Olav Vestøl - Academia.edu (original) (raw)

Papers by Olav Vestøl

The International Hydrographic Review

A unified Chart Datum for the whole Baltic Sea is required for the use of global navigation satel... more A unified Chart Datum for the whole Baltic Sea is required for the use of global navigation satellite systems (GNSS) in accurate 3-D bathymetric surveying and navigation, enabling for automated shipping with increased efficiency and improved maritime safety. So far, the zero levels of nautical maps were derived from the mean sea level (MSL) of different local tide gauges. The inherent height datum differences between neighboring map sheets are a fundamental infrastructural obstacle for implementing and using new cross-border navigation services based on electronic nautical maps. The Baltic Sea Hydrographic Commission, with its Chart Datum, Water Level and Currents Working Group (CDWCWG), has therefore decided to implement a harmonized vertical reference in the Baltic Sea (BSHC18 conference, 2013; Schwabe et al., 2020) called the Baltic Sea Chart Datum 2000 (BSCD2000). The first milestone was the agreement between the Baltic Sea countries on the fundamental standards of the BSCD2000,...

Journal of Geodetic Science

Coordinates in global reference frames are becoming more and more common in positioning whereas m... more Coordinates in global reference frames are becoming more and more common in positioning whereas most of the geospatial data are stored in registries in national reference frames. It is therefore essential to know the relation between global and national coordinates, i.e., the transformation, as accurately as possible. Officially provided pan-European transformations do not account for the special conditions in the Nordic and Baltic countries, namely crustal deformations caused by Glacial Isostatic Adjustment. Therefore, they do not fulfill the demands for the most accurate applications like long-term reference frame maintenance. Consequently, the Nordic Geodetic Commission (NKG) has developed customized and accurate transformations from the global ITRF to the national ETRS89 realizations for the Nordic and Baltic countries. We present the latest update, called the NKG2020 transformation, with several improvements and uncertainty estimates. We also discuss its significance and practi...

EGU General Assembly Conference Abstracts, Apr 1, 2019

Journal of Marine Science and Engineering, 2017

EUREF, Symposium of …, 2003

Summary We discuss the relationship of EVRS2000 and EVRF2000 to future national height systems in... more Summary We discuss the relationship of EVRS2000 and EVRF2000 to future national height systems in Europe and specifically in Finland, Norway, and Sweden. The EVRF2000 in these countries is based on their second precise levellings and the height differences ...

Journal of Geodesy, 2012

In Norway, as in the rest of Fennoscandia, the process of Glacial Isostatic Adjustment causes ong... more In Norway, as in the rest of Fennoscandia, the process of Glacial Isostatic Adjustment causes ongoing crustal deformation. The vertical and horizontal movements of the Earth can be measured to a high degree of precision using GNSS. The Norwegian GNSS network has gradually been established since the early 1990s and today contains approximately 140 stations. The stations are established both for navigation purposes and for studies of geophysical processes. Only a few of these stations have been analyzed previously. We present new velocity estimates for the Norwegian GNSS network using the processing package GAMIT. We examine the relation between time-series length and precision. With approximately 3.5 years of data, we are able to reproduce the secular vertical rate with a precision of 0.5 mm/year. To establish a continuous crustal velocity field in areas where we have no GNSS receivers or the observation period is too short to obtain reliable results, either interpolation or modeling is required. We experiment with both approaches in this analysis by using (i) a statistical interpolation method called Kriging and (ii) a GIA forward model. In addition, we examine how our vertical velocity field solution is affected by the inclusion of data from repeated leveling. Results from our geophysical model give better estimates on the edge of the network, but inside the network the statistical interpolation method performs better. In general, we find that if we have less than 3.5 years of data for a GNSS station, the

Journal of Geodesy, 2006

Precise leveling, tide-gauge recordings and time series from continuous GPS stations are all sour... more Precise leveling, tide-gauge recordings and time series from continuous GPS stations are all sources of information about the ongoing postglacial land uplift in Fennoscandia. This article describes how to gather these three sources of data together in a least-squares collocation adjustment in order to calculate uplift rates, as well as new heights for the benchmarks in the leveling network. The estimated reliability of the resulting uplift model is in general better than 0.4 mm/year, decreasing in areas of fewer data.

Journal of the Geological Society, 2010

... To investigate the significance and possible extent of the shorter-wavelength crustal deforma... more ... To investigate the significance and possible extent of the shorter-wavelength crustal deformation in ... The b-values may vary significantly, however, dependent on local stress conditions. While earthquake swarms are common in a variety of tectonic regimes, they are particularly ...

Changes to mean sea level and/or sea level extremes (e.g., storm surges) will lead to changes in ... more Changes to mean sea level and/or sea level extremes (e.g., storm surges) will lead to changes in coastal impacts. These changes represent a changing exposure or risk to our society. Here we try to synthesize our understanding of past and present observed sea level changes for Norway, as well as providing sea level projections up until 2100. Our primary focus is changes to mean sea level but we also give updated return heights for each coastal municipality in Norway. We first analyse observed sea level changes from the Norwegian tide gauge network and from satellite altimetry. After the tide gauge data have been corrected for the effects of glacial isostatic adjustment, we show that 20 th century sea level rise in Norwegian waters is broadly similar to the global average rise. Contributions to the observed sea level change and variability are discussed. We find that rate of sea level rise along the Norwegian coast is significantly higher for the period 1993-2014 than for the period 1960-2010. It is unclear, however, to what extent this higher rate represents natural variability rather than a sustained increase owing to global warming. Our regional sea level projections are based on findings from the Fifth Assessment Report (AR5) of the Intergovernmental Panel for Climate Change (IPCC), and the Coupled Model Intercomparison Project phase 5 (CMIP5) output. Average projected 21 st century relative sea level change in Norway is-0.10-0.35 m (5 to 95% model ranges which is the likely range in AR5; P>66%) for RCP2.6,-0.05-0.45 m for RCP4.5, and 0.10-0.65 m for RCP8.5. The relative sea level projections can differ as much as 0.50 m from place to place. This pattern is governed by the vertical uplift rates. Quantifying the probability of levels above the likely range (i.e., the upper tail of the probability distribution) remains difficult because information is lacking. And of particular concern is that the ice sheet contribution might have a skewed distribution, which would mean values in its upper tail would be quite large. Finally, we show how the estimated return heights can be combined with our regional sea level projections to provide allowances. Allowances give the height by which an asset needs to be raised so that the probability of flooding remains preserved for a given sea level change. A possible attractive option in planning.

Future height systems in the Nordic countries, their relation to the EVRS2000 and to INSPIRE GIS ... more Future height systems in the Nordic countries, their relation to the EVRS2000 and to INSPIRE GIS standards by Working Group for Height Determination of the Nordic Geodetic Commission Jaakko Mäkinen (Jaakko.Makinen@fgi.fi), Martin Lidberg, Klaus Schmidt, Mikko Takalo, Mikael Lilje, Karsten Engsager, Per-Ola Eriksson, Casper Jepsen, Per-Anders Olsson, Veikko Saaranen, Runar Svensson, and Olav Vestøl.

There is a growing need for geodetic reference frames that on a national level support the increa... more There is a growing need for geodetic reference frames that on a national level support the increasing use of global positioning services. Today, the vast majority of countries have their own national reference frame. In Europe this frame is normally aligned to ETRS89. This system is co-moving with the Eurasian tectonic plate. Global Navigation Satellite Systems (GNSS) and global positioning services are normally 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 timedependent transformation. A solution is to align the national reference frame directly to a global reference frame. In such a frame, the coordinates of a point fixed to the ground will change with time, a fact leading to the expression dynamic reference frame (DRF). To be prepared for future challenges, the Nordic Geodetic Commission (NKG) initiated a pilotproject on DRF in Iceland....

Journal of Geodesy

We present the official land uplift model NKG2016LU of the Nordic Commission of Geodesy (NKG) for... more 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 northwestern coast of Denmark, but generally within the range of − 0.5 to 0.5 mm/a.