Journal of Geodesy (submitted) 1 Fitting gravimetric geoid models to vertical deflections 2 3 W.E. Featherstone ( ) 4 Western Australian Centre for Geodesy & The Institute for Geoscience Research, 5 Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia 6 Tel: +61 8 9266-2734; Fax: +61 8 9266-2703; Email:
[email protected] 7 8 D.D. Lichti 9 Department of Geomatics Engineering & The Centre for Bioengineering Research and 10 Education, Schulich School of Engineering, The University of Calgary, 11 2500 University Drive NW, Calgary, Alberta, T2N 1N4, Canada 12 Tel: +1 403 210-9495; Fax: +1 403 284 1980; Email:
[email protected] 13 14 Abstract . Regional gravimetric geoid and quasigeoid models are now commonly fitted 15 to GPS-levelling data, which simultaneously absorbs levelling, GPS and quasi/geoid 16 errors due to their inseparability. We propose that independent vertical deflections are 17 used instead, which are not affected by this inseparability problem. The formulation is 18 set out for geoid slopes and changes in slopes. Application to 1080 astrogeodetic 19 deflections over Australia for the AUSGeoid98 model shows that it is feasible, but the 20 poor quality of the historical astrogeodetic deflections led to some unrealistic values. 21 22 Keywords : Gravimetric geoid errors, vertical deflections, vertical datum errors 23 24 1. Introduction 25 Fitting regional gravimetric geoid or quasigeoid models to GPS-levelling data has 26 become a widespread practice. A principal objection to this is the inseparability of 27 errors among the levelling and local vertical datum (LVD), GPS and gravimetric 28 quasi/geoid model (cf.