Listen
12 Ergebnisse
Ergebnisse nach Hochschule und Institut
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 Areal rainfall estimation using moving cars. Computer experiments including hydrological modeling(Copernicus, 26.09.2016) Rabiei, Ehsan; Haberlandt, Uwe; Sester, Monika; Fitzner, Daniel; Wallner, MarkusThe need for high temporal and spatial resolution precipitation data for hydrological analyses has been discussed in several studies. Although rain gauges provide valuable information, a very dense rain gauge network is costly. As a result, several new ideas have emerged to help estimating areal rainfall with higher temporal and spatial resolution. Rabiei et al. (2013) observed that moving cars, called RainCars (RCs), can potentially be a new source of data for measuring rain rate. The optical sensors used in that study are designed for operating the windscreen wipers and showed promising results for rainfall measurement purposes. Their measurement accuracy has been quantified in laboratory experiments. Considering explicitly those errors, the main objective of this study is to investigate the benefit of using RCs for estimating areal rainfall. For that, computer experiments are carried out, where radar rainfall is considered as the reference and the other sources of data, i.e., RCs and rain gauges, are extracted from radar data. Comparing the quality of areal rainfall estimation by RCs with rain gauges and reference data helps to investigate the benefit of the RCs. The value of this additional source of data is not only assessed for areal rainfall estimation performance but also for use in hydrological modeling. Considering measurement errors derived from laboratory experiments, the result shows that the RCs provide useful additional information for areal rainfall estimation as well as for hydrological modeling. Moreover, by testing larger uncertainties for RCs, they observed to be useful up to a certain level for areal rainfall estimation and discharge simulation.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 Pedestrian and transit accessibility on a micro level. Results and challenges(University of Minnesota, 2016) van Eggermond, Michael; Erath, AlexanderIn thispaper, we connect two notions of accessibility that are more often than not considered separately: pedestrian accessibility and transit accessibility. We move away from the notion of zonal accessibility and measure fine-grained accessibility using door-to-door travel times. Two pedestrian networks are compared to a baseline scenario considering Euclidean distances for a large metropolitan area in which each individual building is considered as an activity opportunity. It is shown that pedestrian accessibility to jobs differs when pedestrian distances are approximated with different networks that are more representative of reality. Stop-to-stop public transport travel times are extracted from an agent-based simulation of public transport smart card data. The effect of less-than-optimal connections from transit to the pedestrian network, a local measurement, can be seen when calculating the accessibility to all destinations in the city. We suggest moving away from Euclidean-based distance analyses. Limitations can be found in the data available; the connection of buildings to the network becomes important, as does the inclusion of pedestrian crossings. For an inclusive accessibility measure, it will be necessary to calculate generalized costs for pedestrians and generate different pedestrian networks that reflect the limitations of different user groups.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation The role of location in residential location choice models. A review of literature(University of Minnesota, 2014) Schirmer, Patrick M.; van Eggermond, Michael; Axhausen, Kay W.Geospatial data available to researchers has increased tremendously over the last several decades, opening up opportunities to define residential location in multiple ways. This has led to a myriad of variables to define "location'' in residential location choice models. In this paper, we propose a common classification for location variables and categorize findings from a wide range of studies. We find similar preferences but different measurement methods and market segments for locations across different study regions. Recent studies consider the residential unit as choice alternative, making it possible to include a detailed description of the built environment. However, these studies are still limited in number and the inclusion of socioeconomic environment is more common. Transport land-use models can benefit from the inclusion of points of interest, such as schools, network distances, and the distance to previous locations. For the results of location choice models to be transferable to different disciplines, and avoid multi-collinearity, it is necessary to present different model specifications, including variables of interest in different disciplines.01A - Beitrag in wissenschaftlicher Zeitschrift