The two-frequency coherence function for the fluctuating ionosphere: Narrowband pulse propagation

This article presents a detailed numerical investigation of the two-frequency coherence function for HF wave propagation in the fluctuating ionosphere. Earlier published expressions for the coherence function are transformed to a form suitable for numerical calculation and employed in a study with an empirical plane stratified background ionosphere and a power-law spectrum of the electron density fluctuations. Our results show that the coherence function in general has a rather complicated behaviour and that it does not fall off quickly with increasing difference frequency. Under these circumstances, the case of wideband pulses require particular considerations which are presented in the companion article. The case of narrowband pulses is considered in detail and in that case the fluctuations have some influence on the pulse distortion, especially compared with the regular dispersion caused by the smooth background. They cause pulse stretching and sometimes affect the pulse amplitude through diffraction. (C) 1997 Elsevier Science Ltd.