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abstract
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TROPOSPHERIC EFFECTS(CLOUD ATTENUATION) ON SIGNAL TRANSMISSION

Abstract:

This report describes model simulations of a new approach to measuring atmospheric liquid water and solid water for use in operational weather forecasting and weather and climate research and also to finds its effect on earth-space propagation. The approach involves using the Salonen model on radiosonde data provided by the British Atmospheric Data Center (BADC), U.K. Results are presented from radiosonde data in Indian region over one- year period.

Introduction TROPOSPHERIC EFFECTS:

Microwave and millimetre signals are attenuated when traversing through the atmosphere due to the effects of precipitation, clouds and atmospheric gases. The precipitation effects are generally most severe in satellite communications, but the frequent presence of clouds causes attenuation for a larger proportion of time. The cloud attenuation becomes increasingly severe for low margin systems operating at the bands of 30/20 GHz and 50/40 GHz. Water vapour, cloud liquid water and solid water are the critical factor in determining attenuation in the earth’s atmosphere at millimetre wavelengths, as well as playing an important role in global climate system. Therefore, it is important that the amount of water vapour, cloud liquid and solid water in the atmosphere is correctly quantified. Previous radio wave propagation studies, below 50 GHz, have concentrated on the effects of rain on satellite-earth links, where it is the dominant cause of attenuation. Above 50 GHz, oxygen, water vapour and cloud have a significant impact on propagation, and also the effect of rain is very prominent. Particularly absorption band for oxygen molecules occurred at 60 GHz and 120 GHz. Since water vapour has a continuous presence in the atmosphere and clouds have a much greater occurrence than rain, it is important that impacts of both cloud and water vapour are properly investigated. For water vapour particles 23 GHz and 180 GHz are the two absorption bands in microwave and millimetre wave frequency band. Much work has been done on the statistics of rain effects, but the statistics of cloud effect are relatively unknown. A new calculation method (Salonen Model) is approached for cloud attenuation using vertical profiles of temperature and humidity as input parameters that can be calculated using radiosonde data.