We have developed two range gating laser imaging systems, which base on modulated gain method and centroid algorithm respectively. The system based on centroid algorithm uses a pulse laser as transmitter and CCD with image intensifier, through delaying gated receiver repetitiously to acquire a series of 2D time-slicing image to restore the three-dimensional rang image. The imaging system based on modulated gain mainly adopts the same pulse laser is used and CCD with image intensifier with constant and modulated gain over time, which can capture two different intensity images of echo pulse respectively in order to restore the three-dimensional range image. We conduct a series of experiments with the tow system, and the results are consistent with the actual practical ones. By comparing result of laser imaging based on the two systems, we summarize the different strength and weaknesses, requirements, and challenges to lay a solid foundation for later experiments.
Gain modulation imaging technique is one of the prominent schemes for scannerless lidar. By controlling the gate width, it’s easy to suppress backscatter noise and make the image more accurately. Imaging range and accuracy of gain modulation laser imaging become a research focus at present. According to the principle of imaging, the signal energy and the noise energy reaching the imager can be found. Further signal-to-noise ratio can be obtained. Previous theoretical models consider only linear gain condition. However the influence of laser pulse width and other factors are less taken into consideration. These models will have a certain deviation with the actual one. By simulating the nonlinear gain with consideration of the laser pulse width and lambert spherical radiation, more accurate SNR model of gain modulation laser imaging is obtained. On this basis, the established SNR model can be used to estimate the experimental distance with good imaging effect. It provides the theoretical basis for subsequent experiment system parameter selection and image processing.
A range gated laser imaging system has been designed and developed for high precision three-dimensional imaging. The system uses a Nd:YAG electro-optical Q-switched 532nm laser as transmitter, a double microchannel plate as gated sensor, and all the components are controlled by a trigger control unit with accuracy of subnanosecond. An experimental scheme is also designed to achieve high precision imaging; a sequence of 2D “slice” images are acquired in the experiment, and these images provide the basic data for 3D reconstruction. Basing on the centroid algorithm, we have developed the 3D reconstruction algorithm, and use it to reconstruct a 3D image of target from the experimental data. We compare the 3D image with the system performance model, and the results are corresponding.