Study on near infrared radiation attenuation based on distribution database of raindrops

In order to study the attenuation of near infrared radiation by rainfall and quantitatively estimate the effects of rainfall on near infrared devices, on the basis of the establishment of two-element function model of raindrop distribution, a method for establishing the database of raindrop distribution was proposed. After the fitting of raindrop distribution data measured by LAWS and PARSONS in Washington region of the United States, raindrop distribution database was established. And then, combining with Mie scattering theory and attenuation coefficient formula, the relationship curves between extinction efficiency factor and raindrop diameter under 1μm, 2μm and 3μm wavelength near infrared radiation were obtained. Under the condition that rainfall was respectively 0.25mm/h, 1.25mm/h, 2.5mm/h, 12.5mm/h, 25mm/h and 50mm/h, the attenuation coefficients of near infrared radiation were calculated. The results show that, under different rainfall conditions, normal distribution has better fitting effect on function relation of raindrop spectral distribution. The envelope of extinction efficiency curve increases with the increasing of wavelength. After the fitting of function relation between attenuation coefficient and rainfall intensity, it is found that, the exponential function has the good fitting effect. The calculated results are important for studying the attenuation of near infrared radiation by rainfall.