宽脉冲光子计数偏振激光雷达探测浅水层研究（特邀）

由于受激光脉冲宽度的限制，传统激光雷达无法实现几十厘米的浅水层测量。设计了一个双Gm-APD光子计数偏振激光雷达系统，采用宽脉冲获取薄浅水层的高精度距离像。浅水层的表面光滑，能够保偏；底面粗糙，将发生退偏。根据该偏振现象，通过发射水平线偏振光，接收系统中采用一个偏振分光棱镜将前后表面信号光分离，然后分别被两个Gm-APD探测。该系统不受信号光的脉冲宽度限制，并充分利用Gm-APD的死时间机制，针对超薄浅水层实现三维深度测量。利用基于穆勒矩阵和斯托克斯参量表示的偏振传输原理，理论分析了双Gm-APD偏振激光雷达的分光原理。采用信号复原质心算法抑制距离漂移误差获取高精度距离信息。对于深度从4.5cm变化到8 cm渐变的薄浅水层，底面覆盖了黑、白沙子，探测距离为5 m，在实验上采用6 ns激光脉冲获取了薄浅水层的高精度距离像，测距精度为0.8 cm，有效验证了方案的可行性。该方案能够为机载海洋测绘激光雷达的浅水层测量提供一定借鉴。

Study of wide-pulse photon counting polarization lidar to detect shallow water layer(Invited)

Due to the limitation of laser pulse width,traditional lidar cannot achieve shallow water measurement of tens of centimeters.A polarization lidar with dual Geiger-mode avalanche photodiodes(Gm-APD)was designed to achieve high-precision depth image of shallow water layer by using a wide laser pulse.The surface of the shallow water layer was smooth and had good polarization-maintaining characteristics,whereas the bottom surface was rough and had certain depolarization characteristics.According to this feature,by emitting horizontal linearly polarized light,a polarization beam splitting prism was used in the receiving system to separate the front and rear surface signal lights,and then they were detected by two Gm-APDs respectively.The system was not limited by the pulse width of signal light,and made full use of the dead time mechanism of Gm-APD to realize the depth measurement of ultra-thin shallow water.Using the principle of polarization transmission of the Stokes parameter and Muller matrix,the principle of light splitting of the dual Gm-APD polarization lidar was theoretically analyzed.Signal restoration¢er-of-mass algorithm method was used to restrain the range walk error to obtain high range precision.The thin shallow water layer had a gradient from 4.5 cm to 8 cm in depth,and the bottom surface of which was covered with black and white sand.In the experiment,a 6 ns width laser pulse was used to obtain a high-precision depth image of the thin shallow water layer at the detection distance of 5 m with the accuracy of 0.8 cm.This effectively verifies the feasibility of the scheme.This scheme can provide certain reference for the measurement of shallow ocean water layer in in airborne lidar bathymetry systems.