NMA Analysis Center

The Norwegian Mapping Authority (NMA) has during the last few years had a close cooperation with Norwegian Defence Research Establishment (FFI) in the analysis of space geodetic data using the GEOSAT software. In 2012 NMA has taken over the full responsibility for the GEOSAT software. This implies that FFI stopped being an IVS Associate Analysis Center in 2012. NMA has been an IVS Associate Analysis Center since 28 October 2010. NMA's contributions to the IVS as an Analysis Centers focus primarily on routine production of session-by-session unconstrained and consistent normal equations by GEOSAT as input to the IVS combined solution. After the recent improvements, we expect that VLBI results produced with GEOSAT will be consistent with results from the other VLBI Analysis Centers to a satisfactory level

VLBI Analysis with the Multi-Technique Software GEOSAT

GEOSAT is a multi-technique geodetic analysis software developed at Forsvarets Forsknings Institutt (Norwegian defense research establishment). The Norwegian Mapping Authority has now installed the software and has, together with Forsvarets Forsknings Institutt, adapted the software to deliver datum-free normal equation systems in SINEX format. The goal is to be accepted as an IVS Associate Analysis Center and to provide contributions to the IVS EOP combination on a routine basis. GEOSAT is based on an upper diagonal factorized Kalman filter which allows estimation of time variable parameters like the troposphere and clocks as stochastic parameters. The tropospheric delays in various directions are mapped to tropospheric zenith delay using ray-tracing. Meteorological data from ECMWF with a resolution of six hours is used to perform the ray-tracing which depends both on elevation and azimuth. Other models are following the IERS and IVS conventions. The Norwegian Mapping Authority has submitted test SINEX files produced with GEOSAT to IVS. The results have been compared with the existing IVS combined products. In this paper the outcome of these comparisons is presented

A GNSS velocity field for geophysical applications in Fennoscandia

In Fennoscandia, tectonics, Glacial Isostatic Adjustment (GIA), and climatic changes cause ongoing crustal deformation of some millimetres per year, both vertically and horizontally. These displacements of the Earth can be measured to a high degree of precision using a Global Navigation Satellite System (GNSS). Since about three decades, this is the major goal of the Baseline Inferences for Fennoscandian Rebound, Sea-level, and Tectonics (BIFROST) project. We present a new velocity field for an extended BIFROST GNSS network in the ITRF2008 reference frame making use of the GNSS processing package GPS Analysis Software of MIT (GAMIT). Compared to earlier publications, we have almost doubled the number of stations in our analysis and increased the observation time span, thereby avoiding the early years of the network with many instrument changes. We also provide modelled vertical deformation rates from contributing processes, i.e. elastic deformation due to global atmospheric and non-tidal ocean loading, ice mass and hydrological changes as well as GIA. These values for the vertical component can be used for removal of these contributions so that the residual uplift signal can be further analysed, e.g., in the context of local or regional deformation processes or large-scale but low-magnitude geodynamics. The velocity field has an uplift maximum of 10.3 mm/yr in northern Sweden west of the Gulf of Bothnia and subsidence exceeding 1 mm/yr in northern Central Europe. The horizontal velocity field is dominated by plate motion of more than 20.0 mm/yr from south-west to north-east. The elastic uplift signal sums up to 0.7–0.8 mm/yr for most stations in Northern Europe. Hence, the maximum uplift related to the past glaciation is ca. 9.6 mm/yr. The residual uplift signal after removal of the elastic and GIA contribution may point to possible improvements of the GIA model, but may also indicate regional tectonic and erosional processes as well as local deformation effects. We show an example of such residual signal discussing potential areas of interest for further studies

Towards a dynamic reference frame in Iceland

There is a growing need for geodetic reference frames that on a national level support the increas-ing use of global positioning services. Today, the vast majority of countries have their own national ref-erence frame. In Europe this frame is normally aligned to ETRS89. This system is co-moving with theEurasian tectonic plate. Global Navigation Satellite Systems (GNSS) and global positioning services arenormally aligned to the Earth as a whole through a global reference frame like ITRF2014. Consequently,global positioning services does not give direct access to the national reference frame without a time-dependent transformation.A solution is to align the national reference frame directly to a global reference frame. In such aframe, the coordinates of a point fixed to the ground will change with time, - a fact leading to the expres-sion dynamic reference frame (DRF).To be prepared for future challenges, the Nordic Geodetic Commission (NKG) initiated a pilot-project on DRF in Iceland. Iceland has a very active and complex geodynamic situation. It is located atthe boundary of two tectonic plates and affected by seismic and volcanic activity, recent ice loadingchanges as well as glacial isostatic adjustment (GIA). Due to this, the traditional concept of a static geo-detic reference frame is difficult to maintain at the uncertainty level required by modern applications.Iceland was therefore a natural place to investigate the concept of DRF.This paper focuses on the outcome and conclusions of the DRF project in Iceland. We give tenpreconditions for a DRF. Living on an ever-changing Earth, we see that many of these preconditionshave to be in place regardless of type of reference frame. Through the work in the Nordic countries andNKG, the Nordic area will be well prepared for the future challenges. However, some legal issues forinstance, can be challenging. A two-frame solution combining static- and dynamic- reference framesseems like the best alternative in the foreseeable future

NKG2016LU: a new land uplift model for Fennoscandia and the Baltic Region

We present the official land uplift model NKG2016LU of the Nordic Commission of Geodesy (NKG) for northern Europe. The model was released in 2016 and covers an area from 49° to 75° latitude and 0° to 50° longitude. It shows a maximum absolute uplift of 10.3 mm/a near the city of Umeå in northern Sweden and a zero-line that follows the shores of Germany and Poland. The model replaces the NKG2005LU model from 2005. Since then, we have collected more data in the core areas of NKG2005LU, specifically in Norway, Sweden, Denmark and Finland, and included observations from the Baltic countries as well. Additionally, we have derived an underlying geophysical glacial isostatic adjustment (GIA) model within NKG as an integrated part of the NKG2016LU project. A major challenge is to estimate a realistic uncertainty grid for the model. We show how the errors in the observations and the underlying GIA model propagate through the calculations to the final uplift model. We find a standard error better than 0.25 mm/a for most of the area covered by precise levelling or uplift rates from Continuously Operating Reference Stations and up to 0.7 mm/a outside this area. As a check, we show that two different methods give approximately the same uncertainty estimates. We also estimate changes in the geoid and derive an alternative uplift model referring to this rising geoid. Using this latter model, the maximum uplift in Umeå reduces from 10.3 to 9.6 mm/a and with a similar reduction ratio elsewhere. When we compare this new NKG2016LU with the former NKG2005LU, we find the largest differences where the GIA model has the strongest influence, i.e. outside the area of geodetic observation. Here, the new model gives from − 3 to 4 mm/a larger values. Within the observation area, similar differences reach − 1.5 mm/a at the northernmost part of Norway and − 1.0 mm/a at the north-western coast of Denmark, but generally within the range of − 0.5 to 0.5 mm/a

Time-varying uplift in Svalbard—an effect of glacial changes

International audienceSUMMARY We analyse Global Navigation Satellite System (GNSS) data from Svalbard to understand how uplift rates are controlled by the elastic and viscoelastic response of the solid Earth to changes in glacier mass on annual, interannual, decadal, centennial and millennial timescales. To reveal local patterns of deformation, we filter the GNSS time-series with an enhanced common-mode filtering technique where the non-tidal loading signal is incorporated. This technique reduces the estimated uncertainties for 5-yr time-series from 0.8 to 0.3 mm yr–1. Analysis of the GNSS data with different software–GAMIT, GipsyX, and GINS–produce consistent results that all indicate large temporal variations in uplift. For example, at the Ny-Ålesund GNSS station, uplift varies between 6 and 12 mm yr–1 for different 5-yr periods, and also shows a significant increase in the last 15 yr. We show that this increase is due to climate change-related ice mass loss in Svalbard. We constrain recent glacier retreat on Svalbard using a series of digital elevation models, and then correct the GNSS-derived uplift records for the elastic signal from these ice mass changes. The residual uplift signal is relatively constant, confirming the hypothesis that current ice mass changes exert a strong influence on GNSS observations. The relatively constant record of residual uplift can be used to constrain other geophysical signals such as the viscoelastic response of the solid Earth to ice loading during the Little Ice Age and the Last Glacial Period. We review uplift results from previous viscoelastic modelling studies and show that the residual signal cannot yet be fully explained. Our new uplift results thus motivate the need for new viscoelastic modelling of the glacial isostatic adjustment process in Svalbard

Visualizing and interpreting surface displacement patterns on unstable slopes using multi-geometry satellite SAR interferometry (2D InSAR)

It is well known that satellite radar interferometry (InSAR) is capable of measuring surface displacement with a typical accuracy on the order of millimeters to centimeters. However, when the true deformation vector differs from the satellite line-of-sight (LOS), the sensitivity decreases and interpretation of InSAR deformationmeasurements becomes challenging. By combining displacement data fromextensive ascending and descending TerraSAR-X datasets collected during the summer seasons of 2009–2014, we estimate two-dimensional (2D) InSAR surface displacement. Displacement data are decomposed into vertical and west/east deformation, dip and combined deformation vector, and validated using Global Navigation Satellite System (GNSS) data.We use the decomposed dataset to visualize variations in surface velocity and direction on unstable slopes in a periglacial environmentwith sporadic permafrost in northern Norway. By identifying areas with uplift and subsidence, and detecting velocity changes (downslope acceleration/deceleration) and related areas of extension and compression, we are able to explain driving and controlling mechanisms and geomorphology in two rockslides and one area with solifluction landforms

The New IERS Special Bureau for Loading (SBL)

Currently, the establishment of the International Earth Rotation Service (IERS) Special Bureau for Loading (SBL) is in progress as part of the IERS Global Geophysical Fluids Center (GGFC). The main purpose of the SBL is to provide reliable, consistent model predictions of loading signals that have been thoroughly tested and validated. The products will describe at least the surface deformation, gravity signal and geo-center variations due to the various surface loading processes in reference frames relevant for direct comparison with existing geodetic observing techniques. To achieve these goals, major scientific advances are required with respect to the Earth model, the theory and algorithms used to model deformations of the Earth as well as improvements in the observational data related to surface loading

Relating 3D surface displacement from satellite- and ground-based InSAR to structures and geomorphology of the Jettan rockslide, northern Norway

This study combines remote sensing data from ground- and satellite-based radar to calculate 3D displacement vectors for the Jettan rockslide, Troms, northern Norway. Using 3D displacement vectors, aspect data and strain rates in conjunction with structure (foliation, faults, fractures), geomorphological elements (ridges, scarps, terraces, depressions), topography and borehole data, we identify zones undergoing displacement, e.g., extension and compression, displacement into- or out-of-the-slope and/or various degrees of tilting. Our results show variable 3D displacement velocities, from north to south, that segment the rockslide into distinct domains. Displacement patterns are structurally controlled, as spatial variation in azimuth and plunge of 3D displacement vectors can be related to variation in attitudes of the host-rock foliation, faults and fractures. In the north, a complex graben system surrounded by orthogonal NW–SE and NE–SW-trending geomorphological elements, shows a repeated stepping 3D displacement pattern. This may indicate a complex fault geometry at depth, including stepped and discontinuous slide surfaces. We interpret 3D displacement into-the-slope in the upper part, and out-of-the-slope in the lower part, to be back-rotation of antithetic blocks with planar fractures becoming curved/listric gliding surfaces with depth. Downslope reduction in velocity indicates compression and stacking of blocks. In the southern area, N–S-trending geomorphological elements are arranged parallel to the hillslope. 3D displacement vectors show a more homogenous displacement pattern indicating movement along planar, hillslope-parallel, fracture sets at depth. We propose a structuralcontrolled slope displacement model including alternate planar- and wedge-failure, in addition to displacement along planar and listric fractures merging into foliation at depth. Using the Jettan rockslide as a case study, we show how remote sensing data may aid examination of structural and topographic controls on rockslide kinematics, thus giving new insights into subsurface geometry