Fuse the SAR and SWIM Observations to Produce Better Wave Spectra Measurements

Both the Synthetic Aperture Radar (SAR) and the Surface Waves Investigation and Monitoring instrument (SWIM) can provide global wave spectra measurements. However, each has its limitations. Though SAR can resolve wave propagation directions, the velocity bunching effect limits its measurable range in the wavenumber domain and causes severe attenuation of wave spectra. Conversely, SWIM offers a broader measurable range with less underestimation but produces ambiguous wave spectra in the opposite directions. Consequently, researchers must compromise between accurate wave magnitudes and directional information. In this work, we demonstrate that it is possible to resolve this dilemma by fusing SAR and SWIM measurements. We treat wave spectra from WAVEWATCH III as the true reference and feed them into the SAR and SWIM simulators. These simulators generate wave spectra measurements based on the detection mechanisms of SAR and SWIM. The simulations are conducted under ideal conditions, including no noise, no statistical fluctuations, and assuming perfectly aligned measurement locations between SAR and SWIM. Finally, we evaluate the fused wave spectra using significant wave height and Stokes drift velocity, considering both its direction and magnitude. The results show that the fusion method significantly improves the accuracy of wave spectra measurements, effectively combining the strengths of both SAR and SWIM.