Mysen E.,Geodetic Institute
Journal of Geodesy | Year: 2016
The Kalman filter is derived directly from the least-squares estimator, and generalized to accommodate stochastic processes with time variable memory. To complete the link between least-squares estimation and Kalman filtering of first-order Markov processes, a recursive algorithm is presented for the computation of the off-diagonal elements of the a posteriori least-squares error covariance. As a result of the algebraic equivalence of the two estimators, both approaches can fully benefit from the advantages implied by their individual perspectives. In particular, it is shown how Kalman filter solutions can be integrated into the normal equation formalism that is used for intra- and inter-technique combination of space geodetic data. © 2016 Springer-Verlag Berlin Heidelberg
Mysen E.,Geodetic Institute
Journal of Applied Geodesy | Year: 2015
We have subtracted known contributions from the GOCE gradiometer data that forms the basis of the fourth generation time-wise gravity field solution (TIM4), and mapped the residuals onto a local mascon model covering the south of Norway. Quasigeoids derived from combinations of the mascon adjusted TIM4 solution and EGM08 were then compared to height anomalies of a precise and dense GPS/levelling network. It was found that a mascon adjustment of TIM4 based on the first satellite cycle could improve the consistency between the corresponding quasigeoid and the network by about 0.5 cm. If the data foundation of the mascon solution was expanded to include also the next two-three satellite cycles then an improved consistency between the corresponding quasigeoid and the network height anomalies appeared on all spatial scales. © 2015 by Walter de Gruyter.
Omang O.C.,Geodetic Institute |
Tscherning C.C.,Copenhagen University |
Forsberg R.,Danish National Space Center
International Association of Geodesy Symposia | Year: 2012
In gravity field modeling measurements are usually located on or above the terrain. However, when using the residual topographic modeling (RTM) method, measurements may end up inside the masses after adding the mean topography. These values do not correspond to values evaluated using a harmonic function. A so-called harmonic correction has been applied to gravity anomalies to solve this problem. However, for height anomalies no correction has been applied. To generalize the correction to e.g. height anomalies we interprete that the vertical gravity gradient inside the masses multiplied by height equals the correction. In principle the procedure is applicable to all gravity field functionals. We have tested this generalization of the procedure which consist in determining equivalent quantities in points Q on the mean surface if this surface is in free air. The procedure has as data the reduced values in P inside the masses but considered as being located at the mean surface. Numerical tests with height anomaly data from New Mexico and Norway as control data show that for gravity anomalies the general procedure is better than using the original harmonic correction procedure. © Springer-Verlag Berlin Heidelberg 2012.
Simpson M.J.R.,Geodetic Institute |
Wake L.,University of Calgary |
Milne G.A.,University of Ottawa |
Huybrechts P.,Vrije Universiteit Brussel
Journal of Geophysical Research: Solid Earth | Year: 2011
We show predictions of present-day vertical land motion in Greenland using a recently developed glacial isostatic adjustment (GIA) model, calibrated using both relative sea level (RSL) observations and geomorphological constraints on ice extent. Predictions from our GIA model are in agreement with the relatively small number of GPS measurements of absolute vertical motion from south and southwest Greenland. This suggests that our model of ice sheet evolution over the Holocene period is reasonably accurate. The uplift predictions are highly sensitive to variations of upper mantle viscosity. Thus, depending on the Earth model adopted, different periods of ice loading change dominate the present-day response in particular regions of Greenland. We also consider the possible influence of more recent changes in the ice sheet by applying a second ice model; specifically, a surface mass balance (SMB) model, which covers the period 1866 to 2005. Predictions from this model suggest that decadal-scale SMB changes over the past ∼140 years play only a small role in determining the present-day viscous response (at the sub-mm/yr level in most locations for a range of Earth model parameters). High rates of peripheral thinning from 1995 to 2005 predicted using the SMB model produce large elastic uplift rates (∼6 mm/yr) in west and southwest Greenland. This suggests that in some areas close to the ice margin, modern surface mass balance changes have a dominant control on present-day vertical land motion. Copyright © 2011 by the American Geophysical Union.
Mysen E.,Geodetic Institute
International Journal of Applied Earth Observation and Geoinformation | Year: 2015
We have compared the EGM08/GOCE quasigeoid with the height anomalies of a precise GPS/levelling network in the south of Norway where the GOCE ground tracks are dense and the gravitational signal has been described as rough. It was found that the inclusion of the GOCE gravity potential can improve the quasigeoid fit with the GPS/levelling network by 1.3 cm, and that this improvement takes place onspatial scales larger than 80 km. We therefore expect that GOCE will improve our knowledge of the marinegeoid. It is argued that the obtained results cannot be used in a direct way to increase the precision of the Norwegian height system in general due to the short distances between the network points. © 2013 Elsevier B.V.