Extension of cosmic noise absorption measurements to lower frequencies, using polarized antennas

The cosmic-noise me~hod ?f m eas uring a?solut e ionospheric absorption r equires a rehab Ie knowled ge of t he mtcnslty of the cos mIc radio noise which would be observcd in the complete absence of the ionosphere. At frequencies above 15 Mc/s this extraterrestrial jntensit~ has .hithert~ been estimated by a method which assumes t hat during ionospherically qUIet, l1lghttlme penods, the absorptl?ll ?ccomes negligible. However, t his " qu iet-d ay" m et hod lead s to Important uncertamtles III the value of t he extraterrestria l cos mic radio noise int ensity when it is used at frequencies below about 15 Mc/s.