X波段雷达图像的海浪信息提取
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摘要
海浪是人们最熟悉的海洋现象,也是物理海洋学的一个重要研究领域。近年来,利用X波段导航雷达遥测海浪信息的研究引起了众多学者的兴趣。X波段雷达电磁波入射到海面时,与那些与雷达电磁波波长相当的、由风引起的毛细波产生布拉格(Bragg)散射,后向散射回波被雷达接收器接收,形成“海杂波”,而波长较长的长波通过对毛细波的流体动力调制、倾斜调制、阴影调制作用表现在海杂波图像上,由此可见,X波段雷达图像包含着丰富的海浪信息。因此,如何从X波段雷达图像中准确有效的获取海浪信息对海浪的研究具有重要的科学意义。
本文首先从X波段雷达的海浪成像理论出发,介绍了Bragg共振理论和长波调制理论以及Bragg波和长波在雷达成像过程中的作用。分析了Bragg波通过共振机制后向散射电磁波的机制。介绍了长波对Bragg波的阴影调制、倾斜调制、流体动力调制、轨道调制等调制作用。
在雷达成像理论分析的基础上,本文对从雷达图像中提取海浪信息的算法理论进行了研究。首先对获得的雷达图像时间序列进行三维离散傅立叶(Fourier)变换得到三维雷达图像谱。进而,利用频散关系,从雷达图像谱中获得表层流速。然后,利用流速不为零时的频散关系对雷达图像谱进行滤波。最后,根据雷达图像谱与海浪方向谱之间的经验传递函数得到海浪方向谱,从而得到更多的海浪统计信息,如主波周期、频率、方向等。
最后,对在小麦岛进行的海上试验得到的雷达数据进行反演计算,并将计算结果和相对应的浮标数据进行对比,结果表明由雷达图像反演得到的海浪参数与浮标资料符合较好。这说明通过利用X波段雷达图像提取海浪信息的算法可获得真实可靠的海浪信息,尤其是在海洋状态十分恶劣的情况下,对于海洋的实时监测,具有非常重要的意义。
The ocean wave is a very familiar phenomenon and an important field in physical oceanography. In recent years, considerable interests have been shown in the application of remote sensing techniques to the measurement of the ocean waves by X-band radar. When the electromagnetic waves of the X-band radar reach the sea surface, they would be interacted with the capillary waves caused by wind. Bragg scattering criterion is fulfilled by those waves having a wavelength equal to one half of the electromagnetic wavelength. The radar backscatter is incepted by radar antenna and shown on the radar screen. This phenomenon is called sea clutter. The longer waves become visible in the radar images, because they modulate the short Bragg scattering waves. The modulate mechanisms are consisted of shadowing, orbital modulation, hydrodynamic modulation and tilt modulation. Thus, the radar images contain luxuriant sea state information. It is important to study how to obtain the wave information from X-band radar images accurately and effectively for the research of the ocean wave.
Beginning with the imaging theory of the X-band radar, the theory of Bragg resonance and long wave modulation and their effects on the radar imaging were introduced firstly. The mechanisms of Bragg waves scattering electromagnetic waves were analyzed, and the modulations of the longer wave on the Bragg waves by shadowing, orbital modulation, hydrodynamic modulation and tilt modulation is also introduced.
Based on the analysis of the radar imaging theory, the algorithm for obtaining the wave information from radar images was studied. Firstly, by applying a 3D-FFT algorithm to the time series of radar images the 3D radar image spectrum was obtained. Furthermore, the surface current velocity was gained from the dispersion relation from the radar images. Then, the wave spectral components were filtered, taking into account the dispersion relation with the current velocity. Finally, the wave directional spectrum was acquired according the experiential transfer function between the radar image spectrum and the wave directional spectrum. The other parameters included by the wave information were obtained, such as peak period, peak frequency, wave direction, etc.
Lastly, the radar data gained in the offshore experiment which was carried out on the Small Mai island was calculated and compared with the corresponding buoy data. The compared result is good, showing that the wave information can be gained through the algorithm for obtaining the wave information from radar images effectively. Especially in the rough sea state, it is significant to use this way to monitor the ocean wave.
本文首先从X波段雷达的海浪成像理论出发,介绍了Bragg共振理论和长波调制理论以及Bragg波和长波在雷达成像过程中的作用。分析了Bragg波通过共振机制后向散射电磁波的机制。介绍了长波对Bragg波的阴影调制、倾斜调制、流体动力调制、轨道调制等调制作用。
在雷达成像理论分析的基础上,本文对从雷达图像中提取海浪信息的算法理论进行了研究。首先对获得的雷达图像时间序列进行三维离散傅立叶(Fourier)变换得到三维雷达图像谱。进而,利用频散关系,从雷达图像谱中获得表层流速。然后,利用流速不为零时的频散关系对雷达图像谱进行滤波。最后,根据雷达图像谱与海浪方向谱之间的经验传递函数得到海浪方向谱,从而得到更多的海浪统计信息,如主波周期、频率、方向等。
最后,对在小麦岛进行的海上试验得到的雷达数据进行反演计算,并将计算结果和相对应的浮标数据进行对比,结果表明由雷达图像反演得到的海浪参数与浮标资料符合较好。这说明通过利用X波段雷达图像提取海浪信息的算法可获得真实可靠的海浪信息,尤其是在海洋状态十分恶劣的情况下,对于海洋的实时监测,具有非常重要的意义。
The ocean wave is a very familiar phenomenon and an important field in physical oceanography. In recent years, considerable interests have been shown in the application of remote sensing techniques to the measurement of the ocean waves by X-band radar. When the electromagnetic waves of the X-band radar reach the sea surface, they would be interacted with the capillary waves caused by wind. Bragg scattering criterion is fulfilled by those waves having a wavelength equal to one half of the electromagnetic wavelength. The radar backscatter is incepted by radar antenna and shown on the radar screen. This phenomenon is called sea clutter. The longer waves become visible in the radar images, because they modulate the short Bragg scattering waves. The modulate mechanisms are consisted of shadowing, orbital modulation, hydrodynamic modulation and tilt modulation. Thus, the radar images contain luxuriant sea state information. It is important to study how to obtain the wave information from X-band radar images accurately and effectively for the research of the ocean wave.
Beginning with the imaging theory of the X-band radar, the theory of Bragg resonance and long wave modulation and their effects on the radar imaging were introduced firstly. The mechanisms of Bragg waves scattering electromagnetic waves were analyzed, and the modulations of the longer wave on the Bragg waves by shadowing, orbital modulation, hydrodynamic modulation and tilt modulation is also introduced.
Based on the analysis of the radar imaging theory, the algorithm for obtaining the wave information from radar images was studied. Firstly, by applying a 3D-FFT algorithm to the time series of radar images the 3D radar image spectrum was obtained. Furthermore, the surface current velocity was gained from the dispersion relation from the radar images. Then, the wave spectral components were filtered, taking into account the dispersion relation with the current velocity. Finally, the wave directional spectrum was acquired according the experiential transfer function between the radar image spectrum and the wave directional spectrum. The other parameters included by the wave information were obtained, such as peak period, peak frequency, wave direction, etc.
Lastly, the radar data gained in the offshore experiment which was carried out on the Small Mai island was calculated and compared with the corresponding buoy data. The compared result is good, showing that the wave information can be gained through the algorithm for obtaining the wave information from radar images effectively. Especially in the rough sea state, it is significant to use this way to monitor the ocean wave.
引文
[1]陈宗镛等.海洋科学概论.青岛:青岛海洋大学出版社,1992。
[2]蒋德才.海洋波动动力学.青岛:青岛海洋大学出版社,1992。
[3]管长龙.我国海浪理论及预报研究的回顾与展望.青岛海洋大学学报. 2000, 30(4):549-556.
[4] Barner N.F.. Finding the dDirection of travel of sea waves, Nature, 1954, 174: 1048-1050.
[5] Longuet-Higgins M.S., Fox J.H.. Theory of the almost-highest wave: the inner solution, J. Fluid Mech., 1977, 80: 721-741.
[6] Mitsuyasu H. et al.. Observations of the directional spectrum of ocean wave using a cloverleaf buoy, J. Phys. Oceanogr., 1975, 5(4): 750-760.
[7]孙建. SAR影像的海浪信息反演.博士学位论文.青岛:中国海洋大学, 2005. 1―10.
[8]林敏基.海洋与海岸带遥感应用.北京:海洋出版社,1991.
[9]董庆,郭华东.合成孔径雷达海洋遥感.北京:科学出版社,2005.
[10] Merrill I. Skolnik主编,王军,林强等译.雷达手册,北京:电子工业出版社,2003.
[11] Oudshoorn H. M.. The use of radar in hydrodynamic surveying, Coastal Engineering, 1960,7:59-76.
[12] Willis T.G., and H. Beaumont. Wave direction measurements using sea surveillance radars, Tech. Memo. TR 118, R., Aircraft Establishment, Farnbough, Great Britain,1971.
[13] Evmenov V. W.,et al.. Test of the radar method of defining ocean waves elements, J. Fluid Mech. Sov.Res., 1973,2(5):141-145.
[14] Mattie M. G., Harris D. L.. A system for using radar to record wave direction, Tech. Rep. 79-1,50, U.S. Army Corps of Eng., Coast. Eng. Res. Ctr., Fort Belvoir, Va., 1979.
[15] Hoogeboom P., and W. Rosenthal.. Directional wave spectra in radar images, International Geoscience and Remote Sensing Symposium, IEEE Geosci, and Remote Sensing Soc., Munich, June 1-4, 1982.
[16] Ziemer F., W. Rosenthal, and H. Carlson, Measurements of directional wave spectra by ship radar. IAPSO Symposium, General Assembly Int. Assoc. for Phys. Sci. of the Oceans. Hamburg, Federal Republic of Germany,1983.
[17] Atanassov V., Rosenthal W., and Ziemer F.. Removal of two-dimensional power spectra obtained by processing ship radar images of ocean waves. J. Geophys. Res.,1985, 90:1061-1067.
[18] Young I.R., Rosenthal W. and Ziemer F.. A three dimensional analysis of marine radar images for the determination of ocean waves directionality and surface currents, J. Geophys. Res., 1985,90:1049–1059.
[19] Ziemer F., An instrument for the survey of the directionality of the ocean wave field. In Proc. WMO/IOC Workshop on Operational Ocean Monitoring Using Surface Based Radars, Geneva, Switzerland, 1995, 32:81-87.
[20] Dittmer J.. Use of marine radars for real time wave field survey and Speeding up Transmission/Processing, In Proceedings of the WMO/IOC Workshop on operational ocean monitoring using surface based radars, Geneva, 1995,133-138.
[21] Nieto J. C. Borge, Reichert K., and Dittmer J.. Use of nautical radar as a wave monitoring instrument, Coastal Engineering, 1999,37:331-342.
[22] Senet C. M., Seemann J., and Ziemer F.. The near-surface current velocity determined from image sequences of the sea surface, IEEE Transaction on Geosecience and Remote Sensing, 2001, 39:492-505.
[23] Izquierdo P., Guedes Soares C., Nieto J. C. Borage, and Rodriguez G.R.. A comparison of sea-state parameters from nautical radar images and buoy data, Costal Engineering, 2004, 31:2209-2225.
[24] Hessner K., Reichert K., and Rosenthal W.. Mapping of sea bottom topography in shallow seas by using a nautical radar. 2nd International Symposium on Operationalization of Remote Sensing.,1999.
[25] Shubhra K. Misra, Andrew B. Kennedy, and James T. Kirby. An approach to determining nearshore bathymetry using remotely sensed ocean surface dynamics, Coastal Engineering, 2003, 47:265-293.
[26] Ziemer F., Carsten Brockmann, Robin A. Vaughan, J?rg Seemann and Christian M. Senet, Radar survey of near shore bathymetry within the oroma project. EARSeL Proceedings3, 2004, 2:282-288.
[27] Izquierdo P., Guedes Soares C.. Analysis of sea waves and wind from X-band radar, Coastal Engineering, 2005, 32:1404-1419.
[28] Jessica Drake, F. L. Ludwig. John Vesecky. Using high frequency radar observations of the ocean surface and objective analyses of onshore observations to estimate winds over monterey bay, California. American Meteorological Society 13th Conference on Interactions of the Sea and Atmosphere 8-13 August, Portland,ME, 2004.
[29] Crombie D.D., Doppler spectrum of sea echo at 13.56 Mc/s, Nature, 1955, 175: 681-682.
[30] Wright J.W., Backscattering from capillary waves with application to sea clutter, IEEE Trans. Antennas Propagat. 1966, AP-14:749-754
[31] R.H.斯图尔特著,徐柏德沙兴伟译.空间海洋学,北京:海洋出版社,1991.
[32] Nieto J. C. Borge. Use of nautical radar to study wave fields. German Aerospace Center Remote Sensing Technology Institute, 2nd WORKSHOP ON WATER WAVES Berlin, February 2002.
[33] Stewart, R.H., and J.W.Joy. HF radio measurements of surface currents, Deep Sea Res., 1974, 21:1039-1049.
[34] D.E. Barrick, M.W. Evans, and B.L. Weber. Ocean surface currents mapped by radar, Science, 1977, 198:138-144.
[35] Ziemer F. and Rosenthal F.W.. On the transfer function of a shipborne radar for imaging ocean waves, Proc., IGARSS’87 Symp., Ann Arbor, Michigan, May, 1987.
[36] Nieto J. C. Borge, Rodiguez G. R., and Hessenr K.. Inversion of marine radar images for surface wave analysis, Journal of Atmoshperic and Ocean Technology, 2004, 21:1291-1301.
[37] Ziemer, F. and Gunther H.. A system to monitor ocean wave fields, Proceedings of the Second International Conference on Air-Sea Interaction and Meteorology and Oceanography of the Coastal Zone, Lisbon, Portugal.1994
[38] Alpers W., Ross D.B., and Rufenach C.L.. On the detectability of ocean surface waves by real and synthetic aperture radar, J. Geophys. Res., 1981, 86: 6481-6498
[39] Nieto J. C. and Guedes C.. Analysis of directional wave fields using X-band navigation radar, Coastal Engineering, 2000, 40: 375-391
[2]蒋德才.海洋波动动力学.青岛:青岛海洋大学出版社,1992。
[3]管长龙.我国海浪理论及预报研究的回顾与展望.青岛海洋大学学报. 2000, 30(4):549-556.
[4] Barner N.F.. Finding the dDirection of travel of sea waves, Nature, 1954, 174: 1048-1050.
[5] Longuet-Higgins M.S., Fox J.H.. Theory of the almost-highest wave: the inner solution, J. Fluid Mech., 1977, 80: 721-741.
[6] Mitsuyasu H. et al.. Observations of the directional spectrum of ocean wave using a cloverleaf buoy, J. Phys. Oceanogr., 1975, 5(4): 750-760.
[7]孙建. SAR影像的海浪信息反演.博士学位论文.青岛:中国海洋大学, 2005. 1―10.
[8]林敏基.海洋与海岸带遥感应用.北京:海洋出版社,1991.
[9]董庆,郭华东.合成孔径雷达海洋遥感.北京:科学出版社,2005.
[10] Merrill I. Skolnik主编,王军,林强等译.雷达手册,北京:电子工业出版社,2003.
[11] Oudshoorn H. M.. The use of radar in hydrodynamic surveying, Coastal Engineering, 1960,7:59-76.
[12] Willis T.G., and H. Beaumont. Wave direction measurements using sea surveillance radars, Tech. Memo. TR 118, R., Aircraft Establishment, Farnbough, Great Britain,1971.
[13] Evmenov V. W.,et al.. Test of the radar method of defining ocean waves elements, J. Fluid Mech. Sov.Res., 1973,2(5):141-145.
[14] Mattie M. G., Harris D. L.. A system for using radar to record wave direction, Tech. Rep. 79-1,50, U.S. Army Corps of Eng., Coast. Eng. Res. Ctr., Fort Belvoir, Va., 1979.
[15] Hoogeboom P., and W. Rosenthal.. Directional wave spectra in radar images, International Geoscience and Remote Sensing Symposium, IEEE Geosci, and Remote Sensing Soc., Munich, June 1-4, 1982.
[16] Ziemer F., W. Rosenthal, and H. Carlson, Measurements of directional wave spectra by ship radar. IAPSO Symposium, General Assembly Int. Assoc. for Phys. Sci. of the Oceans. Hamburg, Federal Republic of Germany,1983.
[17] Atanassov V., Rosenthal W., and Ziemer F.. Removal of two-dimensional power spectra obtained by processing ship radar images of ocean waves. J. Geophys. Res.,1985, 90:1061-1067.
[18] Young I.R., Rosenthal W. and Ziemer F.. A three dimensional analysis of marine radar images for the determination of ocean waves directionality and surface currents, J. Geophys. Res., 1985,90:1049–1059.
[19] Ziemer F., An instrument for the survey of the directionality of the ocean wave field. In Proc. WMO/IOC Workshop on Operational Ocean Monitoring Using Surface Based Radars, Geneva, Switzerland, 1995, 32:81-87.
[20] Dittmer J.. Use of marine radars for real time wave field survey and Speeding up Transmission/Processing, In Proceedings of the WMO/IOC Workshop on operational ocean monitoring using surface based radars, Geneva, 1995,133-138.
[21] Nieto J. C. Borge, Reichert K., and Dittmer J.. Use of nautical radar as a wave monitoring instrument, Coastal Engineering, 1999,37:331-342.
[22] Senet C. M., Seemann J., and Ziemer F.. The near-surface current velocity determined from image sequences of the sea surface, IEEE Transaction on Geosecience and Remote Sensing, 2001, 39:492-505.
[23] Izquierdo P., Guedes Soares C., Nieto J. C. Borage, and Rodriguez G.R.. A comparison of sea-state parameters from nautical radar images and buoy data, Costal Engineering, 2004, 31:2209-2225.
[24] Hessner K., Reichert K., and Rosenthal W.. Mapping of sea bottom topography in shallow seas by using a nautical radar. 2nd International Symposium on Operationalization of Remote Sensing.,1999.
[25] Shubhra K. Misra, Andrew B. Kennedy, and James T. Kirby. An approach to determining nearshore bathymetry using remotely sensed ocean surface dynamics, Coastal Engineering, 2003, 47:265-293.
[26] Ziemer F., Carsten Brockmann, Robin A. Vaughan, J?rg Seemann and Christian M. Senet, Radar survey of near shore bathymetry within the oroma project. EARSeL Proceedings3, 2004, 2:282-288.
[27] Izquierdo P., Guedes Soares C.. Analysis of sea waves and wind from X-band radar, Coastal Engineering, 2005, 32:1404-1419.
[28] Jessica Drake, F. L. Ludwig. John Vesecky. Using high frequency radar observations of the ocean surface and objective analyses of onshore observations to estimate winds over monterey bay, California. American Meteorological Society 13th Conference on Interactions of the Sea and Atmosphere 8-13 August, Portland,ME, 2004.
[29] Crombie D.D., Doppler spectrum of sea echo at 13.56 Mc/s, Nature, 1955, 175: 681-682.
[30] Wright J.W., Backscattering from capillary waves with application to sea clutter, IEEE Trans. Antennas Propagat. 1966, AP-14:749-754
[31] R.H.斯图尔特著,徐柏德沙兴伟译.空间海洋学,北京:海洋出版社,1991.
[32] Nieto J. C. Borge. Use of nautical radar to study wave fields. German Aerospace Center Remote Sensing Technology Institute, 2nd WORKSHOP ON WATER WAVES Berlin, February 2002.
[33] Stewart, R.H., and J.W.Joy. HF radio measurements of surface currents, Deep Sea Res., 1974, 21:1039-1049.
[34] D.E. Barrick, M.W. Evans, and B.L. Weber. Ocean surface currents mapped by radar, Science, 1977, 198:138-144.
[35] Ziemer F. and Rosenthal F.W.. On the transfer function of a shipborne radar for imaging ocean waves, Proc., IGARSS’87 Symp., Ann Arbor, Michigan, May, 1987.
[36] Nieto J. C. Borge, Rodiguez G. R., and Hessenr K.. Inversion of marine radar images for surface wave analysis, Journal of Atmoshperic and Ocean Technology, 2004, 21:1291-1301.
[37] Ziemer, F. and Gunther H.. A system to monitor ocean wave fields, Proceedings of the Second International Conference on Air-Sea Interaction and Meteorology and Oceanography of the Coastal Zone, Lisbon, Portugal.1994
[38] Alpers W., Ross D.B., and Rufenach C.L.. On the detectability of ocean surface waves by real and synthetic aperture radar, J. Geophys. Res., 1981, 86: 6481-6498
[39] Nieto J. C. and Guedes C.. Analysis of directional wave fields using X-band navigation radar, Coastal Engineering, 2000, 40: 375-391