# Ocean Wave Inversion Based on a Ku/Ka Dual-Band Airborne Interferometric Imaging Radar Altimeter
## 4 Discussion  
The inversion accuracy of SSH is mainly related to the quality of the observation data and the modulation effect caused by the sea surface motion. Due to the InIRA's excellent characteristics of high SNR and high coherence at small incidence angles, the measured phase is closely related to SSH, which ensures high-quality data. However, in contrast to land, ocean waves have their unique characteristics of movement. According to the InIRA system, the primary factors [44] affecting the ocean waves inversion are velocity bunching and the layover effect. Velocity bunching can produce a substantial nonlinear effect on imaging, and the nonlinear effect is minimized when the WPD along with the ground range. In addition, the layover effect can affect the distortion of the SSH inversion results, and the influence is gradually worse with a decrease in the incidence angle. Due to the fact that the steepness of wind waves is much greater than that of swells, the primary target of the layover effect is the wind waves. Nevertheless, the effect of the layover for the wind waves is the largest when the WPD of wind waves is consistent with the cross-track direction. [PERSON] et al., (2022) [36] estimated the maximum allowed SWH and wind speed at different incidence angles, and the result showed that the OWPs could be inversed based on the InIRA images if the incidence angle was greater than a few degrees, even under high sea state conditions. According to the field measurement data of the mobile weather station, the EWD was southeastward, and the velocity bunching had a small nonlinear effect on the imaging. Therefore, it was predicted that the OWPs could be effectively retrieved based on the DInIRA images by combining the incidence angle configurations and the EWD, which was consistent with the experimental results. The significant factors affecting the inversion of the ocean waves are velocity bunching and the layover effect, sea surface morphology, and the payload performance. In this respect, [PERSON] et al., (2021) [45] analyzed the altimetric accuracy of the X, Ku, and Ka bands under different sea states based on numerical simulations. The experimental results demonstrated that the dynamic wave-related errors of the InSAR altimetry were not sensitive to the frequencies but to the sea states. In other words, the sea states were not the primary reason for the discrepancy in the inversion accuracy of the ocean wave inversion in the Ku and Ka bands. As described in Section 3.3, the dual-band altimetric accuracy was analyzed to further explore the specific causes for this phenomenon, by combining the payload parameters and the sea surface morphology. When SWH = 0.7 m, the altimetric accuracy of the Ka band was higher than that of Ku band, resulting in higher inversion accuracy of the ocean waves. According to Figure 14b, the volumetric decorrelation induced by the sea surface morphology was sensitive to the frequency band. Although the effect of the volumetric decorrelation on the Ku band was not as strong as that of the Ka band, the altimetric accuracy of the Ka band was still more significant than that of the Ku band due  
Figure 16: (**a**) Variation curves of the altimetric accuracy with the ground range direction for different multi-look numbers when SWH = 0.7 m; (**b**) theoretical (solid line) and actual (dotted line) altimetric accuracy when SWH = 0.7 m.  
to the baseline configuration and the extremely short wavelength of the Ka band. It can be inferred that the configuration of the payload parameters was the most effective way to improve the inversion accuracy of the ocean waves. Since the altimetry sensitivity of the satellite-based InIRA system was higher than that of conventional satellite-based InSAR, it was concluded that ocean waves could also be well inversed using the satellite-based DInIRA images. However, the high operational altitude of the satellite could further make the DInIRA have high altimetric ambiguity.