GNSS and SAR Signal Delay in Perturbed Ionospheric D-Region During Solar X-Ray Flares. - Nina, Aleksandra; Nico, Giovanni; Odalovic, Oleg; Cadez, Vladimir M.; Drakul, Miljana Todorovic; Radovanovic, Milan; Popovic, Luka C. (IEEE Geosci. Remote. Sens. Lett., 2020)