ALBERT

Description: This document is intended to provide basic guidance to researchers who work with digital data as well as all stakeholders with an interest in this issue and also provides advice on sources of further information. It was prepared by the Research Data Working Group in the Priority Initiative “Digital Information” of the Alliance of German Science Organisations.

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., subdaily 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 of the updated ESA Earth System Model (updated ESM) for gravity mission simulation studies is organized as follows: The characteristics of the updated ESM along with some basic validation is presented in Volume 1. A detailed comparison to the original ESA ESM (Gruber et al., 2011) is provided in Volume 2, while Volume 3 contains the description of a strategy to derive realistic errors for the de-aliasing model of high-frequency mass variability in atmosphere and ocean.

Description: Der glazial-isostatische Ausgleich in Island infolge des rezenten Abschmelzens der Vatnajökull-Eiskappe wird durch die Viskositätsverteilung im Erdinnern und durch die Details der Abschmelzgeschichte kontrolliert. Interpretationen der Ergebnisse von GPS- und Schweremeßkampagnen im Zeitintervall 1991–2000 bzw. 1992–1999 mit Hilfe lateral homogener Erdmodelle zur Bestimmung der Lithosphärenmächtigkeit, Asthenosphärenmächtigkeit und Asthenosphärenviskosität sind bislang nicht voll zufriedenstellend gewesen. Insbesondere nahe des Eisrandes war die Anpassung der berechneten Landhebung und Schwereänderung an die Beobachtungsdaten nur unzureichend, was mit der Nichtberücksichtigung des Island-Plumes in den lateral homogenen Erdmodellen zusammenhängen kann. In der vorliegenden Arbeit wird für die Modellierung der Landhebung und Schwereänderung ein Programmpaket verwendet, daß die Berechnung auflastinduzierter Störungen eines Maxwellviskoelastischen, inkompressiblen, selbstgravitierenden, sphärischen Erdmodells gestattet. Um das Vorhandensein des Plumes unter dem Vatnajökull zu simulieren, wird eine axialsymmetrische Viskositätsverteilung verwendet, wobei der Plumeradius und die Plumeviskosität freie Parameter sind. Basierend auf seismischen Ergebnissen wird über dem Plume eine 6 km mächtige Lithosphäre angenommen, die sich im peripheren Bereich des Plumes auf 35 km verdickt. Die Abschmelzgeschichte des Vatnajökulls beruht auf Interpretationen geomorphologischer und klimatologischer Untersuchungen und wird durch eine mit dem Plume koaxiale Last mit parabolischem Profil und zeitabhängigem Radius simuliert. Die Ergebnisse der Modellierung favorisieren einen Plumeradius von ~ 80 km und eine Plumeviskosität von (0.3–1.0) × 1018 Pa s.

Description: Die vorliegende Ausgabe des GFZ-Journals „System Erde“ soll einen Einblick in die am GFZ betriebene Forschung zur Seismologie geben.

Description: [...] In this thesis it is shown that the epoch-differenced ionospheric delay correction is sufficient for estimating the tropospheric delay, e.g., the Zenith Total Delay (ZTD), from SF GPS data. Based on this result, the Satellite-specific Epoch-differenced Ionospheric Delay model (SEID) was developed. In the SEID model the ionospheric corrections for SF data are generated from the observations of surrounding reference stations equipped with DF receivers. With the derived ionospheric corrections and the SF data, pseudo L2 data are generated, which can be processed using existing GPS processing software packages without any changes. [...]

Description: The seismicity data file used for this study is represented by the earthquake catalogue CENEC for Europe north of 44°N (Grünthal et al. 2009a). This paper describes in detail how this homogeneous data file in terms of moment magnitudes Mw (with Mw greater than 3.5) has been derived. The degree of harmonization achieved in CENEC is quantitatively analysed in Grünthal et al. (2009b).

Description: The integrated plate boundary in Chile (IPOC) combines 15 broadband stations with strong-motion sensors, GPS, strain sensors and magneto-telluric stations. The Chilean subduction zone setting provides a high background rate of seismicity (crustal, intermediate depth, and plate interface) in a region with exceptionally low ambient noise, particularly at higher frequencies. We have deployed seismic mini-arrays in the vicinity of IPOC stations PB02 and PB07, and installed a third array to the east of these stations near the village of Quillagua, such that all three arrays form a triangle. Each array has 10 elements and an aperture in the km range. The study area lies just to the north of the northern boundary of the rupture area of the Tocopilla earthquake of 2007 Mw=7.7) and just above or slightly to the east of the downdip limit of plate interface seismicity. Installing the mini-arrays in the area of the existing IPOC has the following advantages: • Independent knowledge of background structure and seismicity from existing and ongoing studies. • Should any transients or other unusual signals be found in the array data, we can look for anomalous signals in geodetic and MT recordings, which will help to narrow down possible underlying mechanisms.

Description: The intention of this article is to present the definitions of different functionals of the Earth's gravity field and possibilities for their approximative calculation from a mathematical representation of the outer potential. [...] More or less, what is compiled here is well-known in physical geodesy but distributed over a lot of articles and books which are not cited here. In the first instance this text is targeted at non-geodesists and it should be "stand-alone readable".