• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.3
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• pp.225-231
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• 2011

The satellite clock anomalies, one of the abnormal signal factors of the GPS satellites, can have a significant impact on the GPS measurements. However, it can be difficult to detect the anomalies of the satellites clock before the range of the satellites clock error becomes bigger than the range of the other factors, due to the measurement including error of the orbit, ionosphere delay, troposphere delay, multipath and receiver clock. In order to perform quick and accurate detection by minimization of critical range in anomalies of the satellites clock, this paper suggested a solution to detect precise anomalies of the satellites clock after application of carrier smoothing filter from measurement by dual-frequency and adjustment of errors which can be occurred by other factor and the receiver clock errors. The performance of the proposed method was confirmed by comparing to the satellite clock biases which are provided by IGS.

• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.5
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• pp.341-349
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• 2016

Currently, researches are being actively conducted in assessing seismic performance of nuclear facilities in USA and Europe. In particular, applying this technique of assessing seismic performance to design of isolation systems in nuclear power plants is being performed and then ASCE 4 Draft (2013) is being revised accordingly in the United States. In order to satisfy the probabilistic performance objectives described by seismic responses with certain confidence levels (ASCE 43, 2005), the probability distributions of these responses have to be defined. What is the minimum number of input ground-motions to obtain the probability distribution precise enough to represent the unknown actual distribution? Theoretical basis, for how to determine the minimum number of input ground-motions for given a logarithmic standard deviation to approximate the unknown actual median of the log-normal distribution within a range of error at a certain level of confidence, is introduced by Huang et al. (2008). However, the relationship between the level of confidence and the range of error is not stated in the previous study. In this paper, based on careful reviews on the previous work, the relationship between the level of confidence and the range of error is logically and explicitly stated. Furthermore, this relationship is also applied to derive the minimum number of input ground-motions in order to approximate the unknown actual logarithmic standard deviation. Several recommendations are made for determining the minimum number of input ground-motions in probabilistic assessment on seismic performance of facilities in nuclear power plants.

• Journal of Sensor Science and Technology
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• v.8 no.5
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• pp.394-399
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• 1999

An automobile hot-film air flow sensor is deposited with platinum by sputtering method, patterned by photoresisted lift-off method, annealed in $1,000^{\circ}C$ and passivated with PI-2723. The TCR of the fabricated hot-film is about $3500\;ppm/^{\circ}C$. In the experiment, the output voltage of the sensor is in proportional to the fourth power root in the air mass flow range of 300 kg/h. The error in the full flow range is about ${\pm}0.7%$. In the range of air temperature of $-20^{\circ}C{\sim}120^{\circ}C$, the error is about ${\pm}1%$ that is ${\pm}2%$ lower than that of the reference sensor. Therefore, the fabricated hot-film air flow sensor satisfies the specification for automobile. Lower temperature error of the sensor provides to control the precise air/fuel ratio of automobile engine and results in improvement of a fuel mileage and the less amount of toxic gases emitted by automobile.

• Journal of Biosystems Engineering
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• v.41 no.4
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• pp.319-327
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• 2016

Purpose: Automated guidance systems (AGSs) for mobile farm machinery have several advantages over manual operation in the crop production industry. Many researchers and companies have tried to develop such a system. However, it is not easy to evaluate the performance of an AGS because there is no established device used to evaluate it that complies with the ISO 12188 standard. The objective of this study was to develop a tracking sensor system using five laser distance measurement sensors. Methods: One sensor-for long-range distance measurement-was used to measure travel distance and velocity. The other four sensors-for mid-range distance measurement-were used to measure lateral deviation. Stationary, manual driving, and A-B line tests were conducted, and the results were compared with the real-time kinematic differential global positioning system (RTK-DGPS) signal used by the AGS. Results: For the stationary test, the average error of the tracking sensor system was 1.99 mm, and the average error of the RTK-DGPS was 15.19 mm. For the two types of driving tests, the data trends were similar. A comparison of the changes in lateral deviation showed that the data stability of the developed tracking system was better. Conclusions: Although the tracking system was not capable of measuring long travel distances under strong sunlight illumination because of the long-range sensor's limitations, this dilemma could be overcome using a higher-performance sensor.

• Korean Journal of Remote Sensing
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• v.26 no.3
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• pp.297-304
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• 2010

Since the change in Doppler centroid according to moving targets brings alteration to the phase in azimuth differential signals of synthetic aperture radar (SAR) data, one can measure the velocity of the moving targets using this effect. In this study, we will investigate theoretically measuring the velocity of an object from azimuth differential signals by using range compressed data which is the interim outcome of treatment from the simulated SAR raw data of moving targets on the background of sea clutter. Also, it will provide evaluation for the elements that affect the estimation error of velocity from a single SAR sensor. By making RADARSAT-1 simulated image as a specific case, the research includes comparisons for the means of velocity measurement classified by the directions of movement in the four following cases. 1. A case of a single target without currents, 2. A case of a single target with tidal currents of 0.5 m/s, 1 m/s, and 3 m/s, 3. A case of two targets on a same azimuth line moving in a same direction and velocity, 4. A case of a single target contiguous to land where radar backscatter is strong. As a result, when two moving targets exist in SAR image outside the range of approximately 256 pixels, the velocity of the object can be measured with high accuracy. However, when other moving targets exist in the range of approximately 128 pixels or when the target was contiguous to the land of strong backscatter coefficient (NRCS: normalized radar cross section), the estimated velocity was in error by 10% at the maximum. This is because in the process of assuming the target's location, an error occurs due to the differential signals affected by other scatterers.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.185-190
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• 2006

The correct estimation of the ionospheric delays is very important for the precise kinematic positioning especially in case of the long baseline. In case of triple frequency system, the ionospheric delays can be estimated from the measurements, but, in case of dual frequency system, the situation is not so simple. The precision of those supplied by the external information source such as IONEX is not sufficient. The high frequency component is neglected, and the precision of the low frequency component is not sufficient for the long baseline positioning. On the other hand, the high frequency component can be estimated from the phase range measurements. If the low frequency components are estimated by using the external information source or pseudo range measurements, a more reasonable estimation of the ionospheric delays may be possible. It has already been discussed by the author that the estimation of the low frequency components by using the external information source is not sufficient but fairly effective. The estimation using the pseudo range measurements is discussed in the present paper. The accuracy is not sufficient at present because of the errors in the pseudo range measurements. It is clarified that the bias errors in the pseudo range measurements are responsible for the poor accuracy of the ionospheric delays. However, if the accuracy of the pseudo range measurements is improved in future, the method would become very promising.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.1822-1825
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• 2003

A practical range estimator based on the robust Kalman filter is proposed to solve the range estimation problem for surface to air missile(SAM) homing guidance. Apart from the previous works based on the extended Kalman filter(EKF) with bearing only measurement, the proposed scheme makes use of line-of-sight(LOS) rate to ensure the fast convergency at long-range. In this reason, the robust Kalman filter is considered to deal with LOS rate measurement error. The recursive linear structure of proposed filter is easy to implement and make it possible to reduce computational burdens. Moreover, it shows good estimation performance without specific guidance law such as oscillation proportional navigation guidance(OPNG).

• Journal of the Korea Institute of Military Science and Technology
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• v.11 no.6
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• pp.55-62
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• 2008

An Estimation of VHF datalink range for EW(Electronic Warfare) equipment in the sea environment was studied to predict the datalink range between transmitting and receiving station. We consider refraction and reflection in addition to the basic radar equation. The reflection especially includes propagation factor in case of spherical earth as well as flat earth. The estimation result can predict the real datalink range within 5% error.

• 제어로봇시스템학회:학술대회논문집
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• 2002.10a
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• pp.82.3-82
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• 2002

This paper designs an integrated navigation system that uses the signals from both GPS satellites and pseudolites. While GPS satellite clocks are synchronized, pseudolite clocks are not exactly synchronized even though pseudolite can use 1PPS signal from the GPS receiver. This can cause large range error and can be solved by transmitting the correction information. Assuming that the positions of pseudolites are known, it is possible to determine the true range between two pseudolites. Also, from the measurement of pseudolite signals, the pseudo range between two pseudolites can be calculated. Using the difference between the true range and the pseudo range, each pesudolite can produce correc...

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.11
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• pp.1695-1699
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• 2012

This paper is proposed all digital wide-range clock and data recovery circuit. The Proposed clock data recovery circuit is possible input data rate which is suggested is wide-range that extends from 100Mb/s to 3Gb/s and used an phase error detector which can use a way of over-sampling a data by using a 1/2-rate multi-phase clock and phase rotator which is regular size per $2{\pi}$/16 and can make a phase rotation. So it could make the phase rotating in range of input data rate. Also all circuit is designed as a digital which has a specificity against a noise. This circuit is designed to 0.13um CMOS process and verified simulation to spectre tool.