“…Observation of geocoronal Lyman-α column brightness and its conversion into exospheric H-density models have challenged researchers for decades. In the past, observations have been carried out with high-altitude rockets or satellites (e.g., Kupperian et al, 1959;Johnson, 1961;Rairden et al, 1986;Østgaard et al, 2003) and even by Apollo 16 from the Moon (Carruthers et al, 1976). Theoretical studies have been presented (e.g., Chamberlain, 1963;Thomas and Bohlin, 1972;Fahr and Shizgal, 1983;Bishop, 1991;Hodges Jr., 1994).…”