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

Abstract

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.

Review and perspectives: Understanding natural‐hazards‐generated ionospheric perturbations using GPS measurements and coupled modeling

“…Tsunamis generated by earthquakes often endanger heavily populated coastal areas [e.g., Makela et al, 2011;Heki, 2011;Arrowsmith et al, 2012;Yang et al, 2012Yang et al, , 2014bAstafyeva et al, 2014;Roy et al, 2014;Jin et al, 2015]. The tsunami of 11 March 2011, following the Tohoku-Oki earthquake in Japan, caused over 20,000 fatalities.…”

Comparisons of ionospheric electron density distributions reconstructed by GPS computerized tomography, backscatter ionograms, and vertical ionograms

“…The other is obtained by scanning in frequency because the available radars are not able to scan in elevation [Coleman, 1997]. For the former type, Roy et al [2014] recently developed an ionospheric tomography method based on elevation scan data of the over-the-horizon radar Nostradamus [Bazin et al, 2006], which took into account the whole information of the radar measurement. This novel method indicated that electron density perturbations could affect the raypath geometry and consequently influence the inversion results.…”

Tomographic reconstruction of ionospheric electron density during the storm of 5-6 August 2011 using multi-source data

“…To the lower ionosphere, Occhipinti setted up a new method based on the ray-tracing tool TDR to invert the propagation time 13 . For the more complex data-set of CIT, Roy et al developed a new linear regularization tomography method 14 . These methods improved the accuracy of CIT and promoted the development of CIT algorithm.…”