大随机相位误差下条带模式合成孔径激光雷达成像实验

为了探索大随机相位误差条件下合成孔径雷达(SAL)成像特点和规律,本文采用波长为1 550 nm的线性调频激光器建立了能够产生大的共模随机相位误差的条带模式SAL成像实验装置。利用此装置获得了不同目标回波强度下条带模式SAL成像实验数据,结合条带模式相位梯度自聚焦(PGA)多次迭代处理,获得了高分辨率SAL图像。实验发现在-6. 45π,6. 45π]范围的大随机相位误差下,通过简单的距离压缩和方位匹配滤波,无法实现SAL图像聚焦,图像信噪比仅为3 dB。进一步采用PGA处理,就能很好地校正相位误差,得到聚焦良好的SAL图像,图像信噪比达到43 dB。实验还发现,当存在大共模随机相位误差时,PGA处理展现出非常强的鲁棒性,在回波弱到10-15W的情况下依然有效。在大相位误差存在的SAL系统(如机载SAL)中,PGA处理能有效消除相位误差,实现图像聚焦;另外,增大探测激光功率以提高成像数据信噪比,将有助于提升PGA处理效果。

Stripmap mode synthetic aperture ladar imaging under large random phase errors condition

For exploring the characteristics and regularities of SAL imaging under large random phase error conditions, we build the stripmap mode SAL imaging experiment setup by using a 1 550-nm linear chirp laser. By using this device which can generate large common-mode random phase errors, we obtain stripmap mode SAL imaging experimental data under different target echo intensities. Using the phase gradient autofocus(PGA) algorithm of the stripe pattern, we complete the process with multiple iterations to obtain a high-resolution SAL image. When large random phase error exists in the range of-6.45π, 6.45π], the SAL image cannot be focused by simple distance compression or azimuth matched filtering, and the signal to noise ratio(SNR) of the image can only be 3 dB. By PGA processing, the phase error can be significantly lessened, and a well-focused SAL image with SNR of 43 dB can be obtained. Experiments also show that PGA processing is robust in the presence of common-mode random phase error and the process continues to be valid when echo is as weak as 10^-15 W. It can be concluded that in SAL systems that include large random phase errors(such as airborne SAL), PGA processing can effectively eliminate phase error and achieve sharper image focusing. In addition, increasing the detection laser power to increase the SNR of an image will strengthen effective PGA processing.