Crowdsourcing a cyclist perspective on suggested recreational paths in real-world networks     

Kevin Baker  Kristien Ooms  Steven Verstockt  Pascal Brackman  Philippe De Maeyer  Rik Van de Walle 《制图学和地理信息科学》2017,44(5):422-435

ABSTRACT

Routing and navigation services for leisure activities are conditioned by special needs and trade-offs. The advent of online communities and large crowdsourced datasets offers opportunities to improve the adoption of a user’s perspective in these suggested paths. This paper focuses on achieving two goals. First, the presented methodology analyses a dataset of 190,610 historical GPS traces to gain insights into the appreciation or attractiveness of each edge in a real-world network for a specific leisure activity (i.e. road cycling). Second, as literature on these leisure activities is still sparse, we want to create a thorough understanding of the activities at hand for future work. An appreciation model is proposed and the spread of this score is analyzed in shortest-path alternatives of popular routing engines for this activity. This analysis successfully discriminates these shortest paths based on the scoring value and three morphological parameters of the path. However, the robustness of the model should be improved to ensure the viability of the proposed approach in future work. More specifically, further research on the local optimality of the route choices will be imperative.  相似文献   

Carbon dioxide flux techniques performed during GasEx-98   总被引：2，自引：0，他引：2  

Wade R. McGillis  James B. Edson  Jonathan D. Ware  John W. H. Dacey  Jeffrey E. Hare  Christopher W. Fairall  Rik Wanninkhof 《Marine Chemistry》2001,75(4):851

A comprehensive study of air–sea interactions focused on improving the quantification of CO₂ fluxes and gas transfer velocities was performed within a large open ocean CO₂ sink region in the North Atlantic. This study, GasEx-98, included shipboard measurements of direct covariance CO₂ fluxes, atmospheric CO₂ profiles, atmospheric DMS profiles, water column mass balances of CO₂, and measurements of deliberate SF₆–³He tracers, along with air–sea momentum, heat, and water vapor fluxes. The large air–sea differences in partial pressure of CO₂ caused by a springtime algal bloom provided high signals for accurate CO₂ flux measurements. Measurements were performed over a wind speed range of 1–16 m s⁻¹ during the three-week process study. This first comparison between the novel air-side and more conventional water column measurements of air–sea gas transfer show a general agreement between independent air–sea gas flux techniques. These new advances in open ocean air–sea gas flux measurements demonstrate the progress in the ability to quantify air–sea CO₂ fluxes on short time scales. This capability will help improve the understanding of processes controlling the air–sea fluxes, which in turn will improve our ability to make regional and global CO₂ flux estimates.  相似文献   

Exploring earth system governance: A case study of floodplain management along the Tisza river in Hungary     

Saskia E. Werners  Zsuzsanna Flachner  Piotr Matczak  Maria Falaleeva  Rik Leemans 《Global Environmental Change》2009,19(4):503-511

This paper discusses a recently proposed conceptualisation of ‘earth system governance’ by applying it to floodplain management in the Hungarian Tisza river basin. By doing so it aims to improve our understanding of governance systems facilitating adaptation to a changing world. The conceptualisation of earth system governance consists of three elements: problem structure, principles and research challenges. These three elements are assessed using results from actor interviews and policy review. A regional example of natural resources management is found to be a valid case for earth system governance research. The proposed conceptualisation of earth system governance explains well the main problems, barriers and opportunities for adapting floodplain management to climate change in the Tisza region. Problem structure analysis highlights how previous socio-economic and political orders continue to shape expectations and patterns of conduct. Current barriers can be attributed to a lack of the key governance principles credibility, stability, inclusiveness and adaptiveness. Interviewees perceived the lack of credibility and effective cooperation between organisations as the largest barrier. The research challenges proposed for earth system governance agree well with opportunities identified for adapting Tisza floodplain management, calling for inclusion of actors beyond governments and state agencies, and equitable resource allocation in particular. The analysis suggests that an additional challenge for earth system governance is the prioritisation of actions to support an existing governance system and its actors in adapting.  相似文献   

The importance of three centuries of land-use change for the global and regional terrestrial carbon cycle   总被引：4，自引：0，他引：4  

Jelle G. Van Minnen  Kees Klein Goldewijk  Elke Stehfest  Bas Eickhout  Gerard van Drecht  Rik Leemans 《Climatic change》2009,97(1-2):123-144

Large amounts of carbon (C) have been released into the atmosphere over the past centuries. Less than half of this C stays in the atmosphere. The remainder is taken up by the oceans and terrestrial ecosystems. Where does the C come from and where and when does this uptake occur? We address these questions by providing new estimates of regional land-use emissions and natural carbon fluxes for the 1700–2000 period, simultaneously considering multiple anthropogenic (e.g. land and energy demand) and biochemical factors in a geographically explicit manner. The observed historical atmospheric CO₂ concentration profile for the 1700 to 2000 period has been reproduced well. The terrestrial natural biosphere has been a major carbon sink, due to changes in climate, atmospheric CO₂, nitrogen and management. Due to land-use change large amounts of carbon have been emitted into the atmosphere. The net effect was an emission of 35 Pg C into the atmosphere for the 1700 to 2000 period. If land use had remained constant at its distribution in 1700, then the terrestrial C uptake would have increased by 142 Pg C. This overall difference of including or excluding land-use changes (i.e. 177 Pg C) comes to more than half of the historical fossil-fuel related emissions of 308 Pg C. Historically, global land-use emissions were predominantly caused by the expansion of cropland and pasture, while wood harvesting (for timber and fuel wood) only played a minor role. These findings are robust even when changing some of the important drivers like the extent of historical land-use changes. Under varying assumptions, land-use emissions over the past three centuries could have increased up to 20%, but remained significantly lower than from other sources. Combining the regional land-use and natural C fluxes, North America and Europe were net C sources before 1900, but turned into sinks during the twentieth century. Nowadays, these fluxes are a magnitude smaller than energy- and industry-related emissions. Tropical regions were C neutral prior to 1950, but then accelerated deforestation turned these regions into major C sources. The energy- and industry-related emissions are currently increasing in many tropical regions, but are still less than the land-use emissions. Based on the presented relevance of the land-use and natural fluxes for the historical C cycle and the significance of fossil-fuel emissions nowadays, there is a need for an integrated approach for energy, nature and land use in evaluating possible climate change mitigation policies.  相似文献   

A comparison of baseline methodologies for 'Reducing Emissions from Deforestation and Degradation'     

Michael Huettner  Rik Leemans  Kasper Kok  Johannes Ebeling 《Carbon balance and management》2009,4(1):4-12

Background  

A mechanism for emission reductions from deforestation and degradation (REDD) is very likely to be included in a future climate agreement. The choice of REDD baseline methodologies will crucially influence the environmental and economic effectiveness of the climate regime. We compare three different historical baseline methods and one innovative dynamic model baseline approach to appraise their applicability under a future REDD policy framework using a weighted multi-criteria analysis.  相似文献   

Evaluation of the LISEM soil erosion model in two catchments in the East African Highlands   总被引：1，自引：0，他引：1  

Rudi Hessel  Rik van den Bosch  Olga Vigiak 《地球表面变化过程与地形》2006,31(4):469-486

Under increasing population pressure, soil erosion has become a threat in the East African Highlands, and erosion modelling can be useful to quantify this threat. To test its applicability for this region, the LISEM soil erosion model was applied to two small catchments, one in the Usumbara Mountains, Tanzania, and the other on the slopes of Mount Kenya. Input data for the model were collected in both catchments, as were data on runoff and erosion that were used for calibration and validation of the model. LISEM was first calibrated on catchment outlet data, and afterwards simulated spatial patterns of erosion were compared to available erosion data. The results showed that LISEM can, after calibration, give good discharge predictions for some events, but not for all. However, LISEM generally overpredicted soil loss from the catchments. Comparison with observed erosion patterns did not show overprediction, but according to the model, erosion was more widespread than was observed. There are several reasons for these discrepancies. First, it is difficult to obtain enough accurate data to run the model, such as accurate maps, rainfall data and soil and plant characteristics. Second, it is also difficult to obtain accurate data to evaluate the performance of the model, either for the catchment outlet or spatially, therefore observed erosion rates are also uncertain. Third, the model could not deal correctly with complex events, i.e. those having double rainfall peaks, and might also have difficulties with catchment characteristics such as soil type and the complexity of land use. Finally, LISEM could not deal with events in which throughflow or baseflow played a role, which was to be expected since those processes are not simulated by LISEM. Nevertheless, LISEM could be calibrated to give good discharge predictions for some events, and also gave reasonable results when compared to data obtained from erosion plots. Furthermore, only complex, distributed, storm‐based models such as LISEM can give spatial predictions for single storms. Therefore, it is concluded that if the aim is spatial prediction on an event basis, there is no alternative to complex erosion models such as LISEM, but if the aim is to predict average annual erosion, the data‐demanding, physically based LISEM erosion model may not be the most appropriate model. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

The radiocarbon budget for Mono Lake: an unsolved mystery     

Wallace S. Broecker  Rik Wanninkhof  Guy Mathieu  Tsung-Hung Peng  Scott Stine  Steve Robinson  Andy Herczeg  Minze Stuiver 《Earth and Planetary Science Letters》1988,88(1-2)

Since 1957 the ¹⁴C/C ratio of the dissolved inorganic carbon in Mono Lake has risen by about 60‰. The magnitude of this increase is about four times larger than that expected from the invasion of bomb-produced¹⁴C from the atmosphere. We have eliminated the following explanations: (1) measurement error, (2) an unusually high physical exchange rate for non-reactive gases, (3) inorganic enhancement of the CO₂ exchange rate, and (4) biological enhancement of the CO₂ exchange rate. Clandestine disposal of waste radiocarbon remains a dark-horse explanation.In the course of our investigations we have uncovered evidence for at least one episodic input of radiocarbon-free carbon to the lake over the last 1000 years. We speculate that this injection was related to a hydrothermal event resulting from sublacustrine volcanic activity.  相似文献   

The causes of land-use and land-cover change: moving beyond the myths   总被引：39，自引：0，他引：39  

Eric F. Lambin  B. L. Turner  Helmut J. Geist  Samuel B. Agbola  Arild Angelsen  John W. Bruce  Oliver T. Coomes  Rodolfo Dirzo  Günther Fischer  Carl Folke  P. S. George  Katherine Homewood  Jacques Imbernon  Rik Leemans  Xiubin Li  Emilio F. Moran  Michael Mortimore  P. S. Ramakrishnan  John F. Richards  Helle Sknes  Will Steffen  Glenn D. Stone  Uno Svedin  Tom A. Veldkamp  Coleen Vogel  Jianchu Xu 《Global Environmental Change》2001,11(4)

Common understanding of the causes of land-use and land-cover change is dominated by simplifications which, in turn, underlie many environment-development policies. This article tracks some of the major myths on driving forces of land-cover change and proposes alternative pathways of change that are better supported by case study evidence. Cases reviewed support the conclusion that neither population nor poverty alone constitute the sole and major underlying causes of land-cover change worldwide. Rather, peoples’ responses to economic opportunities, as mediated by institutional factors, drive land-cover changes. Opportunities and constraints for new land uses are created by local as well as national markets and policies. Global forces become the main determinants of land-use change, as they amplify or attenuate local factors.  相似文献   

Retrieval of Suspended Sediment from Advanced Hyperspectral Sensor Data in the Scheldt Estuary at Different Stages in the Tidal Cycle     

Sindy Sterckx  Els Knaeps  Mark Bollen  Koen Trouw  Rik Houthuys 《Marine Geodesy》2013,36(1-2):97-108

Hyperspectral airborne remote sensing images and in-situ data are combined to assess the spatial and temporal sediment dynamics in the tidal Scheldt river. A log-linear empirical relationship has been developed between a near-infrared reflectance difference and total suspended matter. The relationship was shown to be relatively insensitive to the varying cirrus cloud cover occurring during data acquisition. The produced sediment maps show good agreement with known variations of turbidity over the tidal cycle: maximum turbidity around high water, gradual settling of the sediment in the succeeding slack water and resuspension at the onset of the ebb flow stage.  相似文献   

Constraining the time span between the Early Holocene Hässeldalen and Askja‐S Tephras through varve counting in the Lake Czechowskie sediment record,Poland          下载免费PDF全文

Florian Ott  Johanna Serb  Michał Słowiński  Milena Obremska  Rik Tjallingii  Mirosław Błaszkiewicz  Achim Brauer 《第四纪科学杂志》2016,31(2):103-113

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