• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.347-352
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• 2006

Narrowband interference can severely degrade the performance of GPS receivers. Detecting the presence of interference and then characterizing it can lead to its removal. Receivers can be reconfigured to focus on other signals or satellites that are less vulnerable to that interference at that moment. Using hardware reconfigurability of FPGA receivers and characterizing the effect of narrowband interference on the GNSS signal quality lead us to a new RFI mitigation technique in which the highest quality and less vulnerable signal can be chosen at each moment. In the previous work [1], the post processing capability of a software GPS receiver, has been used to detect and characterize the CW interference. This is achieved by passing the GPS signal and the interference through the correlator. Then, using the conventional definition of C/No as the squared mean of the correlator output divided by its variance, the actual C/No for each satellite is calculated. In this work, first the 'Exclusion zone' for each satellite signal has been defined and then by using some experiments the effects of different parameters like signal power, jamming power and the environmental noise power on the Exclusion zone have been analyzed. By monitoring the Doppler frequency of each satellite and using the actual C/No of each satellite using the traditional definition of C/No and actual data from a software GPS receiver, the decision to reconfigure the receiver to other signal can be made.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.9
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• pp.1734-1741
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• 2007

In this paper, the Hybrid SC/MRC-2/4 method in which bit synchronization and phase synchronization were not required was applied to the orthogonal MC DS-CDMA system in which each normalized subcarrier interval and processing gain had the same value, respectively, and the direct sequence spread code of each subcarrier was orthogonal. In the broadband wireless system in which multi-carrier transmission was used, a Doppler frequency shift occurred, which was caused by the difference between the highest subcarrier frequency md the lowest subcarrier frequency. In order to complement phase error caused by the shift, the orthogonal MC DS-CDMA system was analyzed so that the receiving signal could be perfectly synchronized by adjusting the PLL gain suitable for the entire system. As a result of simulations, as the PLL gain was increased, the change in the intervals was close to the case of perfect synchronization however, it became less when the PLL gain reached more than a certain value. Therefore, by selecting a proper PLL gain suitable for the system the orthogonal MC DS-CDMA can be designed in which the Hybrid SC/MRC method is applied.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.505-505
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• 2017

최근 하천의 유량측정에 있어서 ADCP(Acoustic Doppler Current Profiler)의 빈도와 활용범위가 점차적으로 증가하고 있다. 국토교통부의 유량측정을 전담하고 있는 유량조사사업단에서는 최근 저평수기 유량측정은 물론, 중고수위 유량측정에서도 기존 유량측정방법의 단점을 보완하기 위해 ADCP 이동보트법을 적극적으로 활용하고 있다. 현재 ADCP 이동보트법으로 측정된 유량은 제조업체에서 제공되는 소프트웨어로 산정되며 크게 두 가지 문제를 초래하고 있다. 첫째, 제조업체에서 제공한 소프트웨어는 자동으로 품질평가를 할 수 있는 기능이 제한적이고, 사용자가 측정자료를 검토하기 위해 제공되는 표와 그래프 등의 정보가 제조업체마다 일관적이지 않다. 따라서, 측정자료의 품질평가는 측정한 ADCP에 종속되고 제조업체에서 제공된 소프트웨어 기능에 한정되어 효율적인 평가는 저해되고, 일관적이지 못한 결과를 초래하여 측정자의 책임이 증가되고 있다. 둘째, 제조업체에서 제공되는 소프트웨어가 자료의 처리 및 유량 계산에 대한 상이한 알고리즘을 사용하여 제조업체가 다른 ADCP로 동시에 측정된 유량이 서로 다른 결과로 나타나 혼란을 주고 있다. 이러한 이유로 USGS(U.S.Geological Survey)에서는 ADCP를 이용한 이동보트법 측정유량 처리에 대한 소프트웨어인 QRev를 개발하였으며, 일관적이고 효율적인 자료 처리와 계산이 이루어지도록 하고 있다. 본 연구에서는 유량조사사업단에서 수행한 ADCP 이동보트법 측정유량 자료에 대하여 QRev를 이용한 자료의 처리 결과에 대하여 분석하였다. 특히, ADCP로 측정이 불가능한 수면 및 하상 영역에 대한 외삽방법들의 적용 결과 및 제조업체의 기본 설정 값들에 대한 결과를 비교함으로서 QRev에 대한 향후 국내 활용 방향을 제시하고자 한다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.30 no.5
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• pp.389-398
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• 2019

In this paper, we propose a method to detect small unmanned aerial vehicles(UAVs) flying in a real-world environment. Small UAV signals are frequently obscured by clutter signals because UAVs usually fly at low altitudes over urban or mountainous terrain. Therefore, to obtain a desirable detection performance, clutter signals must be considered in addition to noise, and thus, a performance analysis of each clutter removal technique is required. The proposed detection process uses clutter removal and pulse integration methods to suppress clutter and noise signals, and then detects small UAVs by utilizing a constant false alarm rate detector. After applying three clutter removal techniques, we analyzed the performance of each technique in detecting small UAVs. Based on experimental data acquired in a real-world outdoor environment, we found it was possible to derive a clutter removal method suitable for the detection of small UAVs.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.85-85
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• 2023

유량 측정을 위해 도섭법, 횡측선법 등의 인력에 의한 방법이 적용되고 있으나, 이는 야간 및 휴일 측정, 인력 부족 등 여러 제약으로 인해 고수위 홍수를 측정하는 데에 한계가 있다. 이를 해결하기 위해 시공간적 제약이 없는 도플러 방식 초음파유속계(Acousitc Doppler Velocity Meter, ADVM)와 자동유속관측시스템(Portable Automatic Velocity Observation System; PAVOs)이 제안되었다. 이 방법들은 교량에 설치된 장치를 통해 실시간으로 유속이 계측되어 시공간적 제약이 없으며 홍수 관리에 유용하게 사용될 수 있다. 실시간으로 계측된 유속 데이터는 오·결측 값이 발생하며 ADVM의 경우 수위-유량관계식을 활용하는 등 전처리 방법이 활용되고 있지만 전자파표면유속계를 활용한 PAVOs 데이터의 전처리 방법에 대한 연구는 부족하다. 따라서 본 연구에서는 PAVOs에서 실시간으로 계측된 유속 데이터의 전 처리 과정(Pre-processing)을 개발하였다. PAVOs를 통해 측정된 데이터는 5분 단위로 10개의 유속이 한번에 측정되며 비정상성(Non-stationary)인 특징을 가진다. 이 데이터의 전처리 과정으로 오·결측값에 대한 처리 및 보간법 적용 이후 10개 값 중 실제 유속을 판단하고 잡음제거(Denoising)를 수행하였다. 이를 강원도 홍천강에 위치한 홍천교에서 계측된 유속 데이터에 적용하였다. 그 결과 데이터의 상승부와 하강부에서 일정한 경향성을 파악할 수 있다. 이 데이터를 통해 산정한 유량과 실측 기반의 평균유속과 관계를 통해 계산한 유량을 비교해 보았을 때 낮은 편차율을 가지는 것을 확인하였다. 전 처리 된 실시간 유속 데이터를 활용한다면 최고수위가 발생하였을 경우 홍수량을 산정할 수 있을 것이다. 또한, 강우 또는 하천 공사에 의해 변동하는 수위-유량관계곡선식을 실시간으로 개발할 수 있을 것이며 이는 효과적인 홍수관리에 큰 역할을 할 수 있을 것이다.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.19 no.3
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• pp.180-190
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• 2014

It has been customary to exclude top 10-20% of velocity profiles in the Acoustic Doppler Current Profiler (ADCP) measurement due to side lobe effects at the boundary. To better understand the mixing in the Yeongsan estuary, the freshwater advection speed (FAS) was recovered from highly contaminated ADCP data near the surface. The velocity profiles were measured by using ADCP at two stations in the Yeongsan estuary during August 2011: one was located in front of the Yeongsan estuarine dam and the other was deployed near Goha Island. The FAS was recovered from the ADCP data set by applying rigorous post-processing methods and compared with the sediment advection speed (SAS). The SAS was determined by the peak time difference of suspended sediment concentration between two stations in the channel, divided by the distance of two stations. The FAS and the SAS showed very similar value when the freshwater discharge was greater than $2.0{\times}10^7$ ton and the SAS was a bit greater when the freshwater discharge was smaller. Since the FAS was on average about 0.8 m/s greater than the velocity at 0.8 of water depth from the bottom, the net discharge, estimated with recovered FAS and integrated over water depth and tidal cycle, was directed seaward during the high discharge contrary to the onshore direction of the net discharge estimated with 0.8 of water depth from the bottom. Moreover, the velocity shear and Richardson number changed when the FAS was used. Thus, the importance of the true FAS is appreciated in the investigation of the surface layer stability. If currents, temperature and salinity were observed for longer time in the future, it could be possible to more accurately understand the formation and decay of stratification as well as the suspended sediment transport processes.

• Journal of Satellite, Information and Communications
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• v.7 no.3
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• pp.99-104
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• 2012

The United States will proceed with the effort to modernize the GPS system, and one of its main content is to provide L5 signal. L5 will be transmitted in a radio band reserved exclusively for aviation safety services. And, L5, in combination with L1, will improve the position accuracy via ionospheric correction and robustness via signal redundancy. However, The acquisition processing time of L5 takes longer than that of L1 as the code length of L5 is 10 times longer than that of L1. To reduce this acquisition processing time, a higher number of correlators in the aquisition module should be used. However, there is a problem that this causes increase in the complexity of the correlator configuration and the computation power. So, in this paper, we propose L5 signal tracking scheme using tracking results in the GPS L1/L5 receiver. The proposed scheme could reduce the hardware complexity as the GPS L5 signal acquisition module is not needed, and provide fast and stable tracking of L5 signal by aiding L1 tracking results such as PRN, the code phase synchronization, and the Doppler frequency. The feasibility of the proposed scheme is demonstrated through simulation results.

• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.3
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• pp.11-19
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• 2009

Recently, concerns relating to the maintenance of large structures have been increased. In addition, the number of large structures that need to be evaluated for their structural safety due to natural disasters and structural deterioration has been rapidly increasing. It is common for the structural characteristics of an older large structure to differ from the characteristics in the initial design stage, and changes in dynamic characteristics may result from a reduction in stiffness due to cracks on the materials. The process of deterioration of such structures enables the detection of damaged locations, as well as a quantitative evaluation. One of the typical measuring instruments used for the monitoring of bridges and buildings is the dynamic measurement system. Conventional dynamic measurement systems require considerable cabling to facilitate a direct connection between sensor and DAQ logger. For this reason, a method of measuring structural responses from a remote distance without the mounted sensors is needed. In terms of non-contact methods that are applicable to dynamic response measurement, the methods using the doppler effect of a laser or a GPS are commonly used. However, such methods could not be generally applied to bridge structures because of their costs and inaccuracies. Alternatively, a method using a visual image can be economical as well as feasible for measuring vibration signals of inaccessible bridge structures and extracting their dynamic characteristics. Many studies have been conducted using camera visual signals instead of conventional mounted sensors. However, these studies have been focused on measuring displacement response by an image processing technique after recording a position of the target mounted on the structure, in which the number of measurement targets may be limited. Therefore, in this study, a model experiment was carried out to verify the measurement algorithm for measuring multi-point displacement responses by using a DIC (Digital Image Correlation) technique.

• Journal of Korea Water Resources Association
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• v.44 no.5
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• pp.377-388
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• 2011

Surface Image Velocimetry (SIV) is a recently-developed discharge measurement instrument. It uses image processing techniques to measure the water surface velocity and estimate water discharge with given cross section. The present study aims to implement a FSIV (Fixed-type Surface Image Velocimetry) at Soojeon Bridge in the Dalcheon. The hardware system consists of two digital cameras, a computer, and a pressure-type water stage gauge. The images taken with the hardware system are sent to a server computer via a wireless internet, and analyzed with a image processing software (SIV software). The estimated discharges were compared with the observed discharges through Goesan dam spillway and index velocity method using ADVM. The computed results showed a good agreement with the observed one, except for the night time. The results compared with discharges through Goesan dam spillway reached around 5~10% in the case of discharge over 30 m3/s, and the results compared with discharges through index velocity method using ADVM reached around 5% in the case of discharge over 200 $m^3/s$. Considering the low cost of the system and the visual inspection of the site situation with the images, the SIV would be fairly good way to measure water discharge in real time.

• Korean Journal of Remote Sensing
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• v.38 no.3
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• pp.251-263
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• 2022

This paper presents an idea of ScanSAR image formation. For image formation of ScanSAR that utilizes the burst mode for raw signal acquisition, most conventional single burst methods essentially require a step of azimuth stitching which contributes to radiometric and phase distortions to some extent. Time-domain cross correlation could replace SPECAN which is most popularly used for ScanSAR processing. The core idea of the proposed method is that it is possible to relieve the necessity of azimuth stitching by an extension of Doppler bandwidth of the reference function to the burst cycle period. Performance of the proposed method was evaluated by applying it to the raw signals acquired by a spaceborne SAR system, and results satisfied all image quality requirements including 3 dB width, peak-to-sidelobe ratio (PSLR), compression ratio,speckle noise, etc. Image quality of ScanSAR is inferior to that of Stripmap in all aspects. However, it is also possible to improve the quality of ScanSAR image competitive to that of Stripmap if focused on a certain parameter while reduced qualities of other parameters. Thus, it is necessary for a ScanSAR processor to offer a great degree of flexibility complying with different requirements for different applications and techniques.