Performance analysis of the spaceborne laser ranging system

The Spaceborne Laser Ranging System is a proposed short pulse laser on board an orbiting spacecraft.^1,2,3,4 It measures the distance between the spacecraft and many laser retroreflectors (targets) deployed on the Earth’s surface. The precision of these range measurements is assumed to be about ±2 cm (M. W. Fitzmaurice, private communication). These measurements are then used together with the orbital dynamics of the spacecraft, to derive the relative position of the laser ground targets. Assuming a six day observing period with 50% cloud cover, uncertainties in the baseline for target separations of 50 km to 1200 km were estimated to be on the order of 1 to 3 cm and the corresponding values in the vertical direction, ranged from 1 cm to 12 cm. By redetermining the measurements of the relative target positions, the estimated precision in the baseline for a target separation of 50 km is less than 0.3 cm and for a separation of 1200 km is less than 1 cm. In the vertical direction, the estimated precision ranged from 0.4 cm to 4.0 cm respectively. As a result of the repeated estimation of the relative laser target positions, most of the non-temporal effects of error sources as exemplified by the errors in geopotential are reduced. The Spaceborne Laser Ranging System’s capability of determining baselines to a high degree of precision provides a measure of strain and strain rate as shown byCohen, 1979. These quantities are essential for crustal dynamic studies which include determination and monitoring of strain near seismic zones, land subsidence, and edifice building preceding volcanic eruptions. It is evident that such a system can also be used for geodetic surveys where such precisions are more than adquate.     

Zur Geochemie der Diorit-Gruppe

Zusammenfassung Die Granodiorite und QuarzGlimmer-Diorite aus dem Intrusivgebiet von Fürstenstein (Bayerischer Wald), der Diorit des südlichen Vorspessarts mit eingeschalteten Amphibolitschollen und kalifeldspatreichen Schlieren, sowie die Diorite und Hornblendegabbros des mittleren Bergsträßer Odenwaldes wurden geochemisch verglichen. Zur Bestimmung der Haupt-, Neben- und Spurenelemente in 65 Gesteinsproben wurden röntgenspektrometrische, titrimetrische, flammenphotometrische und emissionsspektralanalytische Methoden herangezogen. Zusätzlich fanden 33 chemische Analysen aus der Literatur Verwendung.Die untersuchten Gesteinstypen reichen vom granodioritischen (Bayerischer Wald) über den dioritischen (Spessart) bis zum hornblenditischen (Odenwald) Chemismus, wobei jedes der drei Untersuchungsgebiete eine mehr oder weniger deutliche Gruppierung zeigt. Innerhalb der einzelnen Dioritkomplexe ist nur ein Teil der petrographisch erfaßbaren Gesteinstypen auch durch einen spezifischen Gesteinschemismus gekennzeichnet.Während die Granodiorite des Bayerischen Waldes bis auf die relativ hohen Zr-Gehalte auch im Hinblick auf die Spurenelementführung normale Verhältnisse zeigen, sind die niedrigen Cu-, Ni- und Zn-Gehalte, sowie das hohe K/Rb-Verhältnis in den Odenwald-Dioriten und Hornblendegabbros auffällig. Trotz der großen Streubreite im Hauptchemismus dieser Proben schwanken die SrGehalte nur relativ wenig.Bemerkenswert bei den Spessart-Dioriten ist, daß diese in den Spurenelementgehalten z. T. erheblich unter den von Vinogradov (1962) angegebenen Clarke-Werten bleiben. Die im Diorit eingeschlossenen Amphibolitschollen zeigen deutlich höhere Cu-, Ni- und Zn-Gehalte, sowie niedrigere Sr-und Ba-Gehalte. Die K/Rb-Verhältnisse unterscheiden sich dagegen praktisch kaum. Der Vergleich der Odenwald-Diorite und Hornblendegabbros mit den Amphiboliten zeigt, daß letztere durch niedrigere CaO-Gehalte, etwas größere Zr-Gehalte und ähnlich niedrige Ni-Gehalte gekennzeichnet sind.Im Lichte der geochemischen Ergebnisse wird die Genese der dioritischen Gesteine diskutiert.

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On the geochemistry of the diorite groupComparative investigations of dioritic rocks from Bayerischer Wald, Spessart and Odenwald (South-Germany)

The granodiorites and quartz diorites of the Fürstenstein igneous complex (Bayerischer Wald), the diorites of the Spessart crystalline area (including schollen of amphibolite, and schlieren rich in K-feldspar) as well as the diorites and hornblende gabbros of the central Odenwald igneous complex have been compared. 65 rock specimens have been analyzed for the major and minor elements Si, Ti, Al, Fe³⁺, Fe²⁺, Mn, Mg, Ca, Na, K, P, as well as for the trace elements Zn, Cu, Ni, Rb, Sr, Zr, Ba, and (semiquantitative) V, and Cr using X-ray spectrometric, flame photometric, titrimetric, and UV-spectrometric methods. 33 additional analyses (major and minor elements only) have been taken from literature.The rock types investigated vary from granodiorite to hornblendite in chemical composition. The averages of the three diorite areas plot near quartz diorite, diorite, and gabbro composition, respectively. This grouping is followed very clearly by the trace element content of Zr, Rb and Ba rather than the other ones. The bearing of the geochemical results on the genesis of dioritic rocks is briefly discussed.

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Herrn Prof. Dr. S. Matthes danken wir für sein stetes Interesse am Fortgang der Arbeit sowie für die kritische Durchsicht des Manuskripts. Die Deutsche Forschungsgemeinschaft förderte die vorliegende Untersuchung in dankenswerter Weise durch die Gewährung von Sachbeihilfen und apparativen Einrichtungen.     

Composition-Induced Variations in SIMS Instrumental Mass Fractionation during Boron Isotope Ratio Measurements of Silicate Glasses

An analytical artefact is reported here related to differences in instrumental mass fractionation between NIST SRM glasses and natural geological glasses during SIMS boron isotope determinations. The data presented demonstrated an average 3.4‰ difference between the NIST glasses and natural basaltic to rhyolitic glasses mainly in terms of their sputtering-induced fractionation of boron isotopes. As no matrix effect was found among basaltic to rhyolitic glasses, instrumental mass fractionation of most natural glass samples can be corrected by using appropriate glass reference materials. In order to confirm the existence of the compositionally induced variations in boron SIMS instrumental mass bias, the observed offset in SIMS instrumental mass bias has been independently reproduced in two laboratories and the phenomenon has been found to be stable over a period of more than one year. This study highlights the need for a close match between the chemical composition of the reference material and the samples being investigated.     

Environmental Radioxenon Levels in Europe: a Comprehensive Overview

Activity concentration data from ambient radioxenon measurements in ground level air, which were carried out in Europe in the framework of the International Noble Gas Experiment (INGE) in support of the development and build-up of a radioxenon monitoring network for the Comprehensive Nuclear-Test-Ban Treaty verification regime are presented and discussed. Six measurement stations provided data from 5 years of measurements performed between 2003 and 2008: Longyearbyen (Spitsbergen, Norway), Stockholm (Sweden), Dubna (Russian Federation), Schauinsland Mountain (Germany), Bruyères-le-Châtel and Marseille (both France). The noble gas systems used within the INGE are designed to continuously measure low concentrations of the four radioxenon isotopes which are most relevant for detection of nuclear explosions: ^131mXe, ^133mXe, ¹³³Xe and ¹³⁵Xe with a time resolution less than or equal to 24 h and a minimum detectable concentration of ¹³³Xe less than 1 mBq/m³. This European cluster of six stations is particularly interesting because it is highly influenced by a high density of nuclear power reactors and some radiopharmaceutical production facilities. The activity concentrations at the European INGE stations are studied to characterise the influence of civilian releases, to be able to distinguish them from possible nuclear explosions. It was found that the mean activity concentration of the most frequently detected isotope, ¹³³Xe, was 5–20 mBq/m³ within Central Europe where most nuclear installations are situated (Bruyères-le-Châtel and Schauinsland), 1.4–2.4 mBq/m³ just outside that region (Stockholm, Dubna and Marseille) and 0.2 mBq/m³ in the remote polar station of Spitsbergen. No seasonal trends could be observed from the data. Two interesting events have been examined and their source regions have been identified using atmospheric backtracking methods that deploy Lagrangian particle dispersion modelling and inversion techniques. The results are consistent with known releases of a radiopharmaceutical facility.     

Field calibration of a formula for entrance mixing of river inflows to lakes: Lake Taupo,North Island,New Zealand

Field measurements were used to validate predictions for the initial dilution of negatively buoyant, cold‐water inflows to Lake Taupo, as part of a study to quantify mixing processes associated with the two largest inflows to the lake. The predictions were made using a formulation originally derived for positively buoyant, warm‐water inflows to cooling ponds. The formulation predicts the total dilution of an inflow during its inertia‐dominated phase between its entrance to the lake and the point where buoyancy forces are great enough to cause the inflow to plunge and form a submerged density current. In one of the measured inflows, the inflowing jet was free to entrain from both sides; in the other, entrainment was restricted on one side by attachment of the inflowing jet to the shoreline of a bay just upstream of the plunge point. In the former example, the unmodified coefficients from the cooling pond formulation provided an excellent prediction of initial dilution. In the latter example, entrainment was reduced and different coefficients were derived. In both examples the inflows remained attached to the lake bed throughout their course until their liftoff at depths of 45–55 m to form interflows. The difference between coefficients for the two inflows indicates that the coefficient values should be considered site‐specific. The formulation is not valid for inflows that separate from the bottom of the inflow channel before plunging. The entrance mixing formulation was incorporated in a more general model of lake stratification, DYRESM, which already includes a well‐documented routine for routing underflows down submerged channels on the bed of a lake. Application of the model to the inflows measured in Lake Taupo gave good results for two model outputs that were not involved in the calibration of the entrance mixing formulation, but that are affected by the result of the initial dilution calculation—the temperatures in the river plume after it has plunged, and the insertion depth.     

Dominant amphipods of Posidonia oceanica seagrass meadows display considerable trophic diversity

Gut content examination and trophic markers (fatty acids, stable isotopes of C and N) were combined to delineate the diet of the dominant species of amphipods from Mediterranean Posidonia oceanica seagrass meadows and to highlight trophic diversity among this community. Our results indicate that, although all dominant species heavily relied on macroalgal epiphytes, considerable interspecific dietary differences existed. Carbon stable isotope ratios notably showed that some of the amphipod species favored grazing on epiphytes from leaves or litter fragments (Apherusa chiereghinii, Aora spinicornis, Gammarus aequicauda), while others such as Dexamine spiniventris preferred epiphytes from rhizomes. The remaining amphipods (Caprella acanthifera, Ampithoe helleri and Gammarella fucicola) readily consumed both groups. In addition, SIAR modeling suggested that most species had a mixed diet, and relied on several food items. Fatty acid analysis and gut contents revealed that contributions of microepiphytic diatoms and of benthic and suspended particulate organic matter to the diet of amphipods were anecdotal. None of the examined species seemed to graze on their seagrass host [low 18:2(n‐6) and 18:3(n‐3) fatty acids contents], but Gammarus aequicauda partly relied on seagrass leaf detritus, as demonstrated by the lesser ¹³C‐depletion of their tissues. Overall, our findings suggest that amphipods, because of their importance in the transfer of organic matter from primary producers and detritus to higher rank consumers, are key items in P. oceanica‐associated food webs.     

Nitrous oxide production and denitrification rates in estuarine intertidal saltmarsh and managed realignment zones

Increasing concerns over habitat loss and rising costs of sea defence maintenance due to rising sea levels, has seen increases in the practice of managed realignment and reflooding of former reclaimed areas of intertidal saltmarsh and mudflat around the world. These practices are taking place with little knowledge of their impact on soil biogeochemical processes. Rates of denitrification (using the acetylene inhibition technique) and nitrous oxide (N₂O) production were measured from a long-established saltmarsh (SM) and an adjacent, recently re-flooded managed realignment (MR) site comprising former arable land in the estuary of the River Torridge, Devon, UK. Incubations were carried out in closed chambers in which patterns of tidal flooding were simulated automatically. Measurements were made during periods of flood and non-flood over a total of four tidal inundations with estuarine water. During the latter two flooding episodes floodwater was amended with nitrate (NO₃⁻). Nitrous oxide production in the SM soil generally was lower than in the MR soil, with mean values and standard errors over the whole incubation of 0.27 ± 0.16 mg N₂O-N m⁻² h⁻¹ and 0.65 ± 0.15 mg N₂O-N m⁻² h⁻¹ respectively. Denitrification rates demonstrated a similar trend although generally were an order of magnitude higher than N₂O production, with mean rates and standard errors of 2.88 ± 1.12 mg N₂O-N m⁻² h⁻¹ in the SM soil and 3.39 ± 1.16 mg N₂O-N m⁻² h⁻¹ in the MR soil. The data suggest that both soils are net sinks for NO₃⁻ and net sources for N₂O. Both patterns of tidal inundation and floodwater chemistry affect the process rates in each soil differently. The impact of flooding with NO₃⁻ – amended water was greater on the SM soil than the MR soil, and it is likely that decomposing vegetation buried in the accreting sediments following reflooding at the MR site were supplying a source of N in the soil, and so process rates were less dependent upon external supplies. The act of managed realignment in intertidal zones could therefore result in an increase in mean production of N₂O in intertidal zones, at least in the short term.