ALBERT

Description: The 2014 LoNNe (Loss of the Night Network) intercomparison campaign is the third of four campaigns planned during EU COST Action ES1204. This report provides a brief synopsis of the campaign and its preliminary outcomes. Section 2 describes the measurement locations, the activities of the participants, the instruments used, and the environmental conditions. Section 3 describes a public outreach event held during the campaign. Section 4 provides some preliminary results, outlines the ongoing analyses, and presents research questions for the next campaign to address. Section 5 provides recommendations for the final LoNNe intercomparison campaign in 2016. Section 6 concludes the report.

Description: The ability of any satellite gravity mission concept to monitor mass transport processes in the Earth system is typically tested well ahead of its implementation by means of various simulation studies. Those studies often extend from the simulation of realistic orbits and instrumental data all the way down to the retrieval of global gravity field solution time-series. Basic requirement for all these simulations are realistic representations of the spatio-temporal mass variability in the different sub-systems of the Earth, as a source model for the orbit computations. For such simulations, a suitable source model is required to represent (i) high-frequency (i.e., sub-daily to weekly) mass variability in the atmosphere and oceans, in order to realistically include the effects of temporal aliasing due to non-tidal high-frequency mass variability into the retrieved gravity fields. In parallel, (ii) low-frequency (i.e., monthly to interannual) variability needs to be modelled with realistic amplitudes, particularly at small spatial scales, in order to assess to what extent a new mission concept might provide further insight into physical processes currently not observable. The new source model documented here attempts to fulfil both requirements: Based on ECMWF’s recent atmospheric reanalysis ERA-Interim and corresponding simulations from numerical models of the other Earth system components, it offers spherical harmonic coefficients of the time-variable global gravity field due to mass variability in atmosphere, oceans, the terrestrial hydrosphere including the ice-sheets and glaciers, as well as the solid Earth. Simulated features range from sub-daily to multiyear periods with a spatial resolution of spherical harmonics degree and order 180 over a period of 12 years. In addition to the source model, a de-aliasing model for atmospheric and oceanic high-frequency variability with augmented systematic and random noise is required for a realistic simulation of the gravity field retrieval process, whose necessary error characteristics are discussed. The documentation is organized as follows: The characteristics of the updated ESM along with some basic validation are presented in Volume 1 of this report (Dobslaw et al., 2014). A detailed comparison to the original ESA ESM (Gruber et al., 2011) is provided in Volume 2 (Bergmann-Wolf et al., 2014), while Volume 3 (Forootan et al., 2014) contains a description of the strategy to derive a realistically noisy de-aliasing model for the high-frequency mass variability in atmosphere and oceans. The files of the updated ESA Earth System Model for gravity mission simulation studies are accessible at DOI:10.5880/GFZ.1.3.2014.001.

Description: SEGY and supplementary data of the seismic reflection experiment in the Baza Basin (Southern Spain). Presented are unstacked and unmigrated data of three 2D vibroseis profiles which were carried out in October 2013 and all corresponding raw data.

Description: In this report, we will present the complete derivation of analytical expressions of the EM coupling torque in dependence on the parameters of the fields contributing to it. For this, we choose a special set of spherically harmonic (SH) base functions and present all major steps of the derivation. Our report will be (i) closer to a lecture note than to a scientific paper and should give all readers the possibility to follow the derivations with the related details in the appendix, and can be (ii) used as a formulary for scientists working on this special field of investigation.

Description: This publication is a result of the 13th TRACE conference (Tree Rings in Archaeology, Climatology and Ecology) organized by the Department of Earth and Environmental Sciences at the University of St Andrews on May 6th – 10th, 2014 in Aviemore, Scotland, UK. [...]After review, 18 short papers are published in this volume, giving an overview of the wide spectrum of different fields covered at TRACE.

Description: [...] We develop a regularizing solution procedure accounting for recent theoretical stability estimates. The capabilities of the procedure are shown for a single magnetic field component of the spherical harmonic field expansion beginning from the year 1900 by varying the mantle conductivity model and the degree of smoothness in the regularization. As an example, the radial component of a global (5,5) core-mantle boundary field is calculated for two epochs.

Description: For the motivation behind our investigations, we refer to the introduction of the first part of our report, Hagedoorn & Geiner-Mai (2008). In this part, we will (i) give an analytical description of the topographic surface of the core-mantle boundary (CMB) and derive an approximation for its normal unit vector containing information about the CMB topography, and (ii) derive an expression for the topographic torque as a function of the topographic height, h, and the velocity field, u. For this, we will check the assumptions made when applying the geostrophic approximation to the upper core-surface region. Finally, we will derive analytical expressions for the torque components depending upon the spherical harmonic (SH) coefficients of h and u in a cartesian geocentric coordinate system.

Description: This volume contains extended abstracts from talks and posters presented at the sixth TRACE (Tree Rings in Archaeology, Climatology and Ecology) conference, held in Riga (Latvia) May 3rd – 6th, 2007.

Description: The amplitude spectra of global geophysical phenomena were investigated to motivate research of physical connections between them. The suggested causality was derived from comparison of the spectra, and from cross correlation functions. The following global parameters were discussed: for the earth rotation by the variations of the length of day, for the gemagnetic variation by the global field intensity, changes of the dipole axis and the westward drift, and for climate change by the atmospheric excitation function derived from air pressure variations, and temperature variations. The model of atmospheric excitation, which can be proved most exactly for the annual variation of length of day, is responsible for the 11 and 22 years periods, too. It failed for longer periods e. g., partially for the 30 years periods and completely for the 60 to 80 years periods, which were also discovered in the mean temperature and geomagnetic field variations. Therefore, it was suggested that longer periods in climate change and in the variations of the earth's rotation are caused independently by the same process in the earth core, provided that a physical influence of the geomagnetic field on climate will be accepted in future. The investigation was completed by comparison with the spectra of some local temperature variations in Europe.

Description: In this study two aspects of the geomagnetic field have been investigated. The first part focuses on perturbations of the external field, as seen by the CHAMP satellite and predicted by the Thermosphere-Ionosphere Electrodynamic General Circulation Model, for the purpose of helping to separate out ionospheric sources from the ambient geomagnetic field using a physics based approach. Part two looks at variations of the internal field through an examination of the South Atlantic Anomaly.

Description: The history of the study of Polar Motion began with the derivation of the equations for the rotation of a rigid body by Euler published in 1758. This was followed by further theoretical contributions made by Lagrange (1788) and Poinsot (1834). To confirm the existence of the polar motion of the Earth in terms of a variation of latitude, intensive efforts were undertaken at several observatories toward the end of the 19th century. During the 7th General Conference of the European Arc Measurement in Rome in October 1883, Fergola had already suggested to investigate the problem. The latitude variation was detected by K¨ustner at the Berlin Observatory in 1888. Following this, during the Annual Conference of the Permanent Commission of the ”Internationale Erdmessung” in Salzburg in September 1888, Foerster proposed to consider the variation of latitude more systematically by a Special Commission. Activities began quickly, and after considerable effort the International Latitude Service (ILS) started in September 1899. The paper reviews, in which way the Geodetic Institute Potsdam contributed to the foundation of the ILS and took part in its activities through the work of Helmert, Albrecht,Wanach and Mahnkopf. Based on international scientific cooperation, the results were the rectangular coordinates of the Polar Motion from 1890.0 to 1922.7 at 0.1 year intervals, in particular those derived from the latitude observations at independent stations from 1890.0 to 1899.8, and those derived from the latitude observations at the ILS stations from 1899.9 to 1922.7

Description: The Global Navigation Satellite System (GNSS) plays a significant role in the fields of airborne gravimetry. The objective of this thesis is to develop reliable GNSS algorithms and software for kinematic highly precise GNSS data analysis in airborne gravimetry.

Description: Raw-, SEG-Y and other supplementary data of the amphibious wide-angle seismic experiment carried out in South Turkey, Cyprus and south of Cyprus are presented. The aim of this project was to reveal the crustal structure of the Anatolian plateau, Cyprus and the Eratosthenes Seamount (ESM), south of Cyprus. Simultaneous data acquisition offshore with ocean bottom seismometers and airguns and onshore with seismic land stations and two land shots in South Turkey lead to a 650 km long amphibian seismic profile.

Description: This report as well as the associated data is a supplement to the publication Blöcher et al. (2015) accessible via DOI: 10.1016/j.geothermics.2015.07.008. From 2011-06-01 until 2013-12-31, the measurement and control system at the Groß Schönebeck research platform acquired data from several circulation experiments. Different data values were recorded at a sampling interval of 1 s. Relevant data for understanding and analyzing the hydraulic situation of the system were resampled to a 1 minute interval. From the resampled dataset, additional parameters were derived. Furthermore, if parameters were considered to be essential, but the measurement of these parameters was erroneous, some data were reprocessed. All relevant data and processing steps performed on the data are described within this report. Data described within this report can be accessed via DOI:10.5880/GFZ.b103-15021.1. The presented data was acquired during different research projects by the staff of the International Centre for Geothermal Research as well as Section 4.1 Reservoirtechnologies at the Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences.

Description: Dieser Leitfaden entstand im dreijährigen Projekt „Konzeption und Erprobung von Modellen für forschungsnahe Transferstrukturen in der außeruniversitären Forschung“ – kurz TMod – auf Initiative von zwei Leibniz-Instituten und drei Helmholtz-Zentren unter Projektkoordination durch das Helmholtz-Zentrum Potsdam - Deutsches Geoforschungszentrum GFZ und unter Förderung durch das BMBF, wobei sich der Kreis der Projektpartner im Projektverlauf auf insgesamt neun Einrichtungen erweiterte. Die Beteiligten waren auf der Suche nach zeitgemäßen Instrumenten, mit denen die Ergebnisse und Leistungen ihrer Wissenschaftler effektiver zu echten Innovationen werden. Die unterschiedlichen Erfahrungen, die es bis dahin mit Ausgründungen zur Professionalisierung des Wissens- und Technologietransfers gab, waren sehr unterschiedlich und vorwiegend quantitativ abstrakt aufgearbeitet. Es gab daher gerade bei mittleren und kleinen außeruniversitären Forschungseinrichtungen einen Bedarf nach fundiertem und strukturiertem Anwendungswissen, um eine entsprechende Umstrukturierung zu erleichtern. Das Projekt TMod kam diesem Bedarf mit einer Analyse von Best Practices, der Klärung offener Fragestellungen und einer darauf aufbauenden individuellen Konzeptentwicklungs- und Umsetzungsunterstützung entgegen. Der so entstandene Leitfaden soll wissenschaftliche Einrichtungen, die Ihren Technologietransfer professionalisieren wollen, praktisch unterstützen und sie vom gewonnenen Wissen im Projekt TMod profitieren lassen.

Description: The acronym EMERALD was supposed to stand for ElectroMagnetic Equipment, Raw data And Locations Database. What survived over the years was the EMERALD processing, a set of computer programs to analyse MT time series data, and the EMERALD file format for storing MT data. This document describes the EMERALD file format and how to use it with the C++, C and FORTRAN programming languages. Interface functions also exist for Matlab and Powershell but they are not described here. EMERALD data files typically come in pairs of two files with the same name but differing file name extensions, sometimes called RAW and XTR files. XTR (extract) files are plain ASCII files, which can be read and modified with text editors. RAW files or more generally, EMERALD ‐type data files are in most cases binary and used to store all kind of magnetotelluric (MT) data such as time series, cross‐ and auto spectra and calibration data. The EMERALD ‐type data files store any number of channels of data in matrix form, but do not contain any description of the data. This information is stored in the according XTR file. In 2015 the original XTR files were replaced by a modernized version based on the Extensible Markup Language (XML). The new files have the extension .XTRX.

Description: The dynamic oblateness of the Earth, in terms of the J2 or C20 coefficient of the Earth´s geo-potential has been derived by analysis of LAGEOS Satellite Laser Ranging (SLR) data. Although recent analyses of GRACE (Gravity Recovery and Climate Experiment) mission data of monthly C20 values since 2002 have shown high temporal correlations with LAGEOS results, significant differences still remain. As it is common practice in GRACE data processing to remove a priori the short-term nontidal atmospheric and oceanic induced variations of the gravity potential via the socalled Atmosphere and Ocean De-aliasing Level-1B (AOD1B) products, their use for LAGEOS data processing would allow a direct comparison of results and a rigorous combination of the solutions. Since the consideration of short-term non-tidal atmospheric and oceanic mass redistributions by means of AOD1B time series reveals a significant impact on LAGEOS data processing results, the AOD1B time series has been consistently prolongated back to the advent of LAGEOS-1 in 1976. An analysis for the period 1993-2006 leads to the major findings that the consideration of atmospheric and oceanic mass redistributions result in a considerably reduced seasonal signal in the LAGEOS C20 time series. This in turn reduces the correlation to GRACE significantly by about 30%. This is in opposite to what one would expect, i.e., a better agreement between GRACE and LAGEOS if common standards are applied. Thus, a LAGEOS solution corrected for short-term non-tidal atmosphere and ocean effects is much less sensitive to primarily annual hydrological mass variations than GRACE. In addition, significant semi-annual signals remain. Other indicators such as the unresolved bias between LAGEOS and GRACE in the order of 2·10-10 or LAGEOS orbits and Satellite Laser Ranging (SLR) observation residuals are hardly affected by the AOD1B model.

Description: Although the development of passive margins has been extensively studied over a number of decades, significant questions remain on how mantle and crustal dynamics interact to generate the observed margin geometries. Here, the Orange Basin, located on the south-west African continental margin is investigated. The basin fill is considered to comprise a classic rift-drift passive margin sequence recording the break-up of Gondwana and subsequent opening of the South Atlantic Ocean. Based on interpreted seismic reflection data, a 3D geological model was first constructed. Subsequently, an isostatic calculation (Airy´s model) using a homogeneous middle and lower crust was applied to this geological model to determine the position of the Moho for an isostatically balanced system. Isostatic sensitivity tests were applied to the model, and their gravity response was validated against different crustal structures for the basin. The best-fit model requires dense, presumably mafic material in the middle and lower crust beneath the basin and an abrupt change to less dense material near the coast to reproduce the observed gravity field. The passive margin of the South Atlantic shows typical features of a rifted volcanic continental margin, encompassing seaward dipping reflectors, continental flood basalts and high-velocity/density lower crust at the continent-ocean transition, probably emplaced during initial seafloor spreading in the Early Cretaceous. The Springbok profile offshore western South Africa is a combined transect of reflection and refraction seismic data. This thesis addresses the analysis of the seismic velocity structure in combination with gravity modelling and isostatic modelling to unravel the crustal structure of the passive continental margin from different perspectives. The velocity modelling revealed a segmentation of the margin into three distinct parts of continental, transitional and oceanic crust. As observed at many volcanic margins, the lower crust is characterised by a zone of high velocities with up to 7.4 km/s. The conjunction with gravity modelling affirms the existence of this body and at the same time substantiated its high densities, found to be 3100 kg/m³. Both approaches identified the body to have a thickness of about 10 km. Yet, the gravity modelling predicted the transition between the high-density body towards less dense material farther west than initially anticipated from velocity modelling and confirmed this density gradient to be a prerequisite to reproduce the observed gravity signal. Finally, isostatic modelling was applied to predict average crustal densities if the margin was isostatically balanced. The results imply isostatic equilibrium over large parts of the profile; smaller deviations are supposed to be compensated regionally. The calculated load distribution along the profile implies that all pressures are hydrostatic beneath a depth of 45 km. The presence of lower crustal bodies of high seismic velocities indicates that large volumes of igneous crust formed as a consequence of lithospheric extension. Furthermore, results of a combined approach using subsidence analysis and basin history inversion models are presented. The outcome shows that a classical uniform stretching model does not account for the observed tectonic subsidence. Moreover, it is found that that the thermal and subsidence implications of underplating need to be considered. Another departure from the uniform stretching model is renewed sub-crustal stretching and linked to that uplift in the Cenozoic which is necessary to reproduce the observed phases of erosion and the present-day depth of the basin. The dimension of these events has been examined and quantified in terms of tectonic uplift and sub-crustal stretching. Based on these forward models the heat flow evolution is predicted not only for the available real wells but also for virtual wells over the entire study area. Finally, the hydrocarbon potential and the temperature evolution is presented and shown in combination with inferred maturation of the sediments for depth intervals which comprise potential source rocks.

Description: This study is aimed at a development of numerical method to model the dynamic geoid and the surface plate velocities induced by global mantle flow with the effect of strong lateral viscosity variations (LVV) in conjunction with the effects of selfgravitation and mantle compressibility. I employ the technique, which comprises the combination of the spherical harmonic method, the direct Godunov method used for solving the Stokes and Poisson equations in spherical harmonics with arbitrary boundary conditions, functions of density and radial viscosity, and the iterative method based on the principles suggested by Zhang and Christensen (1993) used for modeling the effect of LVV. The 3-D mantle viscosity model is based on the global seismic tomography model S20a converted to temperature variations. The maximum lateral viscosity contrast in the lithosphere-asthenosphere zone modeled reaches four orders of magnitude. It is found that the influence of LVV on the dynamic geoid is extremely significant: an alteration of the geoid figure due to LVV exceeds 45% of the maximum geoid undulations. The detailed analysis showed that the geoid is affected by both, strong LVV induced in the upper mantle and large-scale LVV induced in the lower mantle. According to the results of this study the separated effects of the upper- and lower-mantle LVV on the geoid figure are nearly additive with respect to the whole-mantle LVV and partly compensating with respect to each other. The mantle flows are strongly affected by LVV as well, especially by the long-wavelength viscosity variations in the lower mantle: global upwellings tend to intensify due to the effects of LVV, while downwellings become weaker. The alteration of the near-surface velocities reaches 30-40% in amplitude not only due to the LVV induced toroidal flow but also due to change in the spheroidal velocity component. I can conclude that the LVV presented in both, upper and lower mantle, play an important part in global modeling, therefore, an incorporation of 3-D viscosity structure into the next generation global dynamic models is a task of vital significance.

Description: The joint project TIPTEQ (from The Incoming Plate to mega-Thrust EarthQake processes) refers to an integrated approach in order to investigate the processes active in the seismogenic coupling zone at the southern Central Chilean margin and to validate their importance for both the initiation of mega-thrust earthquakes and the evolution of the forearc. The lateral variability of these processes and related parameters is investigated along five marine corridors offshore the south Chilean continental margin. The northernmost marine transect is continued onshore with a reflection seismic survey at 38.2◦ S which crosses the hypocenter of the largest ever recorded earthquake, the 1960 Great Chilean earthquake (Mw = 9.5). The processing and structural interpretation of this high-resolution seismic data set is one major task of this thesis. Furthermore, a first-break tomography was conducted to construct a near-surface velocity model. Several tests to validate the tomographic images were conducted and the limitations of the data set and method were explored in detail. The reflection seismic transect lies in the center of an extensive geophysical program comprising magnetotelluric surveys and a large seismological network. An integrative interpretation with the results of the other geophysical groups of TIPTEQ concludes the thesis. The depth section of the TIPTEQ NVR data set shows the subducting Nasca plate below the segmented forearc and a highly reflective overriding South American plate down to a depth of 60 km. High reflectivity directly above the plate interface suggested to be associated with the existence of a subduction channel with a varying thickness of 2 - 5 km down to a depth of at least 38 km. It might continue towards depth. Local seismicity possibly defines the upper bound of the subduction channel. The continental Moho is not clearly imaged. However, one possible location is at 38 - 40 km depth given by the 1960 earthquake hypocenter. The Moho may be continued eastwards to a depth of 35 km where a prominent structure is imaged. This reflector coincides with the modeled Moho interface from a 3–D density model along the Chilean margin. The reflectivity east and above of the 1960 hypocenter area may exhibit alternative eastward continuations of the continental Moho. The position and extent of the continental mantle wedge changes accordingly. Major forearc features such as the crustal Lanalhue Fault Zone and a strong west-dipping reflector perpendicular to the plate interface can be observed. The reflectivity of the oceanic crust increases in depths below 35 km. This increase might be caused by fluid release due to the porosity collapse in basalt. The integrative interpretation links this observation with a zone of high Vp/Vs ratio calculated from the seismological velocity model. Combining all available data sets of seismological, magnetotelluric and gravimetrical findings results in a complex image of the southern Chilean subduction zone, which this thesis addresses to decode.

Description: [...] Studies regarding the theory of this correlation and how to handle it when estimating sub-daily polar motion together with nutation are included in the thesis. Furthermore, it is demonstrated that the common estimation of the terrestrial reference frame and EOPs can be employed to identify a mismatch between the local tie values and the estimated coordinate differences at co-located sites. Thus, the EOPs offer another independent evaluation of the LT values, as mentioned already above for the troposphere gradients. For the studies described in this thesis, it is of vital importance that continuous observations are available for all observation techniques. Therefore, the so-called CONT campaigns of the International VLBI Service for Geodesy and Astrometry (IVS) are well-suited. Such special campaigns with continuous VLBI observations for several days are initiated from time to time in order to demonstrate the full capabilities of VLBI. The studies described in the thesis at hand are based on the two-week CONT campaign scheduled in October 2002, named CONT02.

Description: This study presents methods and field experiments for ground-based GPS altimetry. Although Coarse/Acquisition Code (C/A-code) based methods are introduced, the main part of this work addresses the use of carrier phase-delay observations of the reflected GPS signal and focuses on specular reflection. [...] This study approves the feasibility of ground-based GPS altimetry with the OpenGPS receiver and with only one low-gain and wide field-of-view RHCP antenna using L1 carrier phase-delay observations of reflected GPS signals. The work shows the potential of GPS reflectometry for remote water level monitoring from a safe position in cases where in-situ measurements are not possible, are dangerous or sensors may get destroyed by the highly dynamic sea or glacier environment.

Description: The report contains a description of main results obtained within the research contract between IRE RAS and GFZ Potsdam and results of investigation during period November-December 2007 – the third stage of the contract. The objectives of investigation included (1) elaboration and verification of an innovative phase acceleration-refraction attenuation technique to locate layered and wave structures in the ionosphere and atmosphere; (2) elaborating of a new technique for identification of wave origin of temperature and density fluctuations and determination of the intrinsic frequency of internal gravity waves in the Earth's stratosphere from radio occultation (RO) data; presentation of a technique for evaluating the vertical profiles of the phase, amplitude, horizontal wind perturbations, intrinsic phase speed, kinetic and potential energy of atmospheric waves; (3) maps of waves parameters in the ionosphere and atmosphere showing their regional, seasonal and diurnal variations with aim to establish connections with solar and meteorological activity.

Description: This report studies the vertical crustal motion at tide gauges by analyzing GPS (Global Positioning System) height time series of about 370 GPS stations spanning 1994.0 to 2007.0. The procedure of generating a set of homogeneous GPS time series is described in detail. To estimate the vertical rate, the time series are modelled with seasonal (annual and semiannual) waves and step functions for jumps. To improve the quality of the time series, the ocean tide loading (OTL) corrections are renovated by replacing the OTL corrections derived from new ocean tides model directly on the solutions without re-analyzing the GPS data.

Description: The here presented study contributes to the understanding of convergent plate boundaries in the depth range of their former seismogenic zone aiming at testing inferences and hypotheses of the various kinematic and mechanical concepts presented for the seismogenic zone. Therefore, we use the complete exposure of this part of a former plate interface in the European Alps, one of the best-studied mountain belts that has resulted from successive subduction, accretion and collision, where we analyzed a mélange zone tracing the plate interface zone of the fossil convergent plate margin. Additionally, we included information from Southern Chile, where material, which formerly underwent deformation along the plate interface, was exhumed to the surface by large scale basal accretion at a certain depth to the base of the upper plate. This part of the study provided additive hints for structures and processes occurring along the plate interface zone of convergent plate margins (i.e. within the subduction channel), at least for a restricted PT domain.

Description: The sources for the magnetotelluric method are naturally occurring electromagnetic field variations. Electromagnetic currents are excited over a wide frequency range in the earth’s ionosphere by solar activity and global lighting discharges. While these source are available everywhere on earth and at all times, their signal strength varies considerably. The so-called remote-reference technique is an effective way to improve magnetotelluric data quality by referencing the electromagnetic fields recorded at a local site to simultaneously recorded, undisturbed fields at a remote site. The remote reference approach has become standard for magnetotelluric field work, particularly in areas with high levels of man-made electromagnetic noise; i.e. almost everywhere in central Europe. Identifying a suitable location for a clean remote site is difficult and time-consuming. Maintaining such a site in addition to normal field operations is expensive and logistically challenging. A permanently installed reference station simplifies MT measurements considerably. The radius for which source fields are coherent depends mostly on the frequency content of the signals and the latitude of observations. According to our own tests, signals are coherent at frequencies of up to 10 kHz over distances of 1000 km. After a reconnaissance operation during which several locations all over Germany were tested, we could eventually identify an urban forest near the town of Wittstock in northern Germany as a suitable location for a reference station. A preliminary installation of the reference station was accomplished by mid-2010. The permanent installation in a wooden hut and operating with a range of sensors and sampling rates is available since November 2010. Meanwhile the data of the Wittstock site have been used very successfully to re-process a number of magnetotelluric stations in Germany. This report describes the installation, the type of sensors and the recorded data sets, which are freely available on request. For updated material, please refer to our webpages (http://www.gfz-potsdam.de/en/section/geophysical-deep-sounding/servicesinfrastructure/geophysical-instrument-pool-potsdam-gipp/archive/mt-reference-site/)

Description: Abstract

Description: In August and September 2013, 17 shallow ocean bottom seismograph (S-OBS) stations and 8 land stations had been deployed on and around Muostakh Island (Laptev Sea, Russia) for a time period of 24 days. The specifically designed underwater recording equipment consists of a low-power digital recorder, a standard 4.5Hz 3-component geophone, and a battery pack. These components are enclosed in a watertight cylindrical container safe for operation down to 100m water depth. Land stations were also equipped with 4.5 Hz 1C-geophones as well as with batteries. All instruments recorded continuously with 200 samples per second (sps). The stations were deployed along two profiles covering a region of 8km x 8 km. The tilt of the geophone inside the S-OBS influences the sensor characteristics. Since the orientation and tilt at the ocean bottom was unknown, approximately every 24 hours a calibration signal (a sequence of step-functions) was applied to the sensors of the ocean stations. This might be used to recover the actual sensor characteristics (eigenfrequency and damping). The dataset contains 1) a info-folder with a) a README file; b) a file containing the times when calibration signals occurred (format: recorder_ID - date - time); c) the station table (ASCII; recorder_ID - latitude - longitude - (water)depth); d) a map of the region with the locations of the stations; 2) raw CUBE-formatted data; 3) converted mini-seed-formatted data (hourly files).