• Journal of Positioning, Navigation, and Timing
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• 제9권4호
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• pp.387-395
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• 2020

Accuracy of an integrated Global Positioning System (GPS) / Inertial Navigation System (INS) relies heavily on the visibility of GPS satellites. Especially, its accuracy is dramatically degraded in urban canyon due to signal obstructions due to large structures. In this paper, we propose a new integrated positioning system that effectively combines INS, GPS, ultrasonic sensor, and barometer in GPS-denied environments. In the proposed system, the ultrasonic sensor provides velocity information along the forward direction of moving vehicle. The barometer output provides height information compensated for the pressure variation due to fast vehicle movements. To evaluate the performance of the proposed system, an experiment was carried out by mounting the proposed system on a test car. By the experiment result, it was confirmed that the proposed system bears good potential to maintain positioning accuracy in harsh urban environments.

• 한국대기환경학회지
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• 제21권5호
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• pp.525-535
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• 2005

Using a three-dimensional computational fluid dynamics (CFD) model with the $k-{\varepsilon}$ turbulence closure scheme based on the renormalization group theory, flow regimes in urban street canyons are classified according to the building and street aspect ratios. The transition between skimming flow (SF) and wake interference flow (WIF) is determined with the size of double-eddy circulation generated behind the upwind building. The transition between WIF and isolated roughness flow (IRF) is determined with the flow reattachment distance from the upwind building. The critical aspect ratios at which the flow transition occurs are found and compared with those in previous studies. The results show that the flow-regime classification method used in this study is quite reasonable and that the values of the critical aspect ratios are generally consistent with those in fluid experiments or large-eddy simulation. The regression equation describing a relation between the building and street aspect ratios at the flow-regime transition is presented.

• 정보통신설비학회논문지
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• 제9권3호
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• pp.92-101
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• 2010

Energy efficiency and safe mobility are the two key constituents of the future automobile. The technologies that enable these features are now heavily dependent upon information and communication technology rather than traditional auto-mechanical technology. This paper presents an exploratory project 'Smart&Green Vehicle Project' at Western Michigan University which is to improve the geographical location accuracy of vehicles and to study various applications of making such location data available. Global Positioning System (GPS), Inertial Navigation System (INS), Vehicular Ad-hoc Network (VANET) technology, and data fusion among these technologies are investigated. Testing and evaluation is done on systems which will gather vehicular positioning data during GPS signal loss. Vehicles in urban settings do not acquire accurate positioning data from GPS alone; therefore there is a need for exploration into technology that can assist GPS in urban settings. The goal of this project is to improve the accuracy of positioning data during a loss of GPS signal. Controlled experiments are performed to gather data which aided in assessing the feasibility of these technologies for use in vehicular platforms.

• Wind and Structures
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• 제11권6호
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• pp.455-478
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• 2008

The present study aims to estimate the wind ventilation performance for pedestrian level domains from the air quality point of view. Three typical models of a dense urban area were considered and numerically simulated in order to examine the effects of the geometry of such models on wind flow characteristics, which in turn affect the air quality, within the pedestrian domain of a street canyon located within this area. The calculated flow fields were employed to estimate the exceedance probabilities within the study domain using a new approach: air exchange rate within the domain. The study has been applied to nine cities in Japan: Tokyo, Osaka, Sapporo, Niigata, Fukuoka, Nagoya, Sendai, Yokohama, and Kyoto, based on their mean wind velocity data. The results demonstrated that the exceedance probability analysis of the pedestrian wind environment could be a valuable tool during the design stage of inhabited areas for the evaluation of pollutant-removal efficiency by the applied wind. Also, the calculated probabilities demonstrated substantial dependence on both the geometry of building arrays and the wind conditions of the nine cities.

• 대기
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• 제25권3호
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• pp.473-482
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• 2015

In this study, street canyons with a higher downwind building (so called, step-up street canyons) are considered for understanding characteristics of flow and reactive pollutants' dispersion as a basic step to understand the characteristics in wider urban areas. This study used a CFD_NIMR_SNU coupled to a chemistry module just including simple $NO_X-O_3$ photochemical reactions. First, flow characteristics are analyzed in step-up street canyons with four aspect ratios (0.33, 0.47, 0.6, 0.73) defined as ratios of upwind building heights to downwind building height. The CFD_NIMR_SNU reproduced very well the main features (that is, vortices in the street canyons) which appeared in the wind-tunnel experiment. Wind speed within the street canyons became weak as the aspect ratio increased, because volume of flow incoming over the upwind building decreased. For each step-up street canyon, chemistry transport model was integrated up to 3600 s with the time step of 0.5 s. The distribution patterns of $NO_X$ and $O_3$ were largely dependent on the mean flow patterns, however, $NO_X$ and $O_3$ concentrations were partly affected by photochemical reactions. $O_3$ concentration near the upwind lower region of the street canyons was much lower than background concentration, because there was much reduction in $O_3$ concentration due to NO titration there. Total amount of $NO_X$ in the street canyons increased with the aspect ratio, resulting from the decrease of mean wind intensity.

• 한국정보통신학회논문지
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• 제15권12호
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• pp.2619-2625
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• 2011

최근 차량 항법 장치에서 널리 사용되고 있는 GPS 기술은 다음과 같은 두 가지 문제점을 가지고 있다. 첫째, 빌딩숲, 터널 등과 같은 도시 계곡(Urban Canyon) 지역에서는 GPS 신호 수신이 불가능하다. 둘째, GPS 신호를 이용한 측위는 항상 내재적인 위치 오차율 갖고 있다. 전자는 기존의 많은 연구를 통해 해결되었지만, 후자는 여전히 병행 도로와 같은 지역에서는 부정확한 위치 정보를 운전자에게 제공한다. 이 논문에서는 차량 네트워크와 기타 장비로부터 획득한 영상을 이용하여 차량의 주행 경로를 인식하는 시스템을 제안한다. 제안한 시스템은 실시간 영상 매칭 알고리즘을 이용한다. 또한 영상 매칭 정확도를 높이기 위한 기법 또한 제안한다. 이 논문에서 제안한 시스템은 실시간 주행 실험을 통해 원활하게 동작함을 보였다. 또한 매칭 정확도가 향상됨을 보여주었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2014년도 춘계학술대회 논문집
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• pp.141-144
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• 2014

In urban spaces surrounded by buildings, trees could disperse sound energy, which affect sound level distribution and street canyon reverberation. Therefore, this paper examines the amount of scattered sound energy from a tree in open field by means of a reverberation time (RT). Five trees of different species and crown sizes were considered. The influential factors include crown size and shape, foliage condition, and source-receiver distance. The results show that RT is proportionally increased with the increase of tree crown sizes, which is the most determining factor. The maximum RT measured was 0.34 sec at 4000 Hz for the studied trees in leaf. The presence of leaves increased RT at high frequencies, typically by 0.14 sec at 4000 Hz. With increasing source-receiver distance within 40 m, RT was slightly changed.

• 한국대기환경학회:학술대회논문집
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• 한국대기환경학회 2000년도 추계학술대회 논문집
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• pp.203-204
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• 2000

도시협곡 내에서 형성되는 전형적인 유동장은 협곡내부에서 형성되는 회전류(vortex)이다(Berkowicz, 1998). Oke(1988)에 따르면 단면비가 큰 경우 (W/H＞2.5), 도시 협곡내 유동장은 isolated roughness flow, 단면비가 중간인 경우(1.538

• 한국측량학회:학술대회논문집
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• 한국측량학회 2004년도 추계학술발표회 논문집
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• pp.123-127
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• 2004

Nowadays it is necessary to manage the road system effectively because of the explosive increment of vehicles and goods. To resolve this problems through the fast upgrade of information about position and time of moving vehicles, the combined navigation system using GPS(Global Positioning System) and complementary navigation system, i.e. INS(Inertial Navigation System), DR(Dead Rocking), etc. has been used. Although GPS is popular for the vehicles in the urban canyon because of its few satellites. In this paper, position tracking algorithm is presented, which reduces vehicle position error dramatically by fusing GPS and INS sensors. And the validity of our algorithm is demonstrated by the experimental results with the real car.

• 국토계획
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• 제53권7호
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• pp.109-126
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• 2018

The purpose of this study is to identify the spatial types for thermal environment improvement considering heat flux and its spatial context through empirical orthodox formulas. First, k-means clustering was used to classify values of three kinds of heat flux - latent, sensible and storage heat. Next, from the k-means clustering, we defined a type of thermal environment (type LHL) where improvement is needed for more comfortable and pleasant thermal environment in the city, among the eight types. Lastly, we compared and analyzed the characteristics of each classified thermal environmental types based on land cover types. From the study, we found that the ratio of impervious surfaces, roads, and buildings of the type LHL is higher than those of the type HLH (relatively thermal comfort environment). In order to improve the thermal environment, the following contents are proposed to urban planners and designers depending on the results of the study. a) Increase the green zone rate by 10% to reduce sensible heat; b) Reduce the percentage of impermeable surfaces and roads by 10% ; c) Latent heat increases when water and green spaces are expanded. This study will help to establish a minimum criterion for a land cover rate for the improvement of the urban thermal environment and a standard index for the thermal environmental improvement can be derived.