基于自适应窗的合成孔径激光雷达联合时频成像方法

传统距离-多普勒算法中观测期间多普勒频率为常量的假设在合成孔径激光雷达系统中不再成立.根据合成孔径激光雷达回波信号模型,推导计算了振动对合成孔径激光雷达回波相位的影响.根据实际情况引入振动频率不超过500Hz、振幅不超过0.2mm的机载平台微振动参量,结果表明载机微振动对合成孔径激光雷达成像的方位分辨率影响很大,而对距离分辨率影响不大.采用时频分析成像方法,能够有效克服传统距离-多普勒算法对时变信号处理的局限性.分析比较Wigner-Ville分布、伪WWigner-Ville分布和平滑伪Wigner-Ville分布作为核函数的时频成像结果,均无法兼顾成像分辨率和成像效率.据此本文提出了一种基于自适应窗的联合时频成像方法,根据变异系数和变异阈值的比较自适应地调整子区域窗口大小,从而达到成像分辨率和算法效率的平衡优化.仿真结果表明,本算法对成像分辨率影响不大,成像时间减少近69.87%,适用于合成孔径激光雷达对成像高分辨率和成像效率的要求.

Combined Time-frequency Imaging Method of SAL Based on Adaptive Windowing

Range Doppler algorithm (RDA) is a basic method in synthetic aperture imaging. In RDA, the Doppler frequency is considered as constant, but this hypothesis is not existed in synthetic aperture ladar(SAL). Based on the echo signal model of SAL, the influence of vibration error on the phase is computed and analyzed. On the reference of the national military standard for environment, in the condition of the frequency below 500 MHz and the amplitude below 0.2 mm, the simulation results show that the influence of vibration on the azimuth resolution is severity, but which on the range resolution is trivial. The imaging algorithm based on time frequency analysis can overcome the limit of traditional RD algorithm effectively. Compared the imaging results used WVD, PWVD and SPWVD as kernel, they cannot suffice both the imaging resolution and imaging efficiency. A combined time frequency imaging method based on adaptive windowing is presented to modulate the window size adaptively according to the comparison of variance coefficient and variance threshold, then the counterpoise optimize of imaging resolution and imaging efficiency is achieved. The simulation results show that the imaging resolution of this algorithm is constant, but the imaging time decreases 69.87%, and it can used in SAL for its high imaging resolution and imaging efficiency.