Azimuthal Ocean Wave Emerged in SAR Image Spectra Under Specific Condition

Abstract

AbstractVelocity bunching causes nonlinear modulations in synthetic aperture radar (SAR) images of oceanic scenes. SAR images for the azimuth waves exhibit destructive wavy patterns because of azimuthal distortion caused by velocity bunching. Meanwhile, velocity bunching creates constructive wavy patterns for long waves in certain cases. This paper aims to provide a simple indication for practical interpretation of plausible wavy patterns. A numerical simulation had been performed to address how velocity bunching forms a clear wave‐like pattern caused by orbital motions of a long single swell under a certain condition. More specifically, when the azimuth shifts caused by the orbital motions of the azimuth wave concentrate in the wave trough or crest, the bunching causes a strong single peak in the SAR images. This paper explains the mechanism of displaying plausible wavy patterns from the viewpoint of the ocean wave spectra and this specific condition. First, the simulation was validated for irregular waves generated from ocean wave spectra matching actual buoy data from which SAR images were simultaneously obtained. The SAR image spectra showed longer waves than those of the ocean wave spectra estimated via buoy data. The simulated spectra exhibited a similar trend to the actual SAR image, thus validating the numerical simulation. Next, an additional numerical simulation was conducted for irregular waves under the specific condition. The simulated results suggest that if a significant wave height and wavelength match the specific condition, the long waves in SAR image spectra can be similar to the original ocean wave spectra.