Statistical estimation of mean refractive-index structure constant in clear air

Clear air scintillations are usually estimated by use of the refractive-index structure constant C_n², whose value may be evaluated by means of EM remote sensors or by meteorological measurements. Except for a few experiments in carefully controlled conditions, the value of C_n² evaluated by EM sensors frequently differs from those obtained meteorological soundings. In many cases, using radars or satellite links, EM measurements of C_n² in clear air often appear to be appreciably lower than those predicted by using radiosonde data. This may happen because the atmosphere along the radio path is not entirely turbulent and the stable regions do not contribute appreciably to scintillations. The noted difference has been investigated and a statistical treatment of turbulence occurrence has been considered. Taking into account the random behaviour of C_n² during the measurements, estimation of the mean value of C_n ² has been performed