Introduction to project of refractive index measurement in Prague

Refractivity of the atmosphere has significant influence on the propagation of electromagnetic waves. A refractive index measurement project was launched with the following aims: (a) to obtain statistical and dynamic characteristics of the refractive index at various altitudes; (b) to derive parameters usable in planning microwave links; (c) to approach the relationships between actual meteorological situations and potential adverse propagation conditions. Pressure, temperature and relative humidity of the atmosphere have been measured at TV Tower Prague. Data are collected at 3 altitudes and the sampling rate of the measurements is 15 seconds. Time series of these parameters are processed statistically and the refractive index and its gradient, which determines the rate of electromagnetic wave bending, are calculated. Distribution functions and other statistics of all parameters are calculated. These statistical parameters are used for calculations of probability of multipath fading on radio-relay paths. Results are presented of data processed in the first year. Annual and monthly distributions of refractive index and its gradient as well as examples of extreme gradient occurrences are introduced. Based on these distributions, parameters enabling forecasts of radio-relay link performance are given.