Scintillation modeling with random phase gradient screens

Abstract

Multiple studies of scintillation phenomena have shown that, in certain situations, the intense phase fluctuations of trans-ionospheric radio signals are associated with the scattering on strong electron density gradients. The present study provides a theoretical framework for modeling such types of phase fluctuation events. Using the geometrical-optics approximation and retaining the second-order smallness correction in the expansion of the eikonal function, we relate the phase of the transmitted wave not only to the total electron content (TEC) of the ionosphere but also to the spatial gradient of the TEC. The considered correction term is related to the random refraction of signal rays on large-scale ionospheric structures, an effect, that becomes significant in the presence of strong electron density gradients. To conveniently simulate the wave propagation under such conditions, we propose the random phase gradient screen algorithm. For this purpose, we use the novel spatial electron density gradient product (NeGIX) based on in-situ observations of the Swarm Langmuir probe and ground-based TEC and TEC gradient observations. To illustrate the performance of the algorithm, we apply it to simulate a scintillation event over Europe and in the low-latitude region and compare the simulation results with scintillation indices, measured from GNSS ground observations. We show that in regions of the ionosphere where spatial ionospheric gradients are large, the phase gradient method shows better agreement with the observed scintillation levels than the conventional phase screen approach.