Abstract

This paper is dedicated to study chirped pulse scattering by spherical water drops. Generalized Lorentz-Mie formulae¹ are used to calculate the efficiencies of extinction and backscattering when a chirped pulse is scattered by spherical particles. Gaussian pulses of different linear chirps(b) with a constant pulse filling coefficient(l₀=1.98) have been studied. The calculation illustrated that chirped pulse scattering shows much different peculiarities from carrier wave scattering(Fig.1). The slowly-varying background of the extinction and backscattering curves is damped by the chirp, and when the pulse is deeply chirped, the maxima and minima of the background curves reduce to disappear and the efficiency curves illustrate a step-like dependence on the sphere size. Using the Fourier theorem, we also studied the temporal dependence of the scattered intensity and the pulse distortion(Fig.2). The pulse chirp affects the scattered pattern definitely for moderate and large particle size. Multi-secondary pulses are generated because of the pulse chirp and even sub-secondary pulses will occur if the incident pulse is deeply chirped. The pulsewidths of the scattered secondary and sub-secondary pulses are shorter than that of the incident pulse. The scattered intensity and pulse wave form are dependent on the sign of the pulse chirp but the efficiencies of extinction and backscattering seems blindness which depend only on the amount of the chirp regardless of up-chirp or down-chirp.

© 1996 IEEE