Effect of plane target characteristics on ranging distribution for pulse laser detection

Abstract

Laser proximity fuze is a kind of active detecting system which has been extensively equipped in both conventional and guided missile ammunitions. It uses a pulsed laser for detecting and ranging a target, accurately providing information about target angle and distance. The system emits a short pulse of laser beams which come into contact with the target and receives the light scattered back. After transducing light into electric signal, target range could be obtained with proper signal processing technique. The width and amplitude of the echo could vary if targets are of different characteristics, which leads to distributed target ranging results. Therefore, a better understanding of the relationship between target characteristic and ranging distribution can increase the precision of the pulsed laser proximity detecting system.In this paper, the emitted laser is modeled as a Gaussian pulse. The corresponding impulse response equation and echo equation of the pulsed laser for the planer target are derived. Considering the echo broadening effect, relative broadening ratio is determined from the echo equation. Then the relationships between the echo broadening coefficient and the parameters of tilt angle of planar target, laser divergence angle, and laser pulse width are analyzed. The results show that relative broadening ratio increases with the increase of the tilt angle of planar target or laser divergence angle, and decreases as the laser pulse width decreases. Based on the echo equation of pulsed laser and constant threshold leading edge detection, the probability density function of the planar target ranging is derived analytically. The influences of changing parameters of tilt angle of planar target, power of emitted laser, laser divergence angle, and threshold-to-noise ratio（TNR) on statistical ranging distribution are simulated.Monte Carlo simulation is performed for the whole waveform ranging experiment. The pulsed laser ranging platform is built and 20 m ranging experiment is conducted. The result shows that the ranging probability density distribution from Monte Carlo simulation is close to that from the experiment. As the tilting angle of target increases, ranging mean and variance both increase. When the tilting angles are 0, 20, 40 or 60, the signal-to-noise ratio（SNR) is larger than the TNR, and the ranging distribution is Gaussian. When the tilting angle is 70, the SNR is smaller than the TNR, and the ranging distribution is distorted with a longer rising edge and a shorter falling edge from the original Gaussian profile. This study could provide theoretical basis for the research of the ranging distribution of pulsed laser detector with the consideration of target characteristic.