1. International Reference Ionosphere- Past, Present, and Future: Electron density;Bilitza;Adv. Space Res,1993
2. New prediction and retrospective ionospheric modelling initiative over Europe (PRIME);Bradley,1990
3. Proposed non-vertical sounding data set to be used for map testing;Dick,1993
4. URSI Handbook of ionogram interpretation and reduction;Pigott;World Data Center A, Rep. UAG-23,1972
5. Analysis of Ionograms for Electron Density Profiles;Wright;Radio Sci.,1967