The effect of phase scintillations on the accuracy of phase screen simulation using deterministic screens derived from GPS and ALT AIR measurements

摘要

Radio receivers capable of high-rate sampling such as GPS scintillation monitors and the ALT AIR VHF/UHF tracking radar can measure ionospheric phase fluctuations suitable for scintillation modeling using phase screen techniques. For modeling purposes, the phase variations caused by the refractive effects of electron density irregularities encountered along the propagation path are desired. The phase fluctuations measured by ground-based receivers, however, also include the unwanted effects of diffraction (phase scintillations). In this paper, we investigate the effect of phase scintillations on the accuracy of phase screen simulation when using the phase measured on the ground as a proxy for the ionospheric screen. Using stochastic and deterministic (measured) phase screens, we quantitatively assess the accuracy of this approach by cross-correlating the predicted and measured intensity fluctuations. We find that the intensity cross-correlation is less than unity even in the weak scatter limit, due to the presence of weak phase scintillations. This correlation decreases rapidly with increasing irregularity strength once rapid transitions in the phase (strong phase scintillations) develop. We demonstrate that, when using the measured phase on the ground as a proxy for the ionospheric screen, both the temporal structure of simulated fluctuations and their statistics deviate increasingly from those of the measurements as the turbulence strength increases, especially when strong phase scintillations are present. We also demonstrate that back-propagating the complex signal up to ionospheric altitudes prior to the forward propagation calculation yields improved results, but some errors still remain as a consequence of neglecting amplitude fluctuations which develop inside the random medium.