When using Geiger mode Avalanche Photo Diode (Gm-APD) array lidar for long-distance imaging, the few echo photons make it challenging to get the target position. To solve these problems, this paper proposes a spatial correlation extraction algorithm combined with morphological filtering (SCMF), which uses the spatial correlation of the target to superposition the weight of the pixel histogram, increasing the number of statistical frames, improving the signal-to-noise (SNR) of pixel statistical data and accurately extracting the distance value of the target pixel. Spatial correlation also improves the real-time imaging of the system. According to the time-domain spatial dispersion characteristics of residual noise pixels of small intensity threshold, a local spatial distance correlation logic method is proposed, which only preserves the pixel groups with similar spatial distances and removes the stray background noise pixels. Because the number of pixels in the target pixel group is more than the noise group, a spatial filter module is constructed using morphological filtering to remove the remaining blocky noise group and preserve the target pixel group. The proposed method can achieve long-distance imaging in 0.02s acquisition time through outdoor real imaging experiments. Under the echo condition of 0.0152 Signal to Background ratio (SBR), the SCMF method has 76% target restoration, and the reconstructed image SNR can improve 23 times compared with the peak-picking method, a great improvement has been made in the reconstruction of image denoising.
In recent years, the array Geiger-mode avalanche photodiode (Gm-APD) has become a research hotspot in the world due to its advantages of detection sensitivity, spatial resolution and range resolution. A set of 1064 nm laser active imaging experiment platform is built with the core device of 256×128 pixel domestic self-developed InGaAs material Gm-APD. The data of 500m and 350m targets in external field are obtained, and the three-dimensional distance image, intensity image and photon counting image are reconstructed by using single photon echo signal detection method. Through the experiment, the range resolution of the detector is 0.3m, and the contrast of the photon count intensity image are larger than the intensity image. It is proved that the self-develop array Gm-APD detector with 1064nm lase has good performance, and it can demonstrate the field laser active imaging function, which lays a good research foundation for future practical application.
In the military and civil fields, detecting small aircraft is of great significance. In recent years, the rapid development of LiDAR technology has made it possible to detect small aircraft at long distances. However, the scale change and attitude change make the detection difficult. Therefore, a detection network of multi-attitude small aircraft based on LiDAR anchorfree is proposed in this paper. The network structure is improved on the basis of the CenterNet network; using the encoder-decoder network structure, the extended convolutional module is designed to improve the receptive field and obtain the multi-scale information of the object. The IOU sensing branch is added to the detection header of the network to improve the localization accuracy of the object. The experimental results show that the detection accuracy of the improved network on the self-built simulation data set is 2.12% higher than that before the improvement and finally reaches 92.45%. Therefore, using this method can effectively improve the detection accuracy of the object.
Limited statistical frame number and strong backscatter interference from smoke result in a photon-starved regime, severely limiting the depth imaging capability of array Gm-APD lidar in smoky environment. Here, we propose a depth image estimation algorithm that can significantly improve the integrity of targets in dense smoke environments when signal photons are starved. At the signal level, the algorithm improves the accuracy of extracting signal photons by constructing multi-scale superpixels. At the image level, using edge information of depth images at different scales to guide and fill the original scale depth image achieves efficient noise reduction and improves target integrity. It has been successfully demonstrated under different attenuation lengths and statistical frame numbers. Compared with other state-of-the-art methods, the proposed algorithm has maximum target recovery and structural similarity, especially for the attenuation length (AL) is 3.6 and statistical frame number is 1500 (imaging time is 75ms). This study is of great significance for the fast depth imaging of dynamic targets by array Gm-APD lidar in dense smoke environments.
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