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ocean surface current retrieval and imaging with a new shore-based X-band radar based on time-shifted up-and-down linear frequency modulated signal

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Acta oceanologica Sinica 2021年第3期40卷 112-121页

作者： Yijun He Xin Song Baochang Liu Na Yi Xiuzhong Li School of Marine Sciences Nanjing University of Information Science and TechnologyNanjing 210044China Laboratory for Regional oceanography and Numerical Modeling Pilot National Laboratory for Marine Science and Technology(Qingdao)Qingdao 266237China

This paper proposes a multifunction radar that can not only measure sea currents but also perform sea-surface *** fundamental aspect of the proposed radar comprises transmitting time-shifted up-and-down continuous wave linear frequency modulated signals that allow for the offset of two one-dimensional range images of the sea surface that respectively correspond to the upward linear frequency modulated(LFM)signal and the downward LFM *** to the Doppler frequency shift from the sea surface,a range offset,which is proportional to the radial velocity of the sea surface,occurs between the upward and downward LFM *** using the least-squares linear fitting method in the transformed domain,the range offset can be measured and the current velocity can be ***,we verify the accuracy of current measurement with simulation results.

关键词： shore-based radars signal processing ocean surface currents up-and-down CWLFM

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A new Doppler frequency anomaly algorithm for surface current measurement with SAR

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Journal of oceanology and Limnology 2022年第2期40卷 470-484页

作者： Lihua WANG Yanghua GAO Peng LU Li FAN Yunxuan ZHOU Department of Geography and Spatial Information Techniques Center for Land and Marine Spatial Utilization and Governance ResearchNingbo UniversityNingbo 315211China Institute of East China Sea Ningbo UniversityNingbo 315211China Chongqing Institute of Meteorological Sciences Chongqing 401147China College of Geo-Exploration Science and Technology Jilin UniversityChangchun 130026China State Key Laboratory of Estuarine and Coastal Research East China Normal UniversityShanghai 200062China

Values for Doppler center frequency are calculated from the echo signal at the satellite using the Doppler centroid method and so include the predicted Doppler frequency caused by the relative motion of the satellite and the Earth,which is the main component of Doppler center frequency and must be removed to obtain the Doppler frequency anomaly for ocean current *** this paper,a new Doppler frequency anomaly algorithm was proposed when measuring surface currents with synthetic aperture radar(SAR).The key of the proposed algorithm involved mean filtering method in the range direction and linear fitting in the azimuth direction to remove the radial and the azimuthal component of predicted Doppler frequency from the Doppler center frequency,*** basis is that the theoretical Doppler center frequency model of SAR exhibits an approximately linear characteristic in both the range direction and in the azimuth *** the help of the new algorithm for predicted Doppler frequency removal,the estimation error of Doppler frequency anomaly can be reduced by avoiding employing the theoretical antenna pattern and imperfect satellite attitude parameters in the conventional Doppler frequency *** measurement results demonstrated that,compared to the conventional Doppler frequency with/without error correction method,the proposed algorithm allows for a pronounced improvement in the current measuring accuracy in comparison with the global ocean multi-observation(MOB)*** addition,the eff ectiveness and robustness of the proposed Doppler algorithm has been demonstrated by its application in the high velocity current in the Kuroshio region.

关键词： synthetic aperture radar(SAR) Doppler frequency Doppler frequency anomaly current retrieval ocean surface currents

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