Response characteristics of SWIM’s small-incidence-angle sensors to internal solitary wave

This investigation utilizes surface wave investigation and monitoring (SWIM) L1A data radar altimetry data to analyze internal solitary wave (ISW) signatures in the Sulu Sea, evaluating the detection efficacy of low-incidence-angle radar configurations for ISW surface expressions and quantifying bathymetric modulation effects through systematic analysis of 149 near-seafloor acoustic beam clusters across seven satellite tracks. A spatiotemporal correlation framework was established between SWIM sea surface echoes and concurrent optical/synthetic aperture radar satellite imagery, enabling precise geolocation and morphological characterization of ISW surface convergences/divergences. Distinct perturbation signatures in radar backscatter coefficients (σ0) were observed during the ISW passage. Using ensemble empirical mode decomposition to decompose SWIM echo signals and computing each component’s normalized variance, we selected the component with the maximum variance as the ISW signal. The distinct ISW characteristics in the signal show SWIM’s potential for detecting such waves. We statistically analyzed 258 complete ISW modulated sea surface convergence and divergence areas from 149 near-bottom beams (10, 8, 6, 4, and 2 deg) in the seven-track data of the Sulu Sea. It was found that as the incidence angle decreases, the minimum significant degree of σ0 gradually increases. The minimum significant degree of σ0 in the divergence areas under different incidence angles is larger than that in the convergence areas. Overall, the minimum significant degree of σ0 modulated in the convergence areas shows a more concentrated range of variation.