Spatiotemporal Variation of Internal Solitary Waves in the Northern Bay of Biscay Based on Sequential SAR Images

In the Bay of Biscay, internal solitary waves (ISWs) are frequently generated by the interaction between surface tides and the steep continental shelf topography. Synthetic aperture radar (SAR) is a powerful tool for observing ISWs due to its all-weather, wide-area coverage and high resolution. However, most existing studies focus on the spatial distribution and morphological features of ISWs, with limited investigation into their spatiotemporal evolution. This study examines multiple ISW groups in the northern Bay of Biscay using time-series SAR images. We analyze their evolution by deriving their wavelength and direction from the spatial-spectral distribution and motion data of SAR images. The phase velocity is estimated by tracking surface features across sequential SAR images. Additionally, we propose a novel method to invert ISW amplitude using motion constraints, combining phase velocity and peak-to-peak distance. This approach successfully characterizes ISW dynamics at various life stages, revealing their spatiotemporal variation during propagation. By integrating synchronized tidal data, we identify a clear phase-locking relationship between ISW generation and tidal currents at the continental shelf break. A comparison with in situ data confirms that the SAR-derived ISW dynamics align with traditional measurements, demonstrating the effectiveness of SAR-based ISW studies.