• Journal of Positioning, Navigation, and Timing
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• 제8권3호
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• pp.95-105
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• 2019

A method that applies space-time adaptive signal processing (STAP) algorithm based on an array antenna consisting of multiple antenna elements has been known to be effective to remove wide-band jamming signals in GPS receivers. However, the occurrence of phase distortion in navigation signals has been a problem when navigation signals, from which jamming signals are removed using STAP, are supplied to global positioning system (GPS) receivers. This paper verified the navigation performance degradation as a result of phase distortion. To mitigate this phenomenon, this paper proposes a mode switching scheme, in which a bypass mode is adopted to make the best use of the tracking performance of receivers without performing signal processing when jamming signals are not present or weak, and a STAP mode is employed when jamming signals exceed the threshold value. In this paper, the mode switching scheme is proposed for two environments: when receivers are stationary, and when receivers are moving. This paper confirmed that the performance of position error improved because phase distortion could be excluded due to STAP if the bypass mode was adopted under a condition where the jamming signal power level was below the threshold value in an environment where receivers were stationary. However, this paper also observed that the navigation failed due to the instability of tracking performance of receivers due to phase distortion that occurred at the switching time, although the number of switching could be reduced dramatically by proposing a dual threshold scheme of on- and off-thresholds that switched a mode due to the array antenna characteristics of varying gains according to the jamming signal incident direction in an environment where receivers were moving. The analysis results verified that running the STAP algorithm at all times is more efficient than the mode switching, in terms of maintaining stable navigation and ensuring position error performance, to remove jamming signals in an environment where receivers were moving.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• 제39권1호
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• pp.13-21
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• 2021

High-resolution satellites such as Kompsat-3 and CAS-500 include optical cameras of MS (Multispectral) and PAN (Panchromatic) CCD (Charge Coupled Device) sensors installed with certain offsets. The offsets between the CCD sensors produce geometric discrepancy between MS and PAN images because a ground target is imaged at slightly different times for MS and PAN sensors. For precise pan-sharpening process, we propose a co-registration process consisting the physical sensor modeling and image matching. The physical sensor model enables the initial co-registration and the image matching is carried out for further refinement. An experiment with Kompsat-3 images produced RMSE (Root Mean Square Error) 0.2pixels level of geometric discrepancy between MS and PAN images.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• 제39권1호
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• pp.23-28
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• 2021

Data analysis research using deep learning has recently been studied in various field. In this paper, we conduct a GNSS (Global Navigation Satellite System)-based meteorological study applying deep learning by estimating the ZWD (Zenith tropospheric Wet Delay) through MLP (Multi-Layer Perceptron) and LSTM (Long Short-Term Memory) models. Deep learning models were trained with meteorological data and ZWD which is estimated using zenith tropospheric total delay and dry delay. We apply meteorological data not used for learning to the learned model to estimate ZWD with centimeter-level RMSE (Root Mean Square Error) in both models. It is necessary to analyze the GNSS data from coastal areas together and increase time resolution in order to estimate ZWD in various situations.

• Atmosphere
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• 제31권1호
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• pp.1-15
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• 2021

High-resolution wind resources maps (maps, here after) with spatial and temporal resolutions of 100 m and 3-hours, respectively, over South Korea have been produced and evaluated for the period from July 2016 to June 2017 using Korea Meteorological Administration (KMA) Post Processing (KMAPP). Evaluation of the 10 m- and 80 m-level wind speed in the new maps (KMAPP-Wind) and the 1.5 km-resolution KMA NWP model, Local Data Assimilation and Prediction System (LDAPS), shows that the new high-resolution maps improves of the LDAPS winds in estimating the 10m wind speed as the new data reduces the mean bias (MBE) and root-mean-square error (RMSE) by 33.3% and 14.3%, respectively. In particular, the result of evaluation of the wind at 80 m which is directly related with power turbine shows that the new maps has significantly smaller error compared to the LDAPS wind. Analyses of the new maps for the seasonal average, maximum wind speed, and the prevailing wind direction shows that the wind resources over South Korea are most abundant during winter, and that the prevailing wind direction is strongly affected by synoptic weather systems except over mountainous regions. Wind speed generally increases with altitude and the proximity to the coast. In conclusion, the evaluation results show that the new maps provides significantly more accurate wind speeds than the lower resolution NWP model output, especially over complex terrains, coastal areas, and the Jeju island where wind-energy resources are most abundant.

• International Area Studies Review
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• 제21권4호
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• pp.3-17
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• 2017

The purpose of the paper is to suggest the empirical evidences for the effects of factor prices on the export performance in the Korean manufacturing industries during the period 1975:1-2016:4. The paper is to set up the error correction model derived from the autoregressive distributed lag scheme and to estimate the factor price elasticities of export in the 8 manufacturing industries. The real wage, interest and import price index elasticities of export all were estimated to be statistically significant at 1% level in the most industries with showing negative signs as expected. And the real wage elasticity proved to likely be smaller as the industries become more capital-intensive while the import price index elasticity tended to become larger in industries with larger ratio of imported intermediate goods to output. The empirical results suggest that the declines in input factor prices since the foreign exchange crisis in the end of 1997 have positive effects on the export performance in the Korean manufacturing industries.

• Journal of the Korea Academia-Industrial cooperation Society
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• 제22권1호
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• pp.786-791
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• 2021

In this paper, in order to minimize limitations such as signal interference and positioning errors in existing indoor positioning systems, a smart LED-based positioning system for excellent line-of-sight radio environments and precise location tracking is proposed to improve accuracy. An IEEE 802.4 Zigbee module is mounted on the SMPS board of a smart LED; RSSI and LQI signals are received from a moving tag, and the system is configured to transmit the measured data to the positioning server through a gateway. For the experiment, the necessary hardware, such as the gateway and the smart LED module, were separately designed, and the experiment was conducted after configuring the system in an external field office. The positioning error was within 70cm as a result of performing complex calculations in the positioning server after transmitting a vector value of the moving object obtained from the direction sensor, together with a signal from the moving object received by the smart LED. The result is a significantly improved positioning error, compared to an existing short-range wireless communications-based system, and shows the level at which commercial products can be implemented.

• Journal of the Korea Convergence Society
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• 제12권1호
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• pp.127-132
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• 2021

The intravenous injection monitoring system used by medical institutions was developed to remotely provide patients with the amount of intravenous injected and the termination point of the injection. In order to measure the amount of intravenous injection input, the weight or flow rate of the level going out from the inside to outside of the intravenous injection can be observed with a measuring sensor. The criteria for devices that apply herein are accuracy and vigilance. In addition, it is compact and should be easy to use when installing intravenous injection on patients. In medical institutions, the accuracy of the measured values must be high, and economically inexpensive devices are required. In this study, low-cost small-weight-centered load cell sensors were applied, and algorithms were applied to reduce the artefact by external movement by converging with gyro sensors for accuracy of measurements. As a result, it was possible to reduce the error of measurement, thereby improving the accuracy of the intravenous injection monitoring measurement value.

• Journal of IKEEE
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• 제26권2호
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• pp.271-279
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• 2022

This paper proposes an advanced dead-time compensation method for dual inverter with a floating capacitor. The dual inverter with floating capacitor is composed of double two-level inverters and a bulk electrolytic capacitor. The output voltage of the dual inverter is dropped by the conduction voltage of the power semiconductors. The voltage drop and dead-time cause the fundamental and harmonic distortions of output currents. When supplied power for OEW-load is low, the dual inverter operates as single inverter for effective operation. The dead-time compensation method for the dual inverter operated as single inverter is needed for reliability. The proposed method using band pass filter in this paper compensates dead-time, dead-time error and changed voltage drop error of power semiconductors for the dual inverter and dual inverter operated as single inverter. The effectiveness of the proposed method is verified by simulation results.

• The Journal of the Convergence on Culture Technology
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• 제8권4호
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• pp.445-455
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• 2022

Financial service chatbots are hindering user experience with conversational errors and machine-like responses. This study aims to examine the effect of self-disclosure and emotional expression of an anthropomorphic chatbot on user experience before conversation errors occur in financial services. In financial inquiries, scenarios were designed based on self-disclosure type (positive vs. negative) and emotional expression level(high confident vs. low confident), and online experiments were conducted. The result revealed that when anthropomorphic chatbot provided self-disclosure and emotional expression, the main effect has been shown on trust, annoyance, service recovery, and intention to continuous use. In addition, interaction effects were significant in trust and annoyance. In conclusion, this paper demonstrated that anthropomorphic chatbot's positive self-disclosure and confident emotional expression influenced trust and annoyance.

• Journal of Sensor Science and Technology
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• 제31권1호
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• pp.45-50
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• 2022

Multi-rod type Ag-AgCl electrodes have been developed for use in underwater electric field sensors. The developed cylindrical electrode had a diameter of 50 mm and a height of 130 mm. The electrode had five Ag-AgCl rods with a diameter of 2 mm and a height of 80 mm to enlarge the reaction surface area. Each Ag-AgCl rod was fabricated under the same conditions as the usual anodizing method in an electrolyte. The two developed electrodes were placed in the center of a 500-mm long, 400-mm wide, and 300-mm high acrylic tank filled with artificial seawater, at an interval of 100 mm, to evaluate their characteristics as uniaxial underwater electric field sensors. The underwater external electric field was generated using titanium plate electrodes installed at both ends of the tank. The noise level at 1 Hz of the developed electrode was approximately 3.7 nV/√Hz. The reception of the underwater electric field signal using the developed electrode was linear, within an error of approximately 0.6 %, in the range of 1-10000 ㎶/m at 1 Hz. In addition, its frequency response was flat within an error of 1.1 % in the range of 1-1000 Hz at 10000 ㎶/m.