Estimating uncertainty associated with water stages from a single SAR image

It is the goal of remote sensing to infer information about objects or a natural process from a remote location. This invokes that uncertainty in measurement should be viewed as central to remote sensing. In this study, the uncertainty associated with water stages derived from a single SAR image for the Alzette (G.D. of Luxembourg) 2003 flood is assessed using a stepped GLUE procedure. Main uncertain input factors to the SAR processing chain for estimating water stages include geolocation accuracy, spatial filter window size, image thresholding value, DEM vertical precision and the number of river cross sections at which water stages are estimated. Initial results show that even with plausible parameter values uncertainty in water stages over the entire river reach is 2.8 m on average. Adding spatially distributed field water stages to the GLUE analysis following a one-at-a-time approach helps to considerably reduce SAR water stage uncertainty (0.6 m on average) thereby identifying appropriate value ranges for each uncertain SAR water stage processing factor. For the GLUE analysis a Nash-like efficiency criterion adapted to spatial data is proposed whereby acceptable SAR model simulations are required to outperform a simpler regression model based on the field-surveyed average river bed gradient. Weighted CDFs for all factors based on the proposed efficiency criterion allow the generation of reliable uncertainty quantile ranges and 2D maps that show the uncertainty associated with SAR-derived water stages. The stepped GLUE procedure demonstrated that not all field data collected are necessary to achieve maximum constraining. A possible efficient way to decide on relevant locations at which to sample in the field is proposed. It is also suggested that the resulting uncertainty ranges and flood extent or depth maps may be used to evaluate 1D or 2D flood inundation models in terms of water stages, depths or extents. For this, the extended GLUE approach, which copes with the presence of uncertainty in the observed data, may be adopted.     

Improvement of Global Hydrological Models Using GRACE Data

After about 6 years of GRACE (Gravity Recovery and Climate Experiment) satellite mission operation, an unprecedented global data set on the spatio-temporal variations of the Earth’s water storage is available. The data allow for a better understanding of the water cycle at the global scale and for large river basins. This review summarizes the experiences that have been made when comparing GRACE data with simulation results of global hydrological models and it points out the prerequisites and perspectives for model improvements by combination with GRACE data. When evaluated qualitatively at the global scale, water storage variations on the continents from GRACE agreed reasonably well with model predictions in terms of their general seasonal dynamics and continental-scale spatial patterns. Differences in amplitudes and phases of water storage dynamics revealed in more detailed analyses were mainly attributed to deficiencies in the meteorological model forcing data, to missing water storage compartments in the model, but also to limitations and errors of the GRACE data. Studies that transformed previously identified model deficiencies into adequate modifications of the model structure or parameters are still rare. Prerequisites for a comprehensive improvement of large-scale hydrological models are in particular the consistency of GRACE observation and model variables in terms of filtering, reliable error estimates, and a full assessment of the water balance. Using improvements in GRACE processing techniques, complementary observation data, multi-model evaluations and advanced methods of multi-objective calibration and data assimilation, considerable progress in large-scale hydrological modelling by integration of GRACE data can be expected.     

Investigating parabolic and nebkha dune formation using a cellular automaton modelling approach

Vegetation plays an important role in shaping the morphology of aeolian dune landscapes in coastal and semi‐arid environments, where ecogeomorphic interactions are complex and not well quantified. We present a Discrete ECogeomorphic Aeolian Landscape model (DECAL) capable of simulating realistic looking vegetated dune forms, permitting exploration of relationships between ecological and morphological processes at different temporal and spatial scales. The cellular automaton algorithm applies three simple rules that lead to self‐organization of complex dune environments, including nebkhas with distinctive deposition tails that form in association with mesquite‐type shrubs, and hairpin (long‐walled) parabolic dunes with trailing ridges that evolve from blowouts in association with vegetation succession. Changing the conditions of simulations produces differing landscapes that conform qualitatively to observations of real‐world dunes. The model mimics the response of the morphology to changes in sediment supply, vegetation distribution, density and growth characteristics, as well as initial disturbances. The introduction of vegetation into the model links spatial and temporal scales, previously dimensionless in bare‐sand cellular automata. Grid resolutions coarser than the representative size of the modelled vegetation elements yield similar morphologies, but when cell size is reduced to much smaller dimensions, the resultant landscape evolution is dramatically different. The model furthermore demonstrates that the relative response characteristics of the multiple vegetation types and their mutual feedback with geomorphological processes impart a significant influence on landscape equilibria, suggesting that vegetation induces a characteristic length scale in aeolian environments. This simple vegetated dune model illustrates the power and versatility of a cellular automaton approach for exploring the effects of interactions between ecology and geomorphology in complex earth surface systems. Copyright © 2007 John Wiley & Sons, Ltd.     

Vegetation patterns and diversity along an altitudinal and a grazing gradient in the Jabal al Akhdar mountain range of northern Oman

Little is known about the effects of grazing on vegetation composition on the Arabian Peninsula. The aim of this study therefore was to analyse the vegetation response to environmental conditions of open woodlands along an altitudinal and a grazing gradient in the Jabal al Akhdar mountain range of Oman. The species composition, vegetation structure, grazing damage and several environmental variables were investigated for 62 samples using a nested plot design. Classification analysis and a Canonical Variate Analysis (CVA) were used to define vegetation types and to identify underlying environmental gradients. The relationship between environmental variables and diversity was analysed using correlation coefficients and a main-effects ANOVA. The plant species richness followed a unimodal distribution along the altitudinal gradient with the highest number of species at the intermediate altitudinal belt. The cluster analysis led to five vegetation groups: The Sideroxylon mascatense–Dodonaea viscosa group on grazed and the Olea europaea–Fingerhuthia africana group on ungrazed plateau sites at 2000 m a.s.l., the Ziziphus spina-christi–Nerium oleander group at wadi sites and the Moringa peregrina–Pteropyrum scoparium group at 1200 m a.s.l, and the Acacia gerrardii–Leucas inflata group at 1700 m a.s.l. The CVA indicated a clear distinction of the groups obtained by the agglomerative cluster analysis. The landform, altitude and grazing intensity were found to be the most important variables distinguishing between clusters. Overgrazing of the studied rangeland is an increasing environmental problem, whereas the plant composition at ungrazed sites pointed to a relatively fast and high regeneration potential of the local vegetation.     

Seismic fragility curves for greek bridges: methodology and case studies

This study focusses on the estimation of seismic fragility curves for all common bridge types found in modern greek motorways. At first a classification scheme is developed in order to classify the existing bridges into a sufficient number of classes. A total of 11 representative bridge classes resulted, based on the type of piers, deck, and pier-to-deck connection. Then an analytical methodology for deriving fragility curves is proposed and applied to the representative bridge models. This procedure is based on pushover analysis of the entire bridge and definition of damage states in terms of parameters of the bridge pushover curves. The procedure differentiates the way of defining damage according to the seismic energy dissipation mechanism in each bridge, i.e. bridges with yielding piers of the column type and bridges with bearings (with or without seismic links) and non-yielding piers of the wall type. The activation of the abutment-backfill system due to closure of the gap between the deck and the abutments is also taken into account. The derived fragility curves are subjected to a first calibration against empirical curves based on damage data from the US and Japan.     

Dating of Late Pleistocene terrace deposits of the River Rhine using Uranium series and luminescence methods: Potential and limitations

Uranium-series dating of pedogenic carbonate crusts from fluvial gravels is tested using Optically Stimulated Luminescence (OSL) ages as references. OSL dating yielded ages of 30–15 ka and 13–11 ka, which correlate with the cold periods of the Last Glacial Maximum and the Younger Dryas. These ages are internally coherent and consistent with the geological background and are thus regarded as reliable. Most of the U/Th results scatter widely in the ²³⁰Th/²³²Th vs. ²³⁴U/²³²Th isochron diagram, making regression unrealistic. Semiquantitative age estimates from the data were found to be mostly older than the OSL ages and the geological context. It is suggested that a heterogeneous initial ²³⁰Th input, not relatable to a detrital component, is responsible for the observed discrepancies. This input may be due to bacterial activities and Th transport on organic colloids. It appears necessary to avoid samples where bacteria could have contributed to carbonate precipitation. Further, the relative importance of this problem decreases with sample age, so that U/Th dating of sinters is expected to be more reliable in the >100 ka age range.     

Multistage Variscan magmatism in the central Tauern Window (Austria) unveiled by U/Pb SHRIMP zircon data

U/Pb SHRIMP ages of nine Variscan leucocratic orthogneisses from the central Tauern Window (Austria) reveal three distinct pulses of magmatism in Early Carboniferous (Visean), Late Carboniferous (Stephanian) and Early Permian, each involving granitoid intrusions and a contemporaneous opening of volcano-sedimentary basins. A similar relationship has been reported for the Carboniferous parts of the basement of the Alps further to the west, e.g. the “External massifs” in Switzerland. After the intrusion of subduction-related, volcanic-arc granitoids (374?±?10?Ma; Zwölferkogel gneiss), collisional intrusive-granitic, anatectic and extrusive-rhyolitic/dacitic rocks were produced over a short interval at ca. 340?Ma (Augengneiss of Felbertauern: 340?±?4?Ma, Hochweißenfeld gneiss: 342?± 5?Ma, Falkenbachlappen gneiss: 343?±?6?Ma). This Early Carboniferous magmatism, which produced relatively small volumes of melt, can be attributed to the amalgamation of the Gondwana-derived “Tauern Window” terrane with Laurussia–Avalonia. Probably due to the oblique nature of the collision, transtensional phenomena (i.e. volcano-sedimentary troughs and high-level intrusives) and transpressional regimes (i.e. regional metamorphism and stacked nappes with anatexis next to thrust planes) evolved contemporaneously. The magmas are mainly of the high-K I-type and may have been generated during a short phase of decompressional melting of lithospheric mantle and lower crustal sources. In the Late Carboniferous, a second pulse of magmatism occurred, producing batholiths of calc-alkaline I-type granitoids (e.g. Venediger tonalite: 296?±?4?Ma) and minor coeval bodies of felsic and intermediate volcanics (Heuschartenkopf gneiss: 299?±?4?Ma, Peitingalm gneiss: 300?±?5?Ma). Prior to this magmatism, several kilometres of upper crust must have been eroded, because volcano-sedimentary sequences hosting the Heu- schartenkopf and Peitingalm gneisses rest unconformably on 340-Ma-old granitoids. The youngest (Permian) period of magma generation contains the intrusion of the S-type Granatspitz Central Gneiss at 271?±?4?Ma and the extrusion of the rhyolitic Schönbachwald gneiss protolith at 279?±?9?Ma. These magmatic rocks may have been associated with local extension along continental wrench zones through the Variscan orogenic crust or with a Permian rifting event. The Permian and the above-mentioned Late Carboniferous volcano-sedimentary sequences were probably deposited in intra-continental graben structures, which survived post-Variscan uplift and Alpine compressional tectonics.     

Methane exchange between coal-bearing basins and the atmosphere: the Ruhr Basin and the Lower Rhine Embayment, Germany

A precise knowledge of methane exchange processes is required to fully understand the recent rise of atmospheric methane concentration. Three of these processes take place at the lithosphere/atmosphere boundary: bacterial consumption of methane and emission of bacterial or thermogenic methane. This study was initiated to quantify these processes on a regional scale in the Ruhr Basin and the Lower Rhine Embayment. Since these areas are subject to bituminous coal and lignite mining, natural and anthropogenically-induced methane exchange processes could be studied. The methane emission and consumption rates and their carbon isotope signal were measured at the lithosphere/atmosphere boundary using flux chambers. On most of the soils studied, methane consumption by bacteria was identified. Thermogenic methane was released only at some of the natural faults examined. In active and abandoned bituminous coal mining areas methane emissions were restricted to small areas, where high emission rates were measured. The carbon isotope composition of methane at natural faults and in mining subsidence troughs was typical of thermogenic methane (−45 to −32 ‰ δ¹³C). Methane exchange balancing revealed that natural methane emissions from these two basins represent no source of atmospheric importance. However, methane release by upcast mining shafts dominates the methane exchange processes and is by about two orders of magnitude greater than methane consumption by bacterial oxidation in the soils.     

A Concise History of Dutch River Floods

Based on a brief account of 1,000 years of river floods and flood management in the Dutch Rhine delta, it is argued that vulnerability to river floods depends on the complex interaction of economics, institutions, politics and, to a limited extent, climate. Response functions and thresholds for climate change impacts should take this complexity into account rather than assuming society to be constant or evolving in a straightforward manner.     

German research in transport geography: Life in the space between objective analysis and political advice1

Transportation has been a bone of public contention for decades, the discussion ranging from traffic-calming measures in individual streets to the continual growth of global transport movements. In the last 20 years transport topics have also received increased attention within the discipline of geography, be it academic, professional or in schools, but the topics addressed by today's transport geography have almost nothing in common with the roots of the field. This means that transport geography is a handed-down, hyphenated sub-branch of geography in name only. In fact, the name refers to a field of geography that is experiencing not only all the birthing pains and uncertainties of a discipline in the process of defining a new direction for itself, but also the sense of excitement and thrill of the new. This paper sets out to show both the role transport geography plays as part of human geography with its concepts and paradigms, and also the role it plays within the political debate on transport. An appeal is made to geographers to become more involved in this branch of our science.