Multisatellite data observation for internal wave detection in the southwest coast of Japan

Abstract

We observed sea surface signature of internal waves in ERS SAR and ASTER image over southwest of Japan during 193-2004 period. Wavelet transform has been applied for multi resolution of internal wave detection in image. Proposed method based on Meyer wavelet and Canny edge detector has been useful to delineate internal wave feature in ERS SAR and ASTER image, maintain the continuity of crest line while reduce small strikes from noise. 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, provided the accuracy in classification over than 80%. Spectral reflectance of internal wave signature was derived from ASTER image data. We found out that internal wave feature has higher reflectance at VNIR channel, between 520-660n, and lower reflectance at SWIR channel, between 760-2430nm, due to the absorption and scattering of material. The highest and the lowest reflectance were respectively 660nm and 760-810nm. The observation results show that the internal waves were mostly occurred at north coast off Kitakyushu and NW/W/SW/E coast off Tsushima Island on June to September period, during summer when the layers are strongly stratified. The length of the internal waves was detected between 6-28 km and wavelength between 120m-1.28km. The directions of propagation were varied between NW-SW at eastern channel and N-SW at western channel of Tsushima Strait. The areas where internal wave signatures were detected coincide with T/P data where sea level anomaly data steeply increased between 2-5 cm.