E. ANDRÁSSY, A. MOJZEŠ, E. NOGOVÁ, and O. ČANGEL, “Surface identification of undermined spaces with the use of soil radon emanometry”, Contrib. Geophys. Geod., vol. 51, no. 2, pp. 189–205, Jun. 2021, doi: 10.31577/congeo.2021.51.2.5.