A range accuracy of 3 mm obtained in STIL system
Schematic of the STIL system. 3D rendered depth images of a fist model from a stand-off distance of 10 m with time bin size of 0.07 ns. Insets: photographs of the targets from different viewpoints (left) and plots of the corresponded depth data (right).
Streak tube imaging lidar (STIL) has attracted considerable attention in recent years because of its high range accuracy, high sensitivity, and wide field-of-view (FOV). This technique has been widely applied for target identification and DEM mapping.
The group led by Prof. Deying Chen, from Harbin Institute of Technology, investigates the effect of time bin size on the range accuracy of the STIL system and improves the accuracy of 3D depth images by using an optimal time bin size. The details of the study are reported in Chinese Optics Letters, Vol. 14, No. 2, 2016 (G.C. Ye et al., Effect of time bin size on accuracy of streak tube imaging LIDAR).
The STIL system employed a streak tube camera as the detector, which separates the signal captured along the vertical direction, according to the different arrived times of the target return. Then, a 3D image can be reconstructed from multiple pulses by scanning the scene with a 1D laser fan beam. The theoretical analysis shows that the range accuracy can be improved by decreasing the time bin size based on the peak detection algorithm.
In this study, a modified analytical estimate of the STIL system played a significant role in the analysis of the range accuracy and finer millimeter-scale 3D images were obtained using the improved STIL system. 3D images with different time bin sizes were compared, and the relationship between the range accuracy and the time bin size was established. The finest range accuracy of 3 mm has been obtained using a small time bin size of 0.07 ns. This indicates that a smaller time bin size can help improving the range accuracy.
Prof. Rongwei Fan believes that it is noteworthy that the smaller time bin size will result in a narrower range gate. Therefore, an adequate range gate for the required target should be guaranteed before choosing the optimal time bin size. In the further work, the group will perform research on how to determine the best time bin size when the depth of field is known, and will carry out an outdoor experiment to illustrate the theory at a long stand-off distance.
条纹管成像激光雷达距离误差可减小至3mm
图片说明：实验验证示意图，实验室内对10 m外的目标进行距离成像，时隙尺寸为0.07 ns。成像结果中第一列为不同角度的目标照片，第二列为与之对应的距离像。
条纹管成像激光雷达（STIL）具有高精度、高灵敏度、大视场角等优点，近年来成为激光雷达领域的热门研究课题，并广泛应用于目标识别和高程测绘等领域。
哈尔滨工业大学的陈德应教授课题组通过改变时隙尺寸进一步降低STIL的测距误差，并建立时隙尺寸与测距误差之间的理论关系模型。相关研究结果发表在Chinese Optics Letters 2016 年第2 期上 (G.C. Ye et al., Effect of time bin size on accuracy of streak tube imaging LIDAR)。
STIL系统采用条纹相机将不同距离目标的时域回波信号在空间上展开，进而配合一维线扫描平台实现三维成像。理论分析表明，基于峰值检测算法情况下，减小时隙尺寸则距离误差也相对降低，且二者呈线性关系。
该研究提出了一种改进的条纹管成像激光雷达误差评价模型，基于该模型改进后的STIL系统能够实现毫米级的距离成像。通过实验对比了不同时隙尺寸参数下STIL的三维成像结果，并且建立了二者之间的关系模型。在最优时隙尺寸为0.07 ns情况下获得了最佳距离误差为3 mm的距离像。研究结果表明，减小时隙尺寸可以降低距离误差。
该课题组的樊荣伟教授认为，在通过减小时隙尺寸降低距离误差的同时，还需要保证雷达系统具有足够的距离门宽。所以，下一步的工作将主要集中于研究如何在已知目标景深的情况下确定最佳的时隙尺寸，并在外场条件下对该理论做远距离的实验验证。