Treatment of Tide Gauge Time Series and Marine GNSS Measurements for Vertical Land Motion with Relevance to the Implementation of the Baltic Sea Chart Datum 2000

Abstract

Tide gauge (TG) time series and GNSS measurements have become standard datasets for various scientific and practical applications. However, the TG and geodetic networks in the Baltic Sea region are deforming due to vertical land motion (VLM), the primary cause of which is the glacial isostatic adjustment. Consequently, a correction for VLM, either obtained from a suitable VLM model or by utilizing space-geodetic techniques, must be applied to ensure compatibility of various data sources. It is common to consider the VLM rate relative to an arbitrary reference epoch, but this also yields that the resulting datasets may not be directly comparable. The common height reference, Baltic Sea Chart Datum 2000 (BSCD2000), has been initiated to facilitate the effective use of GNSS methods for accurate navigation and offshore surveying. The BSCD2000 agrees with the current national height realizations of the Baltic Sea countries. As TGs managed by national authorities are rigorously connected to the national height systems, the TG data can also be used in a common system. Hence, this contribution aims to review the treatment of TG time series for VLM and outline potential error sources for utilizing TG data relative to a common reference. Similar consideration is given for marine GNSS measurements that likewise require VLM correction for some marine applications (such as validating marine geoid models). The described principles are illustrated by analyzing and discussing numerical examples. These include investigations of TG time series and validation of shipborne GNSS determined sea surface heights. The latter employs a high-resolution geoid model and hydrodynamic model-based dynamic topography, which is linked to the height reference using VLM corrected TG data. Validation of the presented VLM corrected marine GNSS measurements yields a 1.7 cm standard deviation and –2.7 cm mean residual. The estimates are 1.9 cm and –10.2 cm, respectively, by neglecting VLM correction. The inclusion of VLM correction thus demonstrates significant improvement toward data consistency. Although the focus is on the Baltic Sea region, the principles described here are also applicable elsewhere.

Combined Coastal Sea Level Estimation Considering Astronomical Tide and Storm Surge Effects: Model Development and Its Application in Thermaikos Gulf, Greece

“…Additionally, sea level studies contribute to various scientific purposes. Geodesy encompasses sea level studies, as they contribute to height systems and geoid determinations [55,56]. Moreover, accurate determination of tidal signal is critical for satellite altimetry calibration and precise tidal loading estimation for GNSS stations.…”

Long-Term and Decadal Sea-Level Trends of the Baltic Sea Using Along-Track Satellite Altimetry

“…Figure 4). The ∆N rate is approximately 10-15% of the VLM rate in the Baltic Sea [34]. Figure 6 shows annual DT variations of TG observations (hourly data) before (black) and after (blue) VLM correction for six selected TG stations.…”

Geodetic SAR for Height System Unification and Sea Level Research—Results in the Baltic Sea Test Network

“…All available TG data are un-normalized, i.e., the data represent the actual hourly sea level heights at the TG stations. As the TG data represent relative sea level, the VLM estimates (reaching up to 9 mm/year) can be accounted for separately, e.g., following methodology in [14].…”