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- ItemNon-invasive prospection techniques and direct push sensing as high-resolution validation tools in wetland geoarchaeology – Artificial water supply at a Carolingian canal in South Germany?(Amsterdam [u.a.] : Elsevier Science, 2020) Rabiger-Völlmer, Johannes; Schmidt, Johannes; Linzen, Sven; Schneider, Michael; Werban, Ulrike; Dietrich, Peter; Wilken, Dennis; Wunderlich, Tina; Fediuk, Annika; Berg, Stefanie; Werther, Lukas; Zielhofer, ChristophThe prospection of (geo-)archaeological sites yield important knowledge about the concept and the utilisation of pre-historical and historical infrastructure. The satisfactory conduction of classical prospection methods like archaeological excavations or geoarchaeological vibra-coring might be challenging in the case of large sites or difficult underground conditions. This is particularly problematic in wetlands featuring a high groundwater table and high compaction rates of organic layers. In this study, we provide an alternative and non- to minimal-invasive exploration approach to discover hydro-engineering structures for artificial water supply in the surrounding of a Carolingian summit canal in South Germany. The Early Medieval Fossa Carolina was intended 792/793 CE to bridge the Central European watershed between Rhine-Main and Danube catchments. As the canal was constructed as a summit canal, an artificial water supply at the highest levels seemed very likely or even obligatory. In order to explore these obligatory hydro-engineering features, we use a wide range of on-site and off-site tools in a spatial hierarchical way. Our approach includes the large-scale SQUID magnetic survey and the sighting of historical maps. Furthermore, we integrate high-resolution direct push colour logs, and subsequent vibra-coring for small-scale stratigraphical verification and sedimentological analyses. The SQUID magnetic survey and related depth models discover two pronounced linear anomalies that might represent potential artificial water inlets in the North-Eastern and Northern Sections of the canal. I) In the North-Eastern Section, direct push colour logs, vibra-coring and 14C dating provide no evidence for a Carolingian hydro-engineering feature but reveal a natural lenticular structure of Early Holocene age. II) The linear magnetic anomaly in the Northern Section can be excluded with high probability as a hydro-engineering structure as well. Here, direct push colour logs, vibra-coring, 14C dating and the comparison with a historic map reveal evidence for a historic gravel road. Thus, we have nicely verified the magnetic information but have no prove for an artificial Carolingian water inlet from the Swabian Rezat River that contradicts with assumptions of former studies. © 2020 The Authors
- ItemComparison of novel semi-airborne electromagnetic data with multi-scale geophysical, petrophysical and geological data from Schleiz, Germany(Amsterdam [u.a.] : Elsevier Science, 2020) Steuer, Annika; Smirnova, Maria; Becken, Michael; Schiffler, Markus; Günther, Thomas; Rochlitz, Raphael; Yogeshwar, Pritam; Mörbe, Wiebke; Siemon, Bernhard; Costabel, Stephan; Preugschat, Benedikt; Ibs-von Seht, Malte; Zampa, Luigi Sante; Müller, FranzIn the framework of the Deep Electromagnetic Sounding for Mineral EXploration (DESMEX) project, we carried out multiple geophysical surveys from regional to local scales in a former mining area in the state of Thuringia, Germany. We prove the applicability of newly developed semi-airborne electromagnetic (EM) systems for mineral exploration by cross-validating inversion results with those of established airborne and ground-based investigation techniques. In addition, supporting petrophysical and geological information to our geophysical measurements allowed the synthesis of all datasets over multiple scales. An initial regional-scale reconnaissance survey was performed with BGR's standard helicopter-borne geophysical system deployed with frequency-domain electromagnetic (HEM), magnetic and radiometric sensors. In addition to geological considerations, the HEM results served as base-line information for the selection of an optimal location for the intermediate-scale semi-airborne EM experiments. The semi-airborne surveys utilized long grounded transmitters and two independent airborne receiver instruments: induction coil magnetometers and SQUID sensors. Due to the limited investigation depth of the HEM method, local-scale electrical resistivity tomography (ERT) and long-offset transient electromagnetic (LOTEM) measurements were carried out on a reference profile, enabling the validation of inversion results at greater depths. The comparison of all inversion results provided a consistent overall resistivity distribution. It further confirmed that both semi-airborne receiver instruments achieve the bandwidth and sensitivity required for the investigation of the resistivity structure down to 1 km depth and therewith the detection of deeply seated earth resources. A 3D geological model, lithological and geophysical borehole logs as well as petrophysical investigations were integrated to interpret of the geophysical results. Distinct highly-conductive anomalies with resistivities of less than 10 Om were identified as alum shales over all scales. Apart from that, the petrophysical investigations exhibited that correlating geophysical and geological information using only one single parameter, such as the electrical resistivity, is hardly possible. Therefore, we developed a first approach based on clustering methods and self-organizing maps (SOMs) that allowed us to assign geological units at the surface to a given combination of geophysical and petrophysical parameters, obtained on different scales. © 2020 The Authors
- ItemThe Superconducting Gravimeter CD-034 at Moxa Observatory: More than 20 Years of Scientific Experience and a Reanimation(Basel : Birkhäuser, 2022) Jahr, T.; Stolz, R.In this work, advanced methods and processing schemes for the analysis of data from a Superconducting Gravimeter (SG) will be introduced and their relevance on acquired data proved. The SG CD-034 was installed on Easter of 1999 in the Geodynamic Observatory Moxa of the Friedrich Schiller University Jena, Germany. Initially, the quality of the recorded data was examined, spectra for the detection of the parasitic modes were calculated and the calibration values for the two sensors were determined. Ever since very high-quality gravity data of this SG and most of the other worldwide SGs were made available through the storage archive of the Global Geodynamics Project (GGP later changed to IGETS, International Geodynamics and Earth Tide Service) for global scientific investigations at that time. SG’s such as the one in Moxa (Germany) still deliver significant scientific value for global gravitational field studies as well as for regional/local studies which will be shortly reviewed. Examples are the detection of polar motion, the influence of continental water loading in general and in particular river basin loads, the gravimetric effect of North Sea storm surges and the study of hydro-gravimetric signals, which could be compared with satellite observations and global hydraulic models. The long-term, low-noise operation of complex SG’s requires some effort on maintenance. In order to evaluate the correct operation of the SG, new data processing steps were introduced to assist in the analysis of the data in case of issues with the instrumentation. For example, in 2012/2013 and 2020/2021 severe interference in the gravimeter electronics in Moxa led to a significant loss of data. In both cases, however, the cause could be determined, and the corresponding electronic components renewed. Since July 2021, the SG in Moxa registers again with high data quality comparable or slightly better than before the incident. Initial tests and tidal analyses confirm the validity of the old calibration factors, and the authors now look forward to the re-established long-term recording with excitement and confidence.