• Journal of the Korean Society for Precision Engineering
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• v.34 no.3
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• pp.191-197
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• 2017

Light detection and ranging (LiDAR) is one of the most efficient technologies to obtain the topographic and bathymetric map of coastal zones, superior to other technologies, such as sound navigation and ranging (SONAR) and synthetic aperture radar (SAR). However, the measurement results using LiDAR are vulnerable to environmental factors. To achieve a correspondence between the acquired LiDAR data and reality, error sources must be considered, such as the water surface slope, water turbidity, and seafloor slope. Based on the knowledge of those factors' effects, error corrections can be applied. We concentrated on the effect of the seafloor slope on LiDAR waveforms while restricting other error sources. A simulation regarding in-water beam scattering was conducted, followed by an investigation of the correlation between the seafloor slope and peak timing of return waveforms. As a result, an equation was derived to correct the depth error caused by the seafloor slope.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.4 no.1
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• pp.32-38
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• 2011

Collisions of nearby ships are reported frequently because of bad weathers. A lot of efforts, using radar warning or other navigation security devices, were given to reduce the collisions, but the number of accidents could not be reduced. The main cause is that the ship personel are not watching carefully. In the paper, we propose a novel technique estimating the locations of nearby ships from their whistle blast and delivering the location information using mobile phones. We realized the technique using LabVIEW and showed its usefulness.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.9
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• pp.747-754
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• 2013

This paper describes SCTE(System and Control unit Test Equipment) as an integrated test equipment for airborne SAR system and control unit. SCTE enhances reusability of test equipment by modular design for required functions and strengthens automatic testing and test convenience by providing functions such as script-based testing function and report generation function. Also, it includes a navigation data simulator which can simulate various flight conditions. In this paper, we details SCTE requirements, H/W and S/W design, implementation, and test results with control unit and SAR system.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.18 no.3
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• pp.9-20
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• 2010

Surveillance is an enabler of safety with respect to aircraft separation and as a consequence capacity and efficiency with respect to aircraft operations. The new emerging technology among modern civil aviation surveillance is Multilateration (MLAT) which would affect on the surveillance capacity with both side of surveillance signal and operational properties. Multilateration system is needed to receive the signal which must reach at least 3 ground receivers simultaneously and has the effect that will have on with the ultimate accuracy. In this paper, the principle and the system configuration are reviewed. And its benefit of development is considered with use in situations where it is difficult to locate tranditional radar. This MLAT requires no additional avionics equipment to supply service with more accurate and less expensive. And it is able to enhance performance that meets international standards and extend the investment of air navigation service providers with reducing environmental impact by utilizing a small footprint on existing structures. Finally, it can be added to meet a wide range of coverage requirements and future surveillance needs.

• Journal of Electrical Engineering and Technology
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• v.8 no.3
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• pp.658-665
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• 2013

While the chirp signal is extensively used in radar and sonar systems for target decision in wireless communication systems, it has not been widely used for positioning in indoor environments. Recently, the IEEE 802.15.4a standard has adopted the chirp spread spectrum (CSS) as an underlying technique for low-power and low-complexity precise localization. Chirp signal based ranging solutions have been established and deployed but their ranging performance has not been analyzed in multipath environments. This paper presents a ranging performance analysis of a chirp signal and suggests a method to suppress multipath error by using a type of non-linear chirp signal. Multipath ranging performance is evaluated using a conventional linear chirp signal and the proposed non-linear chirp signal. We verify the feasibility of both methods using two-ray multipath model simulation. Our results demonstrate that the proposed non-linear chirp signal can successfully suppress the multipath error.

• Proceedings of the Korean Society of Computer Information Conference
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• 2008.06a
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• pp.257-262
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• 2008

컴퓨팅 기술의 발전에 따라 선박의 안전항해를 지원하기 위해 Radar, GPS 등 다양한 장비들이 계량, 개발되고 있으며 그들은 선박 항해에 필요한 많은 정보를 제공하고 있다. 하지만 여전히 선박 충돌사고는 끊이지 않고 있으며, 선박 대형화에 힘입어 그 피해도 커지고 있는 실정이다. 이러한 선박 충돌사고는 앞에서 언급한 선박 항해 안전 장비의 성능제약을 받는 야간이나, 해상 환경 악화 시 두드러지게 발생하고 있으며, 특히 제한적인 상황에서 인간의 눈에만 의지해서 항해를 하고 있기 때문이기도 하다. 그래서 이러한 상황에서 Vision기술을 사용하여 카메라를 활용 상대선박을 자동으로 식별하는 시스템을 제안하고자 한다. 이는 선박들이 법적으로 야간이나 각종 장비들이 제한을 받는 상황에서 근처의 다른 선박에게 상황을 전달하기 위해서 등화(불빛)와 형상물을 사용해야한다는 점에서 착안하였다. 제안 시스템을 실제 해상 환경에서 실험하기에 제한점이 많아 프로토타입을 구현하여 실험실 환경에서 실험하고 사용자 평가를 실시하였다. 즉, LED를 가상 등화로 하여 선박에 설치된 것과 동일한 색상과 동일한 위치에 배치하고 이를 카메라를 활용하여 인식 실험을 하였으며 약 90%의 인식률을 보였다. 그리고 이러한 실험화면을 활용하여 항해업무 종사자 15명을 대상으로 사용자 평가를 실시하였으며 대부분의 사람들이 제안된 체계가 해상에서 유용하다고 답변하였다.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.20 no.2
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• pp.18-25
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• 2012

The availability of the GPS signal has been expanded greatly in the field of society overall through the development and construction of the GNSS(Global Navigation Satellite System). Furthermore, in the military, aviation and field of space, the GPS signal is applied widely through the combination of INS consisting of gyroscope and accelerometer, IMU, AHRS with the addition of magnetic sensor. Particularly, the performance of these equipments or sensors is very important with GPS and PAR(Precision Approach Radar) in the flight control of the aircraft. This paper deals with MATLAB simulation and ROLSO(Reduced Order Luenberger State Observer) design to reduce the load of system and realize the stable lateral direction approach control in an appropriate time for reduction of the horizontal error which is importantly considered while an aircraft lands instead of the FOLSO(Full Order Luenberger State Observer) using all measurement values. Consequently, ROLSO is expected to be used for the aircraft's attitude control in the aircraft landing causing the burden to the pilots.

• Journal of Astronomy and Space Sciences
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• v.35 no.4
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• pp.227-233
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• 2018

This study presents the generation and accuracy assessment of predicted orbital ephemeris based on satellite laser ranging (SLR) for geostationary Earth orbit (GEO) satellites. Two GEO satellites are considered: GEO-Korea Multi-Purpose Satellite (KOMPSAT)-2B (GK-2B) for simulational validation and Compass-G1 for real-world quality assessment. SLR-based orbit determination (OD) is proactively performed to generate orbital ephemeris. The length and the gap of the predicted orbital ephemeris were set by considering the consolidated prediction format (CPF). The resultant predicted ephemeris of GK-2B is directly compared with a pre-specified true orbit to show 17.461 m and 23.978 m, in 3D root-mean-square (RMS) position error and maximum position error for one day, respectively. The predicted ephemeris of Compass-G1 is overlapped with the Global Navigation Satellite System (GNSS) final orbit from the GeoForschungsZentrum (GFZ) analysis center (AC) to yield 36.760 m in 3D RMS position differences. It is also compared with the CPF orbit from the International Laser Ranging Service (ILRS) to present 109.888 m in 3D RMS position differences. These results imply that SLR-based orbital ephemeris can be an alternative candidate for improving the accuracy of commonly used radar-based orbital ephemeris for GEO satellites.

• International Journal of Computer Science & Network Security
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• v.23 no.1
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• pp.1-10
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• 2023

Open surface water body extraction is gaining popularity in recent years due to its versatile applications. Multiple techniques are used for water detection based on applications. Different applications of Radar as LADAR, Ground-penetrating, synthetic aperture, and sounding radars are used to detect water. Shortwave infrared, thermal, optical, and multi-spectral sensors are widely used to detect water bodies. A stereo camera is another way to detect water and different methods are applied to the images of stereo cameras such as deep learning, machine learning, polarization, color variations, and descriptors are used to segment water and no water areas. The Satellite is also used at a high level to get water imagery and the captured imagery is processed using various methods such as features extraction, thresholding, entropy-based, and machine learning to find water on the surface. In this paper, we have summarized all the available methods to detect water areas. The main focus of this survey is on water detection especially in small patches or in small areas. The second aim of this survey is to detect water hazards for unmanned vehicles and off-sure navigation.

• Korean Journal of Remote Sensing
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• v.37 no.6_1
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• pp.1657-1667
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• 2021

Anthropogenic activities and natural processes have been causes of land subsidence which is sudden sinking or gradual settlement of the earth's solid surface. Mexico City, the capital of Mexico, is one of the most severe land subsidence areas which are resulted from excessive groundwater extraction. Because groundwater is the primary water resource occupies almost 70% of total water usage in the city. Traditional terrestrial observations like the Global Navigation Satellite System (GNSS) or leveling survey have been preferred to measure land subsidence accurately. Although the GNSS observations have highly accurate information of the surfaces' displacement with a very high temporal resolution, it has often been limited due to its sparse spatial resolution and highly time-consuming and high cost. However, space-based synthetic aperture radar (SAR) interferometry has been widely used as a powerful tool to monitor surfaces' displacement with high spatial resolution and high accuracy from mm to cm-scale, regardless of day-or-night and weather conditions. In this paper, advanced interferometric approaches have been applied to get a time-series of land subsidence of Mexico City using four-year-long twenty ALOS PALSAR L-band observations acquired from Feb-11, 2007 to Feb-22, 2011. We utilized persistent scatterer interferometry (PSI) and small baseline subset (SBAS) techniques to suppress atmospheric artifacts and topography errors. The results show that the maximum subsidence rates of the PSI and SBAS method were -29.5 cm/year and -27.0 cm/year, respectively. In addition, we discuss the different subsidence rates where the study area is discriminated into three districts according to distinctive geotechnical characteristics. The significant subsidence rate occurred in the lacustrine sediments with higher compressibility than harder bedrock.