Signal Fluctuations in Long-Range Overwater Propagation
Abstract
Measurement of overwater propagation in the Pacific on 3 and 9 cm between airborne transmitters and fixed receivers are reported. Within the horizon, the direct and surface- reflected rays formed the usual interference patterns. Beyond the horizon, the 3-cm signal always behaved in general accord with normal-mode theory, the attenuation rate averaging 0.5 + or - 0.2 decibels per (nautical) mile. In roughly the first thirty miles past the horizon, the 9-cm signal had a height-gain and an exponential decay rate (0.9 to 1.9 decibels per mile), both reasonably dependent on measured duct strength. On 9 cm only, all greater ranges comprised a "turbulent region" where a new, lower attenuation rate prevailed, averaging 0.17 + or - 0 .05 decibels per mile, and where there was no average height-gain. Turbulent-region signals were approximately Rayleigh-distributed and the autocorrelation of their fluctuation vanished in, at most, 1.5 seconds. The turbulent-region signal undoubtedly was due to scattering by some high-altitude atmospheric mechanism.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 17, 1950
- Accession Number
- AD1214355
Entities
People
- M. Katzin
- W. S. Ament
Organizations
- United States Naval Research Laboratory