• Geophysics and Geophysical Exploration
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• v.15 no.4
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• pp.199-208
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• 2012

High-amplitude swell noises (HASN) are very difficult to eliminate from the marine seismic data. In this paper, we applied F-X filter and median filter in order to suppress HASN. Test data have been acquired on the northern offshore of the South Shetland Islands in December, 2010. Parts of data have been contaminated by HASN caused by bad weather during the cruise. We applied F-X filter and median filter to test data with HASN. After F-X filtering, most of non-coherent noises and small-amplitude swell noises are eliminated effectively but HASN are still remained significantly. With median filter, HASN was suppressed better than F-X filter, however some of non-coherent noises are still remains. We applied a cascade of two filters and results show HASN and non-coherent noises are suppressed effectively. After the cascade of two filtering, it is possible to define reflection layers clearly on the velocity spectrum and to produce better stacked section with a good signal-to-noise ratio.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.5
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• pp.418-428
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• 2007

In the calculation of wave propagation by Boussinesq equation model, it is very common to experience numerical noises generated from nonlinear interaction and breaking wave occurrence, and the numerical solution is rapidly diverged unless the noises are properly controlled. A comparative study was here undertaken for the characteristics of three different lowpass filters (FFT filter, Gaussian filter and Shapiro filter) which are all designed to be applied to the interim results of numerical calculation. The numerical results obtained with application of respective filter techniques were compared with the results of an existing hydraulic experiment for the aspects of noise suppression, conservation of main signal and altering time. The results show that the Shapiro filter can be best applied with optimal choices of its element number, pass number and filtering tune interval. The combination of the number of filter element off, pass number of 50 or less, and application interval of 100 to 200 time steps generally showed good performance in both accuracy and efficiency of the numerical calculation.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.6
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• pp.561-568
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• 2020

Wave measurements using X-band radar have many advantages compared to other wave gauges including wave-rider buoy, P-u-v gauge and Acoustic Doppler Current Profiler (ADCP), etc.. For example, radar system has no risk of loss/damage in bad weather conditions, low maintenance cost, and provides spatial distribution of waves from deep to shallow water. This paper presents new methods for estimating significant wave heights of X-band marine radar images using Artificial Neural Network (ANN). We compared the time series of estimated significant wave heights (Hs) using various estimation methods, such as signal-to-noise ratio (${\sqrt{SNR}}$), both and ${\sqrt{SNR}}$ the peak period (TP), and ANN with 3 parameters (${\sqrt{SNR}}$, TP, and Rval > k). The estimated significant wave heights of the X-band images were compared with wave measurement using ADCP(AWC: Acoustic Wave and Current Profiler) at Hujeong Beach, Uljin, Korea. Estimation of Hs using ANN with 3 parameters (${\sqrt{SNR}}$, TP, and Rval > k) yields best result.

• Journal of the Korea Computer Graphics Society
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• v.25 no.5
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• pp.1-9
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• 2019

In this paper, we propose a video enhancement method using generative adversarial networks to remove raindrops and restore the background information on the removed region in the coastal wave video imagery distorted by raindrops during rainfall. Two experimental models are implemented: Pix2Pix network widely used for image-to-image translation and Attentive GAN, which is currently performing well for raindrop removal on a single images. The models are trained with a public dataset of paired natural images with and without raindrops and the trained models are evaluated their performance of raindrop removal and background information recovery of rainwater distortion of coastal wave video imagery. In order to improve the performance, we have acquired paired video dataset with and without raindrops at the real coast and conducted transfer learning to the pre-trained models with those new dataset. The performance of fine-tuned models is improved by comparing the results from pre-trained models. The performance is evaluated using the peak signal-to-noise ratio and structural similarity index and the fine-tuned Pix2Pix network by transfer learning shows the best performance to reconstruct distorted coastal wave video imagery by raindrops.

• Journal of the Korean Institute of Navigation
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• v.17 no.1
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• pp.99-105
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• 1993

Underwater acoustic positioning systems have been extensively used not only in surface position fixing but also in underwater position fixing. Recently, these systems have been applied in the field of installation and underwater inspection offshore platforms etc. But in these systems are included the fixing errors as results of a signal with noise and irregular motion of vessel by ocean waves. In this paper to improve the accuracy of the position fixing a Kalman filter is applied to the short baseline(SBL) acoustic positioning system. The optimal position obtained by the Kalman filter is compared with the raw position and it is confirmed that the former is more accurate than the latter.

• Proceedings of the KSRS Conference
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• 2000.04a
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• pp.91-95
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• 2000

위성영상을 이용한 해안선의 추출은 연안 지형의 변화감지의 조간대의 DEM 생성 등 지구과학적인 활용 외에도 지형도와 해도의 수정에도 활용될 수 있다. 바람이 세거나 파랑이 높을 때 돌아오는 레이다의 신호는 육지와 구별이 어렵고 또한 speckle 잡음으로 인하여 SAR를 이용한 해안선 추출은 광학자료에서 사용하는 thresholding 방법이나 간단한 edge detector 등의 방법을 적용하여 좋은 결과를 얻는데 어려움이 있다. 본 연구에서는 SAR 자료를 이용하여 빠르고 정확하게 해안선을 추출할 수 있는 ratio에 기초한 해안선 추출 방법인 MSP-PoA(Maximum Stregth Edged Pruning Ratio of Average)을 경남 낙동강 하구지역의 인공해안선에 대해 적용하여 결과를 분석하였다. 그 결과는 매우 만족할 만 하나, 육지와 해수의 점이적인 특성을 나타내는 조간대가 분포하는 전남 곰소만 지역에서는 SAR intensity의 변화가 크지 않아서 만족할 만한 결과를 얻을 수 없었다. 이러한 지역에 대해서는 SAR의 위상정보를 이용하는 interferogram의 정확도를 정량적으로 평가하는데 사용되는 coherence map을 구하여 해안선을 추출하고자 한다.

• Journal of Ocean Engineering and Technology
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• v.20 no.1 s.68
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• pp.37-42
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• 2006

In the ocean engineering field, information about the ocean environment is important for planning, design, and operation, especially the wave information. High precision wave data is also important for considering environmental problems, like efficient operation of ships. For this purpose, many methods were considered in the past. However, an on-board directing wave measurement system has not been incorporated. The use of conventional marine radar Plane Position Indicator (PPI) images allows the estimation of wave information on a real-time basis, using both space and time information, regarding the evolution of ocean surface waves. In order to achieve data acquisition, the Radar Scan Converter (RSC) has been developed. Three-dimensional analysis was performed. The comparison of wave information derived from this system, and that of wave buoy, shows that this wave field detecting system can be a useful tool.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2006.05a
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• pp.346-351
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• 2006

본 논문은 콘크리트 표면 균열 영상에서 균열의 특징을 추출하기 위해, 영상 처리 기법을 적용하여 균열의 특징(길이, 폭, 방향)을 자동으로 추출 및 처리 할 수 있는 기법을 제안한다. 본 논문에서 적용된 영상 처리 기법으로는 균열 영상의 빛을 보정하기 위하여 모폴로지 기법인 채움(Closing)기법을 적용한다. 균열의 경계를 명확히 추출하기 위하여 고주파 강화 필터링을 적용한 후, 8가지 색상(검정, 빨강, 파랑, 초록, 노랑, 자주, 주황, 하늘)으로 명암 값을 분류하고 그 중 빈도수가 가장 높은 색상을 가진 명암 값을 제거한 후에 추출한 영상을 이진화한다. 이진화된 영상에서 콘크리트 표면 균열의 실거리 측정을 위한 임의의 선을 제거하기 위하여 위치 히스토그램을 적용하여 임의의 선을 제거한다. 임의의 선이 제거된 균열 영상에서 $5\times5$ 마스크를 적용하여 균열을 확대시키고, 3차례에 걸쳐 잡음 제거연산을 수행하여 균열의 후보 영역을 선택한 후, 후보 영역으로부터 특정 균열들을 추출한다. 추출된 특정 균열을 모폴로지 기법인 제거(Opening) 연산을 수행하여 균열의 특징이 일정하게 유지되게 하고 미세하게 끊어진 부분을 보정하여 균열의 특징(길이, 방향, 폭)을 측정한다. 실제 콘크리트 표면 균열영상을 대상으로 실험한 결과, 특정 균열이 효율적으로 추출되었고, 특정 균열의 길이, 방향, 폭의 등이 정확히 추출 및 계산되었다.

• Korean Journal of Remote Sensing
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• v.34 no.6_3
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• pp.1383-1398
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• 2018

Sea surface wind is one of the most fundamental variables for understanding diverse marine phenomena. Although scatterometers have produced global wind field data since the early 1990's, the data has been used limitedly in oceanic applications due to it slow spatial resolution, especially at coastal regions. Synthetic Aperture Radar (SAR) is capable to produce high resolution wind field data. KOMPSAT-5 is the first Korean satellite equipped with X-band SAR instrument and is able to retrieve the sea surface wind. This study presents the validation results of sea surface wind derived from the KOMPSAT-5 backscattering coefficient data for the first time. We collected 18 KOMPSAT-5 ES mode data to produce a matchup database collocated with buoy stations. In order to calculate the accurate wind speed, we preprocessed the SAR data, including land masking, speckle noise reduction, and ship detection, and converted the in-situ wind to 10-m neutral wind as reference wind data using Liu-Katsaros-Businger (LKB) model. The sea surface winds based on XMOD2 show root-mean-square errors of about $2.41-2.74m\;s^{-1}$ depending on backscattering coefficient conversion equations. In-depth analyses on the wind speed errors derived from KOMPSAT-5 backscattering coefficient data reveal the existence of diverse potential error factors such as image quality related to range ambiguity, discrete and discontinuous distribution of incidence angle, change in marine atmospheric environment, impacts on atmospheric gravity waves, ocean wave spectrum, and internal wave.