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