Numerical research on clear imaging of azimuth-traveling ocean waves in SAR images

This paper presents the imaging mechanisms of ocean waves traveling in the azimuth direction by applying a numerical simulation of synthetic aperture radar (SAR) image for moving ocean surfaces. The numerical simulation was originally designed in the time domain to take into account motion-induced modulations. It is known that azimuthal waves are affected by azimuth shifts due to orbital motions of ocean waves, i.e., velocity bunching. The effect of bunching generally results in nonlinear imaging; however, a clear wavelike pattern of a homogeneous wave field propagating to the azimuth direction occurs in SAR imagery under a certain condition. More specifically, if azimuth shifts due to the orbital motions are concentrated on wave crests or troughs, bunching causes a single peak in SAR image planes. Theoretically, it is derived noticeably when the maximum orbital motion of an azimuth-traveling ocean wave is nearly equal to one quarter of its wavelength. To demonstrate this, SAR signals were simulated numerically for ocean waves with and without employing the condition of the clear imaging. The results showed that a wavelike pattern relating to the azimuthal waves can be imaged apparently under the specific condition. In addition, the simulations were performed in the case of the other wave and wind conditions. From the results, it was revealed that the specific condition leads to clear wavelike imaging of azimuthal waves in SAR images if noise is relatively small.