Detection and Estimation of Daily Oceanic Mesoscale Eddies from Spaceborne Global Navigation Satellite System-Reflectometry

The potential of spaceborne Global Navigation Satellite System-Reflectometry (GNSS-R) is explored for detecting and estimating global mesoscale oceanic eddies. A fractional Fourier transform-residual network (F-ResNet) model is used to achieve centimeter-level absolute dynamic topography (ADT), demonstrating a root mean square error (RMSE) of 5.05 cm, which is subsequently used for detecting oceanic eddies based on their height characteristics. Using CYGNSS data from 2020, comprising over 750 million samples, the research demonstrates that GNSS-R technology effectively supports daily oceanic eddy detection, achieving precision rates of 50.63% and 47.80%, recall rates of 89.95% and 90.48%, $F1$ scores of 64.79% and 62.56%, and accuracy rates of 47.92% and 45.52% for cyclonic and anticyclonic eddies, respectively. Although the method proves both effective and feasible, its performance remains suboptimal. To improve detection accuracy, the study explores high-bandwidth signals, whose sharper autocorrelation function enhances ADT retrieval and improves oceanic eddy detection accuracy. Simulation results from the ACE-BOC (15, 10) signal suggest precision rates of 85.51% and 84.14%, recall rates of 91.93% and 91.11%, $F1$ scores of 88.76% and 87.48%, and accuracy rates 79.80% and 77.75% for cyclonic and anticyclonic eddies, respectively. Moreover, supplementary metrics for eddy features indicate significant improvements with high-bandwidth signals. The application of these two signals for sustained, long-term monitoring of oceanic eddies in a specific region is also demonstrated, providing a foundation for eddy tracking. The tracking results show that the ACE-BOC (15, 10) signal can effectively track eddy trajectories, achieving an RMSE of 1.11 km, whereas CYGNSS yields an RMSE of 8.4 km. Finally, this article discusses the characteristics of ACE-BOC and carrier-altimeter signals, highlighting the potential of advanced spaceborne GNSS-R altimeters and discussing future directions in this field.