The Atmospheric and Target Modulations of the Lasers
During the receiving and emitting of lasers in laser imaging, the interactions among atmosphere, targets, and the lasers, namely, the atmospheric and target modulations of the lasers, directly influence the waveform characteristics of the targeted laser e
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The Atmospheric and Target Modulations of the Lasers
During the receiving and emitting of lasers in laser imaging, the interactions among atmosphere, targets, and the lasers, namely, the atmospheric and target modulations of the lasers, directly influence the waveform characteristics of the targeted laser echoes. As a result, various subsequent processes such as information and data acquisition, data processing, image generation, feature extraction, classification and recognition are directly or indirectly influenced. By taking the mechanism of the target detection based on a laser imaging system as the object, this chapter explores the atmospheric and target modulations of lasers. This chapter mainly studies the concepts and characteristics of the atmospheric and target modulations of lasers, the characteristics of the energy and signal modulations, and the influences of the atmospheric and target modulations.
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The Concepts of the Atmospheric and Target Modulations of Lasers
The link of the target detection based on a laser imaging system is usually composed of a system platform, a laser source, the atmosphere, a laser imaging sensor, a GPS, an attitude measurement unit, a data acquisition and processing system, an image generation system, a feature extraction system, a classification and recognition system, a detection and location system, etc. The block diagram of the signal and data link for the target detection based on a laser imaging system constituted by the aforementioned parts is demonstrated in Fig. 2.1. As demonstrated in the link shown in Fig. 2.1, the laser signals radiated by the laser source are expected to experience complicated interaction with the matters in the atmosphere while passing through the atmosphere. Meanwhile, the incident lasers on the target are expected to interact with the target, while the reflected lasers cannot reach the laser imaging sensor unless passing through the atmosphere. © National Defense Industry Press, Beijing and Springer Nature Singapore Pte Ltd. 2018 Y. Hu, Theory and Technology of Laser Imaging Based Target Detection, DOI 10.1007/978-981-10-3497-8_2
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2 The Atmospheric and Target Modulations of the Lasers
Fig. 2.1 The signal and data link for the target detection based on a laser imaging system
Therefore, while carrying out the target detection using laser imaging, laser signals require to contact and interact with the atmosphere and target respectively, so that they can be modulated. The atmosphere is comprised of various gases and suspended impurity particles of various sizes, which show different components and chemical properties. When lasers propagate from the laser source to the targets, they are expected to interact with the gas molecules and particles in the atmosphere, which gives rise to the absorption, scattering, reflection, diffusion, refraction and diffraction phenomena. As to the main influences: (i) the selective absorption of several gas molecules in the atmosphere for the lasers leads to the attenuation of the radiation intensity
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