Ionospheric radio beacon signal analysis and parameter estimation using automatic differentiation

We introduce a new optimization model that uses ray tracing to estimate the ionospheric electron density in volume. Plasma number density is parametrized using a modified Chapman profile for the vertical dimension and B-splines for the horizontal. Sensitivity analysis is required both to model the ray amplitudes and to solve the two-point boundary problem for each ray. Sensitivity analysis is used here using reverse-mode automatic differentiation. The resulting algorithm exhibits no performance penalty compared to variational sensitivity analysis but is simpler to implement.

We show and analyze the regional electron density estimation in a volume resulting from this model. This estimation incorporates pseudorange, accumulated carrier phase, and signal power measurements from high-frequency (HF) beacon networks deployed in Peru. It also integrates incoherent scatter radar, the Jicamarca sounder, and GPS receiver data. In particular we analyze the post sunset event on September 01, 2022. On this evening, the Jicamarca Radio Observatory observed the telltale signs of F-region plasma convective instability associated with so-called ”equatorial spread F”. The postsunset F layer underwent rapid ascent in conjunction with the passage of the pre-reversal enhancement (PRE) of the zonal electric field around sunset. Such rapid ascent is normally taken to be an indicator for subsequent ESF activity. While plasma depletion plumes did indeed pass over Jicamarca following the PRE, they were modest in vertical extent and were observed relatively late in the event. One motivation for examining this dataset is to understand why the depletion plumes observed were poorly developed.