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Publikation Introducing the pedestrian accessibility tool. Walkability analysis for a geographic information system(SAGE, 2017) Erath, Alexander; van Eggermond, Michael; Ordóñez, Sergio A.; Axhausen, Kay W.The indexes for walkability proposed so far refer generally to the closest amenities and public transport stops and the existing network structure. The weights of the attributes do not reflect the independently measured preferences of the users and residents. Design attributes such as the location and type of crossings and walkway design features are usually surveyed in walkability audits. However, such attributes are usually not considered when pedestrian walksheds or other accessibility-based walkability indexes are calculated. Nevertheless, these design attributes are very relevant for actual planning decisions. The proposed walkability index can be behaviorally calibrated, has been implemented as a geographic information system tool, and is published as open source software. The pedestrian accessibility tool allows the evaluation of existing and future urban plans with regards to walkability. The tool calculates Hansen-based accessibility indicators with the use of a customizable specification of the generalized walking costs, and it incorporates user-defined weights of destination attractiveness. The basic user workflow of the tool is summarized. Three case studies show real-world applications of the tool to support the planning of pedestrian infrastructure in an urban context. With indications of potential areas of improvement that have been reported by pilot users working in an urban planning department, hints are also given for future research.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Continuously-fed gravity currents propagating over a finite porous substrate(American Institute of Physics, 31.12.2019) Venuleo, Sara; Pokrajac, Dubravka; Schleiss, Anton J.; Franca, Mário J.We present the results of laboratory investigations of continuously-fed density currents that propagate first over a smooth horizontal bed and then over a porous substrate of limited length. Inflow discharge, initial excess density, and substrate porosities are varied. Density measurements, acquired through an image analysis technique, are performed above the porous layer simultaneously with quasi-instantaneous vertical velocity profiles. After a first phase in which the current sinks into the substrate, freshwater entrainment from the bed begins and, gradually, a mixing layer forms at the interface between the surface flow and the porous bed. Shear-driven and Rayleigh-Taylor instabilities rule the dynamics of this mixing layer. The porous boundary effects are observed in the vertical distributions of both density and velocity, especially in the near-bed region. Here, larger flow velocities are recorded over porous substrates. We argue that these are due to the presence of a longitudinal pressure gradient, which in turn is a consequence of the current mass loss. Its presence over the porous substrate is proved by the current interface longitudinal slope. However, other effects of the presence of the porous substrate, such as the relaxation of the no-slip boundary condition and the bed-normal momentum exchange, also affect the velocity field. The turbulent structure changes significantly over the porous substrate: while streamwise turbulence decreases, shear and bed-normal Reynolds stresses increase in large part of the current depth. Buoyancy instabilities further enhance the bed-normal momentum flux and, in the near-bed region, contribute to turbulent kinetic energy generation together with shear.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Applying bias correction for merging rain gauge and radar data(Elsevier, 13.01.2015) Rabiei, Ehsan; Haberlandt, UweWeather radar provides areal rainfall information with very high temporal and spatial resolution. Radar data has been implemented in several hydrological applications despite the fact that the data suffers from varying sources of error. Several studies have attempted to propose methods for solving these problems. Additionally, weather radar usually underestimates or overestimates the rainfall amount. In this study, a new method is proposed for correcting radar data by implementing the quantile mapping bias correction method. Then, the radar data is merged with observed rainfall by conditional merging and kriging with external drift interpolation techniques. The merging product is analysed regarding the sensitivity of the two investigated methods to the radar data quality. After implementing bias correction, not only did the quality of the radar data improve, but also the performance of the interpolation techniques using radar data as additional information. In general, conditional merging showed greater sensitivity to radar data quality, but performed better than all the other interpolation techniques when using bias corrected radar data. Furthermore, a seasonal variation of interpolation performances has in general been observed. A practical example of using radar data for disaggregating stations from daily to hourly temporal resolution is also proposed in this study.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Measurements and observations in the XXI century (MOXXI). Innovation and multi-disciplinarity to sense the hydrological cycle(Taylor & Francis, 18.01.2018) Tauro, Flavia; Selker, John; Giesen, Nick van de; Abrate, Tommaso; Uijlenhoet, Remko; Porfiri, Maurizio; Manfreda, Salvatore; Caylor, Kelly; Moramarco, Tommaso; Benveniste, Jerome; Ciraolo, Giuseppe; Estes, Lyndon; Domeneghetti, Alessio; Perks, Matthew T.; Corbari, Chiara; Rabiei, Ehsan; Ravazzani, Giovanni; Bogena, Heye; Harfouche, Antoine; Brocca, Luca; Maltese, Antonino; Wickert, Andy; Tarpanelli, Angelica; Good, Stephen; Lopez Alcala, Jose Manuel; Petroselli, Andrea; Cudennec, Christophe; Blume, Theresa; Hut, Rolf; Grimaldi, SalvatoreTo promote the advancement of novel observation techniques that may lead to new sources of information to help better understand the hydrological cycle, the International Association of Hydrological Sciences (IAHS) established the Measurements and Observations in the XXI century (MOXXI) Working Group in July 2013. The group comprises a growing community of tech-enthusiastic hydrologists that design and develop their own sensing systems, adopt a multi-disciplinary perspective in tackling complex observations, often use low-cost equipment intended for other applications to build innovative sensors, or perform opportunistic measurements. This paper states the objectives of the group and reviews major advances carried out by MOXXI members toward the advancement of hydrological sciences. Challenges and opportunities are outlined to provide strategic guidance for advancement of measurement, and thus discovery.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Depth-averaged momentum equation for gravity currents with varying density. Coefficient in pressure term(Taylor & Francis, 31.07.2017) Pokrajac, Dubravka; Venuleo, Sara; Franca, Mário J.Gravity currents are often modelled by means of shallow water equations (SWEs). In these models, simplifications such as the consideration of a constant layer-averaged density are common. This note presents the complete and general derivation of a 2D depth-averaged momentum equation for gravity currents with density and velocity varying in the bed-normal direction. Special attention is given to the pressure term which is evaluated for constant, linear and exponential density profile. The shape of the density profile has implications for the momentum balance: the assumption of constant density leads to an overestimation of the driving force due to pressure gradient by a factor of 33% for linear density profile and up to 50% for an exponential profile. It also leads to an overestimation of celerity in numerical models based on traditional SWEs by factor of 22% and around 40% for linear end exponential density profiles respectively.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Microbially induced calcite precipitation effect on soil thermal conductivity(Emerald, 13.04.2016) Venuleo, Sara; Laloui, Lyesse; Terzis, Dimitrios; Hueckel, Tomasz; Hassan, Mounir MouradEfficiency of energy piles is strongly affected by soil saturation conditions: low water contents considerably decrease their performance thus limiting the possibility to extend their application to arid environments. This paper investigates the microbially induced calcite precipitation (MICP) technique as a potential means of enhancing the soil–pile heat exchange rates by improving the thermal properties of soil. The study puts the focus on measuring the thermal conductivity of untreated and treaded sand at various degrees of saturation. Experimental results clearly show a significant improvement of the thermal conductivity of soil especially for low degrees of saturation. This enhancement is attributed to the mineralised calcite crystals acting as ‘thermal bridges’ between the soil grains, offering a larger surface area for heat exchange compared with the untreated material in which exchanges occur through smaller contact points.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Geostatistical merging of rain gauge and radar data for high temporal resolutions and various station density scenarios(Elsevier, 26.10.2013) Berndt, Christian; Rabiei, Ehsan; Haberlandt, UweThis study investigates the performance of merging radar and rain gauge data for different high temporal resolutions and rain gauge network densities. Three different geostatistical interpolation techniques: Kriging with external drift, indicator kriging with external drift and conditional merging were compared and evaluated by cross validation. Ordinary kriging was considered as the reference method without using radar data. The study area is located in Lower Saxony, Germany, and covers the measuring range of the radar station Hanover. The data used in this study comprise continuous time series from 90 rain gauges and the weather radar that is located near Hanover over the period from 2008 until 2010. Seven different temporal resolutions from 10 min to 6 h and five different rain gauge network density scenarios were investigated regarding the interpolation performance of each method. Additionally, the influence of several temporal and spatial smoothing-techniques on radar data was evaluated and the effect of radar data quality on the interpolation performance was analyzed for each method. It was observed that smoothing of the gridded radar data improves the performance in merging rain gauge and radar data significantly. Conditional merging outperformed kriging with an external drift and indicator kriging with an external drift for all combinations of station density and temporal resolution, whereas kriging with an external drift performed similarly well for low station densities and rather coarse temporal resolutions. The results of indicator kriging with an external drift almost reached those of conditional merging for very high temporal resolutions. Kriging with an external drift appeared to be more sensitive in regard to radar data quality than the other two methods. Even for 10 min temporal resolutions, conditional merging performed better than ordinary kriging without radar information. This illustrates the benefit of merging rain gauge and radar data even for very high temporal resolutions.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Estimation of the Variogram Using Kendall's Tau for a Robust Geostatistical Interpolation(14.01.2017) Lebrenz, Henning; Bárdossy, AndrásThe estimation of an appropriate variogram is a crucial step toward the description of spatial dependence, the geostatistical interpolation of environmental variables, and the subsequent hydrological engineering. The classical variogram in the literature ideally necessitates a normal distribution of the variable and is not robust against outliers within the data. These presumptions are hardly given under empirical conditions and, therefore, a new estimation method is proposed for the variogram. The new method is based on the description of spatial dependence by the robust rank coefficient τ and generalizes the method from the Gaussian to the general case of empirical distributions. The conversion of the robust estimate using a Monte-Carlo simulation and subsequent quantile-quantile transformation with the empirical marginal distribution performs the generalization. Monthly precipitation data from South Africa serve as the variable and were artificially contaminated with outliers. The effects on the variogram and subsequent geostatistical interpolation were investigated for the proposed, classical, and four existing robust variogram models in this comparative study. The investigation revealed that the proposed variogram describes a distinct spatial dependence structure under empirical conditions, which is robust against outliers. The cross validation of the linear estimator demonstrates that the proposed variogram tends to improve the bias and spread of the resulting error distribution, and hence the quality of the geostatistical interpolation.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Spall experiments for the measurement of the tensile strength and fracture energy of concrete at high strain rates, International Journal of Impact Engineering 32(Elsevier, 2006) Schuler, Harald; Mayrhofer, Christoph; Thoma, Klaus01A - Beitrag in wissenschaftlicher ZeitschriftPublikation Elemente der Werkstoffformulierung für Beton und deren Verwendung in der Kurzzeitdynamik(Ernst & Sohn, 2007) Schuler, Harald01B - Beitrag in Magazin oder Zeitung