TY - JOUR

T1 - Observing ocean mass variability with spring gravimeters: Storm surge induced signals on the north sea island helgoland

AU - Weise, Adelheid

AU - Timmen, Ludger

AU - Deng, Zhiguo

AU - Gabriel, Gerald

AU - Rothleitner, Christian

AU - Schilling, Manuel

AU - Voigt, Christian

N1 - Funding information: We thank Andreas Güntner (Helmholtz-Zentrum Potsdam – Deutsches GeoForschungsZentrum, GFZ, Scintrex CG6-69) for permitting to use the data of their gravimeter. We thank an anonymous reviewer for valuable remarks and corrections.The investigations were funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy – EXC – 2123 QuantumFrontiers – 390837967 at Leibniz Universität Hannover.

PY - 2020

Y1 - 2020

N2 - Climate change is broadly discussed due to water level rise almost worldwide. Additionally, ocean-related risks driven by atmospheric dynamics are amplified, as tidal amplitudes in coastal areas and storm surges, which threaten coastal areas and the unique Wadden Sea in the German Bight. Investigations of the oceans in general and of the North Sea particularly are done by satellite technics as altimetry and the satellite mission GRACE-FO. Terrestrial geodetic measurements are needed for corrections and validation of the results. Several methods are in use in order to measure water level variations (tide gauges) and load related deformation (GNSS). Our key question is: Are accurate continuous gravimetric observations sensitive to non-tidal oceanic loading of the sea floor? For the first time, three spring-type gravimeters were installed on the island Helgoland in the North Sea, predominantly in winter season, to observe surrounding maximal water mass variations during the winter period 2018/2019. In spite of the non-linear instrumental drift, gravity variations exceeding 100 nm/s2* over periods of 1 – 3 days could significantly be separated. Partly they are assigned to water level variations due to storm events, e. g. Zeetje (1. 1. 2019) and Benjamin (8. 1. 2019), and wind directions, accordingly. A rough modelling of the estimated corresponding water mass load with maximum water level rise of 2 m in the German Bight agree with the observed attraction effects and with the vertical displacement observed in gravity and by GNSS. We conclude that we succeeded on the island Helgoland to measure gravimetrically the non-tidal mass variations and the related crustal deformation in the North Sea. It should be further continued during winter seasons. Even more appropriate may be the installation of an iGrav superconducting gravimeter benefitting from its small, linear instrumental drift. Finally, this research will contribute to tidal and non-tidal ocean mass variability models and will support the monthly modelling of the geopotential field from the satellite mission GRACE-FO, where the so-called de-aliasing products for short-term variations in atmosphere and ocean are needed.

AB - Climate change is broadly discussed due to water level rise almost worldwide. Additionally, ocean-related risks driven by atmospheric dynamics are amplified, as tidal amplitudes in coastal areas and storm surges, which threaten coastal areas and the unique Wadden Sea in the German Bight. Investigations of the oceans in general and of the North Sea particularly are done by satellite technics as altimetry and the satellite mission GRACE-FO. Terrestrial geodetic measurements are needed for corrections and validation of the results. Several methods are in use in order to measure water level variations (tide gauges) and load related deformation (GNSS). Our key question is: Are accurate continuous gravimetric observations sensitive to non-tidal oceanic loading of the sea floor? For the first time, three spring-type gravimeters were installed on the island Helgoland in the North Sea, predominantly in winter season, to observe surrounding maximal water mass variations during the winter period 2018/2019. In spite of the non-linear instrumental drift, gravity variations exceeding 100 nm/s2* over periods of 1 – 3 days could significantly be separated. Partly they are assigned to water level variations due to storm events, e. g. Zeetje (1. 1. 2019) and Benjamin (8. 1. 2019), and wind directions, accordingly. A rough modelling of the estimated corresponding water mass load with maximum water level rise of 2 m in the German Bight agree with the observed attraction effects and with the vertical displacement observed in gravity and by GNSS. We conclude that we succeeded on the island Helgoland to measure gravimetrically the non-tidal mass variations and the related crustal deformation in the North Sea. It should be further continued during winter seasons. Even more appropriate may be the installation of an iGrav superconducting gravimeter benefitting from its small, linear instrumental drift. Finally, this research will contribute to tidal and non-tidal ocean mass variability models and will support the monthly modelling of the geopotential field from the satellite mission GRACE-FO, where the so-called de-aliasing products for short-term variations in atmosphere and ocean are needed.

KW - Crustal deformation

KW - Mass variability in oceans

KW - Spring gravimeter

KW - Tidal and non-tidal gravity variations

KW - Wind-driven storm surge

UR - http://www.scopus.com/inward/record.url?scp=85091503948&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:85091503948

VL - 127

SP - 163

EP - 173

JO - AVN Allgemeine Vermessungs-Nachrichten

JF - AVN Allgemeine Vermessungs-Nachrichten

SN - 0002-5968

IS - 4

ER -