How Different Analysis and Interpolation Methods Affect the Accuracy of Ice Surface Elevation Changes Inferred from Satellite Altimetry

Satellite altimetry has been widely used to determine surface elevation changes in polar ice sheets. The original height measurements are irregularly distributed in space and time. Gridded surface elevation changes are commonly derived by repeat altimetry analysis (RAA) and subsequent spatial interpolation of height change estimates. This article assesses how methodological choices related to those two steps affect the accuracy of surface elevation changes, and how well this accuracy is represented by formal uncertainties. In a simulation environment resembling CryoSat-2 measurements acquired over a region in northeast Greenland between December 2010 and January 2014, different local topography modeling approaches and different cell sizes for RAA, and four interpolation approaches are tested. Among the simulated cases, the choice of either favorable or unfavorable RAA affects the accuracy of results by about a factor of 6, and the different accuracy levels are propagated into the results of interpolation. For RAA, correcting local topography by an external digital elevation model (DEM) is best, if a very precise DEM is available, which is not always the case. Yet the best DEM-independent local topography correction (nine-parameter model within a 3,000 m diameter cell) is comparable to the use of a perfect DEM, which exactly represents the ice sheet topography, on the same cell size. Interpolation by heterogeneous measurement-error-filtered kriging is significantly more accurate (on the order of 50% error reduction) than interpolation methods, which do not account for heterogeneous errors

Perennial Supraglacial Lakes in Northeast Greenland Observed by Polarimetric SAR

Supraglacial liquid water at the margins of ice sheets has an important impact on the surface energy balance and can also influence the ice flow when supraglacial lakes drain to the bed. Optical imagery is able to monitor supraglacial lakes during the summer season. Here we developed an alternative method using polarimetric SAR from Sentinel-1 during 2017-2020 to distinguish between liquid water and other surface types at the margin of the Northeast Greenland Ice Stream. This allows the supraglacial hydrology to be monitored during the winter months too. We found that the majority of supraglacial lakes persist over winter. When comparing our results to optical data, we found significantly more water. Even during summer, many lakes are partly or fully covered by a lid of ice and snow. We used our classification results to automatically map the outlines of supraglacial lakes, create time series of water area for each lake, and hence detect drainage events. We even found several winter time drainages, which might have an important effect on ice flow. Our method has problems during the peak of the melt season, but for the rest of the year it provides crucial information for better understanding the component of supraglacial hydrology in the glaciological system

Versuche über die Innervation der Glandula Parotis

http://tartu.ester.ee/record=b1869450~S1*es

Külföldi játékszín

több tudósokkal kiadja BajzaElőbeszéd -- Galotti Emilia / németból Lessing után Kazinczy Ferenc -- Lessing -- A gyűrű : vígjáték / németből Schröder után Bajza -- Schröde

Facile Synthesis of a Stable Side-on Phosphinyne Complex by Redox Driven Intramolecular Cyclisation

Alkyne complexes with vicinal substitution by a Lewis acid and a Lewis base at the coordinated alkyne are prospective frustrated Lewis pairs exhibiting a particular mutual distance and, hence, a specific activation potential. In this contribution, investigations on the generation of a WII alkyne complex bearing a phosphine as Lewis base and a carbenium group as Lewis acid are presented. Independently on potential substrates added, an intramolecular cyclisation product was always isolated. A subsequent deprotonation step led to an unprecedented side-on λ5-phosphinyne complex, which is interpreted as highly zwitterionic according to visible absorption spectroscopy supported by TD-DFT. Low-temperature 31P NMR and EPR spectroscopic measurements combined with time-dependent IR-spectroscopic monitoring provided insights in the mechanism of the cyclisation reaction. Decomposition of the multicomponent IR spectra by multivariate curve resolution and a kinetic hard-modelling approach allowed the derivation of kinetic parameters. Assignment of the individual IR spectra to potential intermediates was provided by DFT calculations. © 2020 The Authors. Published by Wiley-VCH Gmb

The hydrostatic control of load-induced height changes above subglacial Lake Vostok

Lake Vostok, East Antarctica, represents an extensive water surface at the base of the ice sheet. Snow, ice and atmospheric pressure loads applied anywhere within the lake area produce a hydrostatic response, involving deformations of the ice surface, ice–water interface and particle horizons. A modelling scheme is developed to derive height changes of these surfaces for a given load pattern. It is applied to a series of load scenarios, and predictions based on load fields derived from a regional climate model are compared to observational datasets. Our results show that surface height changes due to snow-buildup anomalies are damped over the lake area, reducing the spatial standard deviation by one-third. The response to air pressure variations, in turn, adds surface height variability. Atmospheric pressure loads may produce height changes of up to 4 cm at daily resolution, but decay rapidly with integration time. The hydrostatic load response has no significant impact neither on ICESat laser campaign biases determined over the lake area nor on vertical particle movements derived from GNSS observations

Deterministic positioning of nanophotonic waveguides around single self-assembled quantum dots

The capability to embed self-assembled quantum dots (QDs) at predefined positions in nanophotonic structures is key to the development of complex quantum-photonic architectures. Here, we demonstrate that QDs can be deterministically positioned in nanophotonic waveguides by pre-locating QDs relative to a global reference frame using micro-photoluminescence (μPL) spectroscopy. After nanofabrication, μPL images reveal misalignments between the central axis of the waveguide and the embedded QD of only (9 ± 46) nm and (1 ± 33) nm for QDs embedded in undoped and doped membranes, respectively. A priori knowledge of the QD positions allows us to study the spectral changes introduced by nanofabrication. We record average spectral shifts ranging from 0.1 nm to 1.1 nm, indicating that the fabrication-induced shifts can generally be compensated by electrical or thermal tuning of the QDs. Finally, we quantify the effects of the nanofabrication on the polarizability, the permanent dipole moment, and the emission frequency at vanishing electric field of different QD charge states, finding that these changes are constant down to QD-surface separations of only 70 nm. Consequently, our approach deterministically integrates QDs into nanophotonic waveguides whose light-fields contain nanoscale structure and whose group index varies at the nanometer level. © 2020 Author(s)

The hydrostatic control of load-induced height changes above subglacial Lake Vostok

Lake Vostok, East Antarctica, represents an extensive water surface at the base of the ice sheet. Snow, ice and atmospheric pressure loads applied anywhere within the lake area produce a hydrostatic response, involving deformations of the ice surface, ice-water interface and particle horizons. A modelling scheme is developed to derive height changes of these surfaces for a given load pattern. It is applied to a series of load scenarios, and predictions based on load fields derived from a regional climate model are compared to observational datasets. Our results show that surface height changes due to snow-buildup anomalies are damped over the lake area, reducing the spatial standard deviation by one-third. The response to air pressure variations, in turn, adds surface height variability. Atmospheric pressure loads may produce height changes of up to ±4 cm at daily resolution, but decay rapidly with integration time. The hydrostatic load response has no significant impact neither on ICESat laser campaign biases determined over the lake area nor on vertical particle movements derived from GNSS observations.Fil: Richter, Andreas Jorg. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de la Plata. Facultad de Cs.astronomicas y Geofisicas. Laboratorio Maggia.; ArgentinaFil: Schröder, Ludwig. Technische Universität Dresden; AlemaniaFil: Scheinert, Mirko. Technische Universität Dresden; AlemaniaFil: Popov, Sergey V.. Polar Marine Geosurvey Expedition; Rusia. Saint Petersburg State University; RusiaFil: Groh, Andreas. Technische Universität Dresden; AlemaniaFil: Willen, Matthias. Technische Universität Dresden; AlemaniaFil: Horwath, Martin. Technische Universität Dresden; AlemaniaFil: Dietrich, Reinhard. Technische Universität Dresden; Alemani

Zur weichselzeitlichen Entwicklungsgeschichte der unteren Saar (Rheinisches Schiefergebirge)

Durch den Bau des Saarkanals im Zuge des Umlauftals Ayl-Wawern-Biebelhausen entstand ein fast 2 km langer Aufschluß, der über die Entwicklung der Saar von der letzten Kaltzeit bis heute neue Erkenntnisse brachte. An zwei günstigen Stellen sind mehr als 12 m mächtige Sande erhalten geblieben, die aufgrund des Fehlens der vulkanischen Eifelassoziation im Schwermineralspektrum und wegen eindeutiger Verzahnung mit Solifluktionsschutt ins Weichselglazial gestellt werden müssen. Diese Sande liegen auf dem etwa 2 m mächtigen Basisschotter, der ebenfalls als letztglaziale Ablagerung gedeutet werden muß. In einem Stillwassersediment (schlurfiger Ton), das auf den Mäanderdurchbruch hinweist, wurde ein Stück Kiefernholz gefunden, das ein Alter von 15 800 ± 300 Jahre aufweist. In den als Hochwasserablagerungen gedeuteten Sanden konnten 3 verschiedene, recht gut ausgebildete Paläoböden ausgemacht werden. Mit Hilfe der Pollenanalyse und zweier C14-Daten konnten die Böden zeitlich bestimmt werden. Der älteste ist mit großer Wahrscheinlichkeit während des Amersfoort-Interstadials ausgebildet worden. Der mittlere Boden ist, im Gegensatz zu den beiden anderen, in einer trockeneren, warmen Phase des Weichselfrühglazials entstanden und wird deswegen ins Brørup-Interstadial gestellt. Sein wesentliches Merkmal ist das Vorkommen von Haselpollen. Der oberste Boden muß ins Spätglazial datiert werden. Da weder im Boden noch in der darüberliegenden Fließerde die Schwermineralien der Eifelassoziation (Laacher Vulkan) gefunden wurden, ist dieser Boden älter als das Alleröd. Er wird als Bildung im Bölling-Interstadial aufgefaßt. Aufgrund dieser Ergebnisse lassen sich über die Entwicklungsgeschichte der unteren Saar sehr viel detailliertere Aussagen machen als das bisher der Fall war.researc