@book{ BA43461053, author = "International Scientific Radio Union. World Wide Soundings Committee and Piggott, W. R. and Rawer, K. (Karl)", title = "URSI handbook of ionogram interpretation and reduction of the World Wide Soundings Committee", publisher = "Elsevier ; Van Noastrand", year = "1961", series = "URSI monographs", number = "", URL = "https://ci.nii.ac.jp/ncid/BA43461053" }