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An improved and extended GPS derived velocity
field of the postglacial adjustment in
Fennoscandia Martin Lidberg1,3, Jan M.
Johansson1, Hans-Georg Scherneck1, Sten
Bergstrand1, Glenn A. Milne2 1. Chalmers
University of Technology, Onsala Space
Observatory, SE-439 92 Onsala, Sweden. 2.
Department of Earth Sciences, University of
Durham, UK 3. National Land Survey, Gävle,
Sweden Contact information lidberg_at_oso.chalmers.s
e / Phone [phone]

• Purpose of research
• To be able to model station motions in
  Fennoscandia caused by Glacial Isostatic
  Adjustment (GIA). For geodetic and positioning
  applications this is commonly recognized as
  intraplate deformation.

• Work done
• We have analyzed 3000 days of continuous GPS
  observations between January 1996 and June 2004
  from stations in northern Europe
• we present 3D velocities for 53 permanent GPS
  stations
• we compare to current accepted GIA model for the
  area (120 km lithosphere, viscosity of 81020 and
  1022 Pas for upper and lower mantle, Milne et al
  2001)

• GPS analysis
• The GAMIT/GLOBK software package from MIT
• 10 elevation cut off angle
• troposphere zenith delay parameters (every 2nd
  hour)
• daily troposphere gradient parameters
• the Niell (1996) mapping functions
• ambiguities fixed to integers (as far as
  possible)
• regional analysis combined with global analysis
  from SOPAC using GLOBK
• daily combinations adjusted to the ITRF2000
  position and velocity field

Computing velocities While computing velocities
from daily position estimates, we solve for
annual and semi-annual periodic cycles, remove
outliers, and introduce shift parameters at
antenna changes.
Realistic s estimates
Least square solution

• Chi2 of weighted means against segment length for
  the averages
• computed chi2 of weighted means
• chi2 modeled for 1st order GM process

Plot for Umeå, using the program Tsview. (Herring
2003)
Estimated ?02

• Results
• Our approach for reference frame realization has
  demonstrated global consistency with the ITRF2000
  velocity field at the sub-mm/yr level.
• Uncertainties at 0.2 mm/yr and 0.5 mm/yr for
  horizontal and vertical components respectively
  (1s) for stations with longest records (from
  internal and external assessments)
• maximum vertical rate of 10.6 mm/yr at Umeå,
  which is somewhat south of current estimated
  location of land uplift maximum
• comparison to GIA model show systematic larger
  velocity values for the model, which suggest
  possibilities for improvement of the model
  parameters.

n
Assume 1st order GM process
v(i) av(i-1) w(i) 0 lt a lt 1
Compute weighted means of the residuals,
including weights for the means - then compute
weighted scatter of the weighted means
e
chi2/dof of mean ??(1-exp(-m/?))
u
Averaging time correlation time parameter
Averaging time (days)

King RW, (2002) Documentation for the GAMIT GPS
analysis software, MIT Internal Report, 206 pp
(http//www-gpsg.mit.edu/simon/gtgk/GAMIT.pdf) Ki
ng RW, Herring TA, (2002) Global Kalman filter
VLBI and GPS analysis program, MIT Internal
Report, 98 pp (http///www-gpsg.mit.edu/ simon/
gtgk/GLOBK.pdf) Herring T (2003) MATLAB Tools for
viewing GPS velocities and time series. GPS
solutions 7194-199. Lidberg M, Johansson J M,
Scherneck H-G, Davis J L (2005) An improved and
extended GPS derived velocity field of the
postglacial adjustment in Fennoscandia. Journal
of Geodesy (submitted).
References Johansson J M, Davis JL, Scherneck
H-G, Milne GA, Vermeer M, Mitrovica JX, Bennett
RA, Jonsson B, Elgered G, Elósegui P, Koivula H,
Poutanen M, Rönnäng BO, Shapiro II (2002)
Continous GPS measurements of postglacial
adjustment in Fennoscandia 1. Geodetic result.
Journal of geophysical research, vol. 107, no.
B8, 10.1029/2001B000400. Milne GA, Davis JL,
Mitrovica JX, Scherneck H-G, Johansson JM,
Vermeer M, Koivula H (2001) Space-Geodetic
Constraints on Blacial Isostatic Adjustments in
Fennoscandia. Science 291, 2381-2385. Scherneck
H-G, Vermeer M, Mitrovica JX, Milne GA (2002)
BIFROST Observing the Three-Dimensional
Deformation of Fennoscandia. In Ice Sheets, Sea
Level and the Dynamic Earth Geodynamic series
29 American Geophysical Union.