..Working Group for Geodynamics ..Chair: Hans-Georg Scherneck

Short activity report 2003-2004

The NKG Working Group for Geodynamics coordinates measurement campaigns, primarily gravity, in the postglacial rebound area in Fennoscandia. Currently we are in a transition phase between Relative Gravity measurements using spring gravimeters of Lacoste-Romberg type to Absolute Gravimetry using instruments of JILA/Faller/Micro-g-Solutions type. Thanks to an ongoing project at IfE, University of Hannover (Germany) in conjunction with the GRACE satellite project, AG-observations could be significantly increased both temporally and spatially. The first GRACE Ground Truth campaigns took part in 2003. They coincided with another scheduled, regular campaign by BKG, Frankfurt/M. (Germany). Completed by the observations carried out by FGI, Masala (Finland), 22 stations were observed in 2003, seven of which by several of the teams. Thus, the ambitions of the document on an Absolute Gravity Plan for NKG of 2003 could be exceeded. Several new stations have been added to the originally proposed ones. Completions of the site list will appear as the project will respond to requests, primarily issued within the ECGN project, for collocation of gravity observations with tide gauges and GPS stations.

As an effort to phase out the relative instruments, final observations of the land upflift profiles have been carried out in 2003. This concerns the lines at 63 and 56 degrees north. Observations on the lines at 61 and 65 degrees with spring gravimeters are more or less considered as terminated. They may be observed in the future anticipating the advent of small, portable absolute gravimeters. A final report is considered for praparation to the autum meeting of the NKG Presidium.

A new Absolute gravimeter has been obtained in 2004 by the University of Agriculture at Ås (Norway). This instrument participates in the 2004 campaigns.

The WG for Geodynamics has arranged a workshop meeting at Gävle 15-16 April. This meeting was also the platform for communication of first scientific results and technical experiences from the 2003 Absolute gravity measurements. The minutes from this meeting and complementary documents are available via the home page of the WG (http://holt.oso.chalmers.se/hgs/NKGWG/index.html , see under News). The minutes will complete the overview of the activities of the group in detail.

The WG for Geodynamics is currently involved in devising a Nordic Geodetic Observing System, comprising the absolute gravity stations, GPS, VLBI, SLR sites and tide gauges.