The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY (한국해양학회지:바다)

The Korean Society of Oceanography (한국해양학회)
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Accuracy of HF radar-derived surface current data in the coastal waters off the Keum River estuary

금강하구 연안역에서 HF radar로 측정한 유속의 정확도

  • Lee, S.H. (Department of Oceanography, BK21 Saemangeum Environmental Research Team, Kunsan National University) ;
  • Moon, H.B. (Department of Oceanography, BK21 Saemangeum Environmental Research Team, Kunsan National University) ;
  • Baek, H.Y. (Department of Oceanography, BK21 Saemangeum Environmental Research Team, Kunsan National University) ;
  • Kim, C.S. (Department of Oceanography, BK21 Saemangeum Environmental Research Team, Kunsan National University) ;
  • Son, Y.T. (Department of Oceanography, BK21 Saemangeum Environmental Research Team, Kunsan National University) ;
  • Kwon, H.K. (Department of Oceanography, BK21 Saemangeum Environmental Research Team, Kunsan National University) ;
  • Choi, B.J. (Department of Oceanography, BK21 Saemangeum Environmental Research Team, Kunsan National University)
  • 이상호 (군산대학교 해양학과, BK21새만금환경연구팀) ;
  • 문홍배 (군산대학교 해양학과, BK21새만금환경연구팀) ;
  • 백혜연 (군산대학교 해양학과, BK21새만금환경연구팀) ;
  • 김창수 (군산대학교 해양학과, BK21새만금환경연구팀) ;
  • 손영태 (군산대학교 해양학과, BK21새만금환경연구팀) ;
  • 권효근 (군산대학교 해양학과, BK21새만금환경연구팀) ;
  • 최병주 (군산대학교 해양학과, BK21새만금환경연구팀)
  • Published : 2008.02.29
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Abstract

To evaluate the accuracy of currents measured by HF radar in the coastal sea off Keum River estuary, we compared the facing radial vectors of two HF radars, and HF radar-derived currents with in-situ measurement currents. Principal component analysis was used to extract regression line and RMS deviation in the comparison. When two facing radar's radial vectors at the mid-point of baseline are compared, RMS deviation is 4.4 cm/s in winter and 5.4 cm/s in summer. When GDOP(Geometric Dilution of Precision) effect is corrected from the RMS deviations that is analyzed from the comparison between HF radar-derived and current-metermeasured currents, the error of velocity combined by HF radar-derived current is less than 5.1 cm/s in the stations having moderate GDOP values. These two results obtained from different method suggest that the lower limit of HF radar-derived current's accuracy is 5.4 cm/s in our study area. As mentioned in previous researches, RMS deviations become large in the stations located near the islands and increase as a function of mean distance from the radar site due to decrease of signal-to-noise level and the intersect angle of radial vectors. We found that an uncertain error bound of HF radar-derived current can be produced from the separation process of RMS deviations using GDOP value if GDOP value for each component is very close and RMS deviations obtained from current component comparison are also close. When the current measured in the stations having moderate GDOP values is separated into tidal and subtidal current, characteristics of tidal current ellipses analyzed from HF radar-derived current show a good agreement with those from current-meter-measured current, and time variation of subtidal current showed a response reflecting physical process driven by wind and density field.

금강하구 연안역에서 HF radar로 측정한 유속의 정확도를 평가하기 위해 HF radar의 마주보는 radial 유속들을 비교하고, HF radar로 측정한 유속을 현장측정 유속과 비교하였다. 비교 자료들에 대한 회귀선과 편차는 주성분 분석(Principal Component Analysis)으로 구하였다. HF radar site를 연결하는 선의 중간지점에서 마주보는 radial vector를 비교하였을 때 RMS 편차는 동계에 4.4 cm/s, 하계에 5.4 cm/s이었다. HF radar와 유속계로 측정한 유속성분을 비교하여 분석된 RMS 편차에서 GDOP(Geometric Dilution of Precision) 효과를 제거하였을 때 HF radar의 합성 속도 측정오차는 GDOP 값이 적절한 정점들에서 5.1 cm/s 이내였다. 서로 다른 두 방법에 의해 구해진 이 결과는 연구해역에서 HF radar로 측정된 유속의 정확도 하한이 5.4 cm/s임을 제시한다. 기존의 연구에서와 같이 RMS 편차는 섬 주변에 있는 관측점에서 크게 되고, 두 radar에서 평균거리가 멀어질수록 신호 대 잡음수준과 radial vector 교차각의 감소로 인해 증가하였다. GDOP 값을 이용한 오차분리 과정에서 속도성분별 GDOP 값이 유사하고 비교 유속의 성분별 RMS 편차도 비슷한 값을 보이는 경우 HF radar 유속의 오차가 불확실한 값으로 도출될 수도 있음이 밝혀졌다. GDOP가 정상적인 radar 관측 범위 내에 있는 정점에서 측정된 유속을 조류와 해류로 분리하였을 때 HF radar 유속에서 구해진 조류타원의 특성은 유속계로 측정된 타원특성과 잘 부합하였고, 해류의 시간적 변화는 바람과 밀도장의 외력에 의한 물리적 과정을 반영하는 반응을 보였다.

Keywords

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