基于散斑抑制的合成孔径激光成像雷达的结构和工作模式

Structure and Operating Mode of Synthetic Aperture Laser Imaging Ladar for Speckle Reduction

目标漫反射产生的激光回波散斑效应严重影响合成孔径激光成像雷达(SAIL)的成像质量。在体系结构上提出了抑制散斑效应的系统性解决方案,建立了SAIL结构和工作模式设计的理论基础。研究了SAIL中与目标分辨单元尺寸、啁啾波长变化、目标相关性质和接收面光强随机分布有关的散斑统计特性。定义了SAIL光学接收天线的散斑孔径积分场复相干函数,它是天线孔径相关函数和目标分辨单元相关因子的卷积,其宽度就是可实现的孔径合成长度,给出了实现较大的孔径合成长度的发射口径、接收口径和实际孔径合成长度的设计原则,发现和分析了由啁啾散斑移动产生的拍频信号波动。最后建议采用滑动聚束模式来有效使用散斑效应造成较短的孔径合成尺度,因为其光束扫描宽度对SAIL移动距离有放大作用。同时也提出了具有多发射机/多接收机的多通道结构以提高回波散斑光场的探测率。

In a synthetic aperture imaging ladar（SAIL）,the imaging quality is greatly degraded from the laser speckle effect of diffused target.A systematic solution to reduce speckle is given,and thus the theoretic basis is founded for the design of SAIL structure and operating mode.The speckle characteristics relating to the scale of target resolution element,the wavelength change from laser chirp,the correlation of target surface and the uncertain distribution of intensity at receiver plane are investigated.A complex coherence function of integrated speckle over antenna aperture is defined,it is a convolution between the correlation of antenna profile and the complex correlation factor of the speckle from a resolution element and its width is the possible length for aperture synthesizing.A design principle for transmitter aperture,receiver aperture and used length for synthesizing is given to achieve a long synthesizing length.And a fluctuation phenomenon of beat signal due to the speckle wandering caused by the chirp is also discovered and analyzed.Then a sliding spotlight mode which has a magnification from the SAIL movement to the beam scan is considered to effectively utilize the limited length of aperture synthesizing.A multi-channel transmitter/receiver construction is proposed to enhance the detectability of speckled echo.