Wavelet Analysis for Internal Wave Detection in ERS SARand ASTER Image Data

摘要

On this paper, wavelet analysis has been used for internal wave detection in ERS SAR and ASTER image data over Tsushima strait, southwest of Japan, during 1993-2004 period. Various wavelet transforms, e.g. Haar wavelet, Symlet wavelet, Biorthogonal wavelet, Coif wavelet and Daubechies wavelet, are tested comparably with different level of synthesize image on horizontal, diagonal, and vertical detail, and approximation to study the internal wave characteristic in image.Internal wave features were detected as elongated pattern in image with higher wavelet coefficient (>36) than sea surface (<10) on horizontal and vertical detail coefficient of image transforms at level 2-5. The decomposition image shows thetendency that the decomposition of internal wave feature using wavelet transform tends to follow the wavelet function. This may reduced the height of leading wave. Smoother result of internal wave shape can be formed using higher scale resolutionof image at level 5 and higher number of vanishing moments such as Daubechies wavelet-db5), Symlet wavelet-sym5, and Discrete Meyer wavelet. The compactly supported wavelet function with orthogonal basis with scale function and FIR filter, such as discrete Meyer function is proposed for smoothness of feature, space save coding, and to avoid depashing in image.So far, the detection processes were performed well on the internal waves data that occurred at north coast off Kitakyushu and NW/W/SW/E coast off Tsushima Island on June to September period whose lengths were detected between 6-28 km and wavelength between 120m-1.28km. The directions of internal wave propagation were varied between NW-SW at eastern channel and N-SW at western channel of Tsushima Strait.