Improvement of range accuracy of range-gating laser radar using the centroid method

Streak tube imaging lidar with kilohertz laser pulses and few-photons detection capability

Lidar using active light illumination is capable of capturing depth and reflectivity information of target scenes. Among various technologies, streak tube imaging lidar (STIL) has garnered significant attention due to its high resolution and excellent precision. The echo signals of a STIL system using single laser pulse are often overwhelmed by noise in complex environments, making it difficult to discern the range of the target. By combining high-frequency laser pulses with the repetitive sweep circuit, the STIL system enables efficient detection of few-photons signal in weak-light environments. Additionally, we have developed a robust algorithm for estimating the depth and reflectivity images of targets. The results demonstrate that this lidar system achieves a depth resolution better than 0.5 mm and a ranging accuracy of 95 um. Furthermore, the imaging of natural scenes also validates the exceptional 3D imaging capability of this system.

Speed Measurement of the Moving Targets Using the Stepping Equivalent Range-Gate Method

In this paper, we proposed a stepping equivalent range-gate method (S-ERG method) to measure the speed and the distance of the moving target for range-gated imaging lidar. In this method, the speed is obtained by recording the time at which the moving target passes the front and back edges of the range gate, the distance information can also be obtained by the front and back edges of the range gate at the same time. To verify the feasibility of this method, a stationary target and a moving target with different speeds were measured by the S-ERG method. By using the S-ERG method, we not only obtained the distance information of the stationary target and the moving target at the front and back edges of the range gate, respectively, but also obtained the speed of the moving target. Compared to speeds measured by rotational displacement sensors, the speed measurement error of the S-ERG method is less than 5%, whether the target is far away or close to the range-gated lidar system, and this method is almost independent of the delay step time. The theoretical analysis and experimental results indicate range-gated imaging lidar using the S-ERG method has high practicality and wide applications.

Range resolution modeling for 3D gated range-intensity correlation imaging based on a statistical theory

This paper systematically establishes a range resolution model for 3D gated range-intensity correlation imaging (GRICI) based on the law of error propagation and statistical theory, and especially takes the high-repetition frequency characteristic of 3D GRICI into consideration. The model can theoretically guide the setting of the GRICI system parameters to obtain a higher range resolution compared with existing modeling methods. This paper also verifies the correctness of the proposed model through simulation and experiments, and quantitatively analyzes the influence of the accumulated pulse number in a single frame. In addition, the range resolution for our 3D GRICI system is measured under the guidance of the proposed model, and it reaches the millimeter order.

Bayesian reconstruction method for underwater 3D range-gated imaging enhancement

We investigate a systematic improvement for 3D range-gated imaging in scattering environments. Drawbacks including absorption, ambient light, and scattering effect are studied. The former two are compensated through parameter estimation and preprocessing. With regard to the scattering effect, we propose a new 3D reconfiguration algorithm using a Bayesian approach that incorporates spatial constraints through a general Gaussian Markov random field. The model takes both scene depth and albedo into account, which provides a more informative and accurate restoration result. Hyper-parameters for the statistical mechanism are evaluated adaptively in the procedure and an iterated conditional mode optimization algorithm is employed to find an optimum solution. The performance of our method was assessed via conducting various experiments and the results also indicate that the proposed method is helpful for restoring the 2D image of a scene with improved visibility.

Multipulse gate-delayed range gating imaging lidar

We present a technique to reconstruct a higher resolution of depth map of range gating imaging lidar by applying the delays of the gates to a typical range gating lidar system during the detection of each returned laser pulse with the encoding of the returned signal. With the consequent delays of the gate, the depth of the scene is extended accordingly. A multipulse gate-delayed range gating lidar system is designed to prove the resolution improvement from 6 to 1.5 m. The unchanged peak power of the laser, the widths of the laser pulse and the sampling period result in a simple structure of the lidar system.

Varied threshold with laser flight time in scannerless range-gated ladar

We present a method based on maximum-likelihood estimation to calculate the threshold of the number of converted photoelectrons according to Poisson and Gaussian statistics. The calculations for detection and false-alarm probabilities are given including a proposal of error probability. An efficient approach of setting threshold according to laser flight time is discussed as the laser power decreases in propagation. Comparison of the fixed threshold and the varied threshold in Poisson and Gaussian statistics is provided. The varied threshold approach tends to keep the error probability at the lowest level. This varied threshold approach is found to have a similar effect on ranging accuracy as a threshold-fixed approach.