# Ocean Wave Inversion Based on a Ku/Ka Dual-Band Airborne Interferometric Imaging Radar Altimeter
## 5 Conclusions  
In this study, the inversion results of ocean waves in Ku and Ka bands are compared as a first-time attempt, to the best of the authors' knowledge, based on airborne DInIRA field observation data. Firstly, the echo data of the Ku and Ka bands are processed one by one, and the SSHs under different frequency bands are inversed based on the interference phase difference. Secondly, the 2D OWS are calculated based on the SSH inversion results and the FFT2, the OWPs are extracted from the OWS. The results show that the inversion result of WPD is consistent with the environmental wind direction. The SWH inversion biases retrieved by the Ku and Ka bands are, respectively, equal to 0.38 m and 0.27 m, the MWW inversion biases for the swells are 16.75 m and 3.67 m, and the MWW inversion biases for the wind waves are 2.32 m and 0.57 m. Overall, the swells and the wind waves can be effectively retrieved by the DInIRA, and the inversion accuracy of the SWH and the MWW in the Ka band is better than those in the Ku band. Finally, in this paper, we explained and discussed the results from the perspective of altimetric accuracy, concluding that the Ku band is more sensitive to random noise than the Ka band, which can lead to its worse inversion accuracy of ocean waves in this airborne campaign as compared with the Ka band.  
Even though some of the system parameters in this airborne DInIRA campaign are limited by the payload performance and the current technical conditions, the small-angle-based DInIRA system has shown great potential in high-accuracy SSH measurement. This study additionally validated the inversion capability of ocean waves in Ku and Ka bands, which will improve the knowledge of the Ka band at small angles and provide a reference for the parameter design of the DInIRA system.  
Conceptualization, C.M., D.L., G.C. and F.Y.; methodology, C.M. and D.L.; software, C.M., L.P. and Z.Q.; validation, L.P. and D.S.; formal analysis, Z.Q., L.P. and W.W.; investigation, L.P.; resources, C.M. and H.S.; data curation, F.Y. and H.S.; writing--original draft preparation, C.M. and L.P.; writing--review and editing, C.M. and L.P.; visualization, L.P.; supervision, C.M. and D.L.; project administration, C.M.; funding acquisition, C.M. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Key Research and Development Program of Shandong Province (grant no. 2019 GHZ023), the National Natural Science Foundation of China (grant nos. 41906155 and 42030406), the \"WenHai\" Project Fund and the Twin Oceans Project Fund of Shandong Province for Pilot National Laboratory for Marine Science and Technology (Qingdao), (grant nos.  
2021 WHIZZB1600 and 2022 QNLM050301), the Strategic Priority Research Program of the Chinese Academy of Sciences, (grant no. XDA19090141), and the Fundamental Research Funds for the Central Universities, (grant no. 202213045).  
**Data Availability Statement**: Not applicable.  
**Acknowledgments:** The authors would like to acknowledge the support of everyone who assisted with the airborne experiment involved in this study. The authors would also like to thank the anonymous reviewers and the editors for their comments and suggestions that improved the manuscript. The authors would like to express their gratitude to EditSprings ([[https://www.editsprings.cn](https://www.editsprings.cn)]([https://www.editsprings.cn](https://www.editsprings.cn)), accessed on 6 June 2022) for the expert linguistic services provided.  
**Conflicts of Interest**: The authors declare no conflict of interest.