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7 August 2015 The influence of laser spot size on the micro-Doppler spectrum
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Abstract
Micro-Doppler effect, which is induced by micro motion of target or any structure on the target, is a frequency modulation that generates sidebands about the target’s Doppler frequency shift, such as mechanical vibration or rotation.

When a target’s motions incorporate micro motions, the radar echo signal will contain micro-Doppler characteristics related to these motions. Therefore, the micro-Doppler effect provides a new approach to obtain the dynamic properties of targets, which can be used to accomplish the detection and identification of targets, such as the identification of different types of helicopters.

Scattering of the laser spot from a target surface modulates the Doppler signal, causes broadening of the signal spectrum, and, adds uncertainty to the signature analysis. A mathematic model of cone spin, which is a typical micro motion, is built first in this paper. Furthermore, an analyzed equation is deduced to predict the micro-Doppler spectral broadening of acquired medium current signals in situations of different laser spot size. It is found that the beam spot size on the target affects the resulting spectral broadening.

Finally, an experiment based on the scaled model is performed to verify the simulation. A narrow-linewidth single frequency fiber laser is employed to detect the cone target at different laser spot size by coherent detection with constant detect distance and laser power.

The experimental result shows that the beam spot size on the target affects the resulting spectral broadening caused by speckle, which corresponds to the simulation result. The experimental broadening was consistently greater than the theoretical broadening due to other effects that also contribute to the total broadening.
© (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Dehua Zhang, Haiyang Zhang, Zheng Zheng, Hongzhi Yang, Changming Zhao, and Suhui Yang "The influence of laser spot size on the micro-Doppler spectrum", Proc. SPIE 9623, 2015 International Conference on Optical Instruments and Technology: Optoelectronic Measurement Technology and Systems, 962305 (7 August 2015); https://doi.org/10.1117/12.2193431
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