2. Beynon Idea

[7]  The idea of exclusion of possible systematic errors is from Beynon and Rangaswamy [1968] as follows. To determine the collision frequency, one needs absolute measurements of the radio wave absorption L at their vertical reflection from the ionosphere (the A1 method). The absorption is related to the electron concentration N and collision frequency n_e via the absorption coefficient by

(5)

where f is the wave frequency, h₀ is the height if the ionosphere bottom, and hr is the height of the signal reflection. Knowing the frequency dependence of the absorption L(f) and having vertical profile of the electron concentration N(h), one can obtain from (5) the vertical profile of the electron collision frequency n_e(h). In the case when the n_e(h) is known, one can determine the N(h) profile.

[8]  The problem of n_e(h) profile determination was realized in the following way [Beynon and Rangaswamy, 1968]. The radio wave absorption at two frequencies f₁0E and f₂>f₀E was measured. The signals at the first and second frequencies were reflected at the bottom of the E and F regions, respectively. Ionograms h'(f) of the vertical sounding (VS) were registered simultaneously. It was assumed that the vertical profile of the electron collision frequency is known from the bottom of the D region up to the reflection height h_r(f1) of the signal at the first frequency f₁. Therefore the absorption L(f₁) together with the virtual height h'(f₁) were used to find the N₀ and a parameters of the model N(h) profile

(6)

where N₀ is the electron concentration at h₀=60 km. The values of the N₀ and a parameters were found by solving the system of equations:

where m' is the group refraction index and n _M is the collision frequency of monoenergetic electrons [Budden, 1965]. The absorption was calculated using the generalized magneto-ion theory [Budden, 1965]. The obtained model profile N(h) was used for calculation of the input into the absorption at a frequency f₂ of the height interval from h₀ to h_r(f₁).

[9]  Then taking into account model (6), the N(h) profile in the E and F regions was restored from ionograms. At the final stage, the n_e(h) profile was fitted corresponding to the absorption D L(f₂) falling on the height interval from h_r(f₁) to h_r(f₂). The determined by this method separate n_e(h) profiles in the height interval 100-150 km agree with the gas-kinetic estimates [Beynon and Rangaswamy, 1968].