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ABSTRACTS FROM AGS98


Permanent GPS Tracking Network in the South Atlantic

Tilo Schöne1, Hans Werner Schenke1, Mario Pohl1,
Richard Wonnacott2 and Andrés Zakrajsek3

1 Alfred Wegener Institute, Bremerhaven, Germany
2 Chief Directorate Surveys and Mapping, Cape Town, South Africa
3 Instituto Antártico Argentino, Buenos Aires, Argentina

The availability of the Global Positioning System (GPS) with its capability to determine high precision coordinates has led to a change of the role of Geodesy. Using repeated GPS campaigns combined with measurements of permanent tracking stations, Geodesy is able to determine recent plate tectonic movement vectors direct from measurements.

The Antarctic continent as a whole and the Weddell Sea region / Antarctic Peninsula in the South Atlantic ocean is one of the most interesting regions for studying plate tectonics since it plays an important role in the global tectonic evolution during the past 170 Ma. In contrast to this importance is the lack of permanent GPS stations on the southern hemisphere. Due to the harsh climate, the remoteness of this region and the limited and expensive telecommunication opportunities only a small number of ICIS stations exist in this area (e.g. O'Higgins).

During the last austral summer, four new permanent stations were installed. The configuration of this network will improve the general GPS network design in the South Atlantic area. Two stations, Sanae IV (South. Africa, 7lº40'S / 2º51'W) and Belgrano II (Argentina, 77º52'S / 34º38'W') belong to the east Antarctic craton, Gough Island station (South Africa, 40º21'S / 9º53'W') belong to the African plate, Jubany (Argentina, 62º14'S / 58º41'W) to the South Shetland Islands micro plate.

Together with the existing ICTS stations at Santiago (Chile), Hartebeesthoek (South Africa) and O’Higgins (Germany), and the permanent GPS station at Palmer (U.S.A.) all improved monitoring of the plate movement as well as ionospheric investigations will be possible. The network will be expanded in future with an Ashtech Z-XII receiver as permanent tracker at Rothera station (UK, 67º34'S / 68º8'W).

Geodetic GPS receivers of the types TRIMBLE 4000 SSi with the remote download option and Ashtech Z-XII are used for our program. On the stations Sanae IV and Gough Island, a data transfer to a host computer in South Africa is performed every second day, on Belgrano II and Jubany a data transfer is only possible during the austral Summer periods. In the winter, the data are stored on the PC.

The receiver at Jubany was already in operation for one year (in 1997). Currently, the recorded GPS-measurements are processed. A second point was measured during the SC.AR 98 GPS campaign and will be used for the geodetic tie to previously established GPS networks (e.g. SCAR95).

The receiver at Sanae IV was installed in March 1997, but failed after one month of operation.

In December 1997 the receiver was replaced and moved to a more tectonic stable position.

Gough Island station is in operation since December 1997.

For the permanent GPS tracker at Belgrano II a new pillar was erected. A geodetic tie to the marker which was used during the SCSAR95 GPS campaign, vas measured.

The work of the wintering teams at Belgrano II, Jubany, Gough Island and Sanae to maintain the GPS equipment is acknowledged.


Verification of Global Geoid Models by Tide Gauge Measurements

Tilo Schöne and Hans Werner Schenke

Alfred Wegener Institute, Bremerhaven, Germany



With the availability of the Global Positioning System (GPS), a fast easy and weather independent tool for co-ordinate determination exists. Especially in Antarctica, this system is widely used for geoscientific research.

Co-ordinates determined from GPS observations are normally referenced to an ellipsoid like WGS84. The ellipsoidal heights need for local surveys to be converted to orthometric heights. This is typically done by using regional or global geoid models (e.g. EGM96). Due to the lack of gravity anomalies in Antarctica, here, the accuracy of global geoid models is limited. For the earlier OSU91A model, differences of up to 10 m were found.

From the combination of high precision geodetic co-ordinates and tide gauge measurements, a independent verification of the accuracy of geoid models is possible. During the SCAR95 and the SCAR98 GPS campaigns geodetic ties were measured between the GPS reference markers and the tide gauge benchmarks. In addition, new tide gauges were deployed, long term and short term.

For comparison, a local mean sea level was computed from tide gauge observations. However, due to the relatively short recording time, these values do not represent the sea surface height (or the geoid). Due to the importance and uniqueness of tide gauge records Antarctica, also short term sea level records were used for these studies. From one year observation periods an accuracy of a few centimetres for the m.s.l. can be presumed, from shorter time spans the error may rise to a meter.

A good agreement between the m.s.l. and the geoid has been found in the region of the South Shetland Islands. Here, the difference is only a few centimetre. At the Antarctic Peninsula, the difference rjses up to the meter level. Further south a difference of up to 1.7 m were determined.

We explain this large difference by sparse data in the original gravity anomalies of this region used for the determination of global geoid models. For the area of the South Shetland Islands, also gravity anomalies determined from the altimetric mission of the satellite GEOSAT are included. But south of 66ºS, only a few gravity anomalies were included. Therefore, the resulting geoid height errors are larger.

For comparison the differences between the m.s.l. and the earlier geoid model OSU91 were determined. In the southern part of the Antarctic Peninsula the differences are up to 2.5 m. This larger difference indicates the major improvement of the new EGM96 geoid model.

In future, the availability of permanent GPS trackers tied to tide gauge sites can be used to monitor the tide gauge benchmarks. On the basis of long term time series from GPS and tide gauge records also the separation between vertical movement arising from post glacial rebound and sea level changes can be determined.

CAMPBELL ICE TONGUE MONITORING UNDER SEA TIDAL EFFECTS (ROSS SEA - ANTARCTICA)

A.Capra*, S.Gandolfi*, C.Stocchino**

Kinematic GPS measurements have been made on some floating ice sheets and ice tongues in an area approximately of 100 km around Italian base in Antarctica. In particular the Campbell ice tongue has been deeply investigated. Taking into account the methods precision, the vertical movement determined with GPS measurements has been in good accordance with tidal undulation obtained with tide gauge curve prevision and tide gauge measurements,

The effect of ice thickness variation on ice tongue undulation from the ice front to the grounding ice zone was determined. Moreover the effect of the floating mass on oscillation amplitude with the comparison between the results obtained with an antenna on the ice tongue and another one located on the ice pack in correspondence of the first one was made.

The experiments can contribute, unitely to glaciological, geophysical and idraulic studies and researches, to define dynamic models of ice floating glaciers and for the evaluation of Antarctica glaciers mass balance.

A.Capra*, S.Gandolfi*, C.Stocchino**

*DISTART Dept. - Viale Risorgimento 2, Bologna - Italy
Phone: +39-51-6443104
Fax: +39-51-6448073
E-mail: capra@distart.ing.unibo.it

**C.N.R. - Genova- Via De Marini 6,
16149 Genova - Italy
Fax : +39-10-6475600
ITALY


The New Bathymetric Charts of the Southern Weddell Sea
(AWI-BCWS)

Hans Werner Schenke

Alfred Wegner Institute
For Polar and Marine Research
Columbusstraße
D-27568 Bremerhaven
Germany
Phone: +49-471-4831-222
fax: +49-471-4831-149
E-mail: schenke@awi-bremerhaven.de

The southern and eastern Weddell Sea and tile Southern Atlantic comprise the marin operation of the German ice-breaking RV "Polarstern", which began operations in 1983. On the basis of multibeam and single beam data collected on more than 40 "Polarstern"-expeditions in this region and additional echosoundings provided by national hydrographic offices, research institutions and the Digital Bathymetric Data Center (DCDB) of the International Hydrographic Organization (IHO) a series of six sheets of the AWI BCWS in the scale of 1:1.000.000 covering southern and eastern Weddell Sea, from 66ºS to 78ºS and from 68°W to 0ºE/W were recently compiled. The coverage of these sheets follows in general the index of the General Bathymetric Charts of the Oceans (GEBCO) Ocean Plotting Sheets (OPS), using Merator projection with a standard parallel at 65ºS, 70ºS an d 76ºS.

The coast line data and the glaciological information was extracted from the IFAG/AWI digital topographic data base. Due to the multifarious and sparse data in theregion additional geophysical and geographical information was used for a special semi-automatic bathymetric terrain modelling.



Major submarine structures were provided with new geographic names, following the regulations of the GEBCO Subcommittee for Undersea Feature Names (SCUFN). The bathymetric contours and the coast lines were included in the latest GEBCO Digital Atlas 1997 (GDA '97) which is available on CD-ROM.

On the basis of the six sheets 1:1.000.000 a generalized bathymetric chart in the scale of 1:3.000.000 covering the entire southern Weddell Sea was compiled and recently printed. This new set of bathymetric charts provide an invaluable contribution to most other scientific disciplines.


TECTONIC EVOLUTION OF THE SCOTIA ARC WITHIN THE PACIFIC MARGIN OF GONDWANALAND
(Poster)

I.W.D. Dalziel, L.A. Lawver, and L.H. Gahagan

We review the development of the Scotia arc within the framework of the time-space evolution of the Pacific margin of Gondwanaland. The poster consists of a number of panels depicting "windows" in time from prior to the development of the southern ocean basins to the present day. The scenario uses data from the ocean basins to position the major continents, and geologic, paleomagnetic, and geochronologic data to position the crustal fragments of West Antarctica and the New Zealand microcontinent. New aspects include the extensional development of the Falkland/Malvinas plate and rotation of the Ellsworth-Whitmore block and the Lafonian microplate prior to the onset of seafloor spreading, and the formation of the Marie Byrd Land crustal block by amalgamation of "outer" and "inner" provinces.

The development of the Scotia arc region is highlighted within the overall scenario of the development of the Pacific margin, so that present-day tectonics measured by satellite geodesy can be viewed in its full context of relative motion between the African, South American, and Antarctic plates, and of the minor crustal fragments that play a critical role.

I.W.D. Dalziel, L.A. Lawver, and L.H. Gahagan
Institute for Geophysics, University of Texas at Austin
4412 Spicewood Springs Road
Austin, Texas 78759-8500, USA

METEOROLOGICAL ASPECTS DURING THE INITIAL SUMMER SEASON (NOVEMBER-DECEMBER) AT PATRIOT HILLS, ANTARCTICA

Dr. Jorge F. Carrasco

Patriot Hills is located at the end of the Ellsworth Mountains. Along to its northern side, a blue ice field serves as a runway for C-130 aircrafts. Near to the hills the Chilean Air Force and the Chilean Antarctic Institute have deployed a summer camp (80º 08' S, 81º 16' W.) in order to carry out scientific field works.

Three campaigns of one-month long since 1995 have permitted to study some aspects of the basic meteorology of a practically unknown place. Numerical simulations of the antarctic surface wind field indicate that Patriot Hills and surrounding areas are affected by a katabatic wind regime that descends from the antarctic plateau into the Ronne-Filchner Ice Shelves.

Local wind observations at Patriot Hills Camp confirm that the area is often affected by these cold katababic airflows. Precipitation events of light snow are associated with decaying lows that pass to the north of Patriot Hills. General aspects of the observed meteorological conditions at Patriot Hills will be presented at the meeting.

Dr. Jorge F. Carrasco
Dirección Meteorológica de Chile
Casilla 717 Santiago, Chile
E-mail: clima@meteochile.cl

THE COMPARISON OF RECENT VOLCANISM IN THE ANTARCTIC PENINSULA REGION WITH THE PRESENT PLATE MOTION - A CONCLUSIONARY APPROACH TO THE DEVELOPMENT OF THE MAGMATIC ARC

Veit, A.1, Miller, H.1 and del Valle, R. A.2

Early Mesozoic to recent subduction-related magmatism is well described from the Antarctic Peninsula region [1]. In Plio-Pleistocene alkaline magmatism replaced the andesites [2]. Obviously, there must have been some changes in the upper mantle conditions beneath the Antarctic Peninsula, which caused to this development.

Between Eocene and Miocene, subduction and arc-related magmatism ceased due to successive collision of several oceanic-ridge segments with the Antarctic Peninsula [3]. The Pliocene subduction west of the South Shetland Islands led to the opening of a marginal basin in the Bransfield Strait, which is not a back-arc basin sensu stricto, because arc-related magmatism ceased by the time Bransfield Strait opened [4]. Low angle ridgetrench, collisions tectonic features and low convergence velocities caused by subduction of hot oceanic lithosphere near spreading ridges characterises the regional tectonic environment [3].

Cenozoic lithosphere extension and related magmatism is reported for the northern part of the Antarctic Peninsula [3]. A north-westward shift in trench location occurred in a direct response to the cessation of oceanic ridge spreading at the nearby Drake Passage [4]. The segmentation of the Antarctic Peninsula through transform faults, together with strike-slip faults fonned several crustal blocks which were probably rotated. At the inter-section of such a strike slip fault set with a set of transform faults, the James Ross Island Volcanic Group alkali-basalts, mugearites and hawaiites erupted in a pull apart basin like tectonic environment [5].

The Cenozoic volcanism, in the Antarctic Peninsula region, is divided into two main volcanic provinces: A) the Bransfield Strait volcanics on the Pacific-side and B) the James Ross Island Volcanic Group (JRIVG), including the Seal Nunataks volcanics at the Weddell-Sea coast. The back-arc basalts of the JRIVG are quite similar in their chemical composition to younger back-arc basin basalts of the South Shetland Islands. A migration of the South Shetland magmatic arc due to the development of the Bransfield Strait basin reduced the volcanic activity on the Weddell Sea side of the Antarctic Peninsula.

The eruption centres of the JRIVG at the Seal Nunataks are tectonically controlled by intersection of transformfaults and strike slip faults [5]. Outcrops of young volcanic rocks on Livingston Island are well preserved and located directly on the magmatic arc [6]. The geological and geochemical comparison of both regions will provide more information on the development and transition of the Antarctic@en-insula and the present South Shetlands magmatic arc. The upper mantle conditions under the South Shetlands and the Bransfield Strait are still the main target of several geoscientific studies [7]. However, most of the studies on back-arc basins concentrate on oceanic environments [4], but information on the development of ensialic back-arc basins is still incomplete.

The geological and geochemical information will improve our knowledge on the South Shetlands magmatic arc and will allow to elucidate plate motion directions. Measurement of present plate motions as done during the GAP 98 campaign with a geodetic GPS system, coupled with geocheniical data may yield a new insight on the geology of the Antarctic Peninsula.

Ref.: [1] Saunders, A. D., Tamey, J. & Weaver, S. D., Earth and Planetary Sience Letters, 46, 344-360, (1980);

[2] Smellie, J. L., In: LeMasurier, W. E. & Thomson, J. T. (1990), A.G.U., Antarct. Res. Ser. 48, 303-353, (1990);

[3] Garrett, S. W. & Storey, B. C., In: Coward, M. P., Dewey, J. F. & Hancock, P. L. (eds.), Geological Society Special Publication No. 28, 419-431, (1987);

[4] Saunders, A. D. & Tamey, J., In: Floyd, P. A., 1991, Oceanic Basalts, 219-263, Blackie and Son Ltd. (1991);

[5] Veit, A., Miller, H. & del Valle, R. A., Ber. Deutsche Mineralog. Ges., Beih. Eur. J. Mineral. 9, No. 1, 370, (1997);

[6] Smellie, J. L., Pallas, R., Sabat, F. & Zheng, X., Journal of South American Earth Sciences, 9, 314, 265-272, (1996);

[7] Hole, M. J. & Saunders, A. D., Mineralogical Magazine, 60, 173-189. (1996).

This work is funded by the BMBF 03 PL 022 D project.

VEIT, A.1, MILLER, H.1 and DEL VALLE, R. A.2

1 Institut f. Allg. u. Angew. Geologie
Universitdt Miinchen
Luisenstr. 37
80333 Miinchen, Germany
andreas.veit@iaag.geo.uni-miinchen.de

2 Department of Geology and Geography
Instituto Antártico Argentino
Cerrito 1248
1010 Buenos Aires, Argentina.


GEODETIC GPS IN THE SOUTH ATLANTIC AND ANTARCTICA

KEVIN DIXON

Since 1991, HMS Endurance has been using the Global Positioning System to provide relative control for remotely sensed imagery and shore-based navigation aids within the South Atlantic and Antarctica. Absolute position came from Transit satellite derived coordinates.

The availability of data from the International GPS Service for Geodynamics, recent improvements in commercial GPS hardware and software have enabled absolute control to be established with respect to the International Terrestrial Reference Frame to the order of a few centimetres.

Modifications to the field survey procedures have allowed the GPS data collected by HMS Endurance to contribute to a better understanding of the geoid and tectonic processes within the Scotia Arc region.

This paper presents the GPS observed network compiled to date as well as possible future developments.

Kevin Dixon
HPI, The United Kingdom Hydrographic Office
Admiralty Way
Tauton, Somerset, TA1 2DN
United Kingdom

Exploitation of satellite radar data for investigating Antarctic ice features

Uwe Müller, Jörn Sievers, Henning Walter

Bundesamt für Kartographie und Geodäsie
Federal Agency for Cartography and Geodesy
(formerly Institut für Angewandte Geodäsie / IFAG)
Frankfurt am Main

The question of the ice mass balance in Antarctica nowadays constitutes a central issue for investigations on the effects of man-made influences on the global climate. The Antarctic ice shelves are in this context assigned a key role. On the one hand the global ocean circulation processes are driven by the formation of cold bottom water beneath the ice shelves, whereas on the other hand a variation of the ice masses feeding the ice shelves corresponds directly with sea level changes.

For the investigation area "Ekströmisen", located in the western part of Neuschwabenland, the velocity field of the ice flowing off the land and of the floating ice shelf were calculated by means of interferometric evaluation methods for ERS-1/2 SAR data. For determining the ice mass passing the groundling line of an ice shelf, which is the decisive glaciological parameter for the ice mass balance, aircraft and satellite remote sensing data as well as in-situ measurements are referred to for calculating the necessary digital elevation models. This data was also needed in order to ensure precise localization of the grounding line between the inland ice sheet and the floating ice shelf.

The investigation is a methodological contribution to the optimal combination and synergetical use of multisensoral remote sensing data and ground truth measurements for dynamic glaciological issues. It was a joint research project of the BKG and the Forschungsstelle für physikalische Glaziologie (FPG, Research Centre for Physical Glaciology) of the University of Münster, Germany.


German activities in the frame of the SCAR GPS Campaigns and geodetic indications on the geokinematics of the Antarctic Peninsula Region

R. Dietrich1, R. Dach1, J. Perlt1, H.-W. Schenke2, T. Schöne2, M. Pohl2, G. Soltau3, G. Engelhardt3, H.-W. Mikolaiski3, G.Seeber4, F. Menge4, W. Niemeier5, H. Salbach5, K. Lindner6, H.-J. Kutterer6, M. Mayer6, H. Miller7, A. Veit7

1 Technische Universität
Dresden, lnstitut für Planetare Geodäsie
D-01062 Dresden,
E-mail: dietrich@ipg.geo.tu-dresden.de

2 Alfred-Wegener-institut für Polar- und Meeresforschung
Bremerhaven Columbusstraße,
D-27568 Bremerhaven

3 Bundesamt für Kartographie und Geodäsie,
Außonstelle Leipzig Karl-Rothe-Straße 10,
D-04105 Leipzig

4 Universität Hannover,
Institut für Erdmessung Schneiderberg 50,
D-30167 Hannover

5 Technische Universität Braunschweig,
lnstitut für Geodäsie und
Photogrammetrie Gaußstraße 22,
D-38106 Braunschweig

6 Universität Karlsruhe,
Geodätisches lnstitut Englerstraße 7,
D-76128 Karlsruhe

7 Universität München,
Institut für Allgemeine und Angewandte Geologie
Luisenstraße 37,
D-80333 München

In the frame of the SCAR GPS Campaigns Germany contributed with two larger expeditions in 1995 and in 1998. In 1996 and 1997 several minor observation activities took place.

The obtained observations were analysed with different software packages (Gamit/globko, BERNESE, GIPSY, GEONAP). The station coordinates are referred to ITRF using IGS stations.

First preliminary comparisons of the results of repeated baseline determinations indicate significant kinematic motions in the region of the Antarctic Peninsula.


COMPLEX SUBGLACIAL TOPOGRAPHY REVEALED UNDER THE ANTARCTIC ICE SHEET AT PATRIOT HILLS

Andrés Rivera1, Gino Casassa2, Rubén Carvallo3, Heiner Lange4

The first detailed ice thickness measurements at Horseshoe Valley, Patriot Hills (80ºS/81ºW) have been obtained by means of radio-echo soundings, carried out as part of the project "Glaciologic studies at Patriot Hills, Antarctica", sponsored by the Chilean Antarctic Institute, during campaigns in 1996 and 1997, which have revealed important subglacial relief, with numerous subglacial valleys and peaks.

A ground-based digital impulse radar system was used, which allowed to obtain profiles of subglacial topography. The following transmitters were used: a "Bristol" transmitter developed by the University of Bristol, UK, with a maximum output voltage of 670 Vpp an "OSU" transmitter made at The Ohio State University, USA, with a maximum output voltage of 1600 Vpp and a "Narod" model developed by the University of British Columbia, Canada, with a maximum output voltage of 1100 Vpp.

The antennas consisted of resistively-loaded dipoles, selecting after several experiments an antenna length of 20 m, which results in a central frequency of 2.5 MHz. The best results were obtained using the OSU transmitter, with a maximum penetration of 1300 m of ice. The receiver consisted of a digital Tektronics Tekscope oscilloscope connected to the receiving antennas, transferring the data through a serial port to a portable PC, where they were stored in the hard disk.

The complete system was mounted on fiberglass sledges, with a separation of 60 m between receiver and transmitter. The mean ground speed was 20 km/h, with a time interval of 2 s between traces, which results in an average horizontal separation of 11 m between measurements.

In order to obtain a geographic position for each thickness measurements, a GPS receiver was mounted on the snowmobile. In 1996 a geodetic-quality Topcon Turbo SII GPS was used, and in 1997 a topograhic-quality Trimble Geoexplorer 11, capturing data at a 5 s interval. By means of a differential correction with GPS data obtained simultaneously at base camp, the horizontal precision attained was 1 m in 1996 and 5 m in 1997.

The radar profiles can be analysed in two formats: A-diagrams and R-diagrams. The A diagram, where A denotes amplitude, allows to analyse each trace separately, each composed of 500 points, in a standard graph where the horizontal axis represents the return time and the vertical axis the signal amplitude.

The R-diagram (raster) allows to display the total trace sequence as an image file, each trace corresponding to a column, assigning a colour for each amplitude range. In the vertical axis, the R-diagrams show the horizontal travel distance on the ground.

A total of 118 radar profiles were measured in 1996 and 1997, all located within a distance of 32 km from base ramp. Considering a maximum penetration of 1300 m of ice, and a mean surface elevation of 800 masl, this indicates that the bed is located at places well below sea level.

The subglacial morphology shows many prominent features, such as deep troughs and steep subglacial peaks.

A series of internal layers could be detected as well, which could be followed for several km, usually subparallel to the surface, but with a strong vertical inflection towards the mountains, resulting in some cases in a moraine band or dirt band at the blue ice surface.

1. Departamento de Geografía
Facultad de Arquitectura y Urbanismo
Universidad de Chile
Marcoleta 250
Santiago, CHILE

2. Instituto de la Patagonia
Universidad de Magallanes,
Casilla 113-D,
Punta Arenas, CHILE

3. Departamento de Electricidad
Facultad de lngeniería
Universidad de Magallanes,BR> Casilla 113-D,
Punta Arenas, CHILE

4. Terrasat S.A.
E-mail : heiner@iname.com
Santiago, CHILE


GEODETIC FIELDWORK AT TERRA NOVA BAY ITALIAN BASE (VICTORIA LAND - ANTARCTICA)

A.Capra, S.Gandolfi, F.Mancini, L.Vittuari

Since 1989 a geodetic GPS network has been monumented and surveyed in order to supply a reference system for several studies: crustal deformations in the Mount Melbourne volcano area, global geodynamics, glacier movement monitoring, mapping, etc.

Four surveys of the network for crustal deformation control of Mount Melbourne have been performed in 90-91, 93-94, 95-96 and 97-98. A project of research and study of volcano area started in 95-96 in conjunction with geophysics, based on the integration of geodetic data, tiltmeter and seismological observations

Here are presented a preliminary results of forth GPS network surveying that was carried out during the 1997-98 Italian expedition.

As a contribute to the study of antarctic and global geodynamics, the 0100 station, coordinates emanation point of Italian Geodetic network, has been included in SCAR GPS Epoch campaigns 96 and 98 and it became a permanent GPS station in January 1998.

Now the data acquired from the station are stored at TNB base and the GPS receiver set up and storage is remotely controlled from Italy. The installation of permanent GPS station and the first data acquisition are here presented.

A dedicated satellite link for data downloading in network will be ready in 1998-99 or in 1999-2000, by those time the station will be included in IGS permanent GPS tracking stations.

In the same the data from tide gauge installed at TNB could be included in GLOSS network. The pressure tide gauge is acquiring discontinuously since 1995 and it has been connected to GPS geodetic network.

A.Capra, S.Gandolfi, F.Mancini, L.Vittuari
DISTART Dept.
Viale Risorgimento 2
Bologna - Italy
Phone: +39-51-6443104
Fax: +39-51-6448073
e-mail : capra@distart.ing.unibo.it
ITALY

Observation of surface topography and ice-flow near Patriot Hills, Antarctica

Heiner Lange
Terrasat S.A.
heiner@iname.com
Santiago, Chile

Gino Casassa
Instituto de la Patagonia
Universidad de Magallanes
Casilla 113-D
Punta Arenas, Chile

Andrés Rivera
Departamento de Geografia
Facultad de Arquitectura y Urbanismo
Universidad de Chile
Marcoleta 250
Santiago, Chile

As part of the project "Glaciological studies at Patriot Hills, Antarctica", funded by the Chilean Antarctic Institute (INACH), two field campaigns were conducted in 1996 and 1997, using GPS-technology for measuring ice-flow and surface topography near Patriot Hills (80º18'S, 81º22'W) and on a traverse across Horseshoe Valley, which contributes to feed Hercules Inlet, in the vicinity of the grounding line of Ronne Ice Shelf.

In Nov./Dec. 1996 over 150 stakes were placed on ice and firn which were measured by differential GPS. Two reference points were established on rock at Patriot Hills. Baseline lengths vary from 60 m to about 27 km. During the last field campaign (Nov./Dec. 1997) almost all stakes were re-observed by differential GPS.

Due to the use of different receiver types (Topcon and Leica), observation techniques (static, rapid static, stop and go) and processing software (TurboSurvey, SKI, GeoGenius), the resulting data sets are more heterogeneous than desired. However, careful processing of the GPS data of the stakes yields precisions which are adequate for computing ice flow velocities and strain rates.

Our experience related to the field procedures, data processing and precision obtained are discussed. The results of the two campaigns, representing the ice-flow and surface topography in the project area are presented in form of tables, profiles and maps.

THE SCARP PROJECT, A LINK BETWEEN ACTIVE ANDEAN AND ANTARCTIC TECTONICS

Ian Dalziel (1), Frederick Taylor (1), Michael Bevis (2), and Robert Smalley (3)

The SCARP project focuses on the relationship between the South American and Antarctic plates, and the partitioning of strain across the North and South Scotia Ridge transform faults and the intervening Scotia Plate. It thus links the CAP project that is aimed at definition of active deformation at the leading western edge of the South American plate, and work by the Antarctic geodetic community. CAP and SCARP both employ the Multi-modal Occupation Strategy (MOST) developed in part by CAP.

The MOST strategy has allowed development of a much larger network than originally planned, and will provide continuous infrastructure for GPS projects in the region. The first SCARP field effort in 1996-7 was to install continuous tracker stations in Punta Arenas, Chile, Ushuaia, Argentina and Chilean Base Frei in Antarctica. During the second field season 1997-8, we installed an additional continuous tracker at Puerto Williams, Chile, and began selecting, monumenting and measuring sites for mobil measurements. A total of 16 mobil sites were installed and measured in Argentina (12 in Tierra del Fuego and 3 in Argentinian Patagonia). An additional 3 sites were installed, but have not yet been measured, in Chilean Patagonia. We plan to communicate any results that are available by the date of the symposium.

Ian Dalziel (1), Frederick Taylor (1), Michael Bevis (2), and Robert Smalley (3)
(1) Institute for Geophysics, University of Texas at Austin
(2) University of Hawaii at Manoa
(3) University of Memphis, Tennessee

Tectonic evolution of the Scotia arc within the Pacific Margin of Gondwanaland (Poster)

I.W.D. Dalziel, L.A. Lawver, and L.H. Gahagan

We review the development of the Scotia arc within the framework of the time-space evolution of the Pacific margin of Gondwanaland. The poster consists of a number of panels depicting "windows" in time from prior to the development of the southern ocean basins to the present day. The scenario uses data from the ocean basins to position the major continents, and geologic, paleomagnetic, and geochronologic data to position the crustal fragments of West Antarctica and the New Zealand microcontinent. New aspects include the extensional development of the Falkland/Malvinas plate and rotation of the Ellsworth-Whitmore block and the Lafonian microplate prior to the onset of seafloor spreading, and the formation of the Marie Byrd Land crustal block by amalgamation of "outer" and "inner" provinces.

The development of the Scotia arc region is highlighted within the overall scenario of the development of the Pacific margin, so that present-day tectonics measured by satellite geodesy can be viewed in its full context of relative motion between the African, South American, and Antarctic plates, and of the minor crustal fragments that play a critical role.

I.W.D. Dalziel, L.A. Lawver, and L.H. Gahagan
Institute for Geophysics, University of Texas at Austin
4412 Spicewood Springs Road
Austin, Texas 78759-8500, USA


Mass Balance Studies at Patriot Hills, Antarctica

Gino Casassa
Instituto de la Patagonia
Universidad de Magallanes
Casilla 113-D
Punta Arenas, Chile

Andrés Rivera
Departamento de Geografia
Facultad de Arquitectura y Urbanismo
Universidad de Chile
Marcoleta 250
Santiago, Chile

Heiner Lange
Terrasat S.A.
heiner@iname.com
Santiago, Chile

Mass balance studies have been undertaken at Patriot Hills (80º18'S, 81º22'W) in the period 1995-1997, within the project "Glaciological studies at Patriot Hills, Antarctic", with the sponsorship of the Chilean Antarctic Institute (INACM). The main goal is to determine the state of balance of the Antarctic ice sheet at Patriot Hills, by means of glaciological, geophysical and geodetic measurements.

Patriot Hills is located at the southernmost edge of the Ellsworth Mountains, with a maximum elevation of ca. 1250 m, protruding 400 m above the surrounding ice sheet. A bare ("blue") ice field about 8 km long by 2 km wide exists at the northern flank of the hills, due to local meteorological conditions and ice flow in the vicinity of the mountains. The ice around Patriot Hills drains to Hercules Inlet, located about 50 km northeast, at the grounding line of the Ronne ice shelf.

Four field campaigns have been carried out: a 10-day reconnaissance in January 1995; and subsequent 30-day campaigns in Nov. 1995, Nov.-Dec. 1996 and Nov.-Dec. 1997. The campaigns of 1995 covered an area of 6 km, surveying 28 stakes on firn and ice plus three control points on rock, by means of a Wild T2 theodolite and an electronic distance meter. Also, discrete radar measurements of ice thickness were made in 1995.

In 1996 and 1997 a strain grid composed of about 95 stakes, a length of 30 km and a width of 2 km was established on Horseshoe valley, located between Patriot Hills and Douglas Peaks. The position of all stakes was measured with differential GPS. A profiling radar system was used as well for measuring ice thickness and internal layers in the glacier

Ablation and accumulation rates for the 3-year interval have been computed based on comparing stake heights for each period, by using firn density obtained at snow pits near base camp. Net ablation, with a maximum annual value of 7 cm water eq. has been detected on the blue ice field, while a mean annual net accumulation of 5 cm water eq. was observed on the ice sheet away from the mountains.

No significant difference in ice sheet elevation was observed between January and November of 1995, suggesting that the ice is in near-equilibrium at Patriot Hills.

THE EFFECT OF TEC VARIATION ON GPS MEAUSUREMENTS IN ANTARCTICA

Al Bayari O., Capra A., Mancini F., Vittuari L.

Ionospheric refraction on GPS carrier phase measurements introduces errors on baseline solution value that cannot be completely solved with the dual frequency technique that consider the ionosphere as an undisturbated region (geometric effect) with an associated constant vertical gradient of Total Electron Content (TEC).

Also non-geometric effects play an important role, mainly in equatorial and polar regions where, due to magnetic storms and solar activity, severe ionospheric conditions occur causing small-scale irregularities, like scintillation phenomena, which gives difficulties in ambiguity resolution.

We found this effect particularly relevant in Antarctica regions GPS measurements.

With the aim to model and to reduce part of this effect we have computed and compared different TEC values from several methods (GPS code and phase measurements, baseline length method, zero-baseline method and "Bernese" ionospheric parameters estimator).

The relations between TEC variation and signal noise and cycle slips detection were researched. Then the effects of different computed values on relative position (coordinates of points) or baseline length value were investigated.

Al Bayari O., Capra A., Mancini F., Vittuari L.
DISTART Dept.
Viale Risorgimento 2
Bologna - Italy
Phone: +39-51-6443104
Fax: +39-51-6448073
e-mail : capra@distart.ing.unibo.it
ITALY

Determination of geodetic reference, surface topography and ice dynamics in the region of Schirmacher Oasis/Dronning Maud Land

R. Dietrich, W. Korth, R. Metzig, J. Perlt
Technische Universität Dresden
Institut für Planetare Geodäsie
D-01062 Dresden, Germany
E-mail: dietrich@ipg.geo.tu-dresden.de

To combine classical geodetic observations, GPS observations and data from moving platforms (e. g. remote sensing satellites) a precise common geodetic reference frame is needed.

We discuss the horizontal and vertical datum realization as well as the combined use of different techniques for the determination of surface geometry and ice motion. The application of SAR interferometry is especially treated in this context.


Geodetic Observations at Syowa Station, Antarctica and some results

Katsutada Kaminuma
National Institute of Polar Research (NIPR)
9-10, Kaga-1, Itabashi, Tokyo 173, Japan
E-mail : kaminuma@nipr.ac.jp
fax : +81-3-3962-5741

The Japanese Antarctic Station Syowa (69S, 39E) was established in East Ongul Island, Lutzow-holm Bay, East Antarctica for the International Geophysical Year (IGY) in 1957.

Syowa Station was selected as one of the 36 subset (A) stations of the International Absolute Gravity Base station Network (IAGBN) by IAG. The measurements were made three times using four different absolute gravimeters in 1992, 1993 and 1995.

Since IGY, the following geodetic observations have been carried out in the vicinity of Syowa Station:

  1. Gravity: a) Continuous recording of gravity for detecting earth tides using LaCoste-Romberg gravity meter type D and G. b) Continuous observation by a superconducting gravimeter was started in March 1993;
  2. Oceanic tide : Continuous recording since 1966;
  3. Geomagnetism: a) Base line measurement. b) Continuous recording of long-period and short-period geomagnetic variations, and total intensity;
  4. GPS / DORIS beacon: Tracking continuously;
  5. PRARE Ground Station: The PRARE (Precise Range and Range-rate Equipment) ground station was established in March 1997 and is automatically tracking for European Remote Sensing Satellite 2 (ERS-2).
As Syowa Station is located on a small island (East Ongul Island), the height above sea level of the antenna phase centre (P) point can be levelled accurately, and 10cm accuracy of geoid height will be obtained. Using PRARE tracked radar-altimeter data, it is also plan to obtain accurate surface configuration around Syowa Station.

VLBI measurements were made among Syowa Station, Kashima (358S, 1407E), Japan and Tidbinbilla (35.2S, 149E), Australia in 1990. VLBI measurements of 48hrs are planned four times in a year among Syowa, Australia and Japan in 1998. The first VLBI experiment with Hobart (Australia) and Hartebeesthoek (South Africa) was carried out from 08UT, 9th to 08UT, 11th Feb. 1998 using 11 meters S/X band antenna at Syowa station. The second one was made from 08UT, 11th to 08UT, 13th May 1998. All recorded tapes of the first experiment were reached to NIPR at the end of April, 1998 and correlator processing is undergoing at the National Astronomical Observatory, Mitaka. A route for repeat levelling survey was established in East Ongul Island in 1982. The levelling measurements were repeated in 1996 and 1997.