Abstract
Ocean currents are a key element in ocean processes and in meteorology, affecting material transport and modulating climate change patterns. The Doppler frequency shift information of the synthetic aperture radar (SAR) echo signal can reflect the dynamic characteristics of the sea surface, and has become an essential sea surface dynamic remote sensing parameter. Studies have verified that the instantaneous Doppler frequency shift can realize the SAR detection of the sea surface current. However, the validation of SAR-derived ocean current data and a thorough analysis of the errors associated with them remain lacking. In this study, we derive high spatial resolution flow measurements for the Kuroshio in the East China Sea from SAR data using a theoretical model of shifts in Doppler frequency driven by ocean surface current. Global ocean multi observation (MOB) products and global surface Lagrangian drifter (GLD) data are used to validate the Kuroshio flow retrieved from the SAR data. Results show that the central flow velocity for the Kuroshio derived from the SAR is 0.4–1.5 m/s. The error distribution between SAR ocean currents and MOB products is an approximate standard normal distribution, with the 90% confidence interval concentrated between −0.1 m/s and 0.1 m/s. Comparative analysis of SAR ocean current and GLD products, the correlation coefficient is 0.803, which shows to be significant at a confidence level of 99%. The cross-validation of different ocean current dataset illustrate that the SAR radial current captures the positions and dynamics of the Kuroshio central flow and the Kuroshio Counter Current, and has the capability to monitor current velocity over a wide range of values.
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Acknowledgements
We acknowledge the data made available by the European Space Agency, the Copernicus Marine Service for the global ocean multi observation products and Drifter Data Assembly Center for the global surface Lagrangian drifter data.
Funding
The National Natural Science Foundation of China under contract Nos 42176174 and 41706196; the Open Research Fund of the State Key Laboratory of Estuarine and Coastal Research under contract No. SKLECKF202104; the Zhejiang Provincial Natural Science Foundation of China under contract No. LY22D010002; the National Science Foundation for Post-doctoral Scientists of China under contract No. 2020M683258; the Chongqing Technology Innovation and Application Development Special Project under contract No. cstc2020jscx-msxmX0193; the Sichuan Science and Technology Program under contract No. 2018JY0484.
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Wang, L., Shi, B., Zhou, Y. et al. Radial velocity of ocean surface current estimated from SAR Doppler frequency measurements—a case study of Kuroshio in the East China Sea. Acta Oceanol. Sin. 40, 135–147 (2021). https://doi.org/10.1007/s13131-021-1883-2
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DOI: https://doi.org/10.1007/s13131-021-1883-2