Lindstrom, R.; Vastberg, A.: 'Using the Swedish Ionosonde Network', IET Conference Proceedings, 1994, p. 376-378, DOI: 10.1049/cp:19940526
IET Digital Library, https://digital-library.theiet.org/;jsessionid=385rju6tc7lls.x-iet-live-01content/conferences/10.1049/cp_19940526