• 한국수산과학회지
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• 제32권3호
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• pp.368-373
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• 1999

Topex/Poseidon sea surface heights are compared to tide gauge sea levels in the South Indian Ocean in the period of January 1993 to December 1995. A user's handbook (AVISO) for processing sea surface height data was used in this study. Topex/Poseidon sea surface heights were obtained from satellite data at the proximity of tide gauge stations. These data were reproduced by a linear interpolation with the interval of 10 days and were processed by the Gaussian filter with a 60-day window. The tide gauge sea levels were obtained in the same manner as the satellite data. The main results on RMS (Root-Mean-Square) and CORR (CORRelation coefficient) in our study were shown as follows: 1) on the characteristics between two data (in-situ and model data), the results (RMS=2.96 cm & CORR=$92\%$ in the Amsterdam plateau, and RMS=3.45 cm & CORR=$59\%$ in the Crozet plateau) of the comparison of Topex/Poseidon sea surface heights with tide gauge sea levels, which was calculated by in-situ data of obsewed station showed generally low values in RMS and high values in CORR against to the results (RMS=4.69 cm & CORR=$79\%$ in the Amsterdam plateau, and RMS= 6.29 cm & CORR= $49\%$ in the Crozet plateau) of the comparison of Topex/Poseidon sea surface heights with tide gauge sea levels, which was calculated by model data of ECMWF (European Center for Medium-range Weather Forecasting), and 2) on the characteristics between two areas (Kerguelen plateau and island), the results (RMS=3.28 cm & CORR= $54\%$ in the Kerguelen plateau) of open sea area showed low values in RMS and high values in CORR against to the results (RMS= 5.71 cm & CORR=$38\%$ in the Kerguelen island) of coast area, respectively.

• 한국해양환경ㆍ에너지학회지
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• 제13권2호
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• pp.112-120
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• 2010

이 논문에서는 Yura 해역에서 폭풍 중 24시간 연속으로 측정된 freak wave가 포함된 파랑자료를 분석하여 비선형 파도의 통계적 특성을 살펴보았다. 파고의 초과확률분포는 Edgeworth-Rayleigh(ER) 분포와, Rayleigh 분포를 이용하여 계측된 자료와 비교하였다. 파형이 stationary 상태를 유지하는 10시간 동안 계측된 파랑자료(파랑의 개수가 4600 내외)에서는, 파형의 분포는 Gram-Chalier분포가 Gaussian분포보다 파랑자료와 일치를 한다. 전반적인 파고의 확률분포는 Rayleigh($H_{rms}$)분포를 잘 따르는 것을 볼 수 있다. Freak wave 발생확률은 Rayleigh($m_{o}{^{1/2}}$) 분포로 잘 표시가 되며, ER 분포는 과대하게 예측하는 것을 볼 수 있다. 30분간 계측된 파랑자료(파랑 개수가 250개 내외)에서 freak wave가 발생된 경우는 ER 분포가 freak wave 발생확률과 잘 일치한다. 그러나 전반적인 파고의 발생확률이 과대평가된다. Freak wave가 발생하지 않은 경우는 거의 모든 파고에 걸쳐 Rayleigh($H_{rms}$)분포가 계측된 파고분포와 잘 일치를 한다. 파고가 10 m 이하의 freak wave의 파고확률분포는 10 m 이상의 파고를 가지는 freak wave와 비슷한 경향을 보인다. $H_{max}/H_{1/3}$은 파형의 kurtosis와 연관이 있는 것을 보여주었다. Freak wave의 발생은 높은 kurtosis 값과 관계가 있으며, freak wave가 발생하는 임계 kurtosis 값이 존재할 가능성이 있을 것으로 추정된다.

• 한국전자파학회논문지
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• 제28권10호
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• pp.788-793
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• 2017

본 논문에서는 거친 바다표면의 마이크로파 반사를 계산할 수 있는 이론적 모델의 정확도를 검증한다. 우선 Pierson-Moskowitz 해양 스펙트럼을 이용하여 거친 바다표면을 생성하였다. 생성된 바다표면의 유의파고와 유효높이(root-mean square height)값을 추정하여 풍속에 따른 유의파고, 유효높이 관계식을 유도하였고, 다른 측정 데이터들과 비교하였다. 수치해석적 방법을 이용하여 다양한 거칠기 조건(풍속)에서 생성된 바다표면의 반사계수를 계산하였고, 기존에 반사계수를 계산하기 위해 사용하는 이론적 모델인 Ament 모델, PO(Physical Optics) 모델, GO(Geometrical Optics) 모델, B-M(Brown-Miller) 모델과 비교하였다. 비교적 거칠기가 매우 낮은 경우($kh_{rms}$<0.4, k는 파수, $h_{rms}$는 RMS 높이) 외에는 Ament 모델은 정확하지 않았다. 또한 거칠기가 크지 않은 바다($kh_{rms}$<10)에서는 PO, GO, B-M 모델들의 정확도가 보장되지만, 풍속이 높아 거칠기가 높은 바다($kh_{rms}$>10)에서는 입사각이 $70^{\circ}$ 이하에서는 PO 모델과 GO 모델이 수치해석결과와 비교적 잘 일치하였으며, $80^{\circ}$ 이상에서는 B-M 모델이 수치해석 결과와 비교적 잘 일치함을 보였다.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2008년도 International Symposium on Remote Sensing
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• pp.313-316
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• 2008

Although the positioning accuracy of the Global Positioning System (GPS) has been studied extensively and used widely, it is still limited due to errors from sources such as the ionospheric effect, orbital uncertainty, antenna phase center variation, signal multipath and tropospheric influence. This investigation addresses the tropospheric effect on GPS height determination. Data obtained from GPS receivers and co-located surface meteorological instruments in 2003 are adopted in this study. The Ministry of the Interior (MOl), Taiwan, established these GPS receivers as continuous operating reference stations. Two different approaches, parameter estimation and external correction, are utilized to correct the zenith tropospheric delay (ZTD) by applying the surface meteorological measurements (SMM) data. Yet, incorrect pressure measurement leads to very poor accuracy. The GPS height can be affected by a few meters, and the root-mean-square (rms) of the daily solution ranges from a few millimeters to centimeters, no matter what the approach adopted. The effect is least obvious when using SMM data for the parameter estimation approach, but the constant corrections of the GPS height occur more often at higher altitudes. As for the external correction approach, the Saastamoinen model with SMM data makes the repeatability of the GPS height maintained at few centimeters, while the rms of the daily solution displays an improvement of about 2-3 mm.

• 대한공간정보학회지
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• 제17권3호
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• pp.71-79
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• 2009

본 연구에서는 단일 고해상도 영상으로부터 그림자와 건물 연직선을 이용한 3차원 건물 정보 추출 알고리즘을 확장하여 메타정보가 없는 단일 고해상도 영상에서도 3차원 건물 정보 추출 생성 방법을 제안하고, 이를 통해서 3차원 건물 모델 생성 가능성에 대해서 연구하였다. 제안된 방법은 메타정보가 없는 영상에서 기준 건물을 선택하고, 기준 건물에 높이를 부여하여 이로부터 센서와 태양의 고도각 및 방위각을 추정한다. 스테레오 IKONOS 위성영상에서 추출한 건물의 높이를 실제 높이라고 가정했을 때, 제안된 방법으로 메타정보를 이용하지 않고 IKONOS 영상으로부터 추출한 20개의 건물 높이 RMS 오차는 3m 미만이었으며, 5개의 건물 수평 위치를 1:1000 수치지형도의 건물 수평 위치와 비교한 결과, RMS 오차가 3m 미만이었다. 또한 제안된 방법을 구글어스로부터 추출한 영상에 적용한 결과, 17개 건물 높이의 RMS 오차가 3m 미만이었다. 제안된 방법으로 생성한 3차원 건물 모델을 육안으로 비교한 결과, 메타정보를 이용하여 생성한 3차원 건물 모델과 유사한 높이 패턴을 보여주었다. 이를 통해서 제안된 방법으로 메타정보가 없는 고해상도 영상에서 3차원 건물 모델이 추출될 수 있다고 판단하였다.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume I
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• pp.520-523
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• 2006

Whereas it is well known that the surface roughness parameters, the RMS height and the correlation length, of a natural soil surface are underestimated with a short surface profile, it is not clear how much the underestimated surface parameters affect the backscattering coefficients of the surface for various incidence angles and polarizations. The backscattering coefficients of simulated and measured surface profiles are computed using the integral equation method (IEM) and analyzed in this paper to answer this question. It is shown that the RMS error of the backscattering coefficients between 5-m- and 1-m-long measured surface profiles is 1.7 dB for vv-polarization and 0.5 dB for hh-polarization at a medium range of incidence angle ($15^{\circ}{\leq}{\theta}{\leq}70^{\circ}$), while the surface roughness parameters are significantly reduced; from 2.4 cm to 1.5 cm for the RMS height s and from 35.1 cm to 10.0 cm for the autocorrelation length l. This result is verified with numerous simulations with various roughness conditions and various wavelengths.

• 대한원격탐사학회지
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• 제29권6호
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• pp.631-644
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• 2013

Significant Wave Height (SWH) data measured by satellite altimeters (Topex/Poseidon, Jason-1, Envisat, and Jason-2) were validated in the seas around Korea by comparison with wave height measurements from marine meteorological buoy stations of Korea Meteorological Administration (KMA). A total of 1,070 collocation matchups between Ku-band satellite altimeter data and buoy data were obtained for the periods of the four satellites from 1992 to the present. In the case of C-band and S-band observations, 1,086 matchups were obtained and used to assess the accuracy of satellite SWH. Root-Mean-Square (RMS) errors of satellite SWH measured with Ku-band were evaluated to roughly 0.2_2.1 m. Comparisons of the RMS errors and bias errors between different frequency bands revealed that SWH observed with Ku-band was much more accurate than other frequencies, such as C-band or S-band. The differences between satellite SWH and buoy wave height, satellite minus buoy, revealed some dependence on the magnitude of the wave height. Satellite SWH tended to be overestimated at a range of low wave height of less than 1 m, and underestimated for high wave height of greater than 2 m. Such regional characteristics imply that satellite SWH should be carefully used when employed for diverse purposes such as validating wave model results or data assimilation procedures. Thus, this study confirmed that satellite SWH products should be continuously validated for regional applications.

• 대한기계학회논문집A
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• 제25권9호
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• pp.1391-1399
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• 2001

The AE measurement is one of the most convenient methods for detecting contacts between the slider and the disk. The AE method has been widely used in the investigation of the tribology of sliding interfaces due to its convenience. We examined the relationship between the AE signal and the flying height of a slider. We investigated the influence of the disk linear velocity on the AE rms signal by using the AE measurement system. The experiment also gives the relationship between the take-off velocity and the disk surface conditions. To investigate the behavior of the slider further, the variances of the AE signals are analyzed. The experimental results indicate that the increase in the magnitude of the AE rms signal does not necessarily mean the slider/disk contacts.

• 한국연소학회지
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• 제12권1호
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• pp.1-10
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• 2007

Analytical investigation of acoustic wave scattering from turbulent premixed flames was conducted to evaluate the acoustic energy amplification/damping. Such acoustic energy change is attributed to the acoustic velocity jump due to flame's heat release. Small perturbation method up to second order and stochastic analysis were utilized to formulate net acoustic energy and the energy transfer from coherent to incoherent energy. Randomly wrinkled flame surface is responsible for the energy transfer from coherent to incoherent field. Nondimensional parameters that govern net acoustic energy were determined: rms height and correlation length of flame front, incident wave frequency, incidence angle, and temperature ratio. The dependence of net acoustic energy upon these parameters is illustrated by numerical simulations in case of Gaussian statistics of flame front. Total net energy was amplified and the major factors that affect such energy amplification are incidence angle and temperature ratio. Coherent (incoherent) energy is damped (amplified) with rms height and correlation length of flame front.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.97-101
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• 2000

The AE measurement is one of the most convenient methods for detecting contacts between slider disk. The AE method has been widely used in the investigation of the tribology of sliding interfaces due to the convenience of using AE sensor. In this study, we examined the relationship between the AE signal and the flying height of a slider. We tried to know the influence of the disk velocity on the AE rms signal by using the AE measurement system. The experiment also gives the relationship between the take-off velocity and the disk surface state. To investigate the behavior of the slider further, the variances of the AE signal are analyzed. The results about a subambient pressure slider indicate that the increase in the magnitude of AE rms signal does not necessarily mean the slider/disk contacts.