3D local and global scale ionospheric tomography with multi- parameter (OTH, GPS, Occultations, SuperDarn) inversion: a new method adapted to study the dynamics of the Ionosphere

Most recent methods in ionospheric tomography are based on the inversion of the total electron content (TEC) 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 ionisation and is not sensitive to the lower ionospheric structure. We aim to combine this with a tomographic method of the lower ionosphere based on the full inversion of over-the- horizon (OTH) radar data. Our methodology is taking into account, numerically and jointly, the effect that the electron density perturbations are induced not only by the speed of electromagnetic waves but also by 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. Combining both GPS and OTH radar data, our tomographic method improves the resolution of the ionospheric structure as GPS and OTH radar data are mainly sensitive to different altitudes. OTH radar data is recorded for one azimuth at a time, consequently tomography by OTH radar could be limited to 2D grid following the azimuth and covering different altitude. Therefore adding GPS data with various satellite-receiver paths leads to a better coverage and enables us to invert the data on a 3D grid with better resolution. Additionally, the 3D grid could be also used for SuperDARN: a dense network of 35 OTH radars located in the Northern and Southern polar region. This opens terrific perspectives in the knowledge of ionosphere of the polar regions. We will present here some preliminary results of our method applied to a single SuperDARN radar. Our preliminary results are discussed using a synthetic checkerboard test. We finally present the ionospheric TEC perturbation observed by 1100 GPS receivers during the total solar eclipse over the US on 21 August 2017 with the objective to explore it with our tomographic method, in order to fully understand the atmospheric/ionospheric physics process during eclipse events.