Application of ray-traced tropospheric slant delays to geodetic VLBI analysis

The correction of tropospheric influences via so-called path delays is critical for the analysis of observations from space geodetic techniques like the very long baseline interferometry (VLBI). In standard VLBI analysis, the a priori slant path delays are determined using the concept of zenith delays, mapping functions and gradients. The a priori use of ray-traced delays, i.e., tropospheric slant path delays determined with the technique of ray-tracing through the meteorological data of numerical weather models (NWM), serves as an alternative way of correcting the influences of the troposphere on the VLBI observations within the analysis. In the presented research, the application of ray-traced delays to the VLBI analysis of sessions in a time span of 16.5 years is investigated. Ray-traced delays have been determined with program RADIATE (see Hofmeister in Ph.D. thesis, Department of Geodesy and Geophysics, Faculty of Mathematics and Geoinformation, Technische Universität Wien. http://resolver.obvsg.at/urn:nbn:at:at-ubtuw:1-3444, 2016) utilizing meteorological data provided by NWM of the European Centre for Medium-Range Weather Forecasts (ECMWF). In comparison with a standard VLBI analysis, which includes the tropospheric gradient estimation, the application of the ray-traced delays to an analysis, which uses the same parameterization except for the a priori slant path delay handling and the used wet mapping factors for the zenith wet delay (ZWD) estimation, improves the baseline length repeatability (BLR) at 55.9% of the baselines at sub-mm level. If no tropospheric gradients are estimated within the compared analyses, 90.6% of all baselines benefit from the application of the ray-traced delays, which leads to an average improvement of the BLR of 1 mm. The effects of the ray-traced delays on the terrestrial reference frame are also investigated. A separate assessment of the RADIATE ray-traced delays is carried out by comparison to the ray-traced delays from the National Aeronautics and Space Administration Goddard Space Flight Center (NASA GSFC) (Eriksson and MacMillan in http://lacerta.gsfc.nasa.gov/tropodelays, 2016) with respect to the analysis performances in terms of BLR results. If tropospheric gradient estimation is included in the analysis, 51.3% of the baselines benefit from the RADIATE ray-traced delays at sub-mm difference level. If no tropospheric gradients are estimated within the analysis, the RADIATE ray-traced delays deliver a better BLR at 63% of the baselines compared to the NASA GSFC ray-traced delays.     

Deriving incline values for street networks from voluntarily collected GPS traces

ABSTRACT

When producing optimal routes through an environment, considering the incline of surfaces can be of great benefit in a number of use cases. For instance, steep segments need to be avoided for energy-efficient routes and for routes that are suitable for mobility-restricted people. Such incline information may be derived from digital elevation models (DEMs). However, the corresponding data capturing methods (e.g. airborne LiDAR, photogrammetry, and terrestrial surveying) are expensive. Current low-cost and open-licensed DEM (e.g. Shuttle Radar Topography Mission [SRTM] and Advanced Spaceborne Thermal Emission and Reflection Radiometer [ASTER]) generally do not have sufficient horizontal resolution or vertical accuracy, and lack a global coverage. Therefore, we have investigated an alternative low-cost approach which derives street incline values from GPS traces that have been voluntarily collected by the OpenStreetMap contributors. Despite the poor absolute accuracy of this data, the relative accuracy of traces seems to be sufficient enough to compute incline values with reasonable accuracy. A validation shows that the accuracy of incline values calculated from GPS traces slightly outperforms incline values derived from SRTM-1 DEM, though results depend on how many traces per street segment are used for computation.     

Regional climate changes drive increased scaled-chrysophyte abundance in lakes downwind of Athabasca Oil Sands nitrogen emissions

Several limnological and paleolimnological investigations have linked enhanced atmospheric nitrogen (N) deposition to nutrient enrichment and increased primary production. The Athabasca Oil Sands Region (AOSR) in northeast Alberta, Canada is a significant source of N emissions, particularly since development intensified during the 1990s, and recent paleolimnological investigations provide evidence of increased lake production in adjacent areas subject to enhanced N deposition. The AOSR, however, has also experienced atmospheric warming since ca. AD 1900, and therefore the relative effects of nutrient deposition and climate changes on lake production remain unclear. We undertook a factorial-design paleolimnological assessment of 16 lakes in northwest Saskatchewan to quantify changes in abundance and species composition of scaled chrysophytes over the past 100 years. Study sites included both N-limited and P-limited lakes within control regions, as well as lakes that receive enhanced N deposition from the AOSR. We hypothesized that a change in algal communities within N-limited AOSR-impacted lakes, without concurrent changes in the other lake groups, would suggest AOSR-derived N as a driver of enhanced primary production. Instead, marked increases in concentrations of scaled chrysophytes, mainly Mallomonas crassisquama, occurred in the recent sediments in cores from all four lake groups (N-limited vs. P-limited, impacted vs. control), suggesting that regional climate change rather than N deposition was the paramount process enhancing chrysophyte production. Because chrysophyte abundances tended to be higher in deep, lower-pH lakes, and chrysophyte time series were fit best by lake-specific generalized additive models, we infer that climate effects may have been mediated by additional catchment and/or lake-specific processes.     

Isoprene and Its Oxidation Products Methyl Vinyl Ketone, Methacrolein, and Isoprene Related Peroxides Measured Online over the Tropical Rain Forest of Surinam in March 1998

Airborne measurements of volatile organic compounds (VOC) were performed overthe tropical rainforest in Surinam (0–12 km altitude,2°–7° N, 54°–58° W) using the proton transferreaction mass spectrometry (PTR-MS) technique, which allows online monitoringof compounds like isoprene, its oxidation products methyl vinyl ketone,methacrolein, tentatively identified hydroxy-isoprene-hydroperoxides, andseveral other organic compounds. Isoprene volume mixing ratios (VMR) variedfrom below the detection limit at the highest altitudes to about 7 nmol/molin the planetary boundary layer shortly before sunset. Correlations betweenisoprene and its product compounds were made for different times of day andaltitudes, with the isoprene-hydroperoxides showing the highest correlation.Model calculated mixing ratios of the isoprene oxidation products using adetailed hydrocarbon oxidation mechanism, as well as the intercomparisonmeasurement with air samples collected during the flights in canisters andlater analysed with a GC-FID, showed good agreement with the PTR-MSmeasurements, in particular at the higher mixing ratios.Low OH concentrations in the range of 1–3 × 10⁵molecules cm^-3 averaged over 24 hours were calculated due to lossof OH and HO₂ in the isoprene oxidation chain, thereby stronglyenhancing the lifetime of gases in the forest boundary layer.     

The late-and post-Variscan tectonic evolution of the Western Border fault zone of the Bohemian massif (WBZ)

 Paleostress analysis and evaluation of the stratigraphic unconformities reveal an extremely polyphase development of one of the most prominent fault zones of Central Europe, usually known as the Franconian Line (FL). Because the FL is just one fault zone, although it is the most important fault zone within a complex fault system, a more appropriate term is used herein: Western Border fault zone of the Bohemian massif (WBZ). The reconstruction of the paleostress history was carried out by analysing sequences of individual strain increments that belong to the same stratigraphic “units” (e.g., late-Variscan granites, Tertiary basalts). A succession of at least 15 paleostress directions and tectonic regimes have been determined since late-Variscan time. Received: 7 July 1996 / Accepted: 24 October 1996     

Carbonyl Sulfide (COS) in the Surface Ocean and the Atmospheric COS Budget

Carbonyl sulfide (COS) mixing ratioswere measured in the marine atmosphere and in airequilibrated with surface sea water during severalcruises in the North Sea and western NorthAtlantic. In April 1994, North Sea waters weresupersaturated with respect to the atmosphere,resulting in oceanic emissions of COS. Saturationratios varied between the equilibrium value of one inthe central North Sea and high values of >15 in theElbe Estuary. We observed weak diel cycles of surfacewater COS during a three day drift station. During theunderway parts of the cruise, diel COS variations weremasked by the high geographical variability of COSconcentrations in the German Bight. In August 1994, weobserved a pronounced diel cycle of COS off theFlorida coast with saturation ratios varying betweenthe equilibrium value of one in the early morning andmaximum values of four to five in the afternoon. InMarch 1995, we found COS supersaturation as well asextensive undersaturation in the western NorthAtlantic between Norfolk, VA, and Bermuda. Suchundersaturation in marine surface waters results inregional and seasonal uptake of atmospheric COS. Basedon our data and those of other researchers, weestimate the global oceanic COS net emission to bebetween 1.3 and 2.5 Gmol yr^-1. This estimate is significantly smaller than previous ones which had notconsidered the possibility of COS uptake by theoceans. COS hydrolysis in the ocean has a significantinfluence on the atmospheric turnover time of COS,which we estimate to be 5.7 yr. This may contribute tothe lack of an observable increase in atmospheric COSlevels despite substantial anthropogenic emissions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Origin of tourmaline and oxide minerals from the metamorphosed Rampura Agucha Zn-Pb-(Ag) deposit, Rajasthan, India

Summary The sediment-hosted exhalative Rampura Agucha Zn-Pb-(Ag) deposit in Rajasthan, India, contains a number of oxide minerals which have been formed as a result of high-grade metamorphism. Gahnite (Zn_0.66–0.75Fe_0.13–0.24Mg_0.06–0.13Al_1.98–2.01O₄) is a common minor phase in the ores and formed from breakdown of sphalerite and Al-rich silicates. Pyrophanite-ilmenite solid solution (Fe_0.42–0.68Mn_0.32–0.58Ti_0.99–1.01O₃) is very rare and occurs, intergrown with rutile, as a result of unmixing of a Ti-Fe-Mn bearing precursor mineral.Dravite-rich tourmaline with Fe/(Fe+Mg) ratios around 0.02 occurs at the hanging wall contact of the orebody with the paragneisses and is intergrown with the ore minerals. Tourmaline from the stratabound ores is distinguished from schorl-rich tourmaline of two pegmatite samples which show Fe/(Fe+Mg) ratios of 0.43 and 0.62, respectively. It is argued that dravite-rich tourmaline (or another B-rich precursor mineral) is of premetamorphic origin. This dravite-rich tourmaline recrystallized during high-grade metamorphism when the metamorphic fluid, represented by H₂O-CO₂±CH₄-N₂ inclusions, was trapped.Amphiboles, muscovites and biotites from metamorphic rocks of the deposit display radiometric³⁹Ar/⁴⁰Ar cooling ages between 788 and 909 Ma.

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Dravit-reicher Turmalin und Oxide der metamorphen Zn-Pb-(Ag) Lagerstätte Rampura Agucha, Rajasthan, Indien

Zusammenfassung Die sedimentär-exhalative Zn-Pb-(Ag) Lagerstätte Rampura Agucha in Rajasthan, Indien, beinhaltet eine Reihe von Oxidmineralen, die infolge der hochgradigen Regional-metamorphose gebildet wurden. Gahnit (Zn_0.66–0.75Fe_0.13–0.24 Mg_0.06–0.13Al_1.98–2.01O₄) ist eine häufig anzutreffende Phase, die sich aus Sphalerit und Al-reichen Silikatphasen gebildet hat. Pyrophanit-Ilmenit (Fe_0.42–0.68Mn_0.32–0.58 T_0.99–1.01O₃) ist sehr selten und bildet, aufgrund der Entmischung eines Ti-Fe-Mn hältigen Vorläuferminerals, Verwachsungen mit Rutil.Dravit-reicher Turmalin mit einem Fe/(Fe+Mg) Verhältnis um 0.02 bildete sich gleichzeitig mit den Sulfidmineralen am Kontakt des Erzkörpers mit den hangenden Paragneisen der Lagerstätte. Dieser Turmalin unterscheidet sich klar von Schörlreichem Turmalin mit Fe/(Fe+Mg) Verhältnissen von 0.43 und 0.62 von zwei Pegmatiten. Die Herkunft dieses prämetamorphen Dravit-reichen Turmalins (oder dessen Vorgängerminerals) ist unklar. Dieser Turmalin rekristallisierte während der Metamorphose, wobei er das metamorphe H₂O-CO₂±CH₄-N₂-Fluid in Form von primären Einschlüssen einschloß.Amphibol, Muskowit und Biotit wurden mittels³⁹Ar/⁴⁰Ar-Methode datiert und liefern radiometrische Abkühlungsalter zwischen 788 und 909 Ma.

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With 8 Figures     

Comment on the paper by S. Kielbassa and H., Duddeck: Stress — Strain fields at the tunnelling face — Three-dimensional analysis for two-dimensional technical approach

Rock Mech. Rock Engng. 24 (3), 115–132, 1991.     

Åland GPS levelling campaign in 1987

In October 1987 a four day satellite GPS campaign was performed over the Åland archipelago to test the possibility of connecting the Swedish and Finnish national height systems. This paper summarizes the gained experiences using 5 WM 101 GPS receivers and the PoPS software.The computing results for the connection between the two height systems are considerably dependent on the choice of geoidal undulation model and systematic error parameter model. Using the NKG Scandinavian geoid 1989, which is probably the most accurate geoid available for the region, and a bias and tilt parameter model the difference between the Swedish RH70 system and the Finnish N60 system is estimated to 11.4 ± 4.0 cm. An independent check is provided by two connecting border bench marks in northern Scandinavia yielding the difference 19.2 ± 4.2 cm. In view of that merely single frequency GPS receivers were used together with the PoPS software, we consider this result most satisfactory.