霧中を伝搬するレーザ送信ビームの広がりの伝達関数の測定とその伝達関数を用いたビーム伝搬解析

Abstract

In a past study, we developed a laser radar system for estimating slant visibility, which is the visibility along the glide path of an airplane and proposed the new laser radar equation, considering the divergence of the transmitting laser beam in bad weather conditions, like rain, fog and snow, in order to obtain the exact slant visibility in various weather conditions. This equation corresponds well to practical data and estimated visibilities coincide well with actual ones in various weather conditions.In the present study, to confirm the appropriateness of the new laser radar equation, the scattering angle characteristics of a laser beam propagating through fog is measured by using an optical Fourier transform system and an artificial fog generator. As a result of this experiment, the spatial spread functions of broadening of the forward beam caused by the fog scattering are derived from the obtained data as angle distribution.Using these spread functions, the analysis of broadening of a laser beam propagating through fog in laser radar operation using a computer. This computer analysis reveals the alternation of the pattern of the transmitting laser beam through fog. As a result, broadening and scattering characteristics of the transmitting beam in foggy condition were found and the spreads of transmitting beam derived from the calculated results well explain the concept of the new equation.The analyzed results compared well with practical data for laser radar. And the slant visibilities derived from the analyses well coincided the actual ones.