Analysis of geodetic satellite (Geos I) observations in North America

Geos I observations made at thirty optical and four Secor stations were analyzed in the geometric and short-arc modes for the purpose of detecting systematic distortions in the North American Datum. The results indicate that the Nad at its origin (Meades Ranch, Kansas) requires an easterly rotation in azimuth and a westerly rotation in the prime vertical plane, both in the magnitude of one second of arc to fit the satellite data. There is also evidence of the need for a reduction in scale of about 1:200.000.     

A study on the combination of satellite, airborne, and terrestrial gravity data

Satellite gravity missions, such as CHAMP, GRACE and GOCE, and airborne gravity campaigns in areas without ground gravity will enhance the present knowledge of the Earths gravity field. Combining the new gravity information with the existing marine and ground gravity anomalies is a major task for which the mathematical tools have to be developed. In one way or another they will be based on the spectral information available for gravity data and noise. The integration of the additional gravity information from satellite and airborne campaigns with existing data has not been studied in sufficient detail and a number of open questions remain. A strategy for the combination of satellite, airborne and ground measurements is presented. It is based on ideas independently introduced by Sjöberg and Wenzel in the early 1980s and has been modified by using a quasi-deterministic approach for the determination of the weighting functions. In addition, the original approach of Sjöberg and Wenzel is extended to more than two measurement types, combining the Meissl scheme with the least-squares spectral combination. Satellite (or geopotential) harmonics, ground gravity anomalies and airborne gravity disturbances are used as measurement types, but other combinations are possible. Different error characteristics and measurement-type combinations and their impact on the final solution are studied. Using simulated data, the results show a geoid accuracy in the centimeter range for a local test area.     

Evaluating EOF modes against a stochastic null hypothesis

In this paper it is suggested that a stochastic isotropic diffusive process, representing a spatial first order auto regressive process (AR(1)-process), can be used as a null hypothesis for the spatial structure of climate variability. By comparing the leading empirical orthogonal functions (EOFs) of a fitted null hypothesis with EOF modes of an observed data set, inferences about the nature of the observed modes can be made. The concept and procedure of fitting the null hypothesis to the observed EOFs is in analogy to time analysis, where an AR(1)-process is fitted to the statistics of the time series in order to evaluate the nature of the time scale behavior of the time series. The formulation of a stochastic null hypothesis allows one to define teleconnection patterns as those modes that are most distinguished from the stochastic null hypothesis. The method is applied to several artificial and real data sets including the sea surface temperature of the tropical Pacific and Indian Ocean and the Northern Hemisphere wintertime and tropical sea level pressure.     

Improvement of the geoid in local areas by satellite gradiometry

Summary Satellite gradiometry is studied as a means to improve the geoid in local areas from a limited data coverage. Least-squares collocation is used for this purpose because it allows to combine heterogeneous data in a consistent way and to estimate the integrated effect of the attenuated spectrum. In this way accuracy studies can be performed in a general and reliable manner. It is shown that only three second-order gradients contribute significantly to the estimation of the geoidal undulations and that it is sufficient to have gradiometer data in a 5°×5° area around the estimation point. The accuracy of the geoid determination is strongly dependent on the degree and order of the reference field used. An accuracy of about ±1 m can be achieved with a reference field of (12, 12). There is an optimal satellite altitude for each reference field and this altitude may be higher than 300 km for a field of low degree and order. The influence of measuring errors is discussed and it is shown that only gradiometer data with accuracies better than ±0.05 E will give a significant improvement of the geoid. Finally, some results on the combination of satellite gradiometry and terrestrial gravity measurements are given. The proposed method seems to be well suited for local geoid determinations down to the meter range. It is especially interesting for unsurveyed and difficult areas because no terrestrial measurements are necessary. Furthermore, it has the practical advantage that only a local data coverage is needed.     

Sedimentationszyklen und stratigraphisch-fazielle Probleme der Randfazies des Unteren Muschelkalkes (Kernbohrung Mersch/ Luxemburg)

Zusammenfassung Ausgehend von einem Vergleich randnaher Normprofile und der faziellen Analyse eines vollständigen Bohrprofils wird für die Randfazies des Unteren Muschelkalkes ein Sedimentationsmodell entwickelt, das auf der Basis klimatisch und epirogenetisch bedingter Untergliederungen des Profils neue Parallelisierungsmöglichkeiten mit beckenwärtigen Faziesbereichen eröffnet.Hervorstechendste Merkmale des Bohrprofils sind rhythmisches Auftreten von Magnesit — der als sedimentäre Bildung bislang nur in Zusammenhang mit chloridischen Evaporiten bekannt war —, eine sedimentologisch und geochemisch begründete zyklische Gliederung sowie intensive Bioturbation und zugleich durchgehende Vergipsung.Die Zyklen sind formal gekennzeichnet durch Koppelung von tonigem Sandstein mit geringen Eisen- und hohen Magnesiumgehalten einerseits und von rotem Ton und Silt mit hohen Eisen- und niedrigen Magnesiumwerten andererseits. Die Zyklen werden als Wechselfolge von litoralen Sedimentationsphasen in subtropischem Klima und Abschnürungsphasen mit Hungersedimentation in aridem Klima interpretiert. Der syndiagenetisch gebildete Magnesit ist dabei Tonsedimentationsphasen genetisch zugeordnet. Anhand der Verteilung der vier nicht-detritischen Hauptminerale Dolomit, Gips, Anhydrit und Magnesit wird der Diageneseablauf rekonstruiert.Nach einer Diskussion der Bildungsumstände und der Korrelierbarkeit bieten sich die Werksteinzone der Randfazies und die Spiriferinabank der Beckenfazies als sedimentologische Zeitmarke an.

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A depositional model of the marginal facies of the Lower Muschelkalk (Middle Triassic) is developed by comparison of near-marginal profiles and a facies analysis of a complete drilling record. It is based upon climatologically and epirogenetically caused partitions of the profile and opens new possibilities of correlation with basinal areas.Significant features of the drilling record are rhythmic occurrences of magnesite in sediments only known in connection with chloridic evaporites, a cyclic deposition based on sedimentological and geochemical criteria, and intensive bioturbation with a gypsification throughout.The cycles are formally marked by the correlation of clayey sandstone with low iron and high magnesium contents at the one hand and of red clay and silt with high iron and low magnesium values at the other hand. The cycles are interpreted as an alternation of littoral sedimentation under a subtropical climate and of stages of lagoonal conditions or emersion under an arid climate. The magnesite syndiagenetically formed is genetically attached to stages of clay sedimentation. The process of diagenesis is reconstructed studying the distribution of four main non-detrital minerals: dolomite, gypsum, anhydrite, and magnesite.After discussion of the depositional conditions and the possibilities of correlation, the Werkstein-Zone of the marginal facies and the Spiriferina-Bank of the basinal facies are thought to be sedimentological time markers.

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Résumé Une conception de la formation du facies marginal du Muschelkalk inférieur est développée sur la base d'une comparaison entre les profils normés de la région de sondage Mersch/Luxembourg et l'analyse facielle du profil complet de la carotte de ce sondage. A partir des divisions en partie causées par les climats et par des mouvements épirogénétiques, cette conception donne une nouvelle possibilité de corrélation avec le facies situé plus au centre du bassin sédimentaire.Le forage étudié est caractérisé par la présence rythmique de magnésite, qui, jusqu'à présent, était seulement connu en tant que formation sédimentaire, avec des évaporites, par une répartition cyclique basée sur des observations sédimentologiques et géochimiques et par une bioturbation intensive ainsi qu'une gypsification générale.Les cycles sont caractérisés formellement par le couplage d'un grès argileux à faible teneur en fer et à forte teneur en magnésium d'une part et d'argile rouge à forte teneur en fer et à faible teneur en magnésium d'autre part. Les cycles sont interpretés comme une séquence alternante comprenant une sédimentation littorale en climat subtropical et une sédimentation lagunaire ou d'émersion en climat aride. La magnésite formée syndiagénétiquement est donc coordonnée à une phase sédimentaire argileuse. Le cours de la diagénèse est reconstruit à partir de l'étude de la répartition des quatre minéraux principaux non-détriques: dolomite, gypse, anhydrite et magnésite.A la suite de la discussion des conditions de formation et des possibilités de corrélation la « Werkstein-Zone » du facies marginal et la « Spiriferina-Bank » du facies central apparaissent comme des indicateurs sédimentologiques chronostratigraphiques.

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