Earth's rotation on the crust can also be estimated (Willis et al., 2005b; Gambis et al., 2006). Most recent results show a sub-millarcsecond accuracy (equivalent at 15 mm in the position of the axis of rotation at the North pole).
<figure><img src="image_50.png" /></figure>

**Figure 19:** Horizontal velocity of 37 DORIS sites located in stable plate interiors. DORIS vectors with 99% confidence ellipses (white) are compared to PB2002 estimates (black). Grey areas are orogens defined by Bird (2003). Names correspond to the DORIS acronyms of the last observed station for each site. Velocities are expressed into ITRF2000. Source Soudarin and Crétaux, J. Geod., 2006.

# VI. GEOPHYSICAL APPLICATIONS OF THE DORIS SYSTEM

As a 10 mm precision is now achievable for weekly station coordinates, DORIS can now detect smaller signal in amplitude, such as a change in station coordinates due to the presence of a close-by Earthquake (see Table 5 and Willis et al., 2004).

A more exhaustive study was initiated by Willis and Ries, 2005 to identify station whose coordinates were showing some anomalous signal, either natural (Earthquake, volcano, corrosion of support,...) or caused by human activity.

This study was completed through the IDS, using the IDS Analysis forum, where analysis groups could share their experience and results in these problems.

Being able to detect and correct these problems, helped all groups to provide better geodetic results, leading a better (less biased) estimation of station velocities. This allowed a better estimation of global plate tectonics either on a global basis (Soudarin and Cretaux, 2006), see Figure 19.
<figure><img src="image_51.png" /></figure>

**Figure 20:** GPS (upper case) and DORIS (lower case) and GPS/DORIS collocated sites (upper case ending with _D) velocities relative to Nubia. Stars indicate locations of Nubia/Somalia Euler pole. Source Nocquet et al., J. Geod., 2006.

<figure><img src="image_52.png" /></figure>

**Figure 21:** Total zenith delay at Ny-Alesund during CONT02 from VLBI (solid line), GPS (dashed line), and DORIS (crosses). From Snajdrova et al., J. Geod., 2006

It is also possible to investigate plate tectonics on a regional basis, for example in

the case of Africa, for which the GPS infrastructure is not as dense as other places
and where DORIS provides some valuable information (Nocquet et al., 2006), see Figure 20.

Other geophysical studies looked at more local geophysical aspect, for example in Antarctica, where the DORIS system is well suited (accumulation of passes due to the sun-synchronous orbits of the SPOT

satellites) and for which a specific pilot experiment was organized (Patrick et al., 2003; Amalvict et al., 2007).

Finally, regional studies were also conducted around the Himalayan regions using simultaneously GPS and DORIS, in order to better understand the subtleties of the local tectonic (Bettinelli et al., 2006).

## VII. IONOSPHERIC SOUNDING USING DORIS DATA

Finally, the fact that DORIS beacons transmit their signal simultaneously on 2 frequencies rather far apart (2 GHz and 400 MHz) allow, as for other techniques like GPS or VLBI to use data from these 2 frequencies to measure the signal delay due to the propagation in the ionosphere. This can lead to derivation of specific ionospheric map (global or regional). More recently, Li and Parrot, 2006 showed that it

is possible to see within the signature of the DORIS data residuals the effects of large ionospheric perturbations related to major Earthquakes (Trigunait et al., 2004). A future DORIS receiver is currently being built for the CITRIS satellite (Bernhardt et al., 2006), in order to study ionospheric scintillations in conjunction with GPS data also recorded at very high frequency on-board the satellite.

## VIII. TROPOSPHERIC SOUNDING USING DORIS DATA

DORIS data are also affected when crossing the lower part of the atmosphere (troposphere). Snajdrova et al. showed that DORIS results are consistent with results

derived from geodetic space technique (VLBI and GPS) as well as with atmospheric models or water vapor radiometer data, see Figure 21.

## IX. CONCLUSIONS

In conclusion, during the last four years, the applications of the DORIS system exceeded the original applications of precise orbit determination of low earth orbiting satellite, to geodesy (terrestrial reference

maintenance) and geophysics (tectonics, volcanology). More recently, new applications within the field of atmospheric sciences also arose. Future satellite carrying a new generation of DORIS receiver also
planned in the near future, ensuring the and geophysical time series.
effective availability of long-term geodetic

X. DORIS BIBLIOGRAPHY (2003-2007)

DORIS peer-reviewed articles published in international journals, between 2003 and 2007, from http://ids.cls.fr/html/report/peer-reviewed_journals.html)

Altamimi, Z; Boucher, C; Willis, P. 2005a.
Terrestrial Reference Frame
requirements within GGOS
perspective. THE GLOBAL
GEODETIC OBSERVING SYSTEM,
JOURNAL OF GEODYNAMICS 40
(4-5): 363-374, DOI: 10.1016/
j.jog.2005.06.002

Altamimi, Z; Boucher, C; Gambis, D. 2005b.
Long-term stability of the terrestrial
reference frame, *ADVANCES IN
SPACE RESEARCH* 36(3): 342-349,
DOI: 10.1016/j.asr.2005.03.068.

Altamimi, Z.; Collilieux, X.; Boucher, C. 2006. DORIS Contribution to ITRF2005, in DORIS Special Issue, P. Willis (Ed.), *JOURNAL OF GEODESY* 80(8-11):625-635, DOI: 10.1007/s00190-006-0065-5

Amalvict, M.; Willis, P.; Shibuya, K. 2007.
Status of DORIS stations in Antarctica
for precise geodesy, in *Dynamic
Planet - Monitoring and
Understanding a Dynamic Planet with
Geodetic and Oceanographic Tools, P.
Tregoning, C. Rizos, (Eds.), IAG
Symp., 130:94-102

Barlier, F. 2005. The DORIS system, A fully
operational tracking system to get

orbit determination at centimeter
accuracy in support of Earth
observations. *COMPTES RENDUS
GEOSCIENCE* 337 (14):1223-1224,
DOI: 10.1016/j.crte.2005.07.007

Bernhardt, P.A.; Siefring, C.L.; Galysh, I.J.;
Rodilosso, T.F.; Koch, D.E.;
MacDonald, T.L.; Wilkens, R.;
Landis, G.P. 2006. Ionospheric
applications of the scintillation and
tomography receiver in space
(CITRIS) mission when used with the
DORIS radio beacon network, in
DORIS Special Issue, P. Willis (Ed.),
*JOURNAL OF GEODESY* 80(8-
11):473-485, DOI: 10.1007/s00190-
006-0064-6

Bernhardt, PA; Siefring, CL 2006. New
satellite-based systems for ionospheric
tomography and scintillation region
imaging, *RADIO SCIENCE*, 41 (5):
Art. No. RS5S23 JUL 25 2006, DOI :
10.1029/2005RS003360

Bettinelli, P.; Avouac, J.P.; Flouzat, M.;
Jouanne, F.; Bollinger, L.; Willis, P.;
Chitrakar, G.R. 2006. Plate Motion of
India and Interseismic Strain in the
Nepal Himalaya from GPS and
DORIS Measurements, in DORIS
Special Issue, P. Willis (Ed.),
*JOURNAL OF GEODESY* 80(8-11):567-589, DOI: [10.1007/s00190-006-0030-3](https://doi.org/10.1007/s00190-006-0030-3)

Choi, KR; Ries, JC; Tapley, BD. 2004. Jason-1 Precision Orbit Determination by combining SLR and DORIS with GPS tracking data, *MARINE GEODESY*, 27 (1-2):319-333, DOI: [10.1080/0149041049 0465652](https://doi.org/10.1080/01490410490465652)

Doornbos, E. ; Willis, P. 2007. Analysis of DORIS range-rate residuals for TOPEX/Poseidon, Jason, Envisat and SPOT, *ACTA ASTRONAUTICA* 60(8-9), 611-621, DOI: [10.1016/j.actaastro.2006.07.012](https://doi.org/10.1016/j.actaastro.2006.07.012)

Fagard, H. 2006. Twenty years of evolution for the DORIS permanent network: from its initial deployment to its renovation, in DORIS Special Issue, P. Willis (Ed.), *JOURNAL OF GEODESY* 80(8-11):429-456, DOI: [10.1007/s00190-006-0084-2](https://doi.org/10.1007/s00190-006-0084-2)

Feissel-Vernier, M.; Le Bail, K.; Beriot, P.; Coulot, D.; Ramillien, G., Valette, J.J. 2006. Geocentre motion measured with DORIS and SLR, and predicted by geophysical models, in DORIS Special Issue, P. Willis (Ed.), *JOURNAL OF GEODESY* 80(8-11):637-648, DOI: [10.1007/s00190-006-0079-z](https://doi.org/10.1007/s00190-006-0079-z)

Gambis, D. 2006. DORIS and the Determination of the Earth's Polar Motion, in DORIS Special Issue, P. Willis (Ed.), *JOURNAL OF GEODESY* 80(8-11):649-656, DOI: [10.1007/s00190-006-0043-y](https://doi.org/10.1007/s00190-006-0043-y)

Haines, BJ; Bertiger, WIB; Desai, S; Kuang, D; Munson, L; Young, L; Willis, P. 2003. Initial results for Jason-1, Towards a 1-cm orbit, *JOURNAL OF THE INSTITUTE OF NAVIGATION* 50 (3):171-179

Haines, BJ; Bar-Sever, YE; Bertiger, W; Desai, S; Willis, P. 2004. New strategies for the 1-cm Precise Orbit Determination, *MARINE GEODESY* 27 (1-2):299-318, DOI: [10.1080/01490410490465300](https://doi.org/10.1080/01490410490465300)

Jayles, C; Costes, M. 2004. Ten centimeters orbits in real-time on-board of a satellite: DORIS-DIODE current status. *ACTA ASTRONAUTICA* 54 (5): 315-323, DOI: [10.1016/S0094-5765(03)00048-1](https://doi.org/10.1016/S0094-5765(03)00048-1).

Jayles, C.; Nhun-Fat, B.; Tourain, C. 2006. DORIS: System Description and Control of the Signal Integrity, in DORIS Special Issue, P. Willis (Ed.), *JOURNAL OF GEODESY* 80(8-11):457-472, DOI: [10.1007/s00190-006-0046-8](https://doi.org/10.1007/s00190-006-0046-8)

Le Bail, K. 2006. Estimating the noise in space-geodetic positioning: the case of DORIS, in DORIS Special Issue, P. Willis (Ed.), *JOURNAL OF GEODESY* 80(8-11):541-565, DOI: [10.1007/s00190-006-0088-y](https://doi.org/10.1007/s00190-006-0088-y)

Lemoine, J.M.; Capdeville, H. 2006. A corrective model for Jason-1 DORIS Doppler data in relation to the South Atlantic Anomaly, in DORIS Special Issue, P. Willis (Ed.), *JOURNAL OF GEODESY* 80(8-11):649-656, DOI: [10.1007/s00190-006-0043-y](https://doi.org/10.1007/s00190-006-0043-y)
GEODESY 80(8-11):507-523, DOI:
[10.1007/s00190-006-0068-2](https://doi.org/10.1007/s00190-006-0068-2)

Li, F.; Parrot, M. 2006. Total Electron Content
Variations Observed by a DORIS
Station During the 2004
Sumatra-Andaman Earthquake, in
DORIS Special Issue, P. Willis (Ed.),
*JOURNAL OF GEODESY* 80(8-
11):487-495, DOI: [10.1007/s00190-
006-0053-9](https://doi.org/10.1007/s00190-006-0053-9)

Luthcke, SB; Zelensky, NP, Rowlands, DD; Lemoine, FG; Williams, TA. 2003. The 1-centimeter orbit, Jason-1 Precision Orbit Determination using GPS, SLR, DORIS, and altimeter data, *MARINE GEODESY* 26 (3-4):399-421, DOI: [10.1080/0149041039<br>0256727](https://doi.org/10.1080/0149041039<br>0256727)

Meisel, B; Angermann, D; Krugel, M; Drewes, H; Gerstl, M; Kelm, R; Muller, H; Seemuller, W; Tesmer V. 2005. Refined approaches for terrestrial reference frame computations, *ADVANCES IN SPACE RESEARCH* 36(3) : 350-357, DOI: [10.1016/<br>j.asr.2005.04.057](https://doi.org/10.1016/j.asr.2005.04.057)

Morel, L; Willis P. 2005. Terrestrial reference
frame effects on sea level rise
determined by TOPEX/Poseidon,
*ADVANCES IN SPACE RESEARCH*,
36(3) : 358-368, DOI : [10.1016/j.asr.<br>2005.05.113](https://doi.org/10.1016/j.asr.2005.05.113)

Noll, C.; Soudarin, L. 2006. On-line Resources
Supporting the Data, Products, and
Information Infrastructure for the
International DORIS Service, in
DORIS Special Issue, P. Willis (Ed.),

*JOURNAL OF GEODESY* 80(8-
11):419-427, DOI: [10.1007/s00190-
006-0051-y](https://doi.org/10.1007/s00190-006-0051-y)

Nocquet, J.M.; Willis, P., Garcia, S. 2006. Plate kinematics of Nubia-Somalia using a combined DORIS and GPS solution, in DORIS Special Issue, P. Willis (Ed.), *JOURNAL OF GEODESY* 80(8-11):591-607, DOI: [10.1007/s00190-006-0078-0](https://doi.org/10.1007/s00190-006-0078-0)

Patrick, BA; Corvino, AF; Wilson, CJL. 2003. Ice-flow measurements and deformation at marginal shear zones on Sorsdal Glacier, Ingrid Christensen Coast, East Antarctica. *ANNALS OF GLA CIOLOGY, VOL 37*: 60-68.

Snajdrova, K; Boehm, J; Willis, P; Haas, R; Schuh H. 2006. Multi-technique comparison of tropospheric zenith delays derived during the CONT02 campaign, *JOURNAL OF GEODESY* 79(10-11):613-623, DOI: [10.1007/<br>s00190-005-0010-z](https://doi.org/10.1007/s00190-005-0010-z)

Soudarin, L.; Cretaux, J.F. 2006. A model of present-day tectonic plate motions from 12 years of DORIS measurements, in DORIS Special Issue, P. Willis (Ed.), *JOURNAL OF GEODESY* 80(8-11):609-624, DOI: [10.1007/s00190-006-0090-4](https://doi.org/10.1007/s00190-006-0090-4)

Stepanek, P.; Hugentobler, U.; Le Bail, K. 2006. First results of DORIS data analysis at Geodetic Observatory Pecný, in DORIS Special Issue, P. Willis (Ed.), *JOURNAL OF GEODESY* 80(8-11):657-664, DOI: [10.1007/s00190-006-0071-7](https://doi.org/10.1007/s00190-006-0071-7)
Tavernier, G; Granier, JP; Jayles, C; Sengenes, P; Rozo, F. 2003. The current evolutions of the DORIS system. INTEGRATED SPACE GEODETIC SYSTEMS AND SATELLITE DYNAMICS, ADVANCES IN SPACE RESEARCH 31 (8): 1947-1952, DOI: 10.1016/S0273-1177(03)00155-8.

Tavernier, G; Fagard, H; Feissel-Vernier, M; Lemoine, F; Noll, C; Ries, J; Soudarin, L; Willis P. 2005. The International DORIS Service (IDS), ADVANCES IN SPACE RESEARCH 36(3):333-341, DOI: 10.1016/j.asr.2005.03.102

Tavernier, G.; Fagard, H.; Feissel-Vernier, M.; Le Bail, K.; Lemoine, F.; Noll, C.; Noomen, R.; Ries, J.C.; Soudarin, L.; Valette, J.J.; Willis, P. 2006. The International DORIS Service: genesis and early achievements, in DORIS Special Issue, P. Willis (Ed.), JOURNAL OF GEODESY 80(8-11):403-417, DOI: 10.1007/s00190-006-0082-4

Trigunait, A; Parrot, M; Pulinets, S; Li, F. 2004. Variations of the ionospheric electron density during the Bhuj seismic event. ANNALES GEO-PHYSICAE 22 (12): 4123-4131.

Williams, S.D.P.; Willis, P. 2006. Error Analysis of Weekly Station Coordinates in the DORIS Network, in DORIS Special Issue, P. Willis (Ed.), JOURNAL OF GEODESY 80(8-11):525-539, DOI: 10.1007/s00190-006-0056-6

Willis, P. 2007. Analysis of a possible future degradation in the DORIS geodetic results related to changes in the satellite constellation. ADVANCES IN SPACE RESEARCH, in press, DOI: 10.1016/j.asr.2006.11.018

Willis, P; Heflin, MB. 2004. External validation of the GRACE GGM01C gravity field using GPS and DORIS positioning results. GEOPHYSICAL RESEARCH LETTERS 31 (13): art. no.-L13616, DOI: 10.1029/2004GL020038.

Willis, P; Haines, B; Bar-Sever, Y; Bertiger, W; Muellerschoen, R; Kuang, D; Desai, S. 2003. TOPEX/Jason combined GPS/DORIS orbit determination in the tandem phase. INTEGRATED SPACE GEODETIC SYSTEMS AND SATELLITE DYNAMICS, ADVANCES IN SPACE RESEARCH 31 (8): 1941-1946, DOI: 10.1016/S0273-1177(03)00156-X.

Willis, P; Ries, JC. 2005. Defining a DORIS core network for Jason-1 Precise Orbit Determination based on ITRF2000, Methods and realizations, JOURNAL OF GEODESY 79 (6-7):370-378, DOI: 10.1007/s00190-005-0475-9

Willis, P; Haines, B; Berthias, JP; Sengenes, P; Le Mouel, JL. 2004a. Behavior of the DORIS/Jason oscillator over the South Atlantic Anomaly. COMPTES RENDUS GEOSCIENCE 336 (9): 839-846, DOI: 10.1016/j.crte.2004.01.004.

Willis, P; Tavernier, G; Feissel-Vernier, M;
Lemoine, F., Noll, C.; Ries, J.; Soudarin, L. 2004b. The proposed International DORIS Service. *IAG SYMPOSIUM* 128:207-213

Willis, P.; Bar-Sever, YE; Tavernier, G. 2005a. DORIS as a potential part of a Global Geodetic Observing System. *THE GLOBAL GEODETIC OBSERVING SYSTEM, JOURNAL OF GEODYNAMICS* 40 (4-5): 494-501, DOI: 10.1016/j.jog.2005.06.011

Willis, P.; Boucher, C.; Fagard, H.; Altamimi, Z. 2005b. Geodetic applications of the DORIS system at the French 'Institut geographique national'. *COMPTES RENDUS GEOSCIENCE* 337 (7): 653-662, DOI: 10.1016/j.crte.2005.03.002

Willis, P.; Deleflie, F.; Barlier, F.; Bar-Sever, Y.E; Romans, L.J. 2005c. Effects of thermosphere total density perturbations on LEO orbits during severe geomagnetic conditions (Oct - Nov 2003), *ADVANCES IN SPACE RESEARCH*, 36(3): 522-533, DOI: 10.1016/j.asr.2005.03.095

Willis, P.; Desai, S.D.; Bertiger, W.I.; Haines, B.J; Auriol, A. 2005d. DORIS satellite antenna maps derived from long-term residuals time series, *ADVANCES IN SPACE RESEARCH*, 36(3): 486-497, DOI: 10.1016/j.asr.2005.03.095

Willis, P.; Berthias, J-P.; Bar-Sever, YE. 2006a. Systematic errors in the Z-geocenter derived using satellite tracking data, A case study from SPOT-4 DORIS data in 1998, *JOURNAL OF GEODESY*

79(10-11):567-572, DOI: 10.1007/s00190-005-0013-9

Willis, P.; Jayles, C.; Bar-Sever, Y. 2006b. DORIS, from altimetric missions orbit determination to geodesy, CR Geoscience, in Special Issue, Observing the Earth from Space, A. Cazenave, C. Boucher (Eds), 338(14-15):968-979, DOI: 10.1016/j.crte.2005.11.013

Willis, P.; Lemoine, F.G.; Soudarin, L. 2007a. Looking for systematic error in scale from Terrestrial Reference Frame derived from DORIS data, in Dynamic Planet - Monitoring and Understanding a Dynamic Planet with Geodetic and Oceanographic Tools, P. Tregoning, C. Rizos, (Eds.), IAG Symp., 130:143-151

Willis, P.; Haines, B.J.; Kuang, D. 2007b. DORIS satellite phase center determination and consequences on the derived scale of the Terrestrial Reference Frame. *ADVANCES IN SPACE RESEARCH*, in press, DOI: 10.1016/j.asr.2007.01.007

Zandbergen, R.; Otten, M.; Righetti, PL; Kuijper, D.; Dow, JM. 2003. Routine operational and high-precision orbit determination of Envisat. *INTEGRATED SPACE GEODETIC SYSTEMS AND SATELLITE DYNAMICS*, *ADVANCES IN SPACE RESEARCH* 31 (8): 1953-1958, DOI: 10.1016/S0273-1177(03)00154-6.

Zelensky, N.P.; Berthias, J.P.; Lemoine, F.G.
2006. DORIS time bias estimated
using Jason-1, TOPEX/Poseidon and
ENVISAT orbits, in DORIS Special

Issue, P. Willis (Ed.), *JOURNAL OF GEODESY* 80(8-11):497-506, DOI: 10.1007/s00190-006-0075-3
**French Activities in Ground Gravimetry During
the Period 2003~2006**

M. AMALVICT<fnref n="1" />, R. BAYER<fnref n="2" />, S. BONVALOT<fnref n="3" />, N. DEBEGLIA<fnref n="4" />,

M. DIAMENT<fnref n="5" />, F. DUQUENNE<fnref n="6" />, H. DUQUENNE<fnref n="6" />, G. GABALDA<fnref n="3" />,

J. HINDERER<fnref n="1" />, M.F. LALANCETTE<fnref n="7" />, N. LEMOIGNE<fnref n="2" />, B. LUCK<fnref n="1" />,

G. MARTELET<fnref n="4" />, D. REMY<fnref n="3" />, M. SARRAILH<fnref n="8" /> & G. WOPPELMANN<fnref n="9" />

**Abstract** This report presents the main results obtained by the French teams in the last four years. The time-varying gravity studies with superconducting gravimeters are reported in the paper by Hinderer et al. (this volume). The applications of space

<footnote n="1">¹ Institut de Physique du Globe de Strasbourg, 5 rue Descartes, 67084 Strasbourg Cedex, France</footnote>

<footnote n="2">² ISTEEM, Université Montpellier 2, Place E. Bataillon, 34095 Montpellier Cedex 5, France</footnote>

<footnote n="3">³ Institut de Recherche pour le Développement, UR154/UMR5563, Observatoire Midi-Pyrénées, 14 av. Ed. Belin, 31400 Toulouse, France</footnote>

<footnote n="4">⁴ Bureau de Recherche Géologiques et Minières, 3 av. Claude Guillemin, BP 36009, 45060 Orléans Cedex 2, France</footnote>

<footnote n="5">⁵ Institut de Physique du Globe de Paris, 4 place Jussieu, 75252 Paris Cedex 05, France</footnote>

<footnote n="6">⁶ Institut Géographique National, 2 avenue Pasteur, 94165 Saint-Mandé Cedex, France</footnote>

<footnote n="7">⁷ Servive Hydrographique et Océanographique de la Marine, 13 rue du Chatellier, BP 30316, 29603 Brest Cedex, France</footnote>

<footnote n="8">⁸ Bureau Gravimétrique International, 18 avenue E. Belin, 31401 Toulouse Cedex 4, France</footnote>

<footnote n="9">⁹ Centre Littoral de Géophysique, Université de La Rochelle, av. Michel Crépeau, 17042 La Rochelle, France</footnote>

<footnote>diament@ipgp.jussieu.fr</footnote>
gravity to hydrology, cryosphere studies and geodynamics studies are reported in the paper by Biancale et al. (this volume).

The report is divided in four parts. In the first one, works on the measurement, representation and modeling of the gravity field are presented. Methodological progresses are described in mobile gravimetry, data interpolation, processing and interpretation of gradiometry and representation of the gravity field by wavelet frame. The second part is devoted to local studies, especially to works in the fields of geodynamics, geology or volcanology. The third part presents efforts in view of the improvement of the national gravimetric infrastructure: establishing of a combined gravity and geodetic network, renewal of the old gravity coverage by linking it with the new network, reprocessing of old data. Activity in absolute gravimetry is the subject of the fourth part: three instruments are now used in France and foreign countries for scientific purposes in geodynamics, tectonics, hydrology and for intercomparisons of instruments.

**Key words** absolute gravity, field gravity, gradiometry, gravity modeling, gravity networks

## Un bilan de l'activité des équipes françaises dans le domaine de la gravimétrie au sol (période 2003-2006)

**Résumé** Ce rapport présente les principaux résultats obtenus par les équipes françaises dans le domaine de la gravimétrie au cours des quatre dernières années. La gravimétrie temporelle d'observatoire utilisant les stations équipées de gravimètre supraconducteur fait l'objet d'un rapport séparé (Hinderer et coll., ce volume). De même l'exploitation des données de gravimétrie satellitaire pour l'hydrologie, l'étude de la cryosphère ou la géodynamique est résumée dans le rapport de Biancale et coll. (ce volume).

Le rapport est divisé en quatre parties. Dans la première, les travaux liés à la mesure du champ de pesanteur, à sa représentation et à sa modélisation sont présentés. Les progrès méthodologiques concernant la gravimétrie mobile, l'interpolation des données, le traitement et l'interprétation de la gradiométrie et la représentation du champ par ondelettes sphériques sont décrits. La seconde partie est consacrée aux études locales, en particulier aux travaux d'intérêt géodynamique, géologique ou
volcanologique. La troisième partie présente les efforts réalisés en vue de l'amélioration de l'infrastructure gravimétrique du pays : établissement d'un réseau combiné de gravimétrie et de géodésie, amélioration de la couverture gravimétrique nationale par rattachement au nouveau réseau et retraitement des données anciennes.
Les activités en gravimétrie absolue font l'objet de la quatrième partie : trois instruments sont désormais utilisés en France et à l'étranger pour des études scientifiques touchant à la géodynamique, à la tectonique, à l'hydrologie, et pour l'inter comparaison des instruments.

***Mots clefs*** gravimétrie absolue, levés gravimétriques, gradiométrie, modélisation gravimétrique, réseaux gravimétriques

# I. MEASURE, REPRESENTATION AND MODELING OF THE GRAVITY FIELD

In the recent years, our knowledge of the Earth gravity field has dramatically increased thanks to improvements in ground (land and sea) data acquisition using new measuring systems (new relative and absolute instruments, full tensor gradiometry measuring devices, airborne surveys, etc...) and to the new available satellite gravity data as the ones provided by the GRACE mission. This called for improvement and new development in data acquisition, data processing and interpretation methods as much as in the gravity field representation.

New methodologies were studied in order to create high-resolution gravity maps in oceanic areas. In the oceans, different types of data (satellite altimetric data and marine gravity data for example) can be used and merged to preserve their

specific information content. Nevertheless, the results of such data mixing are usually not optimal in precision and resolution. In some geodynamical areas the bathymetry can be taken as a “data interpolator” by the use of neuronal methods, improving the quality of the gravity mapping [Lequentrec-Lalancette et al., 2006].

Concerning the airborne gravimetry, several studies were devoted to the improvement of the measuring devices [Verdun et al., 2005] or on data processing [Abbassi, 2006]. These studies often used the French-Swiss Alps survey [Verdun et al., 2003] as a test area. A specific instrumental development had been carried out at the Laboratoire de Recherche en Géodésie (IGN) and the École Supérieure des Géomètres et Topographes with a view to perform
gravity measurements on vehicles [de Saint-Jean et al., 2005a and b, 2006].

The rebirth of gravity gradiometry some decades after the extinction of torsion balance surveys thanks to the development of full tensor gradiometry (FTG) measurements led to an increasing use of these data in geophysical prospecting. In addition, the European space gravity mission GOCE, to be launched in 2007, should also provide

gravity gradients measurements. As a consequence several studies aimed at improving or developing dedicated methods for gradiometry data denoising and interpretation [Mikhailov and Diament, 2006; Pajot et al., 2006; Guillen et al., 2006]. The collocation method was studied and the planar covariance functions were explored to compute the geoid parameters [Moreaux et al., 2004 and 2005].

<figure><img src="image_53.png" /><figcaption>**Figure 1:** free-air anomalies over the Marquesas archipelago obtained by merging GRACE, satellite altimetry and sea-surface data. After [Panet, 2005].</figcaption></figure>

One of the major questions we will have to face due to the availability of new global satellite gravity data will be to compare and merge satellite data with ground and airborne ones. Comparison is a

mandatory task in order to calibrate and validate the satellite data. Merging is also a mandatory task in order to be able to extend towards the high frequencies the information provided by satellite data.
Indeed, merging allows taking full
advantage of both satellite and
ground/airborne data in order to provide a
complete and accurate picture of the
gravity field. This is a key question both
for carrying geodynamic studies at various
scales and for geoid computations. A
significant advance was obtained by the
development and implementation of a
wavelet based representation of the gravity
field [Panet et al., 2004; Chambodut et al.,
2005; Panet, 2005; Panet et al., 2006].
Figure 1 shows the free-air anomalies over
the Marquesas archipelago obtained by
merging GRACE, satellite altimetry and
sea-surface data. Its resolution is 35 km
and precision about 1 mGal; furthermore
only 9500 wavelets were used instead of
nearly 300 000 spherical harmonics
required in the classical spherical
harmonics representation.

The analysis in terms of density
inhomogeneities of these gravity models
using a continuous wavelet analysis was
also developed [Panet et al., 2006]. It
allowed providing significant results as to
the origin of intraplate volcanism in
French Polynesia, a question that has been
intriguing for decades. Indeed, [Panet et
al., 2006] evidenced a plume beneath
Society Islands and on the contrary
suggested that no deep structure was
associated to the Marquesas Chain. One
can note that this new method of analysis

of gravity models confirms the efficiency
of the wavelet based potential field
interpretation approaches previously
(before 2003) published by teams in
Rennes University, IPGP and EOST.

In the meantime, improvement of
more traditional methods for identifying
causative bodies was realized. For instance
[Mikhailov et al., 2003] proposed to use
some artificial intelligence technique to
select and cluster the Euler solutions
whereas [Debeglia et al., 2006] proposed a
semi-automatic method for structural and
depth to sources analysis of potential field
data.

The characterization of the crustal
structure in areas of geodynamic interest
by combining gravity with seismological
information also attracted the interest of
several groups. For instance [Tiberi et al.,
2003] developed a joint inversion of
seismic tomography and gravity anomalies
and applied it to the Baikal rift area while
other groups favored sequential inversion.
Whatever the chosen approach is, it must
be noted that taking into account both
gravity anomalies and seismic tomography
yields to a much more realistic modeling
of the inner Earth than using gravity or
tomography data only.

In the field of computing software,
a new version of the processing package
CG3TOOL developed by [Gabalda et al.,
2003] for processing Scintrex microgravity
data has been updated on PC environment
[Beilin, 2005].

The dramatic improvement of
geodetic and gravimetric measurements
accuracy calls also for a new theoretical
development in reference Earth model.
Indeed, till these studies, in order to model
the elasto-gravitationnal deformation, only
a simple spherical (at better ellipsoidal)
radially stratified Earth was considered.

II. LOCAL STUDIES

II.1 The static field

Many studies were carried out in order to
better know the local gravity field in areas
of interest for geodynamic or applied
purposes, to model the sub-surface
structure at various scales and to better
understand the physical processes acting
there. Amongst the numerous surveys that
various groups have been carrying both on
the French territory [Talbot, 2003; Gébelin
et al., 2004; Joly et al., 2006] and
elsewhere, special attention may be given
to the gravity survey of the Marquesas
islands (French Polynesia), a zone where
nearly no gravity measurement was
available. The resulting maps complement
the geological mapping that have been, for
the first time, realized [Savanier et al.,
2005] thanks to a join effort of BRGM and
CEA.

[Métivier, 2004], [Metivier et al., 2005, 2006] and [Greff-Lefftz, 2005] developed a new reference model which takes into account lateral density and rheology variations within the mantle. This model was later applied to predict tides and loading perturbations due to super-plumes and other large wavelength geodynamic features.

Several zones of geodynamic
interest have been the focus of a gravity
study in order to better characterize the
inner structure, this is the case of the
western part of France [Martelet et al.,
2004; Mazabraud et al., 2005], the Corinth
rift [Tirel et al., 2004], the Baikal rift zone
[Tiberi et al., 2003; Petit and Déverchère,
2006], the Molucca sea [Widiwijayanti et
al., 2003, 2004], the Red Sea [Tiberi et al.,
2005], French Polynesia [Panet et al.,
2006], aseismic ridge [Tiwari et al., 2003].
Modeling of volcanic structures based on
detailed gravity surveys has been also
carried out on active volcanoes such as
Soufrière de Guadeloupe [Gunawan, 2005]
or in Chile: Lascar [Pavez, 2005; Pavez et
al., 2006] and Cordon del Caulle
geothermal field [Sepulveda et al., 2005].
The granitic massifs emplaced in extensive context during the late Variscan orogeny in the French Massif Central have been also studied [Gébelin et al., 2006; Martelet et al., 2004; Talbot et al., 2004; 2005].

Finally, other studies devoted to the mechanical response of the lithosphere as for example in the Himalayan region [Hetenyi et al., 2006] were carried out.

<figure><img src="image_54.png" /><figcaption>**Figure 2:** Top: location of time varying measurement stations across the Afar rift. Bottom: Gravity variations between 1985-1998 and 1999. An increase of gravity is clearly observed in the axial part of the rift. After [Ballu et al., 2003].</figcaption></figure>
## II.2 The marine geoid

The European and the French geoids have to be constrained in their oceanic parts, especially in the Mediterranean margin. To that aim, recent surveys were processed and validated by the French Naval Hydrographic and Oceanographic Service

(SHOM) and handed over to the French and European referent (Institut Geographic National, Bureau Gravimétrique International) for these geoid project [Lequentrec-Lalancette and Rouxel, 2006].

## II.3 Time dependent gravity

Here we only mention studies based on the ground monitoring of the time variable gravity that are not linked with gravity observatories such as the one belonging to the GGP network. The studies based on satellite monitored time gravity variations as those provided by the GRACE mission are reported in this volume [Biancale et al.]. Note however, that prior to the availability of GRACE data, several studies aimed at investigating the potential of such information as example for the understanding of large earthquakes, a topic that was a priori out of the scope of the GRACE mission [Mikhailov et al., 2004].

Monitoring of time varying gravity, jointly with spirit leveling or GPS data, as recorded on dedicated ground networks allows to evidence vertical crustal motions and sub-surface mass transport or density variations. This is currently done in some active volcanoes or active zones such as rift zones. For example indications concerning the state of the volcanic edifice

were obtained on the Soufrière de Guadeloupe [Gunawan, 2005]. On the Piton de la Fournaise, such analysis allowed quantifying and model the mass transport related with magmatic intrusions or with changes in the hydrothermal system [Bonvalot et al., 2004; Rémy, 2005].

In the Afar rift zone (Djibouti), [Ballu et al., 2003] evidenced time gravity variations over a time period of several years and evidenced a gravity increase located in the central part of the rift (see Figure 2).

In north Chile, an experiment of measuring crustal deformation related with the earthquake cycle using absolute gravity and permanent GPS has been initiated by IRD, EOST and IPGP (see below in this article).

In Brest, six new absolute gravity measurements have been done at the ECGN (European station) to improve the time series acquisition in the West of
Europe.

In 2004, the study of the oceanic
loading grouped together several French
laboratories in a multi technique
monitoring in the North of France [Llubes
et al, submitted]. This experiment led to
some precise measurements of vertical
movement especially with French laser

FTLRS at the Brest VLBI and RGP
reference station.

In 2006, several groups using
relative and absolute gravity meters started
a long term project in order to monitor and
to model mass transport due to hydrology
in the vicinity of Ploemeur in France
[Jacob et al., 2006].

<figure><img src="image_55.png" /><figcaption>**Figure 3:** Status of the gravimetric IGN measurements on the French Basic Geodetic Network (RBF) on Dec. 31st, 2006.</figcaption></figure>

III. IMPROVEMENT OF THE NATIONAL GRAVITY
NETWORK AND COVERAGE

**III.1 The integrated geodetic and gravimetric network**

The first (CGF65) and second (RGF83)
French gravity networks were established
in 1965 and 1983 respectively [CNIG,
2000]. After the recommendations of the
Comité National Français de Géodésie et

Géophysique (the French branch of the
IUGG) [Louis, 1996] and of the Conseil
National de l'Information Géographique
[CNIG, 2000], the Institut Géographique
National (IGN) begun systematic
measurements of gravity on 1020 points of the French GPS geodetic network (RBF), on the points of the permanent GNSS network, on the nodes of the national first order leveling network, on tide gauges and on points of the older gravity networks. Conversely, since 1998, the Ecole et Observatoire des Sciences de la Terre as well as the Laboratoire de Dynamique de la Lithosphère of Montpellier University have undertaken absolute gravity measurements using Micro-g FG5 apparatus (see section “absolute gravity activities” below).

This work aims at:

* renovating the old gravity network,

* setting up an integrated geodetic and gravimetric network in accordance with the recommendations of EUREF,

* verifying and improving the old gravity coverage in view of a more accurate geoid model.

Integrating the gravimetric and the geodetic network presents decisive advantages:

* to better meet the scientific needs, mainly in geodesy and geodynamics,

* to reduce the cost of monumentation and maintenance.

An accuracy of 10□10⁸ m s² (10 µGal) is expected. IGN has planned to measure 200 points by absolute and relative gravimetry

and 900 points by relative gravimetry. Relative measure-ments started from 2000 with Scintrex CG3M gravimeters owned by the Institut National des Sciences de l'Univers and the Royal Observatory of Belgium. In 2005, the Institut de Recherche pour le Développement (IRD), the Institut de Physique du globe de Paris (IPGP) and the IGN purchased together a Micro-g A10 gravimeter and absolute measurements begun immediately. The stations measured during the campaigns 2000~2006 are shown on Figure 3; see also [Gattacceca, 2005].

In order to assess the correspondence between old and new gravity networks and therefore insure a correct transition of the French Bouguer gravity map into the new Réseau et Carte Gravimétrique de la France, BRGM has been measuring since 2005 relative gravity ties between the RGF83 and the new gravity base stations [Martelet and Debeglia, 2006]. These ties also include the recently established and measured FG5 order-0 absolute reference sites: 7 new determinations were financed by BRGM during the period 1999-2006 and 4 are in project for 2007. In the same time, vertical gradient measurements were performed on these absolute sites.

In the current state of the measurements, most RGF83 and recent base stations have been found coherent,
with respect to their confidence level,
except 3 of them, which differ from about
100 µGal. Whereas significant for
metrologic applications, these local
discrepancies have a negligible influence
on the French gravity map.

In parallel, investigations were
carried out at IGN to improve the
procedures to correct and adjust the

measurements. Special attention was given
to ocean loading correction, gravity
gradient modeling and software
development, see [Beilin, 2005] and
[Duquenne, 2007a].

IGN plans to achieve this
combined network and to compute a new
model of the geoid by the end of 2008.

<figure><img src="image_56.png" /><figcaption>**Figure 4:** Bouguer anomalies prediction discrepancies: this represents the uncertainty of the French Bouguer map.</figcaption></figure>

III.2 Quality control of the French gravity map and network

The two existing French gravity networks
CGF65 and RGF83 and a large part of the
national gravity coverage were established

under the supervision of BRGM. These
data are now integrated in digital form, in
the « Banque Gravimétrique de la France »
(BGF), under the responsibility of the BRGM, and can be accessed via the Infoterre Web portal (http://www.brgm.fr).

In order to improve its national geoid, and be able to address high accuracy gravity-related issues, France plans to update its national gravity network and gravity map by the end of year 2008. In this context, a careful validation and improvement of the existing

gravity data is necessary since the existing gravity stations (about 414000) and base stations (more than 1000) should be tied to the new gravity references.

Integration of new gravity network measurements performed by IGN since year 2000 and existing ones requires that both the gravity data and their position be controlled. The controls address possible distortions:

<figure><img src="image_57.png" /><figcaption>**Figure 5:** Limits of the respective areas covered with leveled GPS points, gravity data and DTM of the "Alvernia" data set.</figcaption></figure>

- between the new and old networks: field gravity tie measurements are done,

- between the new network and the gravity coverage: gravity prediction is performed at the new network base locations using the surrounding gravity

measurements. For this purpose, the accuracy of both the gravity and position of the ~414000 gravity stations must be carefully verified.

The French gravity database (BGF) contains about 414000 gravity stations, divided into 173 surveys.
1. For each survey, in order to identify and correct existing systematic shifts of the gravity stations, methods minimizing the distance of gravity stations to a detailed DTM or to the roads were implemented [Martelet and Sarrailh, 2006] and allowed to rectify the positioning of 41 surveys, at the 1/25000e scale.

2. Once the modifications of positioning were applied, terrain corrections have been re-computed. Indeed, since the main sources of error of the terrain effect are erroneous altitude differences between the stations and the DTM, significant improvement of the terrain corrections was achieved

[Martelet and Debeglia, 2006].

3. In order to assess the overall accuracy of the French gravity database, prediction of the Bouguer anomaly for each station of the database, using the surrounding gravity stations, was performed [Martelet and Debeglia, 2006].

This allowed to: (i) point out about 300 erroneous Bouguer gravity stations (mainly located in the mountainous areas), (ii) quantify the internal accuracy of the French Bouguer map (Figure 4). For 94% of the stations, Bouguer uncertainty is lower than 1 mGal, the mean uncertainty being around 0.3 mGal.

### III.3 Quality control of geoid models

As mentioned above, IGN has planned to compute a new model of the geoid in 2008. This model should take advantage of the integrated geodetic and gravimetric network and of the improvement of the gravity coverage. In addition, IGN has begun a study on quality control of geoid models or other representations of the

gravity field. As a first stage, IGN has built the “Alvernia” data set to test methods and software for geoid modeling. It is presently composed of gravity and terrain data and leveled GPS points, see [Duquenne, 2007b], Figure 5 and ftp://lareg.ensg.ign.fr/pub/duquenne/Test_data_set/.

## IV. ABSOLUTE GRAVITY (AG) ACTIVITIES

### IV.1 Introduction

There are, at the moment, three absolute gravimeters in France: two are FG5s, from

Micro-g Solutions (namely FG5#206 since 1996 and FG5#228 since 2005); one is a
portable A10, also from Micro-g Solutions (A10#014 since 2005). Both types of instruments study the trajectory of a reflecting object freely falling in the vacuum. According to the manufacturer, their respective accuracy is 1 and 10 µGal (observed agreement between instruments). Nevertheless, the actual conditions of the experiment: duration of measurements, meteorological conditions, and so on... can influence the quality of the experiment and the accuracy of the results is decreased but sometimes increased with respect to the nominal accuracy.

As it is well known, gravity is influenced by masses located under (or in the close vicinity of) the instrument and by the position (mainly the height) of the station. This means that in case of repeated

measurements at a given station, any change in gravity can be caused by either a change in mass or a change in altitude (or both phenomena together). This is what will lead to the possible applications of AG instruments: 1) evolution of gravity related to tectonics (change in altitude), hydrology (change in mass water), post-glacial rebound (PGR, in polar regions), 2) actual value or gravity for national gravity networks, 3) long term gravity evolution at home sites, 4) intercomparison of instruments for a better confidence in the result, 5) calibration of SGs from the Global Geodynamics Project (GGP) network. In the following, we present the AG measurements according to this list of topics.

<figure><img src="image_58.png" /><figcaption>**Figure 6:** The new portable absolute gravity meter (A10#014) in field operation (north Chile).</figcaption></figure>

## IV.2 The new portable A10 absolute meter

On contrary to the FG5 meter, the portable A10 meter has been designed to perform

data acquisition in outdoor conditions thanks to a more robust thermal insulation
and more compact packaging of the sensor and acquisition devices (Fig. 6). The A10 #014, acquired jointly by IRD, IGN and IPGP, has been delivered on February 2005. After successful tests and evaluations performed under laboratory conditions on various reference sites in France (IRD Bondy, BIPM, IGN St-Mandé), the instrument is now currently used for scientific purposes (geodynamics, vulcanology, tectonics, hydrology...) and for achieving reference gravity networks in France, Asia and South America. The instrument was operated between April-

October 2005 and July-December 2006 by IGN to achieve the French national gravity network. Between December 2005 and June 2006, it has been operated in the Andes (Chile-Argentina) by IRD to establish local and regional absolute gravity and geodetic networks in active tectonic or volcanic zones in the frame of cooperation research projects. During summer 2005, the instrument has been also used for earth tide studies (determination of the ocean loading in Brest) by IGN and IPGP.

<figure><img src="image_59.png" /><figcaption>**Figure 7:** long-term gravity variations recorded at the Strasbourg-J9 station with SG and AGs. ©Strasbourg's team.</figcaption></figure>
IV.3 Home sites and secondary sites

Strasbourg-J9

FG5#206 is hosted by the Gravimetric Observatory of the ‘École et Observatoire des Sciences de la Terre’ (EOST) in Strasbourg since December 1996. The Strasbourg home station (Strasbourg-J9) is located at 15 km of the city, in a bunker

which is the seat of gravimeters since half a century. Measurements are operated quite regularly: 5 times in 2003, 12 times in 2004, 8 times in 2005 and 9 times in 2006. Three of these measurements are in collocation with an other FG5 (#301 from BKG or #228).

<figure><img src="image_60.png" /><figcaption>**Figure 8:** gravity variations recorded at the Montpellier station with AG. ©Montpellier's team.</figcaption></figure>

A superconducting gravimeter (SG) is continuously recording gravity variations at the station since 1987. The repeated parallel recording of superconducting and absolute gravimeters enables to confirm the variations observed by the instruments and control their behavior. Moreover a 5-6 days recording is the best way to calibrate the SG. Figure 7 presents the observations from the 2

instruments from 1997 to 2005.

The long-term time series monitors the evolution of gravity at the station. The two gravimeters observe an annual signal and a positive trend equal to +1.73 ± 0.17 µGal/yr [Amalvict et al., 2006]. The positive sign corresponds to a subsidence of the station, which is also observed by the continuous GPS antenna installed at the site since 1995.
### Welschbruch

The secondary home site (Welschbruch) of FG5#206 is located in the Vosges Mountains at 30 km of Strasbourg, 765 m height. The site has been measured twice in 2003 and in 2005. FG5#301 from BKG (Germany) measured at this site in 2003. The variation of gravity presents a negative trend equal to -0.96 ± 0.2 µGal/yr corresponding to the expected uplift [Amalvict et al., 2006].

### Montpellier

FG5#228 is hosted by the Centre National de la Recherche Scientifique (CNRS) on

## IV.4 Intercomparisons

Though absolute, the absolute gravimeters have to be intercompared. International intercomparisons of AG are organized every four years at the Bureau International des Poids et Mesures (BIPM) in Sèvres (France). Both FG5#206 and #228 participated in the last intercomparison in 2005 (ICAG05), the discrepancy between the 20 instruments of different types is ± 5µGal.

The 1st Regional Intercomparison was held in November at Walferdange (Luxembourg), hosted by the European Center of Geodynamics and Seismology (ECGS). FG5#206 was part of the comparison with 14 other instruments

the Montpellier campus, seat of 10 measurements in 2005 and 15 in 2006, of which 2 with a parallel recording of FG5#206. Figure 8 presents the time series of gravity values and its seasonal variation.

### Puechagut and Aigoual Observatory

Two secondary sites are located at some distance: Puechagut (1000m) has been visited once in 2005 as well as the Mt Aigoual Observatory (1500m), with parallel recording of the FG5#206. This set of 3 stations is a calibration line for relative gravimeters: 1500 m height difference in 80 km.

(FG5s and 1 A10). The agreement is better than 2 µgal [Francis et al., 2005].

FG5#206 and #228 operated in parallel at the home sites Strasbourg-J9 and Montpellier and at some other French stations (Ploemeur). FG5#206 and #301 from BKG operated in parallel at Strasbourg-J9 in 2003.

A10#014 has been also operated simultaneously in 2006 with FG5 meters in France (FG5#206) and in Chile at the TIGO geodetic observatory (FG5#227 from BKG).
<figure><img src="image_61.png" /><figcaption>**Figure 9:** Gravity and geodetic networks in Chile.</figcaption></figure>
<figure><img src="image_62.png" /><figcaption>**Figure 10:** Co-seismic GPS and absolute gravity changes associated with the 2005 Tarapaca earthquake, north Chile. [Bonvalot et al., 2006b].</figcaption></figure>

## IV.5 Dedicated campaigns of measurements

### Metrology

Metrology is a topic quite close to the idea of intercomparison and ICAG05 was the 1st preliminary key comparison for establishing unit standards. On the other hand, the Syrte Laboratory and the Observatory of Paris project an AG with cold atom for the future Watt balance. FG5#228 measured with FG5#202 (Royal Observatory of Belgium) and FG5#215 (Czech Republic) at the future site of the cold atom gravimeter in 2006. A10#014 will measure there in 2007.

### National and European gravity networks

FG5#206 and #228 establish the 0 order

absolute gravity network of the French gravimetric network, with the Bureau de Recherches Géologique et Minières (BRGM) and the French Geographic National Institute (IGN). Instruments measured gravity, for that purpose, in Nancy (2003), Toulouse (2006), Clermont-Ferrand and Puy de Dôme (2005). These sites had been measured by Sakuma in the 1970s. [Amalvict et al., 2003] show the good agreement of the gravity values at stations measured with Sakuma's apparatus and a new generation gravimeter. Moreover, the stations mentioned in other sections (Strasbourg, Montpellier, Brest and so on...) are also part of the network. In 2005 an 2006, A10#014 was intensively used in France to
determine a dense absolute gravity
network (cf. section on French gravity
network).

Measurements at remote sites such
as the sub-Antarctic scientific stations in
the Indian Ocean are part of the worldwide
coverage of gravity values, part of the
overseas gravimetric network and
calibration lines for marine gravimeters.
FG5#206 operated in Kerguelen, Crozet
and Amsterdam in 2003 and 2005, in the
framework of a project supported by the
French Polar Institute (IPEV). The change
of gravity is monitored and compared with
GPS and DORIS observations [Amalvict
et al., 2007a]. Gravity was measured
(FG5#206) for the first time at Tahiti in
the Pacific Ocean in 2003. The
Observatory at Tahiti is candidate for
hosting a SG in the future. FG5#206 and
#228 also participate to the Iranian gravity
network (cf section Iran). FG5#206 and
A10#014 participated to establish the
Chilean absolute gravity network (cf.
section Chile).

Polar regions

Polar regions are very specific because of
the Post Glacial Rebound (PGR) and
Present Day Ice Melting (PDIM) that AG
measurements can help to separate.

FG5#206 operated in Svalbard,
Spitzbergen (Norway) in 2004. [Sato et al.,
2006] compare previous AG

measurements by several European gravity
teams (decreasing secular rate of -2.5 ±
0.9 Gal/yr) with GPS (6.4 ± 1.5 mm/yr)-
and VLBI (4.8 ± 1.1 mm/yr) positioning
techniques, tide gauge data and PGR and
PDIM models. The comparison points out
the importance of having both precise
modeling and precise observation to
separate PGR from PDI.

In the framework of a project
supported by the French Polar Institute
(IPEV), FG5#206 operated in 2006 the
second AG measurement at Dumont
d'Urville, Terre Adélie (Antarctica). The
value of gravity is the same in 2000 and in
2006, GPS and DORIS positioning
techniques, and predictions by models
confirm the stability of the site (Amalvict
et al., 2007c). Let us note that only four
Antarctic stations are the seat of repeated
AG measurements (Makinen et al., 2007)
and that four Antarctic stations are the seat
of DORIS beacon (Amalvict et al., 2007b).

SG calibration

The calibration of an SG requires 5 or 6
days of parallel recording of FG5 and SG.
FG5#206 recorded gravity in parallel with
SG at Strasbourg-J9 and Svalbard in 2004
and at Mount Stromlo (Australia) in 2006.
An accurate calibration of SGs is
important for the validity of observations
of the GGP network (cf the report “Time
varying gravity with superconducting
gravimeters” in this volume).

<figure><img src="image_63.png" /><figcaption>**Figure 11:** SG and AG observations at Strasbourg-J9 and loading effects. [Amalvict et al., 2004].</figcaption></figure>

## Mean sea level

AG measurements, GPS and tide gauge observations are combined to study the mean sea level at two sites on the Western coast of France, with cooperation between Geosciences Montpellier, CLDG (University of La Rochelle) and the SHOM (Brest). In 2006, FG5#228 measured 3 times at La Rochelle and once at Brest. The first observations at La Rochelle are very close (> 1 µGal) indicating a stability of the levels.

## Tectonics

Due to its sensitivity to the distance to the Earth's center, monitoring the evolution of precise gravity is a good tool to evidence

changes in altitude, mostly related to tectonics (except for the PGR in polar regions). This type of AG measurement is always associated with GPS and other techniques of precise positioning (VLBI, DORIS).

## Rhine Graben

The Rhine graben lies between the Vosges Mountains and the Black Forest (Germany). [Amalvict et al., 2006] compare the trends of AG measurements and GPS continuous observations at three sites displayed in the three geographic regions: *Strasbourg-J9* in the graben, *Welschbruch* in the Vosges and the Black Forest Observatory (*BFO*) in the Black Forest. Gravity and GPS agree for a
subsidence at *Strasbourg*, but the results are not so clear for the other two stations. Cooperation started between EOST, BFO and BKG to extend this study.

## Iran

Geosciences Montpellier is involved since 2000 in AG measurements in Iran for 1) the establishment of the gravimetric Iranian network and 2) for evidence tectonic movements in mountainous regions, in collocation with GPS observations. FG5#228 observed 10 stations in 2005 and FG5#206 observed 8 stations in 2004 and in 2006. The long-term series at Abali has a small negative trend (~ -0.5 µGal/yr or uplift 2 mm/yr). The short-term gravity variations (2005 - 2006) at sites in the Alborz, is positive on the coast of Caspian Sea and on the Southern front of the chain and negative in the interior part.

## Taiwan

Thanks to absolute gravity measurements, the program AGTO (Absolute Gravity of the Taiwanese Orogen) aims at the study of vertical tectonic movements and the transfer of mass in the Southern part of the island. This initiates cooperation between Geosciences Montpellier (France), EOST (France), the National Chiao Tung University (Taiwan) and the Industrial Technology Research Institute (Taiwan).

Two sites were established and measured at the end of 2006; they will be reoccupied in 2008 and 2010 [Masson, 2006].

## Chile

In 2002, IRD, EOST, IPGP jointly with the University of Chile initiated a first experiment dedicated to study the present-day crustal deformation along the active subduction zone in Chile by means of absolute gravity and permanent GPS data [Bonvalot et al., 2003b]. The first gravity surveys realized in 2002 and 2005 allowed setting up a first order network of 15 stations in north and central Chile determined by the FG5 #206 instrument. In 2006, the network was complemented by about 60 new absolute gravity stations observed with the A10 #014. Most of these gravity stations being co-located with continuous GPS stations also installed for monitoring crustal deformation related with the earthquake cycle (Fig. 9). These observations led to estimate the inner accuracy of the gravity network to be within 3 and 5 microGal for FG5 and A10 surveys respectively indicating that the required accuracy for crustal deformation studies was achieved. They also provided the first evidence of local gravity changes associated with a deep subduction earthquake (Mw 7.7 Tarapaca earthquake, June 13, 2005). The observed changes are consistent with the co-seismic
displacements measured by GPS and InSAR and are mostly explained by the crustal vertical motion as predicted by an elastic dislocation model [Bonvalot et al., 2006a and b; Peyrat et al., 2006a and b] (Fig. 10).

Local absolute and relative gravity and GPS networks have been also installed in 2006 on the Lastarria-Azufre volcanic

field (Chile-Argentina). The objective is to monitor crustal deformation and mass transfer associated with the 45 km wide active uplift (up to 30 mm . y-1) evidenced by InSAR data [Froger et al., 2006]. These works also contribute to the determination of reference gravity and geodetic base stations in South America.

## IV.6 Hydrology

When the altitude can reasonably be assumed constant, then a change in gravity is related to the change in underlying masses. Hydrology is the more frequent candidate to explain the observed variations in gravity and the stations are more and more often equipped with water gauges, humidity sensors,

In the framework of ANR ECCO, collocated geodetic techniques (gravimeters, GPS, tilt meters) are combined to evidence transfers of water in continental situation for different scales of time and space at 2 sites in France:

### Larzac Causse

In this karstic region, the seasonal variation of absolute gravity is an indirect evidence of a varying water storage. FG5#228 observed 10 times at 3 sites (La Salvetat, La Blaquererie, Les Canelettes) and FG5#206 observed once at each site in parallel. New measurements are scheduled

in 2007. The absolute gravity values show a seasonal variation (>15μGal) at the three sites, that is correlated to the annual cycle of precipitations. The heavy rains induce gravity and tilts depending on the transfer function of the water and of the associated deformation of the karst.

### Ploemeur (France)

Two gravity stations and three tilt meters are implemented at the pumping station of Ploemeur, in a metamorphic region. The objective is to observe the signal associated with the stopping of the pumping in the deep captive water table and the possible fluctuations of the superficial water table. Both FG5s observed in parallel during 2 weeks in May 2006. The preliminary results are in favor of a small porosity of the superficial underground (< 1%) and of a vertical displacement (< 1mm) associated to the augmentation of pressure when the
pumping stops. The site will be reoccupied
in the future and a seasonal signal is
expected in relation with the rain cycle.

Strasbourg-J9 (France)

The monitoring of the long-term gravity
evolution (with both SG and AG)
demonstrates an annual signal [Amalvict et
al., 2004]. Since 1987, a piezometric
gauge is measuring the water level
changes of the local aquifer, which is
almost unconnected to the regional water
table. Figure 11 shows the agreement
between the total hydrological effect
(Newtonian + elastic loading) of the
Alsatian water table and the gravity
observations.

Brest (France)

AG is measured at the Brest Hydrographic
and Oceanographic Office (SHOM) since

1998. To control and improve the
observations from the tide gauge (150
years time series at Brest), its vertical
positioning has to be known.
Multitechniques campaigns are organized
and the publication of results is in
progress. FG5#206 measured in 2004 and
2005, FG5#228 measured in 2006.

Calern (France)

The gravity variation is monitored for a
decade at the OCA Grasse geodetic
observatory (France) on the Calern
Plateau. Three AG European teams are
measuring gravity: Strasbourg, Brussels
and Montpellier. FG5#206 measured in
2003 and FG5#228 measured in 2005. The
variation of level of the water table is
thought to cause the seasonal signal of the
gravity time series (Fig. 12).

<figure><img src="image_64.png" /><figcaption>**Figure 12:** SLR, GPS and AG time series at the OCA Grasse Observatory. [Nicolas et al., 2006].</figcaption></figure>
V. ACKNOWLEDGMENTS

We thank F. Barlier for his comments on the manuscript and I. Tchiguirinskaia who edited it.

VI. REFERENCES

Abbasi, M. (2006). Etude du traitement de données gravimétriques acquises lors de levés aériens, Ph. Thesis, Université de Toulouse III – Paul Sabatier.

Amalvict M., Debeglia N. & Hinderer J. (2003). The absolute gravity measurements performed by Sakuma in France, revisited 20 years later, in *Gravity and Geoid 2002* GG2002, Tziavos (ed.), Editions Ziti, 76-83.

Amalvict, M., Hinderer, J., Mäkinen, J., Rosat, S., and Rogister, Y. (2004). Long-term and seasonal gravity changes at the Strasbourg station and their relation to crustal deformation and hydrology, *Journal of Geodynamics*, 38, 343-353.

Amalvict, M., Hinderer, J., and Rozsa, S. (2006). Crustal vertical motion along a profile crossing the Rhine graben from the Vosges to the Black Forest Mountains: Results from absolute gravity, GPS and levelling observations, *J. Geodynamics*, 41, 358–368

Amalvict, M., Rogister Y., Luck B. and Hinderer, J. (2007a). Absolute gravity measurements in the Southern Indian Ocean, *IAG Symposia*, vol. 130, 433-437, Springer.

Amalvict, M., Willis P; and Shibuya K. (2007b). Status of DORIS stations in

Antarctica for precise geodesy, *IAG Symposia*, vol. 130, 94-102, Springer.

Amalvict, M., Rogister Y., Hinderer J., Luck B., McQueen H., and Luton G. (2007c). Absolute Gravity Measurements in Terre Adélie (Antarctica) and at Canberra (Australia), in press.

Ballu, V., M. Diament, P. Briole, and J.C. Ruegg (2003). 1985-1999 gravity field temporal variations across the Asal Rift: insights on vertical movements and mass transfer, *Earth Planet. Sci. Lett.*, 208, 41-49.

Beilin J. (2005). Apport de la gravimétrie absolue à la réalisation de la composante gravimétrique du Réseau Géodésique Français. Master thesis, IPGP & IGN.

Bonvalot, S., Calmant S., Gabalda G., Lebellegard P., Remy D. (2003a). Activités de l'IRD en Gravimétrie et Géodésie». In : *Rapport Quadriennal 1999-2002 du CNFGG (Comité National Français de Géodésie et Géophysique)*, 264p.

Bonvalot, S., Comte, D., Dorbath, L., Hinderer, J., Gabalda, G., Luck, B., Ruegg, JC., (2003b). Absolute gravity and GPS measurements in Chile: preliminary results. *Geophysical Research Abstracts*, EAE03-A-13049.
Bonvalot, S., D. Remy, C. Deplus, M. Diament, G. Gabalda, J. Ammann, P. Catherine, T. Staudacher (2004). Constraints on subsurface processes on active volcanoes using microgravity monitoring: Results from Piton de la Fournaise (La Réunion). Oral presentation, *IAVCEI General Assembly*, Pucon, Chile.

Bonvalot, S., J. Hinderer, G. Gabalda, B. Luck, F. Bondoux, D. Comte, L. Dorbath, D. Legrand, D. Remy, J-C. Ruegg (2006a). Absolute Gravity network in Chile: a contribution to geodynamics, geology and geodesy. Oral presentation, *Congreso Geologico Chileno*, Antofagasta, Chile, Agosto 2006.

Bonvalot, S., J. Hinderer, G. Gabalda, B. Luck, F. Bondoux, D. Comte, L. Dorbath, J-C. Ruegg, D. Remy (2006b). Measuring crustal deformation using Absolute Gravity and GPS: Field experiments, results and perspectives in north and central Chile. Oral presentation, *International Conference 1906 Valparaiso Earthquake Centennial*, Santiago, Chile, 6-8 November 2006.

Campos, J., J.-B. de Chabalier, A. Perez, P. Bernard, S. Bonvalot, M.-P. Bouin, O. Charade, A. Cisternas, E. Clévédé, V. Clouard, R. Dannoot, G. Gabalda, E. Kausel, D. Legrand, A. Lemoine, A. Nercessian, G. Patau, J.C. Ruegg, J.-P. Vilotte. Source parameters and GPS deformation of the Mw 7.8 Tarapaca

intermediate depth earthquake (Northern Chile) of June 13, 2005. *Eos Trans. AGU*, 86(52), Fall Meet. Suppl., Abstract S13B-0209, Dec. 2005.

Chambodut, A., I. Panet, M. Mandea, M. Diament, M. Holschneider, and O. Jamet (2005). Wavelet frames: an alternative to spherical harmonic representation of potential fields, *Geophys. J. Int.*, 163, 875-899.

CNIG (2000). Rapport technique du sous-groupe "gravimétrie", groupe de travail "réseaux gravimétriques et géoïde de référence" du Conseil National de l'Information Géographique.

Debeglia N., Martelet G., Perrin J., Truffert C., Ledru P. and Tourlière B. (2006). Semi-automated structural analysis of high resolution magnetic and gamma-ray spectrometry airborne surveys, *Journal of Applied Geophysics*, 58 (1), 13-28.

de Saint-Jean, B.; Melachroinos, S.; Verdun, J.; Duquenne, H.; Cali, J. & Barriot, J.P. (2005a). Fine analysis of lever arm effects in moving gravimetry, in "Proceedings Dynamic Planet 2005".

de Saint-Jean, B.; Melachroinos, S.; Verdun, J.; Duquenne, H.; Cali, J. & Barriot, J.P. (2005b), Calibration of a 3-accelerometer inertial gravimetry system for moving gravimetry, *Newton's Bulletin*.

de Saint-Jean, B., J. Verdun, H. Duquenne, J.P. Barriot, J. Cali, D. Rouxel (2006). Test missions for mobile gravimetry. Poster presentation, International Gravity Field Service Meeting, Istanbul,