• Korean Journal of Remote Sensing
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• v.25 no.5
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• pp.391-398
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• 2009

Variations of mean ionospheric spatial gradient over Korea are analyzed in order to support GNSS (Global Navigation Satellite System) augmentation systems and integrity monitering systems. A software for analyzing the ionospheric spatial gradient is developed using an ionospheric plate model. Daily and annual variations of ionospheric delay and spatial gradient are analyzed using GPS data in 2003 and 2005 respectively. The ionospheric delays and spatial gradients in 2003 were larger than 2005. Also, the south-north gradient, about -1.0mm/km, is nearly two times larger than the east-west gradient. The annual ionospheric spatial gradients over Korea is varied within 2mm/km.

• Journal of the Korean Institute of Intelligent Systems
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• v.18 no.3
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• pp.422-428
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• 2008

In this paper, we propose the robust object detection algorithm with spatial gradient information. To do this, first, we eliminate error values that appear due to complex environment and various illumination change by using prior methods based on hue and intensity from the input video and background. Visible shadows are eliminated from the foreground by using an RGB color model and a qualified RGB color model. And unnecessary values are eliminated by using the HSI color model. The background is removed completely from the foreground leaving a silhouette to be restored using spatial gradient and HSI color model. Finally, we validate the applicability of the proposed method using various indoor and outdoor conditions in a complex environments.

• Journal of Institute of Control, Robotics and Systems
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• v.12 no.9
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• pp.898-904
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• 2006

Ionospheric storms, caused by the interaction between Solar and geomagnetic activities, may degrade the differential GNSS(Global Navigation Satellite Systems) performance significantly, and the importance of the ionospheric storm research is growing for the GBAS(Ground-Based Augmentation System) and SBAS(Satellite-Based Augmentation System) development. In order to support Korean GNSS augmentation system development, a software tool for analyzing the regional ionosphere is being developed and its preliminary results are discussed. After brief description of the ionosphere and ionospheric storm, the research topics on the GBAS applications are discussed. The need for ionospheric spatial gradient analysis is described and some results on the ionospheric spatial gradient during recent storm periods are discussed.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.34S no.1
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• pp.72-79
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• 1997

Most open magnetic resonance imaging systems have used the planar gradient coils whose inductances were minimized through the magnetic energy minimization procedure in the spatial frequency domain. Though the planar gradient coils have smaller inductance than conventional gradient coils, the planar gradient coils often suffer from their poor magnetic field linearity. Scaling the spatial frequencies of the current density function designed by the magnetic energy minimization, magnetic field linearity of the planar gradient coils can be greatly improved with small sacrifice of gradient coil inductance. We have found that the figure of merit of the planar gradient coils, defined by the gradient strength divided by the linearity error and the inductance, can be improved by proposed technique.

• Proceedings of the KOSOMBE Conference
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• v.1994 no.12
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• pp.43-46
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• 1994

A new spatial localization technique using high-order surface gradient coil (SGC) is proposed. Although the Spatial Selection with High-Order gradient (SHOT) can provide a 2-D selection with only one selective RF pulse, the high-order gradient produced by cylindrical-shape coils has not been clinically useful for clinical systems due to the large minimum selection size caused by the limited radial gradient intensity. However, by using the proposed high-order SGCs located near the imaging region, the size of volume selection can be reduced to a clinically useful 1-4 cm in diameter by applying stronger radial gradient with much less gradient driving power. A 40 cm-by-40 cm $r^{2}$ SGC has been designed and constructed, and phantom and volunteer studies have been performed. Experimental results using spatially localized MRI show good agreement to the theoretically predicted behavior.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.15 no.2
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• pp.18-24
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• 2007

The high ionospheric spatial gradient during ionospheric storm is the most concern when applying GNSS(Global Navigation Satellite System) augmentation systems for aircraft precision approach. Since the ionospheric gradient level depends on geographical location as well as the storm, understanding the ionospheric gradient statistics over a specific regional area is necessary for operating the augmentation systems. This paper compares three ionosphere gradient computation methods, direct differentiation between two receivers' ionospheric delay signal for a common satellite, derivation from a grid ionosphere map, and derivation from a plate ionosphere map. The plate map method provides a good indication on the gradient variation behavior over a regional area with limited number of GNSS receivers. The residual analysis for the ionosphere storm detection is discussed as well.

• Journal of Environmental Impact Assessment
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• v.17 no.6
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• pp.357-366
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• 2008

It is certain that urbanization has transformed the ecological consequences severely, but urban ecosystem is not fully understood yet. Urban growth is not like a static form and it spreads spatially and temporally. Therefore in studying urban ecosystem, it is important to relate the spatial pattern of urbanization to ecological processes. Using gradient analysis, we attempted to quantify the urbanization's spatial impacts in Daejeon-city and Cheonan-city, Chungcheong-province, Korea. Because of Multifunctional Administrative City Planning (MACP), a lot of development projects are planned in Chungcheong-province, Korea. It's important to study about original cities' patterns and impacts. These results can be adopted to future city planning. So several measures such as fragmentation, vegetation index, surface temperature, population density, and income rate were computed along a 75km long and 3km wide transect. The results showed that Daejeon-city has a wider urban center, lower vegetation indexes, and higher surface temperature than Cheonan-city. Therefore in the perspective of urban environments and sustainable urbanism, it seems that Cheonan-city is better than Daejeon-city. The changes along the transect have important ecological implications, and quantifying the urbanization gradient is an important step in understanding urban ecology.

• Journal of the Economic Geographical Society of Korea
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• v.16 no.3
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• pp.445-457
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• 2013

This paper aims to investigate changes in the characteristics of urban spatial structure in Korea by regional groups and city size between 2000 and 2010. The characteristics of urban spatial structure is analyzed by Clark's population gradient curve in this paper. Therefore key parameters in population gradient function, such as population density gradients and population density in CBD represent the characteristics of urban spatial structure. The result shows that most of cities in Korea have experienced suburbanization rather than concentration, but small-size cities have experienced concentration during the period.

• Journal of Institute of Control, Robotics and Systems
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• v.18 no.5
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• pp.413-418
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• 2012

This paper presents a multi-robot path planner for environment exploration and monitoring. Robotics systems are being widely used as data measurement tools, especially in dangerous environment. For large scale environment monitoring, multiple robots are required in order to save time. The path planner should not only consider the collision avoidance but efficient coordination of robots for optimal measurements. Nonlinear spring force based planning algorithm is integrated with the spatial gradient following path planner. Perturbation/Correlation based estimation of spatial gradient is applied. An algorithm of tuning the stiffness for robot coordination is presented. The performance of the proposed algorithm is discussed with simulation results.

• Journal of Sensor Science and Technology
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• v.29 no.3
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• pp.141-148
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• 2020

To find food, homes, and mates, some animals have adapted special sensing capabilities. Rather than using a passive method, they discharge a signal and then extract the necessary information from the response. More importantly, they use the slope of the detected signal to find the destination of an object. In this paper, similar strategy is mathematically formulated. A perturbation and correlation-based gradient estimation method is developed and used as a sensing strategy. This method allows us to adaptively sense an object in a given environment effectively. The proposed strategy is based on the use of gradient values; rather than instantaneous measurements. Considering the gradient value, the sampling frequency is planned adaptively, i.e., sparse sampling is performed in slowly varying regions, while dense sampling is conducted in rapidly changing regions. Using a temperature sensor, the proposed strategy is verified and its effectiveness is demonstrated.