利用涡旋光场计算水中前向散射的频率响应  

Frequency-response measurement of forward scattering clutters in water by using vortex beams

作　　者：廖英琦 杨苏辉[1] 宋健 郝燕 徐震 Liao Yingqi;Yang Suhui;Song Jian;Hao Yan;Xu Zhen(School of Optics and Photonics,Beijing Institute of Technology,Beijing 100081,China;Beijing Research Institute of Telemetry,Beijing 100084,China)

机构地区：[1]北京理工大学光电学院,北京100081 [2]北京遥测技术研究所,北京100084

出　　处：《红外与激光工程》2023年第9期107-116,共10页Infrared and Laser Engineering

基　　金：国家自然科学基金项目(61835001)。

摘　　要：载波调制水下探测激光雷达利用散射光和信号光在频域特性上的差异来抑制杂散光,而不同水质中的散射光的截止频率是载波调制水下探测激光雷达设计中的重要参数。测量散射杂波的频率响应需要将目标回波与散射杂波分开,尤其是前向散射,与目标回波空间上重合,不容易被分开。文中提出了一种在载波强度调制激光雷达中分别测量水下目标和散射杂波的频率响应方法,利用散射光和目标反射的信号光在空间相干性上的差异,在回波光路上使用螺旋相位板将其分开并分别采集,再通过傅里叶变换得到它们的频谱。实验结果表明,前向散射杂波具有低通特性,而目标回波的响应是平坦的。将信号与散射在频谱中调制频率处的幅度之比定义为“信杂比”,并且用其来表示探测的有效性:当信杂比大于1时,认为探测到了目标。在较浑浊的水中,为了获得大于1的信杂比,载波的调制频率需要更高,基于蒙特卡洛方法对光子在海水中的传播进行了仿真模拟,结果与实验相符。测距实验也证明了,提高调制频率可以减小浑浊水中的测距误差。当信杂比小于1时,提高调制频率,测距误差降低明显。Objective Lidar is widely used in underwater detection.However,laser is scattered during underwater propagation,and scattering is an important factor limiting the performance of radar systems.Lidar-radar techniques can suppress both forward and backward scattering,where the cut-off frequency of the scattered light is an important parameter.However,unlike backscattering which is easily separated from the target-reflected light in space,forward scattering is difficult to separate from the target-reflected light as they are intertwined in space.Therefore,we propose to separate the forward scattered light from the target-reflected light using vortex beams and analyze its frequency response to obtain the cut-off frequency of forward scattered light.Methods Vortex beams are used to distinguish between forward scattered light and target-reflected light in underwater target detection(Fig.3).The fast Fourier transform is done on the spatially filtered forward scattered light and the target-reflected light to obtain their frequency response(Fig.4).A Monte Carlo-based model for lidar-radar underwater target detection is also developed,and the fast Fourier transform of the forward scattered and reflected light in the echoes is also performed to analyze their frequency response(Fig.1).The simulation results are compared with the experimental results(Fig.2,Fig.6).A ranging experiment is designed to investigate the effect of modulation frequencies less than or greater than the cut-off frequency of forward scattering on the accuracy of ranging(Fig.7).Results and Discussions The experimental results show that scattering has an averaging effect on the modulation,and the high-frequency component is difficult to be maintained in the forward scattering.On the contrary,the high frequency modulation is well maintained in the signal light(Fig.4).The higher the modulation frequency is,the higher the signal-to-clutter ratio is.In addition,in order to achieve a signal-to-clutter ratio of 1,higher modulation frequencies are required in more

关 键 词：散射杂波 涡旋光 频率响应 载波调制 

分 类 号：P229.1[天文地球—大地测量学与测量工程] O436.2[天文地球—测绘科学与技术] O432.12[机械工程—光学工程]