The growing need for a consistent and densified GNSS position and velocity solution for the Nordic and Baltic countries resulted in development of the joint GNSS Analysis Centre of the Nordic Geodetic Commission (NKG) in 2012. We first developed the methods of the operational processing and combination of solutions and then reprocessed the full data history between 1997 and 2017. In this study, we present an ITRF2014 densification for the area including 252 stations having more than 3 years of data. We combined all 20 years of daily solutions with full covariance matrices instead of station-wise analysis and analyzed the noise characteristics of the residual time series. We concluded that the flicker plus white noise uncertainty estimates were more robust than the general power-law estimates. Additionally, we found significant horizontal velocity differences at the co-located stations, pointing out biases not included in the formal uncertainties. The solution is more accurate and denser than any previous estimate, and it will be of great benefit for maintaining the reference frames in the Nordic and Baltic countries, as well as for the geodynamic studies in the area.
The aim of this study was to estimate the noise properties, velocities, and their uncertainties from a time-series of selected (~9 years long) Estonian continuously operating Global Navigation Satellite System (GNSS) stations. Two software packages based on different processing methods, Gipsy–Oasis and Bernese, were used for daily coordinate calculations. Different methods and software (Tsview, Hector, and MIDAS) were used for coordinate time-series analysis. Outliers were removed using three different strategies. Six different stochastic noise models were used for trend estimation altogether with the analysis of the noise properties of the residual time-series with Hector. Obtained velocities were compared with different land uplift and glacial isostatic adjustment models (e.g., ICE-6G (VM5a), NKG2016LU, etc.). All compared solutions showed similar fit to the compared models. It was confirmed that the best fit to the time-series residuals were with the flicker noise plus white noise model (for the North and East component) and generalized Gauss–Markov model (for Up). Velocities from MIDAS, Tsview, and Hector solutions within the same time-series (Gipsy–Oasis or Bernese) agreed well but velocity uncertainties differed up to four times. The smallest uncertainties were obtained from Tsview; the MIDAS solution produced the most conservative values. Although the East and Up component velocities between Gipsy and Bernese solutions agreed well, the North component velocities were systematically shifted.
Recent LiDAR surveys have revealed that on postglacially uplifting coasts of Estonia rhythmic coastal landforms (beach ridge sequences and foredune plains) occur to a considerable extent. We studied four of them to reveal age and periodicity in these multiple ridge systems and discussed their genesis in the Subatlantic (semi‐continental) conditions of the Baltic Sea area. Using recent models of Fennoscandian uplift due to glacial isostatic adjustment (GIA), we constructed Holocene apparent sea level curves for the study sites at Õngu, Mänspe, Haldi and Keibu; converted distance–height shore profiles into time series (including corrections on shore profile non‐linearity and variations in GIA‐eustasy balance); and analysed the patterns using spectral analysis. It was suggested that due to non‐tidal conditions, relatively low‐energy hydrodynamic forcing and small aeolian contribution, the ridges mark ancient shorelines. They are relatively modest in height (mostly 0.2–1 m), form regular and extensive (up to 150 ridges) patterns, and date back to ~9000 years before present. We studied <5‐ka‐old sections. The mean ridge spacing varied, depending also on coastal slope, between 21 and 39 m. Both simple counting and spectral analysis involved some specific limitations, yet the estimates for typical spacing were alike, at 32 (±5) years. The regular nature of the low‐ridge patterns originated from relative sea level lowering and gradual sediment accretion/erosion. However, the progradation was rather uplift‐ than accretion‐driven and the stepwise process in ridge formation was probably not autocyclic. It was governed or modulated by quasi‐periodic 25–40 year cyclicity in local wave forcing, relative sea level variations and wind conditions. Being most likely connected to the North Atlantic Oscillation, the quasi‐regular, decadal‐scale, similarly phased variations may magnify each other's effect on the westerly exposed coasts of Estonia. Additionally, some other (e.g. event‐driven) mechanisms may also be present.
Different types of tide gauges (TG) are used to monitor sea level dynamics around the Baltic Sea. They are usually connected to national levelling network and several of them are linked into regional networks (e.g. Baltic Operational Oceanographic System). The sea level readings are used for nautical navigation, modelling and forecasting of sea level changes. Long-term and historical sea level series are also useful in studying regional land uplift/subsidence or calibrating satellite altimetry data. Both tasks require precise knowledge of interconnections between height systems of countries surrounding the same sea.Presently, however, six different height reference systems are in official use in the Baltic Sea countries. Even though all these systems are based on mean sea level (MSL) observations averaged over different time-periods, but different reference TG and tidal systems have been adopted for national height systems. The differences of national height systems between the countries around the Baltic Sea can reach up to 20 cm. Overlooking this yields undesirable systematic biases between regional TG data. Additionally, the entire Fennoscandia is affected by apparent land uplift at the velocity rate up to +9 mm/year, primarily due to the viscoelastic response of the solid Earth resulting from the de-glaciation of the Pleistocene ice-sheets. Over a time span this causes notable distortions of height system realisations even within a country. Therefore, the land uplift corrections should be also taken into account in sea level series, which are used for modelling and forecasting of sea level changes. A case study in West-Estonian Archipelago involves a recently developed land uplift model EST2013LU, which is based on four repeated highprecision levelling data from 1933 to 2010. Also connections between levelling network and TG series are analysed. The results reveal that discrepancies due to obsoleteness of the heights in the national height system may cause discrepancies in series of nearby located tide gauges up to 7 cm.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.