Comparison of simultaneous atmospheric attenuation measurements at visible light, mid-infra-red (3¿5¿m) and millimetre waves (94GHz)

In this paper we give a review of measurements through the atmosphere of 94 GHz attenuation, mid-infra-red (3¿¿m) and visible wave transmittances. The relationships between these quantities are given as a function of meteorological parameters. In rainshowers the theoretical predictions, based on Mie scattering theory, are in good agreement with the experimental results. During these showers the excess attenuation due to rain is the same for infra-red and visible light. The relationship between infra-red and 94 GHz attenuation depends on the type of shower. Almost the same results are found in snow-and wet snow-showers, except that 94 GHz waves are less affected by snow than infra-red waves and visible light. (Snow: not melting, and air temperature between 0 and 2°C; wet snow: melting snow). During fog, visible light and infra-red are seriously affected, whereas 94 GHz attenuation has been increased only slightly.