To retrieve wind field from SAR images, the development for surface wind field retrieval from SAR images based on the improvement of new inversion model is present. Geophysical Model Functions （GMFs） have been widel...To retrieve wind field from SAR images, the development for surface wind field retrieval from SAR images based on the improvement of new inversion model is present. Geophysical Model Functions （GMFs） have been widely applied for wind field retrieval from SAR images. Among them CMOD4 has a good performance under low and moderate wind conditions. Although CMOD5 is developed recently with a more fundamental basis, it has ambiguity of wind speed and a shape gradient of normalized radar cross section under low wind speed condition. This study proposes a method of wind field retrieval from SAR image by com-bining CMOD5 and CMOD4 Five VV-polarisation RADARSAT2 SAR images are implemented for validation and the retrieval re-suits by a combination method （CMOD5 and CMOD4） together with CMOD4 GMF are compared with QuikSCAT wind data. The root-mean-square error （RMSE） of wind speed is 0.75 m s-1 with correlation coefficient 0.84 using the combination method and the RMSE of wind speed is 1.01 m s-1 with correlation coefficient 0.72 using CMOD4 GMF alone for those cases. The proposed method can be applied to SAR image for avoiding the internal defect in CMOD5 under low wind speed condition.展开更多
Spaceborne synthetic aperture radar(SAR)can provide unique capabilities to measure ocean surface winds under tropical cyclones(TCs),on synoptic scales,and at a very high spatial resolution.In this paper,we first discu...Spaceborne synthetic aperture radar(SAR)can provide unique capabilities to measure ocean surface winds under tropical cyclones(TCs),on synoptic scales,and at a very high spatial resolution.In this paper,we first discuss the accuracy and reliability of SAR-retrieved TC marine winds.The results show that wind retrievals from SAR images are in good agreement with Stepped Frequency Microwave Radiometer(SFMR)measurements,with root-mean-square error(RMSE)and correlation coefficient(CC)of 3.52 m s^(−1) and 0.91,respectively.Based on the marine winds retrieved from SAR images,a relatively simple method is applied to extract the storm intensity(maximum wind speed)and wind radii(R34,R50,and R64)from 234 cross-polarized SAR images,in the Northwest Pacific Ocean from 2015 to 2023.The SAR-retrieved TC wind radii and intensities are compared with the best-track reports,with RMSEs for R34,R50,and R64 being 48.32,41.88,and 38.51 km,and CCs being 0.87,0.83,and 0.65,respectively.In terms of TC intensity,the RMSE and bias between SAR estimates and best-track data are 7.32 and 0.38 m s^(−1),respectively.For TC Surigae(2023),we found that employing a combination of multiplatform SARs,acquired within a short time interval,has the potential to simultaneously measure the intensity and wind structure parameters.In addition,for a storm with a long life cycle,the multitemporal synergistic SARs can be used to investigate fine-scale features of the TC ocean winds,as well as the evolution of TC surface wind intensities and wind structures.展开更多
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 ...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 measurement.In 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,respectively.The 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 direction.With 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 method.SAR 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)products.In 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.展开更多
该文对SAR反演邻近岸海面风场的有关问题进行了深入研究。首先提出了邻近岸海面风向估计方法,在最小距离准则下利用邻近海域的风向估计所需的邻近岸海面风向。然后给出了使用ENVISAT/ASAR的IM成像模式PRI数据反演邻近岸海面风速的方法,...该文对SAR反演邻近岸海面风场的有关问题进行了深入研究。首先提出了邻近岸海面风向估计方法,在最小距离准则下利用邻近海域的风向估计所需的邻近岸海面风向。然后给出了使用ENVISAT/ASAR的IM成像模式PRI数据反演邻近岸海面风速的方法,比较了地球物理模型函数(Geophysical Model Function,GMF)模型性能,提出了海面风速分段反演算法。它们组成了完整的SAR反演邻近岸海面风场方法。通过实验、比较,验证了上述方法的有效性和合理性。展开更多
基金supported by the National Natural Science Foundation of China (Nos.41376010 and 40830959)the Start-up Foundation of Zhejiang Ocean University (No.21105011913)
文摘To retrieve wind field from SAR images, the development for surface wind field retrieval from SAR images based on the improvement of new inversion model is present. Geophysical Model Functions （GMFs） have been widely applied for wind field retrieval from SAR images. Among them CMOD4 has a good performance under low and moderate wind conditions. Although CMOD5 is developed recently with a more fundamental basis, it has ambiguity of wind speed and a shape gradient of normalized radar cross section under low wind speed condition. This study proposes a method of wind field retrieval from SAR image by com-bining CMOD5 and CMOD4 Five VV-polarisation RADARSAT2 SAR images are implemented for validation and the retrieval re-suits by a combination method （CMOD5 and CMOD4） together with CMOD4 GMF are compared with QuikSCAT wind data. The root-mean-square error （RMSE） of wind speed is 0.75 m s-1 with correlation coefficient 0.84 using the combination method and the RMSE of wind speed is 1.01 m s-1 with correlation coefficient 0.72 using CMOD4 GMF alone for those cases. The proposed method can be applied to SAR image for avoiding the internal defect in CMOD5 under low wind speed condition.
基金Supported by the National Natural Science Foundation of China(42305153)Zhejiang Provincial Natural Science Foundation of China(LQ21D060001 and LZJMZ23D05000)+6 种基金East China Meteorological Science and Technology Collaborative Innovation Foundation Cooperation Project(QYHZ202307)Fengyun Application Pioneering Project(FY-APP-2021.0105)Science and Technology Project of Zhejiang Meteorological Bureau(2021YB07,2022ZD06,and 2023YB06)Open Project of Key Laboratory of Meteorological Disaster,Ministry of Education/Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters(KLME202408)Open Grants of the State Key Laboratory of Severe Weather(2024LASW-B22)Innovation and Development Project of China Meteorological Administration(CXFZ2022J040)Youth Innovation Team Fund of China Meteorological Administration(CMA2023QN12)。
文摘Spaceborne synthetic aperture radar(SAR)can provide unique capabilities to measure ocean surface winds under tropical cyclones(TCs),on synoptic scales,and at a very high spatial resolution.In this paper,we first discuss the accuracy and reliability of SAR-retrieved TC marine winds.The results show that wind retrievals from SAR images are in good agreement with Stepped Frequency Microwave Radiometer(SFMR)measurements,with root-mean-square error(RMSE)and correlation coefficient(CC)of 3.52 m s^(−1) and 0.91,respectively.Based on the marine winds retrieved from SAR images,a relatively simple method is applied to extract the storm intensity(maximum wind speed)and wind radii(R34,R50,and R64)from 234 cross-polarized SAR images,in the Northwest Pacific Ocean from 2015 to 2023.The SAR-retrieved TC wind radii and intensities are compared with the best-track reports,with RMSEs for R34,R50,and R64 being 48.32,41.88,and 38.51 km,and CCs being 0.87,0.83,and 0.65,respectively.In terms of TC intensity,the RMSE and bias between SAR estimates and best-track data are 7.32 and 0.38 m s^(−1),respectively.For TC Surigae(2023),we found that employing a combination of multiplatform SARs,acquired within a short time interval,has the potential to simultaneously measure the intensity and wind structure parameters.In addition,for a storm with a long life cycle,the multitemporal synergistic SARs can be used to investigate fine-scale features of the TC ocean winds,as well as the evolution of TC surface wind intensities and wind structures.
基金Supported by the National Natural Science Foundation of China(Nos.42176174,41706196)the Sichuan Science and Technology Program(No.2018JY0484)+4 种基金the Natural Science Key Research Program of Education Department of Sichuan Province(No.18ZA0103)the China Postdoctoral Science Foundation(No.2020M683258)the Provincial Science and Technology Innovation Development Project of China Meteorological Administration(No.SSCX2020CQ)the Chongqing Technology Innovation and Application Development Special Project(No.cstc2020jscx-msxmX0193)the Chongqing Meteorological Department Business Technology Research Project(No.YWJSGG-202017)。
文摘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 measurement.In 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,respectively.The 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 direction.With 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 method.SAR 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)products.In 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.
文摘该文对SAR反演邻近岸海面风场的有关问题进行了深入研究。首先提出了邻近岸海面风向估计方法,在最小距离准则下利用邻近海域的风向估计所需的邻近岸海面风向。然后给出了使用ENVISAT/ASAR的IM成像模式PRI数据反演邻近岸海面风速的方法,比较了地球物理模型函数(Geophysical Model Function,GMF)模型性能,提出了海面风速分段反演算法。它们组成了完整的SAR反演邻近岸海面风场方法。通过实验、比较,验证了上述方法的有效性和合理性。
