# A Calibration Method for Time Dimension and Space Dimension of Streak Tube Imaging [PERSON]
## 3 Calibration Method
### Angle Calibration Experiment  
#### 3.2.1 Angle Calibration Experiment  
For the convenience of later expression, the angle calibration experiment was later referred to as Experiment II, and the process of Experiment II is shown in Figure 8.  
A Leica Nova MS60 multistation was used to record the angles at both ends of the laser footprint on the building in the last experiment. To obtain spot-shaped light more conveniently, we needed an auxiliary laser to perform the experiment, and the laser of lidar  
Figure 6: The average of all centroids under the same delay.  
Figure 7: The centroid curves under different delays.  
was not turned on. Afterward, the laser beam was formed into a point shape and reflected onto the target by a mirror fixed on a rotating platform. The path of laser is shown by the green arrows in the figure; the red arrows indicate the direction of rotation of the mirror, the direction of light spot movement caused by rotation, and the order of streak pattern generation; while the yellow arrows indicate the change of the delay of sweeping voltage and the resulting position change of the streak signals in the images. The laser spot was moved from top to bottom, step by step, on the building along the lineation of the laser footprint of the last experiment by rotating the reflecting mirror, and during this process, the Leica Nova MS60 was used to record the current angle of the laser spot for each step of angle change. In every rotation, the delay time of sweeping voltage should be changed step by step to move the point-shape streak signal from one edge of the image to another edge. The angle change step in this experiment was 0.1 degrees, and the delay change step was 10 ns.  
In the experiment, relative to the distance of the building, the Leica Nova MS60 had to be close enough to the lidar so that the error introduced by different positions of the multistation and lidar could be ignored; otherwise, it had to be eliminated through coordinate transformation between the coordinate system of the total station and the coordinate system of the lidar.  
Under the same delay and angle, we recorded 2000 images to take the average and reduce the influence of jitter. This jitter was mainly imaging jitter in the space dimension, which was different from the previous experiment, where the jitter in the previous experiment was mainly imaging jitter in the temporal dimension. We calculated the centroid of every image and obtained the average value of the centroid under the same delay and angle; thus, more accurate angle information of the signal could be obtained based on its position on the image.  
The time calibration information was also included in the data of Experiment II. The purpose of conducting Experiment I was to show that the light source used in Experiment I was the laser of lidar and that the coordination of the time sequential between the detector and the laser was better than that between the detector and the auxiliary laser in Experiment  
Figure 8: Angle calibration experiment.  
II. Therefore, the time accuracy of Experiment I was better. If the data from Experiment II had been used for time calibration, there would have been a significant error. As evidence, we calculated the standard deviation of two experiments, with Experiment 1 being 0.84 ns and Experiment 2 being 2.52 ns.