Improving trajectory estimation using 3D city models and kinematic point clouds

Accurate and robust positioning of vehicles in urban environments is of high importance for autonomous driving or mobile mapping. In mobile mapping systems, a simultaneous mapping of the environment using laser scanning and an accurate positioning using global navigation satellite systems are targeted. This requirement is often not guaranteed in shadowed cities where global navigation satellite system signals are usually disturbed, weak or even unavailable. We propose a novel approach which incorporates prior knowledge (i.e., a 3D city model of the environment) and improves the trajectory. The recorded point cloud is matched with the semantic city model using a point‐to‐plane iterative closest point method. A pre‐classification step enables an informed sampling of appropriate matching points. Random forest is used as classifier to discriminate between facade and remaining points. Local inconsistencies are tackled by a segmentwise partitioning of the point cloud where an interpolation guarantees a seamless transition between the segments. The general applicability of the method implemented is demonstrated on an inner‐city data set recorded with a mobile mapping system.     

The current performance of the in situ 14C extraction line at ETH

We present the new ¹⁴C extraction line at ETH Zürich. This system is designed to extract in situ-produced cosmogenic ¹⁴C from terrestrial quartz samples, and to obtain pure CO₂ gas for analysis with a gas ion source Accelerator Mass Spectrometry (AMS) system. Samples are degassed at 1550–1600 °C without the use of a fluxing agent. Gas purification is achieved by a series of cryogenic traps and passage through hot Ag and Cu wool/mesh. Graphitization and, thus, sample dilution is not required. Tests to determine the CO₂ recovery after gas extraction and cleaning yielded consistently good recovery rates of >99.8% (n = 7). The ¹⁴C blank contribution from the all-metal tubing system is negligible. Our preliminary procedural blank estimate – deriving mostly from the hot extraction furnace – is <5 × 10^{5 14}C atoms. Extraction tests on two quartz samples by stepped-heating show a quantitative separation of atmospheric ¹⁴C at ≤500 °C from the in situ component above 1200 °C. Based on these data, we estimate to achieve a complete ¹⁴C extraction from a quartz sample.     

The sedimentary signature of ice-contact sedimentation and deformation at macro- and micro-scale: A case study from NW Scotland

Studies on the genesis of subaerial debris flows and associated deposits are relatively rare in the literature, especially in an ice-marginal context of moraine formation. The present contribution reports results from both the macro- and micro-scales of a subaerial depositional setting in order to contribute to closing this gap. At the macroscale, alternating loose, stratified, clast- and matrix-supported diamicts and finely laminated sand units indicate deposition of debris flows and fluvial units in a subaerial, ice-marginal setting that were stacked up to form a terrestrial ice-contact fan. Macroscale and micromorphological analyses show that this fan displays evidence of a three-phased formation: (a) overriding and glaciotectonisation of pre-existing sediments followed by retreat and burial of this core by (b) ice-contact fan deposition dominated by water-rich fluvial deposition with relatively little debris flow activity and (c) a switch to a gravitational sedimentation style with dominantly debris flow deposition and fewer and thinner fluvial units. Thin sections of both the diamict and laminated sand units show evidence of deposition of a mud and fine sand-rich slurry being expelled from the tops of advancing mass flows. Water-rich fine-grained slurries appear to have been progressively overridden and deformed in response to ductile shear occurring at the base of individual flows. Liquefaction and remobilisation of sand within laminated deposits occurred during such basal shear events, resulting in the injection of liquefied sediments into variably deformed laminated sands and clays. Deformation is more likely to have taken place through internal movement of the sediment due to changing porewater conditions and loading upon emplacement. Our approach confirms previous results that highlight the possibilities of increasing the accuracy of sedimentological investigations through combined sedimentological analyses at varying scales.     

Intercrystalline stable isotope diffusion: a fast grain boundary model

We formulated a numerical model for stable isotope interdiffusion which predicts the temperatures recorded between two or more minerals, and the intragranular distribution of stable isotopes in each mineral, as functions of mineral grain sizes and shapes, diffusivities, modes, equilibrium isotopic fractionations, and the cooling rate of a rock. One of the principal assumptions of the model is that grain boundaries are regions of rapid transport of stable isotopes. This Fast Grain Boundary (FGB) model describes interdiffusion between any number of mineral grains, assuming that local equilibrium and mass balance restrictions apply on the grain boundaries throughout the volume modeled. The model can be used for a rock containing any number of minerals, and number of grain sizes of each mineral, several grain shapes, and any thermal history or domain size desired. Previous models describing stable isotope interdiffusion upon cooling have been based on Dodson's equation or an equivalent numerical analogue. The closure temperature of Dodson is the average, bulk temperature recorded between a mineral and an infinite reservoir. By using Dodson's equation, these models have treated the closure temperature as an innate characteristic of a given mineral, independent of the amounts and diffusion rates of other minerals. Such models do not accurately describe the mass balance of many stable isotope interdiffusion problems. Existing models for cation interdiffusion could be applied to stable isotopes with some modifications, but only describe exchange between two minerals under specific conditions. The results of FGB calculations differ considerably from the predictions of Dodson's equation in many rock types of interest. Actual calculations using the FGB model indicate that closure temperature and diffusion profiles are as strongly functions of modal abundance and relative differences in diffusion coefficient as they are functions of grain size and cooling rate. Closure temperatures recorded between two minerals which exchanged stable isotopes by diffusion are a function of modal abundance and differences in diffusion coefficient, and may differ from that predicted by Dodson's equation by hundreds of degrees C. Either or both of two minerals may preserve detectable zonation, which may in some instances be larger in the faster diffusing mineral. Rocks containing three or more minerals can record a large span of fractionations resulting from closed system processes alone. The results of FGB diffusion modeling indicate that the effects of diffusive exchange must be evaluated before interpreting mineral fractionations, concordant or discordant, recorded within any rock in which diffusion could have acted over observable scales. The predictions of this model are applicable to thermometry, evaluation of open or closed system retrogression, and determination of cooling rates or diffusion coefficients.     

A model for coupled fluid-flow and mixed-volatile mineral reactions with applications to regional metamorphism

The effect of fluid flow on mixed-volatile reactions in metamorphic rocks is described by an expression derived from the standard equation for coupled chemical-reaction and fluid-flow in porous media. If local mineral-fluid equilibrium is assumed, the expression quantitatively relates the time-integrated flux at any point in a flow-system to the progress of devolatilization reactions and the temperature- and pressure-gradients along the direction of flow. Model calculations indicate that rocks are generally devolatilized by fluids flowing uptemperature and/or down-pressure. Flow down-temperature typically results in hydration and carbonation of rocks. Time-integrated fluid fluxes implied by visible amounts of mineral products of devolatilization reactions are on the order of 5·10²–5·10⁴ mol/cm². The model was applied to regionally metamorphosed impure carbonate rocks from south-central Maine, USA, to obtain estimates of fluid flux, flow-direction, and in-situ metamorphic-rock permeability from petrologic data. Calculated time-integrated fluxes are 10⁴–10⁶ cm³/cm² at 400°–450° C, 3,500 bars. Fluid flowed from regions of low temperature to regions of high temperature at the peak of the metamorphic event. Using Darcy's Law and estimates for the duration of metamorphism and hydrologic head, calculated fluxes are 0.1–20·10^-4 m/year and minimum permeabilities are 10^-10–10^-6 Darcy. The range of inferred permeability is in good agreement with published laboratory measurements of the permeability of metamorphic rocks.     

Water-assisted migmatization of metagraywackes in a Variscan shear zone, Aiguilles-Rouges massif, western Alps

Migmatitic rocks developed in metagraywackes during the Variscan orogeny in the Aiguilles-Rouges Massif (western Alps). Partial melting took place 320 Ma ago in a 500 m-wide vertical shear zone. Three leucosome types have been recognised on the basis of size and morphology: (1) large leucosomes > 2 cm wide and > 40 cm long lacking mafic selvage, but containing cm-scale mafic enclaves; (2) same as 1 but with thick mafic selvage (melanosome); (3) small leucosomes < 2 cm and < 40 cm) with thin dark selvages (stromatic migmatites). Types 1 + 2 have mineralogical and chemical compositions in keeping with partial melting experiments. But Type 3 leucosomes have identical plagioclase composition (An_19–28) to neighbouring mesosome, both in terms of major- and trace-elements. Moreover, whole-rock REE concentrations in Type 3 leucosomes are only slightly lower than those in the mesosomes, unlike predicted by partial melting experiments. The main chemical differences between all leucosome types can be related to the coupled effect of melt segregation and late chemical reequilibration.

Mineral assemblages and thermodynamic modelling on bulk-rock composition restrict partial melting to  650 °C at 400 MPa. The large volume of leucosome (20 vol.%) thus generated requires addition of 1 wt.% external water. Restriction of extensive migmatization to the shear zone, without melting of neighbouring metapelites, also points to external fluid circulation within the shear zone as the cause of melting.     

Catalyzing mitigation ambition under the Paris Agreement: elements for an effective Global Stocktake

The Global Stocktake (GST) takes a central role within the architecture of the Paris Agreement, with many hoping that it will become a catalyst for increased mitigation ambition. This paper outlines four governance functions for an ideal GST: pacemaker, ensurer of accountability, driver of ambition and provider of guidance and signal. The GST can set the pace of progress by stimulating and synchronizing policy processes across governance levels. It can ensure accountability of Parties through transparency and public information sharing. Ambition can be enhanced through benchmarks for action and transformative learning. By reiterating and refining the long term visions, it can echo and amplify the guidance and signal provided by the Paris Agreement. The paper further outlines preconditions for the effective performance of these functions. Process-related conditions include: a public appraisal of inputs; a facilitative format that can develop specific recommendations; high-level endorsement to amplify the message and effectively inform national climate policy agendas; and an appropriate schedule, especially with respect to the transparency framework. Underlying information provided by Parties complemented with other (scientific) sources needs to enable benchmark setting for collective climate action, to allow for transparent assessments of the state of emissions and progress of a low-carbon transformation. The information also needs to be politically relevant and concrete enough to trigger enhancement of ambition. We conclude that meeting these conditions would enable an ideal GST and maximize its catalytic effect.

Key policy insights

• The functional argument developed in this article may inspire a purposeful design of the GST as its modalities and procedures are currently being negotiated.

• The analytical framework provided serves as a benchmark against which to assess the GST's modalities and procedures.

• Gaps and blind spots in the official GST can and should be addressed by processes external to the climate regime in academia and civil society.

     

Geochemistry and Evolution of Subcontinental Lithospheric Mantle in Central Europe: Evidence from Peridotite Xenoliths of the Kozakov Volcano, Czech Republic

Neogene basanite lavas of Kozákov volcano, located alongthe Lusatian fault in the northeastern Czech Republic, containabundant anhydrous spinel lherzolite xenoliths that providean exceptionally continuous sampling of the upper two-thirdsof central European lithospheric mantle. The xenoliths yielda range of two-pyroxene equilibration temperatures from 680°Cto 1070°C, and are estimated to originate from depths of32–70 km, based on a tectonothermal model for basalticunderplating associated with Neogene rifting. The sub-Kozákovmantle is layered, consisting of an equigranular upper layer(32–43 km), a protogranular intermediate layer that containsspinel–pyroxene symplectites after garnet (43–67km), and an equigranular lower layer (67–70 km). Negativecorrelations of wt % TiO₂, Al₂O₃, and CaO with MgO and clinopyroxenemode with Cr-number in the lherzolites record the effects ofpartial fusion and melt extraction; Y and Yb contents of clinopyroxeneand the Cr-number in spinel indicate 5 to 15% partial melting.Subsequent metasomatism of a depleted lherzolite protolith,probably by a silicate melt, produced enrichments in the largeion lithophile elements, light rare earth elements and highfield strength elements, and positive anomalies in primitivemantle normalized trace element patterns for P, Zr, and Hf.Although there are slight geochemical discontinuities at theboundaries between the three textural layers of mantle, theretends to be an overall decrease in the degree of depletion withdepth, accompanied by a decrease in the magnitude of metasomatism.Clinopyroxene separates from the intermediate protogranularlayer and the lower equigranular layer yield ¹⁴³Nd/¹⁴⁴Nd valuesof 0·51287–0·51307 (_Nd = +4·6 to+8·4) and ⁸⁷Sr/⁸⁶Sr values of 0·70328–0·70339.Such values are intermediate with respect to the Nd–Srisotopic array defined by anhydrous spinel peridotite xenolithsfrom central Europe and are similar to those associated withthe present-day low-velocity anomaly in the upper mantle beneathEurope. The geochemical characteristics of the central Europeanlithospheric mantle reflect a complex evolution related to Devonianto Early Carboniferous plate convergence, accretion, and crustalthickening, Late Carboniferous to Permian extension and gravitationalcollapse, and Neogene rifting, lithospheric thinning, and magmatism. KEY WORDS: xenoliths; lithospheric mantle; REE–LILE–HFSE; Sr–Nd isotopes; Bohemian Massif     

Coastal upwelling along the north coast of Papua New Guinea and El Niño events during 1981–2005

We investigate the relationship between sea surface temperature (SST) cooling and upwelling along Papua New Guinea’s (PNG) north coast before the onset of El Niño events using a hindcast experiment with a high-resolution ocean general circulation model. Coastal upwelling and related SST cooling appear along PNG north coast during the boreal winter before the onsets of six El Niño events occurring during 1981–2005. Relatively cool SSTs appear along PNG north coast during that time, when anomalous northwesterly surface wind stress, which can cause coastal upwelling by offshore Ekman transport appearing over the region. In addition, anomalous cooling tendencies of SST are observed, accompanying anomalous upward velocities at the base of the mixed layer and shallow anomalies of 27°C isotherm depth. It is also shown that entrainment cooling plays an important role in the cooling of the mixed layer temperature in this region.