蓝绿激光雷达进行水下目标探测成像时，由于受到后向散射噪声影响，图像信噪比随着距离增大而急剧下降。为解决此问题，通过分析水下目标图像噪声污染，提出一种图像预处理算法，通过在频域进行噪声抑制及改进型巴特沃斯高通滤波等处理，能够实现目标复原，提高图像信噪比。以自研的条纹管激光雷达完成室内水池水雷探测成像实验，分别对5 m和15 m水下水雷目标激光强度像进行频域预处理。结果表明，提出的算法能有效滤除后向散射噪声，提高图像对比度，获得较为清晰的目标轮廓像。

Image signal-to-noise ratio (SNR) will be reduced with the range increasing because of the influence of backscattering noise when blue-green laser radar is detecting and imaging underwater target. In order to solve this problem, by analyzing the noise types for the underwater target image of the laser radar, an algorithm of image pre-processing is presented, which includes the noise suppression in frequency domain and the improved Butterworth high-pass filters. The pre-processing algorithm can realize the image restoration, and improve the image SNR. The experiments of detecting and imaging the mine in indoor pool are carried out with the streak tube imaging lidar. The algorithm is used for the intensity image of the 5 m and 15 m underwater mine. The results show that the pre-processing algorithm can effectively suppress the backscattering noise of water. The contrast of image is improved. The clear object contour is obtained.