Ground Accessibility Research Articles

Improved A* Algorithm for Mobile Robots under Rough Terrain Based on Ground Trafficability Model and Ground Ruggedness Model.

Considering that the existing path planning algorithms for mobile robots under rugged terrain do not consider the ground flatness and the lack of optimality, which leads to the instability of the center of mass of the mobile robot, this paper proposes an improved A* algorithm for mobile robots under rugged terrain based on the ground accessibility model and the ground ruggedness model. Firstly, the ground accessibility and ruggedness models are established based on the elevation map, expressing the ground flatness. Secondly, the elevation cost function that can obtain the optimal path is designed based on the two types of models combined with the characteristics of the A* algorithm, and the continuous cost function is established by connecting with the original distance cost function, which avoids the center-of-mass instability caused by the non-optimal path. Finally, the effectiveness of the improved algorithm is verified by simulation and experiment. The results show that compared with the existing commonly used path planning algorithms under rugged terrain, the enhanced algorithm improves the smoothness of paths and the optimization degree of paths in the path planning process under rough terrain.

Assessing airport ground access interventions: An integrated approach combining mode choice modeling and microscopic traffic simulation

Airport ground accessibility is an important and integral part of airport planning, which significantly impacts airport attractiveness and its environmental sustainability. In this paper, we propose the combined use of road micro-simulation with meso-scope discrete choice modeling to support the evaluation of airport access interventions. The proposed integrated framework allows us to appraise mode choice and infrastructural interventions simultaneously to accurately assess the performance of airport access road networks in accommodating larger traffic. We validate and demonstrate the benefits of the proposed approach by applying it to a real-world case study based on the Milan–Bergamo Airport (BGY), in which (i) we conduct an ex-post counterfactual analysis to assess the impact of the interventions undertaken to mitigate the large growth (54.6%) in the years 2013–2019, and (ii) evaluate future scenarios up to 2030 considering the additional expected growth and introduction of direct rail services. Results indicate that BGY’s ground access interventions have contributed to effectively accommodating traffic growth by significantly mitigating road congestion and associated pollutant emissions. Results also inform on the need and effectiveness of additional interventions to meet the substantial expected future growth.

A grid-based evolutionary spatial algorithm for airline service design in multi-airport systems

This paper proposes an integrated modeling framework to support airline frequency planning in a multi-airport system. First, a grid-based spatial model is developed to estimate passenger demand as a function of air-service characteristics (such as flight frequency and airfare) and ground accessibility. Second, an evolutionary algorithm is proposed to provide decision support for the allocation of flights to airports belonging to the multi-airport system, subject to fleet availability, flow balance and operational requirements. We apply the proposed approach to model frequent flyer passengers departing from one of the major multi-airport systems in Europe. Our results show that the degree of diversification of a multi-airport system—i.e., the presence of alternative airports—plays a significant role on both the demand and supply sides, providing passengers with more diversified and accessible services and providing airlines with higher operational flexibility and resilience in case of disruptions. Our modeling framework can be extended to capture additional managerial objectives or practical requirements.

Oviposition preference of the forest cockchafer (Melolontha hippocastani Fabr. 1801) at the stand scale depends on oak proportion, canopy openness and ground accessibility

Melolontha hippocastani is a major pest in European mixed and broadleaf forests. Investigating its oviposition behavior, we observed that a dense shrub layer reduces the density of egg clusters and eggs in the soil. Conversely, canopy openness and a large proportion of oak appear as favoring conditions. Melolontha hippocastani is a major pest in European mixed and broadleaf forests. In north-eastern France, an epidemic phase has been observed since 2007, characterized by a high mortality rate of seedlings and young trees, and by massive swarming flights every 4 years. We investigated the oviposition behavior of M. hippocastani in the northern Vosges Mountains. We set up study plots in the infected area after adults had emerged and the females had laid their eggs. We excavated pits and counted the eggs and egg clusters they contained. We also carried out dendrometric surveys. A dense shrub layer had a negative effect on the density of egg clusters and the number of eggs in the soil, while canopy openness and the proportion of oak basal area had positive effects. We hypothesized that a dense shrub layer could create a barrier for females. On the other hand, an open canopy may improve conditions for the larvae in the soil, just as a high proportion of oak trees in the surrounding area may provide a good food source for both larvae and adults. We suggest several research orientations and propose guidelines for forest management in view of our results.

Geospatial Modeling of Containment Probability for Escaped Wildfires in a Mediterranean Region.

Despite escalating expenditures in firefighting, extreme fire events continue to pose a major threat to ecosystem services and human communities in Mediterranean areas. Developing a safe and effective fire response is paramount to efficiently restrict fire spread, reduce negative effects to natural values, prevent residential housing losses, and avoid causalties. Though current fire policies in most countries demand full suppression, few studies have attempted to identify the strategic locations where firefighting efforts would likely contain catastrophic fire events. The success in containing those fires that escape initial attack is determined by diverse structural factors such as ground accessibility, airborne support, barriers to surface fire spread, and vegetation impedance. In this study, we predicted the success in fire containment across Catalonia (northeastern Spain) using a model generated with random forest from detailed geospatial data and a set of 73 fire perimeters for the period 2008-2016. The model attained a high predictive performance (AUC = 0.88), and the results were provided at fine resolution (25 m) for the entire study area (32,108 km2 ). The highest success rates were found in agricultural plains along the nonburnable barriers such as major road corridors and largest rivers. Low levels of containment likelihood were predicted for dense forest lands and steep-relief mountainous areas. The results can assist in suppression resource pre-positioning and extended attack decision making, but also in strategic fuels management oriented at creating defensive locations and fragmenting the landscape in operational firefighting areas. Our modeling workflow and methods may serve as a baseline to generate locally adapted models in fire-prone areas elsewhere.

Assessing airport ground access by public transport in Chinese cities

This article assesses airport ground access by public transport in China. Recent literature has highlighted the economic, environmental and social significance of airport ground access. Existing studies on airport ground access have predominately centred on North America and Europe and, to date, limited attempts have been made to assess the emerging Chinese market. Studies of urban and transport geography have detailed the shifting air connectivity of Chinese cities and the economic impacts, but have paid little attention to ground access to airports. We, therefore, assess the ground accessibility to major Chinese airports based on online map services. Specifically, we characterise airport ground access across entire cities, as well as comparing time and monetary costs for travelling between airports and city centres by private car and public transport. We conclude with suggestions for future research, and call for more systematic data collection related to airport ground access.

Modeling initial attack success of wildfire suppression in Catalonia, Spain

In southern European regions, the few fires that escape initial attack (IA) account for most of the burned area. Nonetheless, limited effort has been conducted to develop spatiotemporal models aiming at improving pre-positioning and deployment of fire-fighting brigades on the first dispatch. To this end, we calibrated a model to assess the probability of containment of fire by IA in Catalonia (northeastern Spain). The model was trained using machine learning algorithms from georeferenced historical fire ignition locations, fire response and weather conditions. Our results indicated that early detection, ground accessibility, and aerial support governed the broad spatial pattern of fire containment probability, with strong gradients that ranged from lowest chances of containment in northwestern mountains to highest in the coastal belt. In turn, weather conditions and fire simultaneity were crucial to explain the differences during wildfire season. We found that fires igniting above the 85th percentile of temperature and wind speed, during simultaneous fire episodes (n > 10), and 12.5 km away from the nearest fire station will probably escape IA, and grow into large events. These hazardous fire danger conditions were met 13 days per year on average during the period 1998–2015, with 5 fire simultaneous episodes escaping IA that burned 1546 ha in total. Results were provided as a set of high-resolution raster grids (100 m), which replicated the most typical weather and fire occurrence scenarios that first responders are likely to face during the wildfire season. This study reveals existing limitations in the dominant fire exclusion policy of Mediterranean areas and advocates for a comprehensive long-term wildfire management solution. Our model may help inform science-based decision-making on IA and general fire response planning in the study area.

Ground and Surface Water Potentials and Accessibility in Kano Municipal, Nigeria: Implication for Geological Constraints

Ground and Surface Water Potentials and Accessibility in Kano Municipal, Nigeria: Implication for Geological Constraints

Accessibility to Italian remote regions: Comparison among different transport alternatives

Historically, for geographically disadvantaged areas or those with a low level of infrastructure, air transport services are often considered to be lifeline services. In the last decades, investments in the airport sector have been promoted as a way to increase accessibility to many Italian regions. On the other side, transport services have also witnessed important changes as the entrance of low cost carriers, the development of high speed railway services or the liberalization of the long distance coach transport sector. These services, together with an improved intermodality, could provide an alternative to access areas of the country.The paper, adopting a policymaker perspective, studies the different transport alternatives available to connect the zones in the catchment area of an airport without scheduled services, computing the minimum generalized cost (GC). Two scenarios are also analyzed in terms of possible strategies to improve accessibility levels reducing the GC. The first one assumes two daily public service obligations from the local airports to two main airports while the second scenario studies the effect of an improvement of the bus connections to the closest airport with scheduled services from the zones in the catchment area of the local airport. Simulations are based on a multimodal national transport model describing the entire Italian long distance supply for the period 2013/2014. It allows the calculation of the GC by road, rail, coach and air services. The GC provides a clear and comparable measure to understand the role of different transport modes in providing domestic connections. Results show how the more an area is remote the more a PSO could be effective while whereas ground alternatives are present the effect of air PSO is reduced. Moreover, improving ground accessibility to the main airports has a wider impact in terms of decrease of the minimum GC and in the number of zones experiencing a reduction. This paper aims to contribute to the literature on the accessibility from areas with a low level of infrastructure. It also represents a support for policy makers when promoting, drafting or reconsidering their own regional air transport programs and as well for airport manager when considering alternatives to improve airport ground accessibility.

Spatial and temporal changes in seasonal range attributes in a declining barren-ground caribou herd

From 1996 to 2015 the Bathurst caribou herd has declined from approximately 349,000 to 20,000 animals. Aboriginal traditional knowledge (TK) has recently observed the later arrival of the herd below the treeline, an attribute of the autumn range. Science also predicts that seasonal range attributes (e.g., area, location) likely vary with population size, and perhaps climate. We used Aboriginal TK and science to identify several seasonal range attributes that were ex­amined for changes through time (decreasing population abundance). Attributes of seasonal ranges for female Bathurst caribou were calculated using satellite radio-collar data from January 1996 through October 2013. Climate data from CircumArctic Rangifer Monitoring and Assessment Network were analyzed for trends from 1979 to 2009. Analyses showed a significant decrease in the area of post-calving and autumn ranges, but no changes in winter and spring ranges. Results supported Aboriginal TK that female caribou have shifted the autumn range farther from the treeline and moved into the forest later in the year. Analysis of climate variables found no trends at the spatio-temporal scale of the post-calving to autumn ranges. Working hypotheses to explain these patterns, which are not mutually exclusive, include reduced predation risk, increased use of core areas at lower population density, and greater utilization of areas of taiga where arboreal and ground lichen availability and accessibility are relatively higher than in the forest. This analysis demonstrates how including Aboriginal TK can lead to stronger connections and results, with potential to provide new and different insights for further investigations.

Evaluation of efficiency of the Common Measures - measures for land accessibility, implemented within land consolidation

By the means of Land Consolidation is understood, in accord with law No. 139/2002 Coll., spending of funds on land consolidations and land offices, provided the accessibility of grounds in public interest. Land consolidations also ensure the conditions for improvement of the ecosystem, protection and reclamation of land resources, waterway management and the increase of the ecological stability of landscape. All mentioned measures are collectively called the Common Measures, rural roads being one of the most significant of these measures as far as the ground accessibility is concerned. According to the Ministry of Agriculture and the Central Land Office (MZe, ÚPÚ) statistics, for instance in 2008, over 707.4 million CZK was spent on the common measures projects from the public funds. Of this sum, 82 per cent was spent on financing of the land accessibility projects – rural roads and objects on them. The Cost & Benefit Analysis (CBA) method was applied. The analysis explains step by step what benefits the investment projects bring and to whom, as well as what and from whom it takes something away. Thus defined effects and impacts are aggregated, converted into financial flows and included in the calculation of criteria indicators. These calculations enable to make decision whether the concerned project is in its consequences generally contributive. There is a difficulty in the method – it is applied ex-ante, which usually leads to the exaggerated input parameters, which may be significantly affected by a number of variable effects (time factor, socio-economic impacts, inflation rate, etc.). The ex-post application of the method cannot be objectively used due to the absence of the statistically processed input data for the analysis. Such data must be collected during the operational period of the realized investments. This is caused by the fact that these analyses consider lifetime of these investments in terms of 25–30 years. The ÚPÚ statistics, however, say that the operational period of most of realized common measures has not reached one half of their lifetime yet. The ex-ante analysis enables to evaluate the possible difficulty and the general benefit of projects, including their impact on the broad spectrum of subjects.  

Light Rail Rapid Transit systems for more sustainable ground accessibility of airports

This paper investigates the potential of Light Rail Rapid Transit (LRRT) to mitigate the environmental and social burden of ground access systems of an airport. This implies, on the one hand, LRRT's capability in mitigating externalities in terms of noise, air pollution/climate change, traffic incidents/accidents and congestion of airport ground access systems and, on the other, the provision of sufficient capacity to accommodate generally increasing volumes of both air passenger and airport employee demand by connecting the airport to its core catchment area. A methodology for assessing the capability of LRRT operating as an airport ground access system is developed. This methodology consists of models to analyze and predict demand and capacity for an LRRT system and models to quantify the externalities of particular airport ground access systems as well as assessing their prospective savings thanks to the introduction of an LRRT system. The methodology is applied to a large European airport – Amsterdam Schiphol (the Netherlands) – using a ‘what-if?’ scenario approach.

Role of the plasmapause in dictating the ground accessibility of ELF/VLF chorus

This study explores the manner in which the plasmapause is responsible for dictating which magnetospheric source regions of ELF/VLF chorus are able to propagate to and be received by midlatitude stations on the ground. First, we explore the effects of plasmapause extent on ground‐based observations of chorus via a 3 month study of ground‐based measurements of chorus at Palmer Station, Antarctica (L = 2.4, 50°S geomagnetic latitude), and data on the plasmapause extent from the IMAGE EUV instrument. It is found that chorus normalized occurrence peaks when the plasmapause is at L ∼ 2.6, somewhat higher than Palmer's L shell, and that this occurrence peak persists across a range of observed chorus frequencies. Next, reverse ray tracing is employed to evaluate the portion of the equatorial chorus source region, distributed in radial distance and wave normal, from which chorus is able to reach Palmer Station via propagation in a nonducted mode. The results of ray tracing are similar to those of observations, with a peak of expected occurrence when the plasmapause is at L ∼ 3. The exact location of the peak is frequency dependent. This supports the conclusion that the ability of chorus to propagate to low altitudes and the ground is a strong function of instantaneous plasmapause extent and that peak occurrence of chorus at a given ground station may occur when the L shell of the plasmapause is somewhat beyond that of the observing station. These results also suggest that chorus observed on the ground at midlatitude stations propagates predominantly in the nonducted mode.

Propagation of whistler-mode chorus to low altitudes: divergent ray trajectories and ground accessibility

Abstract. We investigate the ray trajectories of nonductedly propagating lower-band chorus waves with respect to their initial angle θ0, between the wave vector and ambient magnetic field. Although we consider a wide range of initial angles θ0, in order to be consistent with recent satellite observations, we pay special attention to the intervals of initial angles θ0, for which the waves propagate along the field lines in the source region, i.e. we mainly focus on waves generated with &theta0 within an interval close to 0° and on waves generated within an interval close to the Gendrin angle. We demonstrate that the ray trajectories of waves generated within an interval close to the Gendrin angle with a wave vector directed towards the lower L-shells (to the Earth) significantly diverge at the frequencies typical for the lower-band chorus. Some of these diverging trajectories reach the topside ionosphere having θ close to 0°; thus, a part of the energy may leak to the ground at higher altitudes where the field lines have a nearly vertical direction. The waves generated with different initial angles are reflected. A small variation of the initial wave normal angle thus very dramatically changes the behaviour of the resulting ray. Although our approach is rather theoretical, based on the ray tracing simulation, we show that the initial angle θ0 of the waves reaching the ionosphere (possibly ground) is surprisingly close - differs just by several degrees from the initial angles which fits the observation of magnetospherically reflected chorus revealed by CLUSTER satellites. We also mention observations of diverging trajectories on low altitude satellites.

Evaluation of Airborne Video Data for Land Cover Classification Accuracy Assessment

This research was designed to evaluate the operational utility of airborne video for classification accuracy assessment of satellite imagery. There are a number of logistical advantages in utilizing airborne video data particularly in remote or large catchment regions where ground accessibility can be prohibitively expensive. In a study of land cover characteristics in the Barossa Valley, South Australia, comparisons of Landsat ETM+ classification accuracy assessments were derived from both airborne video and standard ground truthing point sampling techniques. The airborne video data was obtained by randomly frame grabbing 243 individual scenes along four predetermined flight lines and computing classification accuracies and error matrix statistics. These results were then compared with similar statistics derived from 180 randomly chosen ground sampling sites. The costs involved in obtaining both sets of data per sampling pont were also calculated. The results demonstrated that the airborne video data provided similar degrees of accuracy assessment at a cost of approximately one seventh that of the ground survey with the added advantages of increased data collection, overall improved site accessibility and the ability to continually store and review the data. The cost differentiation would become even more pronounced in more remote and inaccessible areas. In general the results of the unsupervised Landsat ETM+ classification were rather poor producing an overall general accuracy of 70% and a Kappa coefficient of 0.65, highlighting the classification difficulties encountered in using commercial satellite imagery for land cover assessments in an area with very heterogeneous fine grained land use patterns.

Evaluation of airborne video data for land-cover classification accuracy assessment in an isolated Brazilian forest

This research was designed to evaluate the operational utility of airborne bispectral video data for reconnaissance assessment of land-cover variability and to document the viability of the video data for classification accuracy assessment. There are distinct logistical advantages utilizing airborne video data in isolated and environmentally sensitive regions where there is limited preexisting aerial photography and poor infrastructure and where ground accessibility is difficult and expensive. In a study of land-cover characteristic in Mato Grosso, Brazil, video data provided important insights into the variability and transitions in land-cover that could be used to identify targets for field work and training areas for subsequent satellite image (Landsat TM) classifications. Comparisons of Landsat TM classification accuracy assessments derived from the airborne video and standard color photography revealed that comparable results can be achieved at a high statistical level of significance (0.01). These results demonstrated that the video data can provide information for accuracy assessments equivalent to more standard photographic point-sample data acquisition missions with the added benefit of easily acquiringfar more data. Results of the supervised Landsat TM classification coupled with a topographic model produced an overall accuracy of 68% with a Kappa coefficient of 0.60, based upon a priori classes identified through evaluation of the airborne data and a site visit.

Airport Choice: An Empirical Study

As a determinant of the air passenger's choice of airport, ground accessibility plays a more dominant role than air carrier level-of-service. Thus, the use of differential flight frequencies as a policy tool to shift air passengers from one airport to another would have only limited potential. These conclusions are based upon an empirical study of air passengers' choice of airport in which a series of multinomial logit models were calibrated using air passenger survey data. These models relate the probability that a given airport will be selected to measures of ground accessibility and air carrier level-of-service associated with each available departure airport. A variety of measures for ground accessibility and air carrier level-of-service were tested in various combinations in models which consistently performed well from a statistical standpoint and in which the ground access measure was consistently the dominant variable.