Report on levelling and GNSS results for stations on the MPQ campus in Garching

This technical report describes the levelling and GNSS (Global Navigation Satellite System) results for stations on the MPQ (Max-Planck-Institut für Quantenoptik) campus in Garching, aiming at the derivation of relativistic redshift corrections for novel clock comparison experiments. The underlying observations were carried out mainly in the year 2016, but supplementary information and data were also considered until the end of 2018. The (relative) accuracy of the levelled heights within the internal network on the MPQ campus is estimated to be better than 1 – 2 mm, which is based on the raw double-run levelling discrepancies and loop misclosures involving also stations on rooftops of buildings. The accuracy of the GNSS (ellipsoidal) heights is estimated to be better than 1 cm. The consistency between the levelled and GNSS heights was evaluated internally by approximating the quasigeoid by a horizontal plane as well as externally by comparing with a gravimetric quasigeoid model, yielding maximum residuals of only 2 – 3 mm

Geodetic-Gravimetric Monitoring of Mountain Uplift and Hydrological Variations at Zugspitze and Wank Mountains (Bavarian Alps, Germany)

In 2004, first absolute gravity (AG) measurements were performed on the top of Mt. Zugspitze (2 sites) and at the foot (1 site) and top (1 site) of Mt. Wank. Mt. Wank (summit height 1780 m) and Mt. Zugspitze (2960 m) are about 15 km apart from each other and belong geologically to different parts of the Northern Limestone Alps. Bridging a time span of 15 years, the deduced gravity variations for Zugspitze are in the order of −0.30 μm/s2 with a standard uncertainty of 0.04 μm/s2. The Wank stations (foot and top) show no significant gravity variation. The vertical stability of Wank summit is also confirmed by results of continuous GNSS recordings. Because an Alpine mountain uplift of 1 or 2 mm/yr cannot explain the obtained gravity decline at Zugspitze, the dominating geophysical contributions are assumed to be due to the diminishing glaciers in the vicinity. The modelled gravity trend caused by glacier retreat between epochs 1999 and 2018 amounts to −0.012 μm/s2/yr at both Zugspitze AG sites. This explains more than half of the observed gravity decrease. Long-term variations on inter-annual and climate-relevant decadal scale will be investigated in the future using as supplement superconducting gravimetry (installed in 2019) and GNSS equipment (since 2018)

Local surface mass-balance reconstruction from a tephra layer - a case study on the northern slope of Mýrdalsjökull, Iceland

Most Icelandic glaciers show high-accumulation rates during winter and strong surface melting during summer. Although it is difficult to establish and maintain mass-balance programs on these glaciers, mass-balance series do exist for several of the ice caps (Bjornsson and others, 2013). We make use of the frequent volcanic eruptions in Iceland, which cause widespread internal tephra layers in the ice caps, to reconstruct the surface mass balance (SMB) in the ablation zone. This method requires information about surface geometry and ice velocity, derived from remote-sensing information. In addition, the emergence angle of the tephra layer needs to be known. As a proof-of concept, we utilize a prominent tephra layer of the Myrdalsjokull Ice Cap to infer local SMB estimates in the ablation area back to 1988. Using tephra-layer outcrop locations across the glacier at different points in time it is possible to determine local mass changes (loss and redistribution) for a large part of the ablation zone, without the use of historic elevation models, which often are not available

Elevation change of Fedchenko Glacier, Pamir Mountains, from GNSS field measurements and TanDEM-X elevation models, with a focus on the upper glacier

Fedchenko Glacier experienced a large thickness loss since the first scientific investigations in 1928. As the largest glacier in the Pamir Mountains, this glacier plays an important role for the regional glacier mass budget. We use a series of Global Navigation Satellite Systems (GNSS) observations from 2009 to 2016 and TanDEM-X elevation models from 2011 to 2016 to investigate recent elevation changes. Accounting for radar wave penetration minimizes biases in elevation that can otherwise reach up to 6 m in dry snow on Fedchenko Glacier, with mean values of 3-4 m in the high accumulation regions. The Seasonal elevation changes reach up to ±5 m. The glacier surface elevation decreased along its entire length over multi-year periods. Thinning rates increased between 2000 and 2016 by a factor of 1.8 compared to 1928 to 2000, resulting in peak values of 1.5 m a-1. Even the highest accumulation basins above 5000 m elevation have been affected by glacier thinning with change rates between -0.2 and -0.4 m a-1 from 2009 to 2016. The estimated glacierwide mass balance rates are -0.27 ± 0.05 m w.e. a-1 for 2000 to 2011 and -0.51 ± 0.04 m w.e. a-1 between 2011 and 2016

Current plate movements across the Mid-Atlantic Ridge determined from 5 years of continuous GPS measurements in Iceland

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