Determination of instantaneous sea surface,wave heights,and ocean currents using satellite observations of the global positioning system

Abstract

Using GPS phase observations in the kinematic mode, we are able to achieve centimeter accuracy in relative three‐dimensional coordinates. This could be verified even for fast‐moving sensors in aircraft, such as airborne photogrammetric cameras, at the time of exposure. Sophisticated kinematic software has been developed resolving cycle slips and carrier‐phase ambiguities during motion. To determine the instantaneous sea surface, the GPS receiver is placed in a free‐drifting buoy with the antenna on top. Differencing the 1‐Hz observations, wave heights can be determined as well as velocity and direction of ocean (tidal) currents.

This article deals with the experiences from a test for the practical realization of this proposal. Hardware installation, software, and data analysis are described. Plans to use such an observational scenario of a GPS buoy array in the North Sea for the calibration of the radar altimeter of the European satellite ERS‐1 are presented.     

Estimation of seismic drift demands for frame structures

A process is outlined and evaluated for the estimation of seismic roof and storey drift demands for frame structures from the spectral displacement demand at the first mode period of the structure. The spectral displacement demand is related to the roof drift demand for the multi‐degree‐of‐freedom (MDOF) structure using three modification factors, accounting for MDOF effects, inelasticity effects, and P‐delta effects. Median values and measures of dispersion for the factors are obtained from elastic and inelastic time history analyses of nine steel moment resisting frame structures subjected to sets of ground motions representative of different hazard levels. The roof drift demand is related to the storey drift demands, with the results being strongly dependent on the number of stories and the ground motion characteristics. The relationships proposed in this paper should prove useful in the conceptual design phase, in estimating deformation demands for performance assessment, and in improving basic understanding of seismic behaviour. Copyright © 2000 John Wiley & Sons, Ltd.     

Heterotype Mischbarkeit zwischen Wolframit- und Rutilgruppe

Zusammenfassung Untersucht wurden die heterotypen Mischsysteme zwischen Wolframit- und Rutilgruppe FeNbO₄-TiO₂, FeNbO₄-FeTaO₄, FeWO₄- FeTaO₄ und FeWO₄-TiO₂. Aus der Stereometrie der Gitter läßt sich abschätzen, daß ein statistischer Übergang beider Gittertypen nicht wahrscheinlich ist.Im System FeWO₄-FeTaO₄ verkleinert sich die Mischungslücke mit sinkender Temperatur und verschwindet nach unten am FeTaO₄-Rand. Infolge des gleichsinnig geneigten Verlaufes beider Phasengrenzen ist die Temperatur der Umwandlung Rutil-Wolframitgitter für FeTaO₄ nicht extrapolierbar, die wahrscheinlich noch unter 570° C liegt.In den Systemen FeNbO₄- TiO₂ und FeNbO₄-FeTaO₄ hat die Mischungslücke ebenfalls gleichsinnig geneigte Begrenzungen. Die Mischungslücke verschwindet in diesen Systemen mit steigender Temperatur schon vor dem Systemrand. Es koexistieren dann in 1. Ordnung zwei heterotype Mischkristalle gleicher Zusammensetzung, aber verschiedenen Molvolumens. Der experimentell gefundene Diagrammtyp wird diskutiert.Aus Extrapolationen von Gitterkonstanten und Volumen von Mischkristallreihen gegen die Systemränder lassen sich diese Daten für die Rutilmodifikation von FeNbO₄ und die Wolframitmodifikation von FeTaO₄ finden, die beide in den experimentell untersuchten Zustandsbereichen instabil gegen die Wolframitmodifikation von FeNbO₄ bzw. die Rutilmodifikation von FeTaO₄ sind.Die Gehalte von Fe₂O₃ + Nb₂O₅ in Rutil (Ilmenorutil) sind Rutil-FeNbO₄-Mischkristalle.     

Shock effects in melilite

Shock recovery experiments on melilite samples in the pressure range from 11 to 50.5 GPa have been performed in order to examine the effects of shock waves on this material. The shocked samples were subsequently studied in the transmission electron microscope. All samples displayed the shock-induced amorphous areas, known as diaplectic glass. The amount of diaplectic melilite glass increased from a few percent at 11 GPa to about 85 percent at 50.5 GPa shock pressure. The shock waves also caused deformational effects as planar faults parallel to (001) and dislocations with a density in the order of 10¹⁰ cm^?2. Regarding the present discussion on the origin and nature of diaplectic glass, diaplectic melilite glass is assumed to be the reversion product of a high-density phase produced in the shock front. Deformed melilites in Ca-Al-rich inclusions from chondritic meteorites studied so far do not contain diaplectic glass. It is assumed that the meteoritic melilites were hot (>1,000° C) and thus plastically deformable by shock waves of rather low amplitudes.     

Interstitial flow through preferential flow paths in the hyporheic zone of the Oberer Seebach,Austria

We investigated interstitial flow velocities in the Oberer Seebach, Austria, with NaCl tracer injections at a sediment depth of 30 cm to estimate the hydraulic conditions experienced by invertebrates inhabiting the hyporheic zone. Flow velocity measured with tracers is taken as travel time of the water along a straight line between injection and sampling points, although the water flows around sediment particles, and thus travels a somewhat longer distance. From sections of stream sediment in which the interstitial spaces were replaced by concrete, we estimated that this difference amounts, on average, to 27% and used this factor to correct the results of our velocity measurements. Corrected interstitial water velocities ranged from 0.01 to 1.32 cm s^-1 and were independent of surface discharge. We also studied spatial flow patterns in the bed sediments with long-term tracer injections. The three-dimensional distribution of tracer concentrations 24 hours after the start of the injection indicated that interstitial water preferentially flows in a complex network of areas of high hydraulic connectivity. Reynolds numbers for flow in the hyporheic pore space ranged from 0.1 to 489, implying that the flow environment varies from laminar up to the zone of transition to turbulent flow. Therefore, invertebrates may have a size-related active choice of areas where either friction drag or pressure drag predominates. The consequence of flow patterns, such as those observed in our study, is that small-scale variability of hydraulic conditions may be an important determinant of the patchy invertebrate distribution in bed sediments.     

The role of radiation in an inversion-capped planetary boundary layer

In an inversion-capped planetary boundary layer (PBL), the structure of the turbulent fluxes as well as the height of the inversion are determined by the interaction of turbulent mixing in the PBL, large-scale subsidence above the PBL and radiational cooling. Here the sensitivity of the inversion height and of the turbulent fluxes due to radiational processes is investigated with the aid of a three-layered model for a well mixed PBL. For an example of the Trade-Wind region, the inversion height (i.e., the difference between surface pressure and pressure at the inversion level) varies between 46 and 257 mb and the surface flux of moist static energy between 417 and 99 W m^-2, if the (mean) radiative net flux divergence for both the inversion and the well-mixed layer is changed over a reasonable range of values. None of the parameterization schemes existing in the literature is able to describe these radiational effects in an appropriate way. This is due to the fact that these parameterizations are either not or not flexibly enough linked to the thermodynamical model parameter. Therefore the demand for an adequate parameterization of the radiational influence in a well-mixed PBL under a subsidence inversion is obvious.     

Discharge experiments simulating chemical evolution on the surface of Titan

Saturn's moon Titan has been considered as one of the few places in our Solar System, where atmospheric and surface conditions could have produced organic compounds essential as precursors for an evolution of life. The Cassini-Huygens mission has provided new data on Titan's atmosphere and surface, which enabled us to simulate the chemical processes occurring under these conditions. Possible lightning events on Titan cannot only produce higher hydrocarbons, but also allow surface water ice to participate in the reaction scenario, resulting in CHO, CHN, and CHON compounds including several molecules relevant for the formation of amino acids and nucleic acids.     

Application of the geomechanical facies approach and comparison of exploration and evaluation methods used at Soultz-sous-Forêts (France) and Spa Urach (Germany) geothermal sites

Earth-reservoirs are increasingly exploited today with the extraction of resources, such as heat and hydrocarbons, and the large-scale emplacement of waste, such as CO₂ sequestration. The characterization, site investigation, predictive modeling and long-term monitoring are dependent on the processes being investigated and modeled. In most cases complex coupled processes have to be addressed in a geologically complex rock mass system. In this paper we present a conceptual holistic framework known as geomechanical facies linking all the scales of investigation, characterization and reservoir development methods. We demonstrate this concept on the work undertaken during the design and development of the enhanced geothermal systems (EGS) systems at the forefront of European Hot-Dry-Rock (HDR) technology, Soultz-sous-Forêts (France) and Spa Urach (Germany). Soultz-sous-Forêts is situated within granitic rocks and an active tectonic graben system in the central part of the Rhine Graben. It presents conditions of lithology, temperature, stress, hydraulics and geochemistry that are very different from those at Spa Urach, located in a very dense gneiss formation in the South German crystalline complex. Spa Urach exhibits more elastic behavior and is set tectonically within an almost inactive strike-slip stress field described in more detail in Sects. “Drill core analysis” and “Hydraulic stimulation at Spa Urach”. This paper compares the exploration and field development methods used at these two sites against the back drop of the geomechanical facies concept. Issues addressed include the key parameters for flow and heat transport properties, coupled hydro-mechanical process identification, the success of the HDR reservoir as a heat exchanger and exploration techniques applicable to the different facies. Identification of the key geomechanical facies gives an indication as to which technologies will prove more efficient in the application of HDR technology. The results of this study will hopefully help in developing heat recovery schemes for the long-term economical operation of future HDR plants and EGS as well as assist in the understanding of engineered geosystems.