The profile of Saturn's ring a as derived from stellar occultations

Stellar occultations behind Saturn's ring A reveal sharp-edged gaps in its outer parts. Observed fluctuations in stellar brightness during one observation can be interpreted as Fresnel's diffraction zones. According to this the sharpness of the edges of the gap are estimated to be under 700 m, which also means that the thickness of ring A in that part cannot exceed a few hundred metres. A further conclusion is that particle size must be a lot less than a few hundred metres.     

Bidirectional reflectance spectrometry of gravel at the Sjökulla test field

The Sjökulla test site is used for testing and calibrating aerial images. The permanent test field is made of four types of gravel (dark gabbro, grey granite, red granite, white limestone) in two sizes (diameters 8–16 mm and 4–8 mm) set in various patterns. The bidirectional reflection properties of the targets together with their temporal changes must be known in order to carry out radiometric and spectral evaluation and calibration.The bidirectional reflectance distribution functions (BRF) of the gravel have been measured several times in the test fields using portable field goniospectrometers belonging Finnish Geodetic Institute (FGI), and once using the European Goniometic Facility (EGO) of the Joint Research Centre (JRC) at Ispra, Italy. Detailed BRFs have been obtained, showing features typical to particulate media, e.g. a small bowl shape, strong backscattering, and smooth wavelength dependence. Temporal range measurements over several years show that the black gabbro and red granite are fairly stable, while the grey granite has changed somewhat over the years and the white limestone has experienced dramatic darkening effects, requiring action to be taken.The measured BRF data have increased the usability of the test field considerably. The results are also useful in the development and validation of scattering models for particulate media. The site has proved to be a good test bench for goniospectrometric instruments, too.     

Lithospheric structure of the Trans-European Suture Zone along the TTZ–CEL03 seismic transect (from NW to SE Poland)

The large-scale CELEBRATION 2000 seismic experiment investigated the velocity structure of the crust and upper mantle between western portion of the East European Craton (EEC) and the eastern Alps. This area comprises: the Trans-European Suture Zone, the Carpathian Mountains, the Pannonian Basin and the Bohemian Massif. This experiment included 147 chemical shots recorded by 1230 seismic stations during two deployments. Good quality data along 16 main and a few additional profiles were recorded. One of them, profile CEL03, was located in southeastern Poland and was laid out as a prolongation of the TTZ profile performed in 1993. This paper focuses on the joint interpretation of seismic data along the NW–SE trending TTZ–CEL03 transect, located in the central portion of the Trans-European Suture Zone. First arrivals and later phases of waves reflected/refracted in the crust and upper mantle were interpreted using two-dimensional tomographic inversion and ray-tracing techniques. This modelling established a 2-D (quasi 3-D) P-wave velocity lithospheric model. Four crustal units were identified along the transect. From northwest to southeast, thickness of the crust varies from 35 km in the Pomeranian Unit (NW) to 40 km in the Kuiavian Unit, to 50 km in the Radom–Łysogóry Unit and again to 43 km in the Narol Unit (SE). The first two units are thought to be proximal terranes detached from the EEC farther to the southeast and re-accreted to the edge of the EEC during the Early Palaeozoic. The origin of the remaining two units is a matter of dispute: they are either portions of the EEC or other proximal terranes. In the area of the Polish Basin (first two units), the P-wave velocity is very low (V_p < 6.1 km/s) down to depths of 15–20 km indicating that a very thick sedimentary and possibly volcanic rock sequence, whose lower portion may be metamorphosed, is present. The velocity beneath the Moho was found to be rather high, being 8.25 km/s in the northwestern portion of the transect, 8.4 km/s in the central sector, and 8.1 km/s in the southeastern sector.     

A diurnal study on the distribution of filter feeding zooplankton: Effect of emergent macrophytes,pH and lake trophy

The objective of the present study was to investigate the importance of emergent macrophytes as refugia in lakes of different trophic status. Furthermore, the effect of water quality on diel changes in the distribution of littoral cladocerans was of interest, with special attention paid on diurnal fluctuations of filter feeder communities, induced by pH changes under a heavy phytoplankton bloom. The study was conducted by investigating littoral cladoceran populations in different zones (inside, at the edge and outside the macrophyte stands) in two basins with divergent water quality. No tendency towards diurnal migration related to emergent macrophytes was observed in the clear-water, mesotrophic Isontalonselkä basin. The dominating cladoceran, Daphnia spp., formed highest densities during daytime in the outer zone. Meanwhile, strong nocturnal cladoceran density peaks in all zones, simultaneous with lowered pH, were witnessed in the very turbid, hypertrophic Kirkkojärvi basin. Reverse horizontal migration was observed in large-bodied filter feeders, Limnosida frontosa and Sida crystallina, conceivably due to predation avoidance from young-of-the-year fish aggregating within the vegetation during the day.     

Surveyed and modelled one‐year morphodynamics in the braided lower Tana River

Field measurements and morphodynamic simulations were carried out along a 5‐km reach of the sandy, braided, lower Tana River in order to detect temporal and spatial variations in river bed modifications and to determine the relative importance of different magnitude discharges on river bed and braid channel evolution during a time span of one year, i.e. 2008–2009. Fulfilling these aims required testing the morphodynamic model's capability to simulate changes in the braided reach. We performed the simulations using a 2‐D morphodynamic model and different transport equations. The survey showed that more deposition than erosion occurred during 2008–2009. Continuous bed‐load transport and bed elevation changes of ±1 m, and a 70–188‐m downstream migration of the thalweg occurred. Simulation results indicated that, during low water periods, modifications occurred in both the main channel and in other braid channels. Thus, unlike some gravel‐bed rivers, the sandy lower Tana River does not behave like a single‐thread channel at low discharge. However, at higher discharge, i.e. exceeding 497 m³/s, the river channel resembled a single‐thread channel when channel banks confined the flow. Although the spring discharge peaks caused more rapid modifications than slower flows, the cumulative volumetric changes of the low water period were greater. The importance of low water period flows for channel modifications is emphasized. Although the 2‐D model requires further improvements, the results were nevertheless promising for the future use of this approach in braided rivers. Copyright © 2013 John Wiley & Sons, Ltd.     

Estimating the inundation area of a massive,hypothetical jökulhlaup from northwest Vatnajökull,Iceland

Jökulhlaups are the consequence of a sudden and significant release of meltwater from the edge of a glacier. Such floods are sourced commonly from ice-dammed lakes, but occasional volcanic eruptions beneath ice can produce intense jökulhlaups due to prodigious rates of meltwater release. Globally, volcanogenic jökulhlaups have caused fatalities and damage to infrastructure within effected catchments. Here, we present the results of one-dimensional hydraulic modelling of the inundation area of a massive, hypothetical jökulhlaup on the Jökulsá á Fjöllum River in northeast Iceland; the floodwater source for this simulation is an eruption within the ice-filled caldera of Bárðarbunga: an active volcano beneath the Vatnajökull ice cap. Remotely sensed data were used to derive a digital elevation model and to assign surface-roughness parameters. We used a HEC-RAS/HEC-GeoRAS system to host the hydraulic model; to calculate the steady water-surface elevation; to visualise the flooded area; and to assess flood hazards. Maximum discharge was set notionally at 180,000 m³ s^?1 and the duration and volume of the jökulhlaup were placed at 39 h and 14 km³, respectively. During the simulated rise to maximum discharge, the mean velocity of the jökulhlaup was 2.8 m s^?1 over a distance of 120 km. At the height of the jökulhlaup an area of 460 km² was inundated. Modelling results showed that, along short reaches, stream-power values exceeded 11,000 W m^?2; such energy conditions would have allowed boulders up to 10-m in diameter to be mobilised by the jökulhlaup. Unsteady flow was simulated along a 22-km reach of the flood tract and it revealed strong spatial and temporal variations in flood power. Besides providing insight into the erosional and depositional effects of a volcanogenic jökulhlaup, the modelling results enable estimates of the relative timing and location of likely flooding hazards.     

Detection of organic biomarkers in crude oils using ToF-SIMS

In this study, we show that time of flight-secondary ion mass spectrometry (ToF-SIMS) can be used to detect organic biomarkers, such as hopanes and steranes, in non-fractionated crude oils, without extraction and chemical preparation. Hopanes and steranes may provide valuable information on the history of life on early Earth, particularly if they are present in fluid inclusions in ancient rocks. Due to the presence of different generations of inclusions in even very small rock samples, it would be advantageous to find a method capable of detecting biomarkers in single oil rich fluid inclusions. The capability of ToF-SIMS for detailed chemical analysis of very small sample amounts makes it a potential technique for such analysis, and in this work this possibility is explored. The presence of hopanes and steranes in four different crude oils of different ages and stages of biodegradation was investigated using ToF-SIMS and GC–MS. By combining analyses of biomarker standards, crude oils and chromatographic oil fractions, specific peaks for the different biomarkers were identified in the ToF-SIMS spectra. The presence of these peaks in the spectra from the crude oil samples could be attributed to the biomarkers based on exact mass determination and by comparison with the spectra from the biomarker containing and biomarker lacking fractions, respectively. In addition, the results show that a significant biomarker signal may be obtained from a 10 μm² oil sample, demonstrating the potential of ToF-SIMS for analysis of single oil bearing fluid inclusions, which in turn may contribute to a better understanding of the early history of life on Earth.     

Detecting vehicle traffic patterns in urban environments using taxi trajectory intersection points

Abstract

Detecting and describing movement of vehicles in established transportation infrastructures is an important task. It helps to predict periodical traffic patterns for optimizing traffic regulations and extending the functions of established transportation infrastructures. The detection of traffic patterns consists not only of analyses of arrangement patterns of multiple vehicle trajectories, but also of the inspection of the embedded geographical context. In this paper, we introduce a method for intersecting vehicle trajectories and extracting their intersection points for selected rush hours in urban environments. Those vehicle trajectory intersection points (TIP) are frequently visited locations within urban road networks and are subsequently formed into density-connected clusters, which are then represented as polygons. For representing temporal variations of the created polygons, we enrich these with vehicle trajectories of other times of the day and additional road network information. In a case study, we test our approach on massive taxi Floating Car Data (FCD) from Shanghai and road network data from the OpenStreetMap (OSM) project. The first test results show strong correlations with periodical traffic events in Shanghai. Based on these results, we reason out the usefulness of polygons representing frequently visited locations for analyses in urban planning and traffic engineering.     

Future fluvial erosion and sedimentation potential of cohesive sediments in a coastal river reach of SW Finland

This study aims to analyse the combined impacts of future discharges and sea levels on erosion–sedimentation potential, and its seasonal changes, in a ~43‐km‐long coastal river reach of South‐west Finland. To our knowledge, this kind of combined study has not been performed before. In addition to surveying the present erosion–sedimentation conditions, the daily erosion–sedimentation potential is simulated with a one‐dimensional hydrodynamic model for the 1971–2000 and 2070–2099 periods by applying four discharge scenarios. Different sea level stages are also employed in the simulations. All scenarios forecast increasing autumn and winter discharges, but diminishing summer discharges. This indicates increasing river channel erosion, particularly during winters and autumns. Although discharge changes have altogether a greater influence on erosion–sedimentation potential, the importance of sea level changes on sedimentation is noticeable in the estuary. The rising sea level scenarios increase the sedimentation potential. In total, by 2070–2099, the erosion potential may increase in most parts of the study area. Copyright © 2013 John Wiley & Sons, Ltd.