When detecting moving targets via photon counting Lidar, the target information contained in the echo photon statistical histogram is distorted, because the target position in a cumulative time changes. To solve the above distortion, this work proposed a method of acquiring moving target structural characteristics from the photon echo statistical histogram via waveform processing. Firstly, the probability distribution model of photon detection echo corresponding to a moving target was established. Then, the mathematical expressions of the laser radar cross section (LRCS) and depth structure corresponding to a moving target were derived by utilizing the photon waveform correction and waveform fitting filtering. Finally, the structural characteristics of a multi-layer moving target with a speed of 20m/s at 10km were obtained. Under the condition of SNR (signal-to-noise ratio) being 1.48, to detect a multi-layer moving target composed of two sub-targets with 0.5×1m, between which the distance was 0.5m, when the detection time was 0.01s (i.e., the cumulative number was 300), the consequential LRCS was 1.009m², and the ratio of LRCS within the moving target was 0.967:1. Meanwhile, the depth within the sub-targets was 0.493m, whose error was less than 0.7%. The proposed method in this work provided theoretical support for the acquisition of moving target detail information and the recognition of moving targets.
With the development of extinction materials, various materials suitable for smoke are widely used. Smoke is essentially composed of solid aerosol. The extinction properties of aerosol are affected by diffusion characteristics. Aerodynamics is used to describe the motion of aerosol particles. Normal 𝑘 - 𝜀 model and DPM model are used to simulate aerosol diffusion process in outdoor environment. The diffusion law of aerosol under different wind speed is analyzed. Distribution characteristics of aerosol mass concentration is studied. Combined with Lambert-Beer law, the effective infrared extinction area of aerosol is calculated. The result shows that the wind speed play an important role in aerosol diffusion in the initial state. When the wind speed is near 1m/s, aerosol can diffuse steadily, and the extinction area will show a trend of rise. In addition, the area of effective concentration will not decrease too fast, but will show a trend of slow rise and begin to decline after 30s.
A multilayer structure of microbial cells can result in multiple attenuations of electromagnetic waves, making the biological particles have a strong extinction ability. However, the influence of various morphologies on infrared band optical extinction performance of biomaterials is unclear. The combination of shape, dimension, and structure parameters is proposed to evaluate and enhance the optical extinction properties of artificial bioparticles. Combined with the preliminary work of our research group, four artificial biological particles were selected to simulate and calculate their extinction performance with different parameters theoretically based on the discrete-dipole approximation method. The results show the extinction properties of bioparticles with different shapes and dimensions in the 3.0 to 5.0 μm and 8.0 to 14.0 μm wavebands. It was found that the chain-shaped particles with more constituent spheres and a bending angle of 60 deg as well as the ellipsoid-shaped particles with an axis ratio of 1:2 exhibit better extinction properties in the above two bands. Among them, the regulation of extinction efficiency can reach ∼13.92 % and 18.16%.
For detecting long-distance moving aerial targets, in order to solve the problem of low accumulation times and weak echo signal, this work proposes a multi-beam staring photon detection method. Firstly, the photon waveform expression of multi-beam staring photon detection is deduced. Then, the relationships between divergence angle, pulse width, single pulse energy, laser repetition frequency and photon probability distortion are discussed. Finally, the method of calculating the system transmitter parameters is obtained. The results show that when the detection target is the F22 flight with a speed of 400m/s at a distance of 10km, the number of beams is set to 40, the launch angle is set to 2mrad, the pulse width is set to 1ns, and the single pulse energy is set to 0.5μJ at the transmitting end. The research results provide a theoretical basis for the system design and realization of long-distance and fast-moving aerial targets.
The space environment is becoming increasingly complicated; therefore, precise detection and identification of space targets are critical to preserving space security. Compared to optical and radar imaging, obtaining space target information using laser echo waveform is more efficient for detection. Based on the skew-normal distribution decomposition, the connection between sub-echoes and target scale following the decomposition of the space target pulse laser echo waveform is explored, and an inversion approach is suggested to identify the scale information of the solar panel utilizing the intersection of skewness and kurtosis contours in the coordinate system of the variables to be solved, based on the high-order moment characteristics of waveforms such as skewness and kurtosis. Using the proposed method, we realized the scale inversion of a 60-cm solar panel of a cube satellite inclined at 45 deg, with the turntable and the detection system placed 80 m apart. The results show that the skewness and kurtosis of the decomposed echo can represent the target size information, and the approach used here can successfully extract the solar panel scale information of a typical satellite, providing methods and data support for space target detection and classification.
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