Topographic and Geodetic Works executed by the Federal Service of Geodesy and Cartography

Alexander Yuskevitch

State Aerogeodetic Enterprise - AEROGEODEZIJA, 6 Bukharestskaja Street
St. Petersburg, 192102, Russia

Map drawing on the Antarctic Continent coincided with its opening by the First Russian Antarctic Expedition under the leadership of Bellinsgauzen and Lazarev when, in 1820, our compatriots came the shelf glacier of the Antarctic coast and for the first time carried out a sea inventory.

1969 was marked by the creation of a two-volume edition of the Atlas of the Antarctic Continent which contains detailed characteristics of the nature of the Continent. The experts of "Roscartographiya" also took part in this work (this Atlas could be named the "Cartographical Encyclopedia of the Antarctic Continent"). The specialists of the State Enterprise "Aerogeodeziya" have taken part in Antarctic expeditions since 1970. The activities were carried out by geodetic land parties from our organisation, comprising 20 Soviet Antarctic Expeditions and 9 Russian Antarctic Expeditions.

These activities can roughly be divided into four stages:

Stage 1 (1970 - 1974)

Stage 2 (1975 - 1984)

Stage 3 (1985 - 1990)

Stage 4 (1991 - to the present).

Stage One - acquaintance with Antarctic conditions, choice of the most effective methods of geodetic activities, checking and use of new technical means in Antarctic conditions. Some special geodetic activities of that period were performed in the eastern part of the Antarctic Continent:

1) Radiogeodetic measurements for definition the length of the space basis about 1400 Kms between stations Novolazarevakaya and Molodezhnaya. The radigeodetic system used was the aircaft radio range-finder (RDS). The whole basis was divided into 3 lines, each of which was measured by a method of internal crossing of the range.The result processing of measurements was carried out with the use of the computer in stationary conditions. The basis length was equal 1377332 m with mistake of measurement ±2 m.

2) The basis measurement between two points of class 1 with the help of the "Quartz" laser range-finder for standardization the aircraft radio range-finder. The basis length was equal 10730,016 m with mistake of measurements -6.9 mm, relative mistake 1:1555000.

3) Linear - angular measurements of a geodetic figure consisting of 7 points and 13 sides (10 triangles). The

calculated mistake of the angle was 1.44, mistake of the side was 5.44 mm. Results of the work are in the Catalogue of coordinates and heights of the points at Molodezhnaya station.

4) Astronomical definitions of the points of classes 1 and 3. The mistakes for class 1 were for latitude - 0".16, for longitude - 0".09. The astronomical definitions of class 3 were used for creation the topographical maps of the scales 1:100000 and 1:200000.

5) The general square of area was about 200,000 km². Map production was carried out by a way of aerotopographical surveying by stereotopographical method. The air photography was made from the plane IL-14 with Russian cameras (focus 100 mm and 50 mm). Synchronously with air photography it was the registration of RDS reading, radio altimeter and pressure altimeter.

Astropoints of class 3 with mistakes of measurements ±2 m were used as a geodetic basis for topographical surveying. The measurement processing was carried out on the computer established permanently at station Molodezhnaya.

Construction of spatial photogrammer nets was carried out on a stereoproector, reduction on a photoreducer, transformation on Seg-V and relief drawing on a stereometer.

In total for the first work period 28 sheets of maps of the scale 1 :100 000 and 52 sheets of the scale 1:200 000 were produced .

Stage Two. Geodetic land activities were carried out mainly in the western part of the Antarctic Continent. This period is characterized by the variety of kinds of geodetic undertakings, which concern:

1. Production of topographical maps of the scales 1:100,000 and 1:200,000. The main aim was development of territory in the interests of science and search of minerals. These activities were a continuation of those begun in eastern Antarctica. Horizontal survey control was carried out using RDS and elevation control through air leveling. 49 sheets of topographical maps of the scale 1:100 000 and 46 sheets of the scale 1:200 000 were published. The whole square of territory measured 146 000 km².

2. Definition the force of gravity on the 9 basic gravimetric points with accuracy of 0.25 mgal.

3. Gravimetric surveying of the scale 1:1000,000 with the help of Russian gravimeters. Surveying was performed with density 1 point per 100 km².

4. Production of the topographical plans of the scale 1:2,000 on areas of the Soviet Antarctic stations: Molodezhnaya, Mirnyi, Novolazarevskaya. Plane table measurement was achieved with contour interval of 1m. The whole square of the surveying measured 12.5km².

Stage Three. Mapping, not only of the physical surface of the Antarctic Continent, but also under the ice, both the underwater part and separate elements of glacial cover. A feature of this stage was the creation of the whole complex of topographical and thematic maps of the scales 1:500,000 and 1:1000,000 based on space photographs and using radar-tracking and seismic sounding. Mapping was done on the territories in the east and west of the Continent.

During this period work on producing topographical plans of the scale 1:2,000 and maps of the scale 1:10,000 on areas of Soviet stations were continued: Novolazarevskaya, Molodezhnaya, Bellinsgausen, Russkaya. Surveying on the scale 1:2,000 was undertaken in an area of 12.3 km^2, and on the scale 1:10,000 in an area of 11.8km². Creation of the complex of the intercommunicated topographical and thematic maps was completed in an area of 400,000 km². For producing topographical maps we used IL-14 and IL-18 airplanes, and MI-8 helicopters .

For determination of the coordinates of the points of sounding, the RDS-2 radio system and SMA-761 satellite dopler equipment was used .

The complex of maps included:

· topographical map of physical surface including glacial surface,

· thematic map of radical relief displaying terrestrial surface without glacial cover.

· thematic map on which horizontals show the thickness of glacial cover.

Stage Four. This stage is characterized by a reduced the volume of land activities, the most important of which are:

1) Dopler observation for artificial satellites of the Earth at first on five Antarctic stations, anb then only on two. The supevision was carring out all the -year-round for construction net of space triangulation and for making more exact the elements of satellite's orbits and also the coodrinates of ground points.

2) Updating of topographical surveying of the scale 1:2,000 on the territory of Russian stations: Bellinsgausen, Novolazarevskaya and Mirny.

3) Selective routs of barometrical leveling.

4) Producing the digital maps with method of digitalization of all creating maps of the scale 1:100,000 and 1:200,000.

In perspective we want to update plans of the scale 1:2,000 for all Antarctic stations and to digitalize all topographical maps of the scale 1:100,000 - 1:1 000,000. We plan also to use GPS-technology for executing the geodetic base instead of astronomical measuring.

"Aerogeodesiya" geodetic activities and maps of the Antarctic Continent with their informative data and accuracy have received high recognition not only in our country, but also among foreign experts.

The received cartographical materials can be effectively used for measuring the physical condition of glacial cover, its thermodynamic processes, for studying the questions about environment, climate, water resources, perspectives in development of the oil and gas shelf areas, construction of the Antarctic stations, field bases, air stations, moorings etc.

With technical plans the choice of a technique and technology of producing the topographical maps on the scale of 1:100,000 and 1:200,000, and also complex of topographical and thematic maps on the scale of 1:500,000 and 1:1000,000 is determined.

It should be noted that during the land activities of each stage, wide use of the most perspective and highly effective means and methods ensured high accuracy and efficiency of mapping of the different territories of Antarctica.

In the organizational plan the following questions are solved:

· organization of the field stations (bases) on shelf glaciers;

· preparation of ice take off and landing strips for airplanes;

· organization of the field camps, ground radiometric and barometric stations on continental ice and in mountains;

· guaranteeing the safe production of works in coastal and continental areas, on shelf glaciers and in mountains;

· the most efficient use of the IL-14 and AN-2 planes, MI-8 helicopters, aircraft technics and guarantee of works by a radio communication.

The State Enterprise "Aerogeodesiya" has accumulated enormous experience in the production of a wide spectrum of topographic, geodetic and cartographical activities in the extreme conditions of Antarctic Continent. We recommend that any organization, at home or abroad, requiring the highly accurate, reliable and operative realization of any kind of geodetic and topographical undertaking on the Antarctic Continent contact our organisation.

Atmospheric Influences on Astrogeodetic Measurements in the Polar Regions

Fedir Zablotskyj

Chair of Geodesy and Astronomy, State University "Lviv Polytechnic"
12, S.Bandera Str., 290646, Lviv, Ukraine

Abstract

The paper outlines the author's research both independent and joint into atmospheric influences on the results of angular and electronic distance measurements in polar regions and, in particular, in Antarctica. A short description of the structural peculiarities of the atmospheric boundary layer is given. Special attention was given to thermal stratification and its influences on the results of astrogeodetic measurements. Investigation into astronomic refraction was conducted on the basis of aerological data. An integral of refraction was computed at different zenith angles for several Antarctic and Arctic stations. Refractive anomalies were calculated by means of refraction tables. The results of the theoretical and experimental investigations of the terrestrial vertical refraction in polar regions are given. Analysis of atmospheric influences on the electronic distance measurements were carried out by means of the refraction index calculation for light-and radio waves. The data of aerological soundings and meteorological gradients in the lowest atmospheric layers were used as initial materials. It should be noted that microwave distance measurements in central Antarctica ensure reliable accuracy because of the minimal air humidity. As regards the electronic distance measurements to satellites the existent models do not quite ensure reliable results for laser and microwave distance measurements due to peculiarities of the meteorological parameter distributions in atmospheric lower layers in the polar regions and, in particular, central Antarctica.

1. Introduction

The aim of the study was to determine the extent of atmospheric influence on the results of angular and electronic distance measurements in the polar regions. It should be noted that satisfactory precision of accounting of atmospheric influences is provided on the whole at the angular and electronic distance measurements to objects, located both in and outside the atmosphere, at zenith distances of less than 70°. Achievement of the precise results at large zenith distances, and especially in the near horizontal zone, is possible only in reliable representation of atmospheric stratification and first of all the boundary and lowest layers. It is accounted for by a heterogeneity of atmospheric structure and its dynamics and first of all by peculiarities of an air temperature and humidity distribution with a height.

2. Some peculiarities of the vertical distribution of air temperature and humidity

In the polar regions, according to long-term monthly mean aerological sounding data, it has been established that the vertical distribution of air temperature in the boundary layer is characterized mainly by stable thermal stratification. In Antarctica two zones, distinguished by meteorological peculiarities, should be marked out:

· Antarctic coast zone - meteorological data of Mirnyj station characterizes most of the Antarctic coast situated as effected of the gravity wind;

· Central Antarctica - the most representative is the Vostok station.

The mean capacity of the ground inversion layer amounts 240m over coast and in Central Antarctica - 720m. The ground inversion intensity makes up in average 2.8 and 17.1°C per year accordingly and its recurrence reaches 75 and 98% [2]. The vertical temperature gradient in the lower 100-metres layer of the continent centre reaches the extremal values on the terrestrial globe ~ 40-50°C/100m. Depending on analysis of skewness A_t and excess E_t coefficients of air temperature in the atmospheric boundary layer it follows that the vertical temperature distribution in the central region of Antarctica does not correspond to normal law both in winter and in summer. An inversion creation in the lower 200-metres layer of Antarctic coast is connected with the gravity wind. Above this layer an ordinary decrease of temperature is observed. The ground inversion is destroyed with weakening of the gravity wind in summer, however, the value of the vertical temperature gradient is not large and it approaches an isothermal gradient. A mean capacity in the central Arctic (Pole region) makes up 1.19km in January and 0.64km in July.

As regards vertical distribution of air humidity in Antarctica, a typical feature is a vividly expressed inversion character due to the temperature inversion. The value variation of air humidity at the Antarctic coast in winter is small in a height- from 1.4 mb at the surface to 0.5 mb at a height of 3km and in summer it decreases uniformly from 4 mb to 1.2 mb. On the whole, the vertical distribution of air humidity is in keeping with the air temperature distribution. In winter, the air humidity in Central Antarctica is extraordinarily small owing to the

lowest near surface air temperature and its value makes up 0.08 mb only. It increases to 0.012 mb at a height of 600m and slow decrease of it is observed then. In summer, the air humidity changes from 0.3 mb to 0.4 mb within the altitude range from 0 to 3km and it is similar to humidity values of a wintry period in Arctica.

It should be noted that an intensive ground inversion of temperature prevents, to a great extent, the development of turbulent heat and water exchange in the lower layers of the atmosphere of the polar regions, especially of central Antarctica.

3. Contribution of the lower atmospheric layers in the formation of refractive quantities

Proceeding from stratification peculiarities of the atmospheric lower layers in the polar regions the investigations for the establishment of representation of these layers with the object of reliable determination of atmospheric corrections were realized by carrying out the angular and electronic distance measurements at the low lines of large lengths. Atmospheric models constructed on the basis of the long-term monthly mean aerological sounding data on a number of Arctic and Antarctic stations were used as initial materials [13]. The computation programs of astronomic refraction angle r and atmospheric correction DS into laser distance measurements to satellites by these models had been worked out. A spherical model of atmosphere was founded in the both cases.

The calculation results are presented for two Antarctic stations only - Mirnyj and Vostok. Such a selection was conditioned because the data obtained by the models of Mirnyj station are representative for corresponding models of the most of coastal Antarctic and Arctic stations which we had analysed. The Vostok station data describe in general the Antarctic Plateau (Central Antarctica). For the Mirnyj station the contribution of the lowest and boundary layers of atmosphere in the formation of the quantities r and DS is preliminary like in the both models and it gives at zenith distance 75° - 5 and 17% accordingly; it is somewhat greater in winter because in the lowest layer 0.04-0.2km the temperature inversion by intensity 1.2° is existed there

and an isothermal stratification takes place practically in summer. This contribution increases in geometric progression at the large zenith distances and exceeds 20% and 40% accordingly at Z=89.8°.

At Vostok station there is a more contrasting picture (Table 1). The contribution of the boundary layer in the summer model is inkeeping with the winter model contribution of Mirnyj station and it is slightly greater owing to the more intensive inversion.

The quantities of astronomic refraction and the contribution of the lowest and boundary layers considerably increase in winter. Thus, an atmospheric influence on the quantity r increases in ~1.5km layer in comparison with the summer period and the refraction component amounts to 70% in the near horizontal zone. The lowest 300-metres layer causes the most considerable contribution. The latter makes up 14% at zenith distance 75 and exceeds 50% at Z=89.8 which is provoked by superintensive inversion in this layer. As to DS corrections, an influence of ground inversion shows to a lesser extent here.

4. Analysis of temperature inversion influence on the astronomic refraction angles

In order to estimate an influence of the temperature inversion on the quantity of common astronomic refraction in the lowest atmospheric layers we made up three atmospheric models for the Vostok station [12]. Model 1 presents aerological sounding data at the isobaric surfaces and model 2 was completed by meteorological parameters at standard altitudes in the 4-6km layer. Model 3 was completed by one-time sounding data every 100m in the lower semi-kilometer layer.

It should be noted that the difference of refraction angles makes up only 0.02" at Z=75° therefore the representation of atmospheric stratification at Z<75° may be very generalized. However, the difference of refraction angles increases essentially at the large zenith distances and it amounts to 40' in the horizon. If we take into consideration that the near-ground layer is presented in model 3 only every 100m then, beyond all manner of doubt, by a more detailed and objective reflection of this layer a still more refraction angles could be obtained and first of all, the lover near-surface layer several tens metres

5. Some results from the terrestrial vertical refraction studies

On the basis of hourly mean monthly values of global solar radiation, albedo, pressure and air humidity at the three Antarctic and two Arctic stations the coefficients of vertical refraction were determined [16]. Their pronounced dependence on the latitude is observed in daily variations; in summer the coefficient changes from 0.1 to 0.5 at Mirnyj station and its levelling takes place at Vostok. In annual variation the refraction coefficient increases approximately three to four times from summer to winter in all polar regions. Its dependence on earth albedo has been ascertained. Thus, at Mirnyj station located on the surface covered by snow and ice (albedo ~ 80%) the refraction coefficient is almost twice that at the Novolazarewskaya station where the albedo does not exceed 30%. The "periods of quiet images" and corresponding them the coefficients of normal refraction have been established. Therefore, at the Novolazarewskaya station these periods begin at Sun heights averaging nearly 7°, moreover they shift in time from the near midnight intervals in summer to the near midday ones in winter. The values of normal coefficients exceed essentially the common ones. The evening "periods of quiet images" comparatively with the morning ones are shifted in time to sunset, moreover the coefficients values are less approximately by 10% in the morning period. At the high-latitude stations these periods come at Sun heights of ~10-15°. A refraction coefficient asymmetry is observed here less in both time and quantity.

Turbulence characteristics and vertical refraction coefficients for January have been determined by hourly observations of temperature and wind speed at seven levels of the lower 30-metres atmospheric layer at the Mizucho station [5]. A determination technique of vertical profile of the temperature by measured wind profile has been approved as well. The difference between calculated and measured air temperatures does not exceed 0.2° for the period from 5 to 20 o'clock. During the night period with increase of temperature inversion these differences amount to 1° at the upper bound of the 30-metres layer[15].

Numerous experimental investigations of vertical refraction influences on the accuracy of trigonometric levelling were carried out during the summer periods of 1978-1981 on the four parts of the Barents and Kara coasts of northern and southern islands of Nowaya Zemlya. Both the single and reciprocal simultaneous measurements of zenith angles were fulfilled on to geodetic points outlying in average at a distance 10-12km. By the results of meteorological observations the vertical gradients of temperature g_t and air humidity g_e were determined and the mean integral gradients ^--g_t and ^--g_e were calculated. The transition periods from normal air stratification to inversion one and conversely were investigated. A correlation degree between meteorological and mean integral gradients was analysed[14].

thick has to be presented in the most detail. Such a representation is necessary not only for the construction "refraction" models on the Antarctic Plateau but also for other regions of Antarctica and Arctica. It follows even from the analysis of the temperature gradients measured in the lower 30-metres layer at the Mizucho station located on the Antarctic Slope [5].

Proceeding from the given peculiarities of atmospheric stratification in Antarctica the seasonal (for January and July) and mean annual models were worked out on the basis of the aerological sounding data at the Mirnyj and Vostok stations [8].

With the aim of using suitability of existent tables for the determination of astronomic refraction in the polar regions the Pulkovo refraction tables of the 4^th edition and the Kazan observatory ones were analysed and after 1985 the Pulkovo refraction tables of the 5^th edition were examined [4,10, 12 etc.]. The mean monthly data of aerological soundings on the five Arctic and ten Antarctic stations as well as one-time sounding data of different polar stations were used for this purpose. Astronomic refraction was calculated both by aerological sounding data and by refraction tables. On the basis of the analysis of refraction anomalies calculated as differences between refraction angles obtained from the aerological sounding data and by refraction tables it is necessary to mark out the following (by the Pulkovo refraction tables of the 5^th edition):

· in summer the refraction anomalies do not exceed 0.3" on absolute value at Z 70° in the Arctic and 0.2-0.3" in Antarctica; during the winter they amount to 0.2-0.3" on the Antarctic coast and 0.3-0.5" in Central Antarctica as well as 0.4" in Arctica. Thus, in summer the refraction tables ensure determination of astronomic refraction to within 0.3" practically on all Antarctica's territory but in winter the account accuracy goes down two times;

· at zenith distances less than 80° the refraction tables allow consideration of the refraction angle to within 1";

· neither refraction tables do not ensure the precise determination of astronomic refraction at Z>80° in polar regions, especialy in Antarctica.

A large number of investigations of astronomic refraction anomalies at the large zenith distances by instrumental method was carried out by the observations of the Sun and bright stars on the southern shore of White Sea, and on Nowaya Zemlya and in other regions [7,9,11]. A principally new technique of astronomic refraction determination in the near horizontal zone was worked out from observations of the upper and lower solar limbs on the same almucantar which allowed the most reliable quantities of astronomic refraction angles (anomalies) in the most difficult zone , from an observations standpoint, to be obtained[21].

On the basis of comparison of measured and calculated coefficients of vertical refraction for the mentioned periods it was established that the change rate of isothermal layer with a height is almost half as much as in the middle latitudes and it makes up about 35 metres an hour [19]. It should be noted that in summer over the mountain stone plots and particularly over a stony tundra considerable turbulence develops in the lower ground air layers in the hours close to midday. Under such conditions the technique of accounting of vertical refraction by the fluctuation of images of aperture sights was approved, so doubling the accuracy of trigonometric levelling [3].

The realized investigations allowed us:

· to elaborate a calculation technique of refraction coefficients for a certain period and a concrete region;

· to establish the most suitable periods of geodetic measurements from the standpoint of refraction influence in polar regions;

· to work out new methods of determination and accounting of the vertical refraction [1,20].

6. Distribution of the electromagnetic wave refraction index

The principal error of distance measurements by microwave and laser rangefinders and radionavigation systems is caused by the propagation inconstancy of refraction air-index both in space and in time. The nature of refraction index propagation in polar regions has some peculiar properties in comparison with the middle and low latitudes. Refraction index modules for light N_S waves and ultra-short N_R ones were calculated for standard heights levels up to 3km from the earth surface for each month of the 11 polar stations [6]. The ratio N_R< N_S predominates in polar regions, and in particular in Antarctica, in contrast to another regions where the refraction index of ultra-short waves is much greater. The most stable difference DN= N_R - N_S is observed in Central Antarctica and its annual amplitude (A) does not exceed 3 units of N. At the Antarctic coast zone the

value DN is positive in January and February only and A£12. In Arctic regions the ratio N_R> N_S is being observed from June till September and annual amplitude of DN amounts to 30 units of N. A daily variation of refraction index both light- and ultra-short waves is not large, a maximal amplitude falls in the autumn period in Arctica and in the spring period in Antarctica (according to data fromMirnyj station) and it does not exceed 6-8 units of N.

On the basis of the distribution analysis of quantities N_R and N_S it follows that the change of refraction index is in general close to the linear law in summer. In winter a deflection of linear regularity is insignificant in coastal Antarctica and the Arctic but it is highly essential in central Antarctica and amounts to 30 units of N in the lower semi-kilometer air layer. The quick decrease of refraction index in height caused by superintensive temperature inversion (it amounts to 45 units of N in the lower 300-metres atmospheric layer in July - August at the Vostok station) gives an error into the results of laser distance measurements to satellites from 6cm at the zenith point to18cm at Z=75° in comparison with the Marini-Murray model [22].

7. The degree of influence of air humidity on microwave distance measurements

For the establishment of the influence degree of air humidity both by the ground microwave distance measurements and GPS observations* in polar regions the following investigations were realized [17,18]. After the meteorological parameters of separate stations the ensemble-averaged values of atmospheric pressure P, temperature t and water vapour pressure e were calculated for the three Antarctica's regions (Table 2):

· Central Antarctica (according to data from Vostok station, the altitude above sea-level is equal 3488 m);

· Antarctic coast zone (11 stations, the average altitude makes up 28 m);

· Antarctic Peninsula (24 stations, the average altitude amounts 12 m);

* Taking into consideration that the network of GPS permanent stations is now in Antarctica and yearly GPS campaigns acquire more and more prevalence (Ukrainian station "Academician Vernadskyj" participated in 1998), two VLBI stations are working permanently and SLR stations are getting ready for permanent observations and it becomes evident that problem of detail investigation of the atmospheric influence peculiarities on the results of such observations is exceptionally topical in this region.

It should be noted that water vapour pressure in Antarctica is much lower than in other continents. At the same time to measure it directly is very complicated and sometimes impossible. Using mean-statistical humidity characteristics for the determination of refraction index at microwave radio distance measurements may cause a refraction index error from 210^-6 in Central Antarctica to 2510^-6 at the Antarctic Peninsula and may increase the relative error of line measurement from 1:500 000 to 1:40 000.

Proceeding from the assumption that is necessary to determine air humidity accurately which should ensure the calculation accuracy of refractive index to within 210^-6, it is possible to achieve by means of the measured air temperature with the help of the functional dependence:

where, a = 2.789, b = 0.192, c= 0.0037 - coefficients obtained from twice measurements daily of water vapour fraction of total mass during three summer and three wintry months at Mirnyj station. Calculation error of humidity d_e is a difference between initial (mean-statistical) humidity quantity and the calculated one by the above formula. For the establishment of the error influence d_e on the determination precision of refractive index the differential dependence ðN/ðe (in N-units) was obtained for each region for January and July. The error d_N of the calculated refractive index is determined by product (ðN/ðe)d_e .

The results obtained show that indirect determination of humidity for radiogeodetic measurements ensure the calculation accuracy of refractive index not less than

210^-6 on the whole Antarctic territory except for the Antarctic Peninsula. In the Arctic the error d_e makes up the following depending on year season and region:

· in the western sector of the Russian Arctic the error d_e    makes up 0.4-0.5 mb in summer and 0.3 mb in winter;

· in the central Arctic these values makes up 0.3 and 0.2 mb.

One of the main errors owing to incorrect determination of refractive index n in the line of radio wave propagation consists of replacement integral mean temperature and humidity values by the average ones and t=(t₁+t₂ /)2 and e=(e₁+e₂ /)2 from measurements on the last points of the line. The errors due to inequality t and, e and were analysed by means of meteorological observation data at the Mizucho station. The high-altitude profiles of temperature and humidity were determined for an arbitrary chosen line with ray height to 30m. The temperature profile was approximated by logarithmic dependence and humidity was calculated after the above formula. The relative errors DS/S obtained by the average monthly (January) values of measured temperatures for the different periods of day and night are given in Table 3.

Thus, for the mentioned conditions the difference t - causes the determination error of refractive index 210^-6 at night time and it must be taken into account for precise measurements. The difference e - may be disregarded. The technique calculated from the refraction index determination, on the basis of the investigations carried out, results in an increase in the accuracy of geodetic measurements in the polar regions.

References

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[18] Zablotskyj F, Savchuk S. Determination of the air humidity at the radio-geodetic measurements in Antarctica. Proceed. of the "All- Union Conference on the lowest spreading of radio waves and on the electromagnetic compatibility". Abstracts of papers, Ulan - Ude, 1990 (Russ.)

[19] Zablotskyj F., Savchuk S. Investigation of the isotermal layer change velocity by the geodetic method. Proceed. of the "5th Meeting on the atmospheric optics". Abstracts of papers, Tomsk, 1991 (Russ.)

[20] Zablotskyj F., Savchuk S. Method of the determination of refraction coefficient for the trigonometric levelling. Author's Certificate N1719886, USSR. Decl. 12.12.1998, N4648696, publ. 15.03.1992 in Inform. Bull., N10 (Russ.)

[21] Zablotskyj F., Savchuk S., Rusyn M. Astronomic refraction determination in the near horizontal zone. Geodezija, Kartografija i Aerofotos'emka, Lvov, 1992, N53 (Russ.)

[22] Zablotskyj F, Savchuk S, Paljanytsja B. On the atmospheric influences at the laser long-range finding. Proceed. of the 1st International Symposium of Laser Technique in Geodesy and Mine Suveying, Ljubljana, Slovenija, 1995

Argentine Participation in Antarctic Surveying Activities from 1901 to 1999: an overview A. Zakrajsek

Instituto Antártico Argentino, Cerrito 1248, 1010 Buenos Aires, Argenina

First Experiences

José María Sobral was probably the first Argentine to be involved in Antarctic surveying. He took part in the 1901-1903 Swedish Antarctic Expedition (led by Dr. Otto Nordenskjöld), and performed several astronomical-fix determinations as well as other surveying activities in the Antarctic field during the campaign.

Astronomical Observations
From 1904 onwards, astronomical techniques were widely used both for static positioning at relevant sites as well as for expedite navigation purposes by Argentine Antarctic field parties.

Classical Surveying Techniques

Triangulation and leveling works were implemented to support the Instituto Antártico Argentino (IAA ) geo-sciences, mainly for glaciological field activities. For several decades the works were typically relying on 1" theodolites, microwave EDMs and geometric/spirit levels. Electronic tacheometers and a laser distance meter were also implemented at a later stage.

Case study: Surface Dynamics of the Northern Larsen Ice Shelf, between the Seal Nunataks and the Jason Peninsula.

US Transit/Doppler Navy Navigation Satellite System(NNSS)

In 1975/76 a joint United States Geological Survey/British Antarctic Survey (USGS/BAS ) field party performed geodetic satellite/doppler-based observations at several sites, mainly for Antarctic satellite imagery geocoding purposes. Some of the sites were directly associated with Argentine Antarctic activities (e.g. Matienzo and Marambio bases).

IAA started using the Transit-doppler satellite-system technique in 1982, mostly in a "stand-alone" positioning approach. Translocation techniques were also implemented, depending upon third party's instrument availability. Astronomical observations were still used for azimuth determinations.

NAVSTAR - GPS (NAVigation System with Time And Ranging - Global Positioning System):

IAA's involvement with the use of GPS in Antarctica in began in 1985, at the beginning of the US, Argentina, Chile (USAC ) aero-geophysical Antarctic surveying project led

by Dr. John L. LaBrecque (Lamont Doherty Geological Observatory). During USAC the IAA made a contribution regarding the decoding of the raw hexadecimal GPS almanac and ephemeris broadcast information in order to optimize the flights due to the limited GPS coverage at that early stage).

At present, several IAA research groups perform their GPS-surveys, mainly based on L1-receivers, typically for geo-referencing purposes.

Precise GPS

During the 1980's, at least two German scientific field parties worked in the vicinity of the Argentine Station Belgrano II. They established a GPS reference station at the base, significantly improving the accuracy of the station coordinates.

In 1993 USGS surveyors performed GPS surveying at Marambio (Seymour) Island, in order to geo-reference Argentine aerial photographs of the Island. A map at 1:10000 scale was produced jointly with Ohio State University.

It was not until the SCAR Epoch95 GPS Campaign (GAP95), that IAA became directly involved with high precision GPS-surveying methods. GAP 95 and its follow-on repeat campaigns (1996 and 1998) represented a dramatic change for Argentine geodesy in several aspects:

· A new site monumentation strategy, aimed at long-term stability, was implemented for the first time at Argentine Antarctic sites.

· Position errors were reduced from "various meters" to "centimeter" levels at 5 locations.

The Argentine geodetic network, undergoing a re-definition process, as well as various other South American countries could greatly benefit from GAP/SCAR GPS Epoch results.

GAP'95/96/98 - SCAR Epoch 95/96/98 GPS Campaigns:

The Antarctic stations Belgrano II, Esperanza, Jubany/Dallmann, Marambio and San Martín were surveyed during the major 1995 and 1998 international GPS Campaigns. Esperanza, Jubany/Dallmann and Marambio sites were also occupied during the 1996 repeat-campaign. GPS instruments were provided by German research institutions at all these locations. Argentine observers participated at Esperanza (ESP1) and Marambio (MAR1).

Long-term GPS monitoring

During the austral winter 1996, IAA performed its first long-term GPS monitoring experience at the ESP1 - GAP95 site using a geodetic receiver provided by the Alfred Wegener Institute for Polar and Marine Research, Germany (AWI ).

In February 1997 a continuous GPS station provided by AWI was installed at Jubany/Dallman (Trimble 4000SSi with Trimble Choke Ring antenna).

In February 1998 a continuous GPS station provided by AWI was installed at Belgrano II (Ashtech Z-XII with Ashtech Choke Ring antenna).

In March 1999 a continuous GPS station provided by the University of Memphis, USA was installed at Orcadas (Ashtech Z-XII with Ashtech Choke Ring antenna).

In April 1999, a continuous GPS station provided by AWI was installed at San Martín (Ashtech Z-XII with Ashtech Choke Ring antenna).

Differential Kinematic GPS

In 1987, during the USAC Project, IAA made its first experience in terms of GPS-differential processing (Pseudo-Range only).

More recently, in December 1998 the British Antarctic Survey (BAS) and IAA performed an aero-geophysical survey in the James Ross Island region, based upon precise GPS-navigation. The GPS data set was jointly processed (phase-differential).

Tide Gauges

Argentina performed several Antarctic sea level monitoring activities in the past, specially at Esperanza and Brown stations (mechanical floating devices). At present 3 tide gauges are operating at Esperanza, Jubany/Dallmann and San Martín stations respectively.

In 1993 a sea level continuous monitoring station provided by the National Oceanic and Atmospheric Administration, USA ( NOAA ) was installed at Esperanza.

In 1996 a sea level continuous monitoring station provided by AWI was installed at Jubany/Dallmann.

In 1998 a sea level continuous monitoring station provided by AWI was installed at San Martín.

Gravity observations

A gravity link between Rio Gallegos (Argentina) and Marambio station was performed in 1979 by P. Skvarca (IAA) and others in order to have Argentine Antarctic gravity measurements connected with IGNS71 (3 sequential flights / 2 "G" - LaCoste & Romberg instruments).

Field gravity (relative) surveys were performed at some Argentine stations as well as in specific areas of interest, e.g. on a longitudinal traverse along the Northern Larsen Ice Shelf.

IAA also participated in airborne gravity Antarctic surveys during USAC (1985-89) and, more recently, with BAS on James Ross Island.

In December 1997, an absolute gravity value was determined at Jubany/Dallmann by German geodesists, using an FG-5 instrument.

Seismological observations (for geodetic purposes)

At Jubany/Dallmann as well as in Belgrano II, seismological equipment provided by AWI was installed during GAP98 for long-term monitoring. Jubany/Dallmann was dismantled in April 1999.

Field Tests of the Portable Absolute Gravimeter for Remote Applications

Yevgen Zanimonskiy

Andrzej Sas-Uhrynowski, Institute of Geodesy and Cartography, Warsaw, Poland

Introduction

Today the globe is covered by a non-uniform gravity network. Network density and the accuracy of the gravity measurement attributed to a site may differ by 1-2 orders of magnitude.

The gravity network in certain parts of the world is still poorly developed but this is not always due to the inaccessibility of the area. For example, in less developed countries and countries of the former Soviet Union there are motorways and urban and village infrastructure so that a network may be improved and accuracy increased by the traditional method of connecting sites using relative gravimeters. Poor network development may also be due to the user's conservatism, based on the presence of precise equipment and the checked and formally authorised techniques of measurement and data representation.

However in areas which are difficult to access, such as mountains, deserts, and polar regions, the repeated moving between sites using ground or air transportation can become too technically difficult or too expensive. As a result the international scientific community (J. Manning, 1999) and governmental organisations, interested in an inexpensive and simple way to improve the quality of the networks, could use a specially adapted absolute gravimeter.

Adapting the Absolute Gravimeter for the Field

One problem with adapting the absolute gravimeter to field measurements is its change in status. The existing absolute gravimeters form the group standard, checked at international comparisons in Paris. The field apparatus, offering slightly lower quality, could be considered as a working tool for measurements, used for direct measurements then checked by means of comparison with the standard.

So far the concept of checking or calibration of a ballistic gravimeter, for uniformity of measurements, has not been internationally applied. However, the need to carry out large projects using various devices from widely differing bases has made calibration essential. Certainly, without legislative registration of separate devices, each developer may be tempted to equate his device to the standard. Nevertheless there are unconditional leaders in accuracy, namely the FG-5 gravimeter, which may be used as the standard for calibrating the portable gravimeter.

On the other hand there is a problem of gravitational stability on the sites used for calibration. Variations of unknown origin limit the accuracy of comparison and require preliminary research and regular repetition of measurements.

The requirements of special gravimeters can be formulated as follows:

· Stability of the systematic error at a level of 5-10mGal within 0.5-1 years (gravimeter autonomy "in Large");

· Ability to carry out measurements automatically after installation at unattended remote localities (gravimeter autonomy " in Small");

· Small dimensions and weight;

· Simplicity of service and repair;

· Low cost of the device and complete set of spare parts;

· Invariability with respect to change of temperature and humidity.

Operation and Maintenance of a Gravimeter

Before a long expedition, the gravimeter should be serviced and checked on the control site and the numerical amendments estimated and fixed. The measurements will be carried out according to the schedule:

· The gravimeter is established on the base of the site and a controlled series of measurements made;

· The instrument is switched to automatic data accumulation mode;

· When used outdoors the gravimeter is covered by a cap, protecting the device from atmospheric influences;

· The control data are transferred by radio to the computing centre;

The structurally autonomous absolute gravimeter comprises two parts:

· Primary gauge - ballistic gravimeter

· System of maintenance, power supply, data transmitter and protection .

The system of maintenance is not specific (A. Donnellan et al.,1999) and can be made of available modules. Therefore, production depends only upon engineering effort with financial support. Design of the primary gauge is much more complicated.

History of the Ballistic Gravimeter

The concept of an autonomous absolute gravimeter arose during the design, creation and research on a field portable ballistic gravimeter. Initially a ballistic gravimeter was operated in laboratory conditions. The devices, approximately equal in accuracy, were developed in several countries. Recently the best apparatus of this class, i.e. the JILAg and the FG-5 have been made the basis for the international group standard.

Twenty five years ago the Kharkov Institute of Metrology began work on the production of a ballistic gravimeter. Subsequently several devices for various purposes were designed: complicated instruments, automobile-mounted, terrestrial and shipborne devices, all with two advantages; their ability to operate in adverse conditions of external environment and their simplicity of operation. Unfortunately the accuracy of these gravimeters is insufficient for geodetic purposes.

Despite research by several groups worldwide, even the small-sized gravimeters which exist cannot be considered suitable for the field as they need to be connected to the net power supply and are intended for use indoors. It is clear that the unique device of this class, namely the A10 absolute gravimeter could be the device suitable for field work. T.M. Niebauer (1999) announced the extremely high characteristics of the device. The high data rate achieved with the new launching chamber will allow kinematic absolute gravity measurements for use on marine and airborne platforms (J.M.Brown et.al.1999). However, despite the great potential of the A10, we consider that, for Remote Geodetic Observatories, special gravimeters should be developed.

Data Accumulation and Errors

It is important to mention that the absence of superfluous tidal variations of gravity in unexplored areas cannot be guaranteed. The amplitude of these oscillations with the periods from 3-24 hours may reach a substantial level (in Borowa Gora observatory it was recorded at the level of 4-6mGal). In coastal areas of Antarctica the obvious problem is caused by ocean tidal loading. The constant component of gravity on the site should thus be estimated by means of continuous measurements, at least for 2-3 days.

To accumulate data to a level of precision of 5-10mGal takes about 3-5 hours. The long time required for these measurements encourages the use of a simpler ballistic gravimeter.

External seismic influences are the main sources of random errors but these errors may be substantially reduced by use of the long period damping system. Besides suppressing external influences, the isolation system also suppresses auto-seismic handicaps by means of a ballistic block. With a symmetrical rise-and-fall method of measurement a source of a handicap is the catapult, launching a test-body. With the free-fall method the mechanism accompanying a test-body in fall is a source of vibration.

The efficiency of such systems can be very high, which is evident in case of a superspring in both the JILAg and FG-5 apparatus. However these highly sensitive mechanical devices with an analogue feedback are not adaptable for field conditions.

A natural feature of remote areas is the absence of artificial seismic handicaps. This fact essentially simplifies the task of data accumulation. Our experience, acquired in

the process of research and development of a portable ballistic gravimeter, shows that, during the night and holiday periods, it is possible to accumulate data within 5 hours with a random error at the level of 10mGal. In coastal areas, obviously, the influence of the ocean produces an additional effect that increases the seismic background. However, this influence is random and stationary, so an increase in data accumulation time cannot necessarily be expected.

In our portable rise-and-fall gravimeter no long period isolation system is implemented. For suppression of auto-seismic effects constructive and methodical solutions are applied. Firstly, using titanium for the test-body and carriage of the catapult made it possible to launch a body with acceleration of 15-20 g. The electromagnet of the catapult with its energy-storing capacitor provides fast shot-and-stop of the mechanism ensuring its stability during measurement. Only the decreasing oscillations of the reference lever have a negative seismic effect on the measurement.

The larger the frequency and the faster the attenuation of these fluctuations, the smaller the effect on the measurements. This is achieved by means of a more rigid fastening of the ballistic block to the base. The base should be not too small. If it is made of ferro-concrete its volume is should be larger than one cubic meter. A suitable variant could be a solid natural rock with a rather flat and horizontal surface of the size of 0.8 x 0.8m. In mountain areas and on exposed rocks the measurements can be successfully conducted without a preliminary benchmark of the bases. This above-mentioned disadvantage rules out using the gravimenter on small bases designed for relative gravimeters. The best way of fixing the ballistic block system to the base is to use anchor screws; however, securing it with a weight, eg. a set of long life batteries, is a practical solution.

The strong correlation between auto-seismic interference and measurements causes variations of systematic error depending on site characteristics. This apparent disadvantage of a system, on the other hand, offers the opportunity to reduce this error. Firstly, software can allow changes to the length of time interval corresponding to a set of test-body acceleration measurements conducted during a single throw. Averaging the acceleration data obtained at several time intervals reduces the influences of the decreasing oscillations. The operator can manually implement the length of measuring time interval; it can also be done automatically with use of a pseudo-random number generator. Secondly, it is possible to control the total time of free movement. Averaging the results obtained in various auto-seismic conditions provides an additional randomisation of the systematic errors.

Gravimeter Testing and Calibration

Up-to-date experiments and analysis demonstrate the value of the simple absolute ballistic gravimeter at remote observatories.

Testing of the portable ballistic gravimeter was carried out on five sites of the Polish Gravity Control Network. The majority of data was collected on sites of a small local network at the Borowa Gora observatory with three sites located in the premises and three outdoors. The volumes of the base pillars varied from 1-6 cubic meters. The gravity measurements on outdoor sites were protected against the rain with a tent and were carried out at temperatures above zero.

The gravimeter was tested for more than three years from 1995 to 1998.

The results obtained by several instruments, including the FG-5 and the JILA-6 were used to calibrate the gravimeter as the working tool of measurement. In the beginning the calibration was conducted twice a year and later only once. National holidays (Easter and Christmas) when several days in row are practically free of artificial seismic interference were chosen for calibration. Calibration was focused on determining the numerical factors used for calculating the amendments for influence of residual gas in the ballistic block and on estimating the random error of a gravimeter relative to the absolute value on the site.

The standard time for averaging the results is always 24 hours. The data to be averaged come from either a series of continuous observations covering one day during a holiday period or from two data sets of several hours duration taken on two consecutive nights during the week.

The analysis of data collected from 1996 to 1999, after both hardware and software upgrading, resulted in error reduction from 70 to 15mGal. Further improvement can be expected when the modern stabilised laser is applied.

Conclusion

The experience gathered over last few years shows that the portable ballistic gravimeter of the Institute of Geodesy and Cartography, Warsaw, can be considered as the prototype for an autonomous absolute gravimeter.

References

J. Manning, Overview of GIANT program, Proc. of AGS99, Warsaw 14-17 July 1999, this issue.

A. Donnellan, B.P. Luyendyk, M.A. Smith, T.A. Rebold, H.I. Awaya, W. Nesbit, G.E. Dace, Deployment of Autonomous GPS Stations in Marie Byrd Land, Antarctica, Eos Trans. AGU, 80(17), Spring Meet. Suppl.,S77,1999.

J.M. Brown, T.M. Niebauer, B. Richter, F.J. Klopping, J.G. Valentine, and W.K. Buxton, A New Miniaturized Absolute Gravimeter Developed for Dynamic Applications, Eos Trans. AGU,80(32), 10 August 1999.

Abstracts

Transantarctic Mountains Deformation Monitoring Network (TAMDEF) South Victoria Land - Initial Results

Larry Hothem, Jerry Mullins and Robert Glover¹
Ian Whillans, Terry Wilson, and Mike Willis²

¹U.S. Geological Survey, Reston, VA
²Byrd Polar Research Center, The Ohio State University, Columbus, OH

TAMDEF is a collaborative GPS campaign initiated in 1996 by Ohio State University scientists in cooperation with the U.S. Geological Survey and sponsored by the National Science Foundation to measure horizontal and vertical deformation in the McMurdo Sound region. An array of 28 GPS stations spans an area approximately 375 km northsouth and 300 km eastwest with the goal of measuring and attempting to differentiate between causes for the rock motions. The expected signals are:

1 crustal rebound - uplift is predicted for the north end of the study area (from considerations of glacial geology) with more uplift predicted at the south end (based on glaciological theory) due to formerly thicker ice in McMurdo Sound region of the Ross Sea; and, either an eastward or westward tilting depending on whether the ice-age glaciers in East Antarctica or West Antarctica thinned or thickened the most.

2 tectonic - there is evidence for active 'normal' fault motion in specific zones in the mountain front and active spreading is predicted across the Terror Rift.

3 volcanic - subsidence is possibly due to the weight of the volcanic material from the Ross Island volcanoes; and, Mt. Erebus is currently active and there may be episodic inflation or deflation.

In this region of Antarctica, model predictions for crustal rebound toward isostasy reach vertical motion rates of 3 to 20 mm per year. The directions and patterns of these predicted motions are mostly distinct. The design

of the deformation monitoring network and the GPS observing campaign strategy was designed to discriminate among them. The GPS surveys form geometrical elements at three spatial scales:

1 Long baselines (100 km) that span the features most expected to show motion according to the hypotheses above - simultaneous tracking time is at least 2 days, often 7 days,

2 Short baseline (10 km) arrays crossing suspected fault zones with inferred neotectonic motions - simultaneous tracking time about 24 hours, and

3 Very short baselines (0.1-0.2 km) at each site to test for local motion due to such processes as frost action -simultaneous tracking time is 0.5-1.0 hours.

All monuments are special stainless steel pins set in the rock that stand about 0.05 m above the rock. Between November 1996 and January 2000, the station arrays were established and repeat measurements completed using dual-frequency late model GPS instruments in combination with choke-ring antennas. Analysis of the measurements from 3 observing campaigns are yielding repeat values in any coordinate ranging generally between 0 and 3 mm for the very shortbaseline 'microfootprint' arrays and 2 to 5 mm for the short and long baseline arrays. Scheduled for the 1999-2000 field season is the last of four independent observing campaigns in this phase of the TAMDEF project for the South Victoria Land region.

Absolute Gravity Measurement at Aboa: Effects of Close-Range Ice and Snow Cover

Jaakko Mäkinen

Finnish Geodetic Institute, P.O.Box15, FIN-02431 Masala, Finland

Activity of Polish Surveyors in Spitsbergen

Leszek Kolondra

Faculty of Earth Sciences, Silesian University, 41-200 Sosnowiec, Poland

Polish geodetic activity in Spitsbergen began during the first Polish expedition in 1934, when some of the last existing white spots on the Spitsbergen map were measured. Among the seven members of this expedition were two surveyors. The triangulation network was established and the area of 260 km² (Amundsenisen area of Wedel Jarlsberg Land) to scale 1:50 000 was measured using terrophotogrammetry. Contemporary Norwegian maps (sheet B12, C12) contain many Polish names from this time, eg. Kopernikusfjellet, Polakkbreen, Curie-Sklodowskafjellet to name a few.

Polish surveyors were next in Spitsbergen during the period 1957-59, participating in the III International Geophysical Year and the International Geophysical Co-operation (1959-60). During this time the Polish Scientific Polar Station was built in Hornsund Fiord on Spitsbergen. In addition the astronomical point was established and terrophotogrammetric surveys were initiated (changes of the front position of glaciers Hans and Werenskiold, and other topographic works, resulting in the production of two maps of glaciers: Werenskiold 1: 5 000 (3 sheets, 42.3 km²) and Penck 1: 2 000 (2 sheets, 5 km²).

Unfortunately, Polish surveying and scientific expeditions to Spitsbergen were interrupted in 1960 for a period of a dozen years and it was only due to the efforts of scientists of Wroclaw University that the next scientific expedition took place. Photogrammetry was not main aim of this search, however, some terrophotogrammetric photos were used to determinate the changes of the front position of glaciers Hans and Werenskiold.

The most important and fruitful period of our activity started in 1978, when the Polish Scientific Polar Station on Spitsbergen was reactivated. The station is still working permanently today, run by the Institute of Geophysics of Polish Academy of Sciences. Many scientific programmes are undertaken also by other regional academic centres not only in the environs of the Polish Polar Station.

Geodetic works are done mainly for specialists other sciences, especially for glaciology. The main topics are:

· Registration of changes of the front positions,

· Determination of surface movement of the Hans Glacier;

· Topographic elaboration (maps of glaciers and their surroundings);

· DTM of glaciers with radar and radio sounding of bedrock;

· Analysis of geometry changes of glaciers (longitudinal profiling by means of GPS techniques and Airborne laser altimetry method;

· Mapping of a macro and mezo cryokarst form on the glacier surface.

The main geodetic and cartographic results (printed) of these activities are shown:

From 1982 we have permanent data on changes of the front position of Hans Glacier (over 100 cycles in different periods) and its surface movement (one week, one day period even - over 30 cycles). We are using the permanent photogrammetric station (autocentering iron ring) to register cyclic observation.

In 1991, together with colleagues from the Norsk Polarinstitutt, Oslo and the Institute of Geography of Academy of Sciences, Moscow, we participated in an international survey programme of a large glacial area. The longitudinal profiles of the Amundsenisen Plateau, Lomonosovfonna and Kongsvegen - Svea Glacier were measured by GPS.

Thanks to co-operation with NASA we have obtained data from airborne laser altimetry surveys over glaciers situated near the Polish Polar Station. Some data were elaborated (Paierl, Mühlbacher and Amundsenisen) and the great reduction in the height of surface glaciers were observed.

The other results of our geodetic activities are published in permanent publications and are presented at scientific conferences, symposiums and workshops in Poland and abroad.

GPS Networks for the Observation of Ice Surface Deformation in Dome C and Talos Dome Areas

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

DISTART - University of Bologna

During the 1996 ITASE Italian expedition a snow/firn core of 90 m was drilled on the topographic top of Talos Dome. In the same area a GPS strain network of 9 stations was established and surveyed to determine ice deformation around the drilling site. GPS measurements were repeated in December 1998.

Results of Dome C and Talos Dome strain networks made during the 1998-99 Italian expedition and the analysis of ice surface deformations are presented.

Recent Results of GPS Networks for Crustal Deformation Control on Terra Nova Bay Area (Antarctica)

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

DISTART- University of Bologna

The Italian geodetic network, located around Terra Nova Bay, Italian base in Antarctica, was monumented in 1990-91 as a reference frame for scientific activities (photogrammetry, cartography, geology) and for the purpose of geodynamics. The network was completely surveyed twice in 1990-91 and 1993-94 and once in December 1998. A geodetic GPS network was also established in 1990-91 for the study of deformation control of the Mount Melbourne volcano. The network has been surveyed four times: 1990-91, 1993-94, 1995 and 1997-98. The resulting coordinate variation was quite small after the fourth repetition, in comparison with method precision.

The results obtained, using two different types of software (Geotracer v. 2.25 and Bernese v.4.0) and

different approaches to GPS data solutions (Lc,L1,L3), were significantly different, probably due to the different algorythms and to the modelisation of ionospheric effects. Thus, a new data processing method presenting a different approach has been created using a third type of software, Gipsy. The results of the Gipsy application and a comparison with the other solutions, are presented. A deformation analysis has been made integrating geodetic measurements with geophysical observations.

In addition, analysis of the data acquired from TNB GPS permanent station is presented, along with the results of measurements obtained from long occupation and far away stations (about 1000 km from each other): TNB1 (Italian base), Dome C station (during Dome C Strain Net surveying in January 1999) and Mc Murdo (USA base).

Appendix 1
Antarctic Geodesy Symposium 1999 Program

18.00 - 20.00
Icebreaker party at the Institute of Geodesy and Cartography

Adam Linsenbarth - Director of the Institute of Geodesy and Cartography - welcome ceremony and presentation of the Institute.

9.00 - 10.30 Chairman: Jan Cisak

Alexander Guterch - President of Polish Committee on Polar Research - geophysicist and organiser of seismic expeditions to Antarctica and Arctic. Prof. Guterch will open the Symposium
Krzysztof Birkenmajer - History of Polish Polar Research

Janusz Sledzinski - "Polish Geodetic Antarctic studies" (Prof. Sledzinski from Warsaw University of Technology was a member of first Polish Antarctic Expedition to A.B. Dobrowolski Station in 1958).

11.00-12.30 Chairman: John Manning

John Manning - Overview of GIANT program
Reinhard Dietrich - "Present Status of the SCAR GPS Epoch Campaigns"
Alessandro Capra - "A Data Base for Physical Geodesy Data Collection and Analysis"

14.00-15.30 Chairman: Reinhard Dietric
Larry D. Hothem - "Transantarctic Mountains Deformation Monitoring Network (TAMDEF), South Victoria Land - Initial Results" (oral & poster)
Bjorn Johns - "Multi-Disciplinary GPS Applications in Antarctica - McMurdo DGPS Base, Science Support, and Operational Surveying."
John Manning - SCAR Group of Specialists on Antarctic Neotectonics (ANTEC)
Alessandro Capra - "Local Geodynamics Studies In Antarctica (Terra Nova Bay- Victoria Land)"

16.00-17.30 Chairman: Larry Hothem

Jaakko Makinen - " Absolute gravity measurement at Aboa: Effects of close range ice and snow cover"
Alessandro Capra - " GPS networks for the observation of ice surface deformation in Dome C and Talos Dome areas"

Alexander Yuskevitch (AEROGEODEZIJA - from St. Petersburg - new Russian member of SCAR WG-GGI) "Topographic and geodetic works executed by Federal Service of Geodesy and Cartography of Russia in Antarctic Continent since 1970"

Guest speaker - Krzysztof Birkenmajer

Friday 16^th July 1999

9.00 - 10.30 Chairman: Alessandro Capra

Nengcheng Chen - "Geostar and Internet Based GIS of Antarctica"

Chunming Chen - "Antarctic Surveying and Mapping Works of China and Recent Progress"

Larry Hothem - "Antarctic Geodetic Activities by U.S. - Underway and Planned (oral & poster).

Fedir Zablotskyj (Ukraine) - "Results of atmospheric influences on astrogeodetic measurements in Polar Regions."

11.00-12.30 Chairman: John Manning

GIANT Meeting - progress on SCAR WG-GGI projects and reports on activities undertaken during season 1998/99

· Permanent Observatories

· Epoch Campaigns

· Physical Geodesy

· GLONASS

· Differential GPS

· Remote Observatories

· Information Access

14.00-15.00 Chairman: John Manning

GIANT Meeting - plans for geodetic work next austral summer 1999/2000

15.30 - onwards   Chairman: Jan Cisak

Technical Tour to the Astro - Geodetic Observatory of the Institute of Geodesy and Cartography in Borowa Góra
(36 km from the Centre of Warsaw)

Evgenij Zanimonskiy - Ukraine - "Autonomous field and laboratory tests of the portable Absolute Gravimeter" (He proposes to have this presentation during technical excursion to the Observatory.)

Ilari Koskelo - Finland - Javad presentation

Appendix 2
List of Participants at AGS99