基于合成频率步进线性调频信号的合成孔径激光雷达成像

Synthetic aperture ladar imaging via synthetic frequency-stepped linearly-chirping signal

为解决合成孔径激光雷达(SAL)所需高重复频率大带宽相干光源问题,提出了合成频率步进线性调频信号(SFSCS)的方案,并进行了基于SFSCS信号SAL(SFSCS-SAL)的成像理论和实验演示研究。采用多台独立的窄带宽高重复频率线性调频激光器构成SFSCS信号,给出了SFSCS-SAL的成像数据方程和图像形成方法。理论分析表明:在一定条件下,SFSCS-SAL的成像处理与常规SAL相同;但是,与单个子脉冲激光器SAL相比,SFSCS-SAL的距离向成像分辨率提高至少N倍(N为构成SFSCS的独立激光器数目)。实验演示中,利用一台1550nm波段的线性调波长激光器,通过光学斩波的方法模拟生成了子脉冲数为3的SFSCS信号。以此SFSCS信号作为探测光源,建立了SFSCS-SAL实验装置,对强散射目标和弱散射扩展目标,均实现了高分辨率成像。实验结果与理论分析一致。

In order to achieve a coherent light source with large modulation bandwidth and high repetition rate for synthetic aperture ladar （SAL）, a Synthetic Frequency-Stepped linearly-Chirping Signal （SFSCS） is proposed and a SAL using SFSCS illu- mination （SFSCS-SAL） is investigated both theoretically and experimentally. The SFSCS is synthesized by multiple independent lasers with relatively narrow chirping bandwidth and high repetition rate. Data equations, as well as the image formation theory, on the SFSCS-SAL are given. The theoretical studies show that under proper conditions, the SFSCS-SAL follows the same image formation theory as a conventional SAL; whereas, the range resolution in an SFSCS-SAL will be raised at least N times compared to that of a SAL with only one piece of sub-pulse laser （N is the number of independent lasers in the SFSCS）. In the experimental demonstration, an SFSCS of N= 3 was produced by optically chopping a linearly wavelength-scanning laser output into 3 sub-pul- ses; an SFSCS-SAL was set up using the SFSCS and high resolution images were obtained with either retro-reflective or diffusive targets. The experimental results are in well agreement with the theoretical analysis.