剪切光束成像技术对纵深目标的成像
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摘要
剪切光束成像技术是一种能透过大气湍流对远距离目标实现高分辨率成像的主动成像技术.现有相关研究中所采用的目标均为二维平面目标,然而现实中的目标一般都具有三维形貌,目标纵深对回波信号产生的延迟或对成像质量产生不利影响.从剪切光束成像理论出发,在二维目标成像模型的基础上建立了三维纵深目标成像模型,并利用该模型研究了两剪切光与参考光间的频差及目标纵深对成像的影响.仿真结果表明,随着拍频的增大,重构图像质量逐渐下降.剪切光束成像技术可通过减小拍频来提高真实目标成像质量.
Sheared-beam imaging technique is a non-conventional imaging method which can be used to image remote objects through atmospheric turbulence without needing any adaptive optics. In this imaging technique, the target is coherently illuminated by three laser beams which are laterally sheared at the transmitter plane and arranged into an L shape. In addition, each beam is modulated by a slight frequency shift. The speckle intensity signals scattered from the target are received by a detector array, and then the image of target can be reconstructed by computer algorithm. By far, most of studies in this field have focused on two-dimensional imaging. In real conditions, however, the surface of targets we are concerned about reveals that different depths introduce various phase delays in the scattering signal from target. This delay causes the phase-shift errors to appear between the ideal target Fourier spectrum and the Fourier spectrum received by detector array. Finally, this would result in poor image quality and low resolution. In this study, a three-dimensional target imaging model is established based on the two-dimensional target imaging model. The influence of modulated beat frequency between sheared beam and reference beam is studied on the objects with depth information, and the result shows that large beat frequency may have an adverse effect on reconstructed images. The simulation we have developed for this three-dimensional imaging model uses three targets with different shapes. Each target is divided into several sub-blocks, and we set different depth values(within 10 m) for these blocks. Then beat frequencies are increased from 5 Hz to about 1 MHz, respectively. At each pair of frequencies, the reconstructed image is recorded. Strehl ratio is used as the measure of the imaging quality. Computer simulation results show that the Strehl ratio of reconstructed images descends with the increase of beat frequency, which is fully consistent with the theory of three-dimensional target imaging proposed before. Meanwhile, we find that the depth distribution of target also has an effect on imaging quality.As for actual space targets, the maximum depth is usually not more than 10 m. Compared with the influence caused by beat frequencies, the effect produced by depth distribution is negligible. Therefore when a space target is imaged,beat frequencies play the major role in reconstructing high-quality image. The results presented in this paper indicate that in order to achieve better imaging quality in the practical application, it is necessary to select the smallest beat frequency according to the detector performance and keep the candidate frequencies away from the low-frequency noise of the detector.
Sheared-beam imaging technique is a non-conventional imaging method which can be used to image remote objects through atmospheric turbulence without needing any adaptive optics. In this imaging technique, the target is coherently illuminated by three laser beams which are laterally sheared at the transmitter plane and arranged into an L shape. In addition, each beam is modulated by a slight frequency shift. The speckle intensity signals scattered from the target are received by a detector array, and then the image of target can be reconstructed by computer algorithm. By far, most of studies in this field have focused on two-dimensional imaging. In real conditions, however, the surface of targets we are concerned about reveals that different depths introduce various phase delays in the scattering signal from target. This delay causes the phase-shift errors to appear between the ideal target Fourier spectrum and the Fourier spectrum received by detector array. Finally, this would result in poor image quality and low resolution. In this study, a three-dimensional target imaging model is established based on the two-dimensional target imaging model. The influence of modulated beat frequency between sheared beam and reference beam is studied on the objects with depth information, and the result shows that large beat frequency may have an adverse effect on reconstructed images. The simulation we have developed for this three-dimensional imaging model uses three targets with different shapes. Each target is divided into several sub-blocks, and we set different depth values(within 10 m) for these blocks. Then beat frequencies are increased from 5 Hz to about 1 MHz, respectively. At each pair of frequencies, the reconstructed image is recorded. Strehl ratio is used as the measure of the imaging quality. Computer simulation results show that the Strehl ratio of reconstructed images descends with the increase of beat frequency, which is fully consistent with the theory of three-dimensional target imaging proposed before. Meanwhile, we find that the depth distribution of target also has an effect on imaging quality.As for actual space targets, the maximum depth is usually not more than 10 m. Compared with the influence caused by beat frequencies, the effect produced by depth distribution is negligible. Therefore when a space target is imaged,beat frequencies play the major role in reconstructing high-quality image. The results presented in this paper indicate that in order to achieve better imaging quality in the practical application, it is necessary to select the smallest beat frequency according to the detector performance and keep the candidate frequencies away from the low-frequency noise of the detector.
引文
[1]Li X Y,Gao X,Tang J,Feng L J 2015 Acta Photon.Sin.44 0611002(in Chinese)[李希宇,高昕,唐嘉,冯灵洁2015光子学报44 0611002]
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[5]Bush K A,Barnard C C,Voelz D G 1996 Proc.SPIE2828 362
[6]Landesman B T,Kindilien P,Pierson R E 1997 Opt.Express 1 312
[7]Landesman B T,Olson D F 1994 Proc.SPIE 2302 14
[8]Voelz D G,Belsher J F,Ulibarri A L,Gamiz V 2002Proc.SPIE 4489 35
[9]Voelz D G,Gonglewski J D,Idell P S 1993 Proc.SPIE2029 169
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[11]Optical Physics Company http://www.opci.com/technologies/speckle-based-imaging[2017-01-09]
[12]Goodman J W(Qin K C,Liu P S,Chen J B,Cao Q Z,translated)2013 Introduction to Fourier Optics(3rd Ed.)(Beijing:Publishing House of Electronics Industry)p54(in Chinese)[古德曼(秦克诚,刘培森,陈家碧,曹其智译)2013傅里叶光学导论(3版)(北京:电子工业出版社)第54页]
[13]Fairchild P,Payne I 2013 IEEE Aerospace Conference Big Sky Montana,USA,March 2–9,2013 p1
[14]Idell P S,Gonglewski J D 1990 Opt.Lett.15 1309
[15]Hutchin R A 1993 Proc.SPIE 2029 161
[16]Cao B,Luo X J,Chen M L,Zhang Y 2015 Acta Phys.Sin.64 124205(in Chinese)[曹蓓,罗秀娟,陈明徕,张羽2015物理学报64 124205]
[17]Chen M L,Luo X J,Zhang Y,Lan F Y,Liu H,Cao B,Xia A L 2017 Acta Phys.Sin.66 024203(in Chinese)[陈明徕,罗秀娟,张羽,兰富洋,刘辉,曹蓓,夏爱利2017物理学报66 024203]
[18]Crawford T M http://www.osti.gov/scitech/biblio/666155[2017-01-09]
[19]Liu P S 1987 Fundamentals of Statistical Optics of Speckle(Beijing:Science Press)p7(in Chinese)[刘培森1987散斑统计光学基础(北京:科学出版社)第7页]
[20]Corser B A 1996 M.S.Dissertation(Lubbock:Texas Tech University)
[21]Dong L 2014 Laser&Infrared 44 1350(in Chinese)[董磊2014激光与红外44 1350]
[22]Si Q D,Luo X J,Zeng Z H 2014 Acta Phys.Sin.63104203(in Chinese)[司庆丹,罗秀娟,曾志红2014物理学报63 104203]
[2]Fienup J R 2010 Imaging Systems Tucson,Arizona,USA,June 7–8,2010 IMD2
[3]Hutchin R A 2012 US Patent 20120162631[2012-06-28]
[4]Hutchin R A 2012 US Patent 20120292481[2012-11-22]
[5]Bush K A,Barnard C C,Voelz D G 1996 Proc.SPIE2828 362
[6]Landesman B T,Kindilien P,Pierson R E 1997 Opt.Express 1 312
[7]Landesman B T,Olson D F 1994 Proc.SPIE 2302 14
[8]Voelz D G,Belsher J F,Ulibarri A L,Gamiz V 2002Proc.SPIE 4489 35
[9]Voelz D G,Gonglewski J D,Idell P S 1993 Proc.SPIE2029 169
[10]Stahl S M,Kremer R,Fairchild P,Hughes K,Spivey B1996 Proc.SPIE 2847 150
[11]Optical Physics Company http://www.opci.com/technologies/speckle-based-imaging[2017-01-09]
[12]Goodman J W(Qin K C,Liu P S,Chen J B,Cao Q Z,translated)2013 Introduction to Fourier Optics(3rd Ed.)(Beijing:Publishing House of Electronics Industry)p54(in Chinese)[古德曼(秦克诚,刘培森,陈家碧,曹其智译)2013傅里叶光学导论(3版)(北京:电子工业出版社)第54页]
[13]Fairchild P,Payne I 2013 IEEE Aerospace Conference Big Sky Montana,USA,March 2–9,2013 p1
[14]Idell P S,Gonglewski J D 1990 Opt.Lett.15 1309
[15]Hutchin R A 1993 Proc.SPIE 2029 161
[16]Cao B,Luo X J,Chen M L,Zhang Y 2015 Acta Phys.Sin.64 124205(in Chinese)[曹蓓,罗秀娟,陈明徕,张羽2015物理学报64 124205]
[17]Chen M L,Luo X J,Zhang Y,Lan F Y,Liu H,Cao B,Xia A L 2017 Acta Phys.Sin.66 024203(in Chinese)[陈明徕,罗秀娟,张羽,兰富洋,刘辉,曹蓓,夏爱利2017物理学报66 024203]
[18]Crawford T M http://www.osti.gov/scitech/biblio/666155[2017-01-09]
[19]Liu P S 1987 Fundamentals of Statistical Optics of Speckle(Beijing:Science Press)p7(in Chinese)[刘培森1987散斑统计光学基础(北京:科学出版社)第7页]
[20]Corser B A 1996 M.S.Dissertation(Lubbock:Texas Tech University)
[21]Dong L 2014 Laser&Infrared 44 1350(in Chinese)[董磊2014激光与红外44 1350]
[22]Si Q D,Luo X J,Zeng Z H 2014 Acta Phys.Sin.63104203(in Chinese)[司庆丹,罗秀娟,曾志红2014物理学报63 104203]