Abstract :
Measurements have been made of the angular propagation noise and amplitude scintillations on a 15km overland path at 1° elevation in northern England. They indicate r.m.s. deviations in angle of arrival ranging between 1" and 10" (4.8¿48¿rad) for aerials of 2m aperture during one year\´s observations. The propagation noise (short-term angle-of-arrival fluctuation) spectrum falls rapidly with increasing frequency and is negligible at frequencies above 1 Hz for this aerial aperture. Little correlation is apparent between the magnitude of the effects and changes in atmospheric humidity, but the r.m.s. level is approximately proportional to mean air temperature (in degC). Autocorrelation analysis on a single path, and crosscorrelation analysis on two adjacent paths, indicate a mean scale of turbulence of about 15m for an inclined path extending from 5 to 300m above the surface. Amplitude scintillations of the received signal give a similar power spectrum to that of angular propagation noise, and a general level of power change of the order of 0.1 dB is observed. The results are similar to those obtained by workers in the USA, and are in fair agreement with theory, although the scarcity of information on atmospheric-turbulence parameters at heights below 300m, and the use of an inclined path, make accurate comparison with theory difficult.
