Simulation of GPS radio occultation signals through Sporadic-E using the multiple phase screen method

Abstract

A phase screen simulation experiment is designed to model radio occultation signals through sporadic-E layers for a GPS transmitter operating at the L1 (1575.42 MHz) frequency. A series of simulations is performed for various sporadic-E parameters in an attempt to validate a linear relationship between the blanketing sporadic-E plasma frequency and the S2 scintillation. The S2-fbEs relationship is found to be linear over a select range of sporadic-E intensities, but shows a nonlinear relationship for lower fbEs values and plateaus at elevated intensities. A spectral method for estimating fbEs from the spatial Fourier transform of the signal intensity is introduced and explored using the final peak frequency of the low frequency plateau. This metric is shown to have direct relationships to key sporadic-E parameters and is resistant to noise in the applied signal. However, it requires strong scatter conditions to form which corresponds to fbEs values above ~4 MHz for typical sporadic-E lengths and thicknesses. A combined approach using the S2 index for moderate events and the final peak frequency of the low-frequency plateau for stronger events will provide improved plasma frequency estimates for the range of observed sporadic-E frequencies.