利用多普勒频移反演ASAR海表面流速
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摘要
为研究中小尺度的海流,以美国西海岸附近海域为研究区域,采用欧空局ENVISAT ASAR IMS数据,首先利用频谱拟合法计算得到影像的多普勒质心;再通过影像的多普勒系数和斜距时间去除卫星与地球之间相对运动产生的多普勒频移,最终得到海表面多普勒质心异常。同时利用布拉格散射模型去除了布拉格波的影响,利用CMOD5模型计算海表面风场,根据风场与雷达视向速度的经验关系去除海面风场的影响,经空间投影,最终得到雷达径向的海表面流速,反演的流速主要分布于-0.3～0.6 m/s。利用研究区域附近的岸基高频地波雷达(HF-radar)数据验证反演结果精度,结果表明,在HF-radar流速与ASAR反演流速-0.2～0.2 m/s差异范围内的标准误差和相关系数分别为0.1 m/s和0.81,反演结果与真实流速较为接近。ASAR反演流速和HF-radar流速结果均表明,在研究区域存在自西向东的沿岸流,最大径向流速达到0.6 m/s。因此,本文所使用的海表面流速反演方法准确有效,适合于中小尺度海流流速的反演。
In order to study the medium or small scale ocean currents, the surface current velocity is retrieved from ESA ENVISAT ASAR IMS image, taking the west coast of the United States as the study area. Firstly, the Doppler centroid of the image is calculated with the spectrum fitting method. The sea surface Doppler centroid anomaly is then obtained by removing the Doppler shift of the relative motion between the satellite and the earth with the Doppler coefficient and the slant range time of the image. The influence of Bragg wave on the current velocity retrieval is further removed by the Bragg scattering model. The influence of sea surface wind is also removed according to the empirical relationship between wind field and radar apparent velocity, where the sea surface wind is calculated by CMOD5 model. After spatial projection, the radial surface velocity of the radar is finally obtained. The inversed current velocity ranges from-0.3 to 0.6 m/s, the accuracy of which is verified by the shore-based HF-radar. The validation results show the inversion results are close to the HF-radar measurements with the standard deviation and correlation coefficient of 0.1 m/s and 0.81, respectively. Both the ASAR and the HF-radar data indicate that a coastal current exists in the study area, with the maximum radial velocity of 0.6 m/s. The results indicated that the sea surface current velocity inversion method adopted in this paper is accurate and effective, and is suitable for the inversion of small and medium-scale ocean current velocity.
In order to study the medium or small scale ocean currents, the surface current velocity is retrieved from ESA ENVISAT ASAR IMS image, taking the west coast of the United States as the study area. Firstly, the Doppler centroid of the image is calculated with the spectrum fitting method. The sea surface Doppler centroid anomaly is then obtained by removing the Doppler shift of the relative motion between the satellite and the earth with the Doppler coefficient and the slant range time of the image. The influence of Bragg wave on the current velocity retrieval is further removed by the Bragg scattering model. The influence of sea surface wind is also removed according to the empirical relationship between wind field and radar apparent velocity, where the sea surface wind is calculated by CMOD5 model. After spatial projection, the radial surface velocity of the radar is finally obtained. The inversed current velocity ranges from-0.3 to 0.6 m/s, the accuracy of which is verified by the shore-based HF-radar. The validation results show the inversion results are close to the HF-radar measurements with the standard deviation and correlation coefficient of 0.1 m/s and 0.81, respectively. Both the ASAR and the HF-radar data indicate that a coastal current exists in the study area, with the maximum radial velocity of 0.6 m/s. The results indicated that the sea surface current velocity inversion method adopted in this paper is accurate and effective, and is suitable for the inversion of small and medium-scale ocean current velocity.
引文
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[20] CURLANDER J C,MCDONOUGH R N.Synthetic Aperture Radar:systems and signal processing[M].HAN C Z,translated.Beijing:Publishing House of Electronics Industry,2014.柯兰德 J C,麦克多诺 R N.合成孔径雷达:系统与信号处理[M].韩传钊,译.北京:电子工业出版社,2014.
[21] European Space Agency.ENVISAT-1 ASAR Products specifications:volume 8 ASAR Products specifications[EB/OL].[2011-10-10].https://earth.esa.int/web/sppa/mission-performance/esa-missions/envisat#product_spec.html.
[22] CHAPRON B,COLLARD F,ARDHUIN F.Direct measurements of ocean surface velocity from space:interpretation and validation[J].Journal of Geophysical Research Oceans,2005,110(C07008):1-17.
[23] CHENG Y X,GE S R,YUAN L F,et al.Research of the ocean wind speed retrieval from space-borne SAR[J].Electronic Test,2016(4):133-134.程玉鑫,戈书睿,袁凌峰,等.星载合成孔径雷达海面风速反演技术研究[J].电子测试,2016(4):133-134.
[24] CHENG Y X,AI W H,KONG Y,et al.Ocean wind retrieval from space-borne synthetic aperture radar images based on wind streaks and external wind direction[J].Marine Sciences,2015,39(12):157-164.程玉鑫,艾未华,孔毅,等.基于影像纹理特征和外部风向的星载SAR海面风场反演研究[J].海洋科学,2015,39(12):157-164.
[25] YANG J S,HUANG W G,ZHOU C B,et al.Coastal ocean surface wind retrieval from SAR imagery[J].Journal of Remote Sensing,2001,5(1):13-16.杨劲松,黄韦艮,周长宝,等.合成孔径雷达图像的近岸海面风场反演[J].遥感学报,2001,5(1):13-16.
[2] HE Y J,LIU B C,ZHANG B,et al.Overview on satellite remote sensing methods for sea surface current measurement[J].Guangxi Sciences,2015,22(3):294-300.何宜军,刘保昌,张彪,等.海面流场卫星遥感方法综述[J].广西科学,2015,22(3):294-300.
[3] LI H M.Retrieval of surface current from SAR image using Doppler shift method[D].Qingdao:Ocean University of China,2015.李慧敏.基于多普勒法的SAR海表流场反演算法研究[D].青岛:中国海洋大学,2015.
[4] GOLDSTEIN R M,ZEBKER H A.Interferometric radar measurement of ocean surface currents[J].Nature,1987,328(6132):707-709.
[5] SHEMER L,MAROM M,MARKMAN D.Estimates of currents in the near shore ocean region using interferometric Synthetic Aperture Radar[J].Journal of Geophysical Research Oceans,1993,98(C4):7001-7010.
[6] ROMEISER R,GRABER H C.Advanced remote sensing of internal waves by space borne Along-Track InSAR—a demonstration with TerraSAR-X[J].IEEE Transactions on Geoscience & Remote Sensing,2015,53(12):6735-6751.
[7] MADSEN S N.Estimating the Doppler centroid of SAR data[J].IEEE Transactions on Aerospace & Electronic Systems,1989,25(2):134-140.
[8] CHANG L,GAO G P,GUO L X,et al.Review on ocean surface current field measurement by space-borne SAR[J].Advance in Marine Science,2015,33(1):107-117.常亮,高郭平,郭立新.星载SAR海洋表层流场反演综述[J].海洋科学进展,2015,33(1):107-117.
[9] CHAPRON B,COLLARD F,KERBAOL V.Satellite synthetic aperture radar sea surface Doppler measurements[C]//FRANK M,VINCENT K.Proceedings of 2nd Workshop on Coastal and Marine Applications of Synthetic Aperture Radar.Paris,France:ESA Special Publication,2003:133-141.
[10] HANSEN M W,JOHANNESSEN J A,DAGESTAD K F,et al.Monitoring the surface inflow of Atlantic water to the Norwegian Sea using ENVISAT ASAR[J].Journal of Geophysical Research Oceans,2011,116(C12008):1-13.
[11] ROMEISER R,RUNGE H,SUCHANDT S,et al.Quality assessment of surface current fields from TerraSAR-X and TanDEM-X Along-Track interferometry and Doppler centroid analysis[J].IEEE Transactions on Geoscience and Remote Sensing,2014,52(5):2759-2772.
[12] KIM J E,KIM D J,MOON W M.Enhancement of Doppler centroid for ocean surface current retrieval from ERS-1/2 raw SAR[C]//DAVID G,STEVE V.IEEE International Geoscience & Remote Sensing Symposium.Alaska,USA:IEEE,2004:3118-3120.
[13] JOHANNESSEN J A,CHAPRON B,COLLARD F,et al.Direct ocean surface velocity measurements from space:improved quantitative interpretation of ENVISAT ASAR observations[J].Geophysical Research Letters,2008,35(22):113-130.
[14] LEAKE J L,WOODWARD G L.Interpretation of Coastal HF radar-derived surface currents with high-resolution drifter data[J].Journal of Atmospheric and Oceanic Technology,2006,24(4):666-680.
[15] ZHANG X R,HUANG Y X,ZHAO X B,et al.Study of ocean surface current inversion algorithm based on space-borne Synthetic Aperture Radar Doppler velocity[J].Meteorological,Hydrological and Marine Instruments,2016,33(1):1-7.张夏荣,黄云仙,赵现斌.基于星载SAR多普勒速度反演海表流场算法的研究[J].气象水文海洋仪器,2016,33(1):1-7.
[16] YANG X B.Sea surface current retrieval based on ASAR data[D].Shanghai:Shanghai Ocean University,2016.杨小波.基于ASAR的时变海表面流场反演研究[D].上海:上海海洋大学,2016.
[17] Coastal Observing Research and Development Center.HF radar national network production TDS[EB/OL].[2011-10-01].http://hfrnet-tds.ucsd.edu/thredds/catalog.html.
[18] WANG S Q.Research on Doppler centroid real-time estimation technology of space borne SAR[D].Beijing:Institute of Electrics,Chinese Academy of Sciences,2005.王绍清.星载SAR多普勒中心实时估计技术研究[D].北京:中国科学院电子学研究所,2005.
[19] XIE T,KUANG H L,CHEN W,et al.Characters of SAR imaging Doppler frequencies caused by Sea surface motion[J].Geomatics and Information Science of Wuhan University,2010(12):1470-1473.谢涛,旷海兰,陈伟,等.海面运动引起的合成孔径雷达(SAR)成像多普勒频率特性[J].武汉大学学报(信息科学版),2010(12):1470-1473.
[20] CURLANDER J C,MCDONOUGH R N.Synthetic Aperture Radar:systems and signal processing[M].HAN C Z,translated.Beijing:Publishing House of Electronics Industry,2014.柯兰德 J C,麦克多诺 R N.合成孔径雷达:系统与信号处理[M].韩传钊,译.北京:电子工业出版社,2014.
[21] European Space Agency.ENVISAT-1 ASAR Products specifications:volume 8 ASAR Products specifications[EB/OL].[2011-10-10].https://earth.esa.int/web/sppa/mission-performance/esa-missions/envisat#product_spec.html.
[22] CHAPRON B,COLLARD F,ARDHUIN F.Direct measurements of ocean surface velocity from space:interpretation and validation[J].Journal of Geophysical Research Oceans,2005,110(C07008):1-17.
[23] CHENG Y X,GE S R,YUAN L F,et al.Research of the ocean wind speed retrieval from space-borne SAR[J].Electronic Test,2016(4):133-134.程玉鑫,戈书睿,袁凌峰,等.星载合成孔径雷达海面风速反演技术研究[J].电子测试,2016(4):133-134.
[24] CHENG Y X,AI W H,KONG Y,et al.Ocean wind retrieval from space-borne synthetic aperture radar images based on wind streaks and external wind direction[J].Marine Sciences,2015,39(12):157-164.程玉鑫,艾未华,孔毅,等.基于影像纹理特征和外部风向的星载SAR海面风场反演研究[J].海洋科学,2015,39(12):157-164.
[25] YANG J S,HUANG W G,ZHOU C B,et al.Coastal ocean surface wind retrieval from SAR imagery[J].Journal of Remote Sensing,2001,5(1):13-16.杨劲松,黄韦艮,周长宝,等.合成孔径雷达图像的近岸海面风场反演[J].遥感学报,2001,5(1):13-16.
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