1(4) GEODETIC ACTIVITIES AT FINNISH ANTARCTIC RESEARCH STATION ABOA Hannu Koivula and Jaakko Mäkinen Finnish Geodetic Institute P.O.Box 15, FIN-02431 Masala, Finland Hannu.Koivula@fgi.fi Abstract. We summarise geodetic activities at the Finnish Antarctic research station Aboa since 1989. In 1989–1992 a regional gravity network was estab- lished. Absolute gravity measurements were per- formed in 1994 and 2001. In 2003 a permanent GPS station was installed. In the future we plan to main- tain the GPS time series, and to perform absolute- gravity measurements at other sites in Queen Maud Land, too. Geodetic Activities at Aboa 1989–2001 The Finnish Antarctic Research Station Aboa (73°02’ S, 13°25’W) in Western Queen Maud Land (Fig. 1) on the nunatak Basen was built in 1988–1989. It is a summer station and has not been occupied every year. The Finnish Geodetic Institute (FGI) has taken part in five of the ten Finnish scientific Antarctic expeditions (FINNARP) organized so far. Here we summarise shortly the activities of the first four of them. For more information see Ollikainen and Rouhiainen (1990), Jokela et al. (1993), Virtanen et al. (1994), Mäkinen (1994, 2001). 0˚ 30˚ 60˚ 90˚ 120˚ 150˚ 180˚ 210˚ 240˚ 270˚ 300˚ 330˚ Aboa Figure 1. Finnish Antarctic Research station Aboa is located at 73 °02’ S, 13 °25’W in Western Queen Maud Land. Finnarp89 (1989/1990) and Finnarp91 (1991/ 1992). A regional gravity survey covering 10000 km 2 was measured using Worden Master and La- Coste&Romberg gravimeters, with 493 points at the spacing of 5 km. Snowmobile and helicopter trans- port, and GPS positioning were used. The Aboa ref- erence station was tied to the International Gravity Standardization Network 1971 through station no. 43846J in Montevideo. A set of benchmarks was built around Aboa and measured with static GPS to create a local coordinate system. Snow accumulation and ice motion were studied on stake lines. A concrete pier was constructed on solid basaltic rock for future abso- lute gravity measurements. Finnarp93 (1993/1994) and Finnarp2000 (2000/ 2001). Absolute gravity was measured by the second author with the JILAg-5 of the FGI in January 1994 and in January 2001. The results (Fig. 2) show an apparent gravity change of +9±7 μgal (one-sigma) over 7 years. The change is thus not statistically sig- nificant. In 2001, the 5.5 km stake line of Sinisalo et al. (2003) was re-surveyed by GPS for snow surface elevations, and density of the top 0.5 m layer sam- pled. A similar local survey within 100 m of the abso- lute site was performed with tachymeter. The GPS station at the neighbouring Swedish base Wasa was occupied during the SCAR epoch 2001 and 2002 GPS campaigns. Gravity at Aboa 60 70 80 90 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 982623000 ugal + Figure 2. The results of two absolute gravity meas- urements in 1994 and 2001 show a slight increase in gravity. Presented at the Fifth International Antarctic Geodesy Symposium AGS’03, Lviv, Ukraina, September 15–17, 2003.