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
Several remotely sensed sea surface salinity（SSS） retrievals with various resolutions from the soil moisture and ocean salinity（SMOS） and Aquarius/SAC-D missions are applied as inputs for retrieving salinity profi...Several remotely sensed sea surface salinity（SSS） retrievals with various resolutions from the soil moisture and ocean salinity（SMOS） and Aquarius/SAC-D missions are applied as inputs for retrieving salinity profiles（S） using multilinear regressions. The performance is evaluated using a total root mean square（RMS） error, different error sources, and the feature resolutions of the retrieved S fields. In the mixed layer of the salinity, the SSS-S regression coefficients are uniformly large. The SSS inputs yield smaller RMS errors in the retrieved S with respect to Argo profiles as their spatial or temporal resolution decreases. The projected SSS errors are dominant, and the retrieved S values are more accurate than those of climatology in the tropics except for the tropical Atlantic, where the regression errors are abnormally large. Below that level, because of the influence of a sea level anomaly, the areas of high-accuracy S values shift to higher latitudes except in the high-latitude southern oceans, where the projected SSS errors are abnormally large. A spectral analysis suggests that the CATDS-0.25° results are much noisier and that the BEC-L4-0.25° results are much smoother than those of the other retrievals. Aquarius-CAP-1° generates the smallest RMS errors, and Aquarius-V2-1° performs well in depicting large-scale phenomena. BEC-L3-0.25°,which has small RMS errors and remarkable mesoscale energy, is the best fit for portraying mesoscale features in the SSS and retrieved S fields. The current priority for retrieving S is to improve the reliability of satellite SSS especially at middle and high latitudes, by developing advanced algorithms, combining both sensors, or weighing between accuracy and resolutions.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
星载微波散射计是获取全球海面风场信息的主要手段,HY-2B卫星散射计的成功发射为全球海面风场数据获取的持续性提供了重要保障。本文利用欧洲中期天气预报中心(EuropeanCenter forMedium-RangeWeatherForecasts,ECMWF)再分析风场数据、...星载微波散射计是获取全球海面风场信息的主要手段,HY-2B卫星散射计的成功发射为全球海面风场数据获取的持续性提供了重要保障。本文利用欧洲中期天气预报中心(EuropeanCenter forMedium-RangeWeatherForecasts,ECMWF)再分析风场数据、热带大气海洋观测计划(TropicalAtmosphereOceanArray,TAO)和美国国家数据浮标中心(National Data Buoy Center,NDBC)浮标获取的海面风矢量实测数据,对HY-2B散射计海面风场数据产品的质量进行统计分析。分析表明,HY-2B风场与ECMWF再分析风场对比,在4~24m·s^-1风速区间内,风速和风向均方根误差(root mean squareerror,RMSE)分别为1.58m·s^-1和15.34°;与位于开阔海域的TAO浮标数据对比,风速、风向RMSE分别为1.03m·s^-1和14.98°,可见HY-2B风场能较好地满足业务化应用的精度要求(风速优于2m·s^-1,风向优于20°)。与主要位于近海海域的NDBC浮标对比,HY-2B风场的风速、风向RMSE分别为1.60m·s^-1和19.14°,说明HY-2B散射计同时具备了对近海海域风场的良好观测能力。本文还发现HY-2B风场质量会随风速、地面交轨位置等变化,为用户更好地使用HY-2B风场产品提供参考。展开更多
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.
基金The National Natural Science Foundation of China under contract No.41276088
文摘Several remotely sensed sea surface salinity（SSS） retrievals with various resolutions from the soil moisture and ocean salinity（SMOS） and Aquarius/SAC-D missions are applied as inputs for retrieving salinity profiles（S） using multilinear regressions. The performance is evaluated using a total root mean square（RMS） error, different error sources, and the feature resolutions of the retrieved S fields. In the mixed layer of the salinity, the SSS-S regression coefficients are uniformly large. The SSS inputs yield smaller RMS errors in the retrieved S with respect to Argo profiles as their spatial or temporal resolution decreases. The projected SSS errors are dominant, and the retrieved S values are more accurate than those of climatology in the tropics except for the tropical Atlantic, where the regression errors are abnormally large. Below that level, because of the influence of a sea level anomaly, the areas of high-accuracy S values shift to higher latitudes except in the high-latitude southern oceans, where the projected SSS errors are abnormally large. A spectral analysis suggests that the CATDS-0.25° results are much noisier and that the BEC-L4-0.25° results are much smoother than those of the other retrievals. Aquarius-CAP-1° generates the smallest RMS errors, and Aquarius-V2-1° performs well in depicting large-scale phenomena. BEC-L3-0.25°,which has small RMS errors and remarkable mesoscale energy, is the best fit for portraying mesoscale features in the SSS and retrieved S fields. The current priority for retrieving S is to improve the reliability of satellite SSS especially at middle and high latitudes, by developing advanced algorithms, combining both sensors, or weighing between accuracy and resolutions.
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。
文摘星载微波散射计是获取全球海面风场信息的主要手段,HY-2B卫星散射计的成功发射为全球海面风场数据获取的持续性提供了重要保障。本文利用欧洲中期天气预报中心(EuropeanCenter forMedium-RangeWeatherForecasts,ECMWF)再分析风场数据、热带大气海洋观测计划(TropicalAtmosphereOceanArray,TAO)和美国国家数据浮标中心(National Data Buoy Center,NDBC)浮标获取的海面风矢量实测数据,对HY-2B散射计海面风场数据产品的质量进行统计分析。分析表明,HY-2B风场与ECMWF再分析风场对比,在4~24m·s^-1风速区间内,风速和风向均方根误差(root mean squareerror,RMSE)分别为1.58m·s^-1和15.34°;与位于开阔海域的TAO浮标数据对比,风速、风向RMSE分别为1.03m·s^-1和14.98°,可见HY-2B风场能较好地满足业务化应用的精度要求(风速优于2m·s^-1,风向优于20°)。与主要位于近海海域的NDBC浮标对比,HY-2B风场的风速、风向RMSE分别为1.60m·s^-1和19.14°,说明HY-2B散射计同时具备了对近海海域风场的良好观测能力。本文还发现HY-2B风场质量会随风速、地面交轨位置等变化,为用户更好地使用HY-2B风场产品提供参考。
