Monteiro , Alan de Andrade, et al. “Ionosondes: a Study on the Use of Electromagnetic Wave Propagation As a Technique to Observe the Ionized Layer of the earth’s Atmosphere ”. Physicae Proceedings, vol. 1, nº 1, maio de 2020, p. 11-12, https://econtents.bc.unicamp.br/eventos/index.php/phyproceedings/article/view/3218.