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The Observation of SAR, Optical and Altimeter Data to Study the Generation of Internal Waves in Tsushima Strait

Yessy Arvelyna(1) and Masaki Oshima(1)

(1) Tokyo University of Marine Science and Technology, 2-1-6 Ecchujima, Koto-ku, Tokyo 135-8533, Japan

Abstract

The internal wave signatures have been detected in ERS1/2 and ASTER images data over the Tsushima Strait, Japan, during 1993-2004 period. The study area is located at northern side of East China Sea, well known as a region where energy for exciting internal tides should be large. Wavelet transform analysis and spectral reflectance analysis have been performed to delineate internal wave from sea surface wave and other oceanic features. Discreet Meyer wavelet transform analysis has been applied for internal wave detection in image, which succeeded in emphasizes the internal wave features 2-4.59 times, on horizontal and vertical detail coefficient of image transforms, compare to wind waves and sea surface features. Discreet Meyer wavelet is proposed for smoothness of feature, space save coding, and to avoid depashing in image.

The observation results show that the profile of a train of internal waves in ERS1/2 SAR and ASTER images data composes a formation of several taller waves, which the leading wave as the tallest one, and smaller depressed waves at one-third section. This shown that non-linier process was taking a part in transformation of internal tide into a train of independent solitary waves. The non-linier internal waves were occurred in north coast off Kitakyushu and NW/W/SW/E coast off Tsushima Island between June-September. The length and wavelength of the internal waves were detected between 6-28 km and 120 m-1.28 km, respectively.

The altimeter data products from Topex/Poseidon and Jason-1 data are used to analyze the ocean dynamic over the study area. In the Tsushima Strait, the geostrophic current generally flows from SW direction yearly around. During summer, the small-scale eddies appear at NE and SE coast off Tsushima Island, due the effect of current flows at south of the Japan Sea. The directions of internal waves were varied between NW-SW at eastern channel and N-SW at western channel of Tsushima Strait, parallel to the direction of the geostrophic currents. Meanwhile at NE coast off Tsushima Island, the internal wave packet propagates to S/SE direction. Internal wave is modeled using Combined of Korteweq de Vries equation. At eastern channel of Tsushima Strait, the internal wave induced current is calculated about 85 cm s-1. The occurrences of internal waves were coincided to the area where the sea surface height anomaly increase steeply, e.g. between 2-6 cm. It is suggested that the internal waves were sourced from south coast off Tsushima Island and south coast off the Japan Sea. They were tidally generated and formed due to bathymetric change.

 

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                 Last modified: 07.10.03