Jean-Philippe Molinié

Effect of ray and speed perturbations on ionospheric tomography by over‐the‐horizon radar: A new method

Most recent methods in ionospheric tomography are based on the inversion of the total electron content measured by ground-based GPS receivers. As a consequence of the high frequency of the GPS signal and the absence of horizontal raypaths, the electron density structure is mainly reconstructed in the F2 region (300 km), where the ionosphere reaches the maximum of ionization, and is not sensitive to the lower ionospheric structure. We propose here a new tomographic method of the lower ionosphere, based on the full inversion of over-the-horizon (OTH) radar data. Previous studies using OTH radar for ionospheric tomography inverted only the leading edge echo curve of backscatter ionograms. The major advantage of our methodology is taking into account, numerically and jointly, the effect that the electron density perturbations induce not only in the speed of electromagnetic waves but also on the raypath geometry. This last point is extremely critical for OTH radar inversions as the emitted signal propagates through the ionosphere between a fixed starting point (the radar) and an unknown end point on the Earth surface where the signal is backscattered. We detail our ionospheric tomography method with the aid of benchmark tests. Having proved the necessity to take into account both effects simultaneously, we apply our method to real data. This is the first time that the effect of the raypath deflection has been quantified and that the ionospheric plasma density has been estimated over the entirety of Europe with an OTH radar.

Inversion of Backscatter Ionograms Optimization by using Simulated Annealing and Genetic Algorithms

The Over-The-Horizon Radars (OTHR) use the refraction of the waves on the ionosphere to reach the targets over the horizon. In order to know the real position of the targets the actual ionospheric characteristics must be estimated. So an inversion method to obtain them has been developed. This inversion method is capable to obtain the parameters of a model of the electronic density profile from some measurements realized with the radar, the backscatter ionograms. To optimize the method two algorithms has been introduced: the simulated annealing and the genetic algorithm.

Surface waves magnitude estimation from ionospheric signature of Rayleigh waves measured by Doppler sounder and OTH radar

Surface waves emitted after large earthquakes are known to induce atmospheric infrasonic waves detectable at ionospheric heights using a variety of techniques, such as high frequency (HF) Doppler, global positioning system (GPS), and recently over-the-horizon (OTH) radar. The HF Doppler and OTH radar are particularly sensitive to the ionospheric signature of Rayleigh waves and are used here to show ionospheric perturbations consistent with the propagation of Rayleigh waves related to 28 and 10 events, with a magnitude larger than 6.2, detected by HF Doppler and OTH radar respectively. A transfer function is introduced to convert the ionospheric measurement into the correspondent ground displacement in order to compare it with classic seismometers. The ground vertical displacement, measured at the ground by seismometers, and measured at the ionospheric altitude by HF Doppler and OTH radar, is used here to compute surface wave magnitude. The ionospheric surface wave magnitude (Msiono) proposed here introduces a new way to characterize earthquakes observing the signature of surface Rayleigh waves in the ionosphere. This work proves that ionospheric observations are useful seismological data to better cover the Earth and to explore the seismology of the Solar system bodies observing the ionosphere of other planets.

Backscatter ionogram inversion validation with the help of a HF radio transmitter

Accuracy in target localization by over-the-horizon radar can be improved with a good knowledge of the propagation channel. An inversion method has been developed in order to provide an electron density profile of an equivalent ionosphere from backscatter ionograms. The method uses the measurements realized by the HF radar during elevation scans. The method has been validated on synthesized and real data by comparing the results with ionospheric forecasts and vertical ionosonde. The equivalent ionosphere determined by inversion will be used to convert group path into ground range and to realize coordinate registration of targets. In this paper, we present first experiments of radio frequency interference (RFI) source localization. RFI source localization is used to estimate the precision of our inversion method.