SAR imaging and hydrodynamic analysis of ocean bottom topographic waves
- 海洋环境－已发表论文 
[ 1] The satellite synthetic aperture radar (SAR) images display wave-like patterns of the ocean bottom topographic features at the south outlet of Taiwan Strait (TS). Field measurements indicate that the most TS water body is vertically stratified. However, SAR imaging models available were developed for homogeneous waters. Hence explaining SAR imaging mechanisms of bottom features in a stratified ocean is beyond the scope of those models. In order to explore these mechanisms and to determine the quantitative relations between the SAR imagery and the bottom features, a two-dimensional, three-layer ocean model with sinusoidal bottom topographic features is developed. Analytical solutions and inferences of the momentum equations of the ocean model lead to the following conditions. ( 1) In the lower layer, the topography-induced waves ( topographic waves hereafter) exist in the form of stationary waves, which satisfy a lower boundary resonance condition sigma = kC(0), here sigma is an angular frequency of the stationary waves, k is a wavenumber of bottom topographic corrugation, and C-0 is a background current speed. ( 2) As internal waves, the topographic waves may propagate vertically to the upper layer with an unchanged wavenumber k, if a frequency relation N-3 < sigma < N-2 is satisfied, here N-2 and N-3 are the Brunt-Waisala frequencies of middle layer and upper layer, respectively. ( 3) The topographic waves are extremely amplified if an upper layer resonance condition is satisfied. The SAR image of topographic waves is derived on the basis of current-modulated small wave spectra. The results indicate that the topographic waves on SAR images have the same wavelength of bottom topographic corrugation, and the imagery brightness peaks are either inphase or antiphase with respect to the topographic corrugation, depending on a sign of a coupling factor. These theoretical predictions are verified by field observations. The results of this study provide a physical basis for quantitative interpretation of SAR images of bottom topographic waves in the stratified ocean.