Ocean and Polar Research

Korea Institute of Ocean Science & Technology (한국해양과학기술원)
권호 표지
DOI QR코드

DOI QR Code

Remote Sensing of Nearshore Currents using Coastal Optical Imagery

해안 광학영상 자료를 이용한 쇄파지역 연안류 측정기술

  • 유제선 (한국해양과학기술원 연안재해.재난연구센터) ;
  • 김선신 (한국해양과학기술원 연안재해.재난연구센터)
  • Received : 2014.12.27
  • Accepted : 2015.03.09
  • Published : 2015.03.30
Download PDF
⟨ Previous Next ⟩

Abstract

In-situ measurements are labor-intensive, time-consuming, and limited in their ability to observe currents with spatial variations in the surf zone. This paper proposes an optical image-based method of measurement of currents in the surf zone. This method measures nearshore currents by tracking in time wave breaking-induced foam patches from sequential images. Foam patches in images tend to be arrayed with irregular pixel intensity values, which are likely to remain consistent for a short period of time. This irregular intensity feature of a foam patch is characterized and represented as a keypoint using an image-based object recognition method, i.e., Scale Invariant Feature Transform (SIFT). The keypoints identified by the SIFT method are traced from time sequential images to produce instantaneous velocity fields. In order to remove erroneous velocities, the instantaneous velocity fields are filtered by binding them within upper and lower limits, and averaging the velocity data in time and space with a certain interval. The measurements that are obtained by this method are comparable to the results estimated by an existing image-based method of observing currents, named the Optical Current Meter (OCM).

Keywords

References

  1. Chickadel CC, Holman RA, Freilich MH (2003) An optical technique for the measurement of longshore currents. J Geophys Res 108(C11):3364. doi: 10.1029/2003JC001774
  2. Guza R, Thornton E, Christensen Jr N (1986) Observations of steady longshore currents in the surf zone. J Phys Oceanogr 16(11):1959-1969 https://doi.org/10.1175/1520-0485(1986)016<1959:OOSLCI>2.0.CO;2
  3. Haas KA, Svendsen IA (2002) Laboratory measurements of the vertical structure of rip currents. J Geophys Res 107(C5). doi: 10.1029/2001JC000911
  4. Holland KT, Holman RA (1993) The statistical distribution of swash maxima on natural beaches. J Geophys Res 98(C6):10271-10278. doi: 10.1029/93jc00035
  5. Holland KT, Holman RA, Lippmann TC, Stanley J, Plant N (1997) Practical use of video imagery in nearshore oceanographic field studies. Ieee J Ocean Eng 22(1):81-92. doi: 10.1109/48.557542
  6. Holland KT, Puleo JA, Kooney TN (2001) Quantification of swash flows using video-based particle image velocimetry. Coast Eng 44(2):65-77. doi: 10.1016/S0378-3839(01)00022-9
  7. Inman DL, Bagnold R (1963) Littoral processes. The sea 3:529-553
  8. Komar PD (1998) Beach processes and sedimentation. Prentice Hall, Upper Saddle River, NJ, 546 p
  9. Longuet-Higgins MS (1970) Longshore currents generated by obliquely incident sea waves: 1. J Geophys Res 75(33):6778-6789 https://doi.org/10.1029/JC075i033p06778
  10. Lowe D (2004) Distinctive image features from scaleinvariant keypoints. Int J Comput Vision 60(2):91-110. doi: 10.1023/B:VISI.0000029664.99615.94
  11. Ruessink B, Miles J, Feddersen F, Guza R, Elgar S (2001) Modeling the alongshore current on barred beaches. J Geophys Res 106(C10):22451-22463 https://doi.org/10.1029/2000JC000766
  12. Stockdon HF, Holman RA (2000) Estimation of wave phase speed and nearshore bathymetry from video imagery. J Geophys Res 105(C9):22015-22033. doi: 10.1029/1999jc000124
  13. Yoon SB, Park WK, Choi J (2014) Observation of rip current velocity at an accidental event by using video image analysis. J Coastal Res SI 72:16-21 https://doi.org/10.2112/SI72-004.1