Performance of an RF impedance probe in the ionosphere

It was reported in a previous letter in this journal [Jackson and Kane, 1959] that an RF impedance technique of measuring ionospheric electron densities yielded results that were a factor of 3 too small. The purpose of this note is to report the improvement obtained in a later rocket flight, NASA 4.07, fired at midday September 14, 1959, at Fort Churchill, Canada. The RF impedance probe consisted of two collinear whips each approximately 0.6 cm in radius and 3 meters long. The assumption that in the ionosphere the probe capacitance C is related to the free-space capacitance C0 by C = KC0 permits the local e= 1 - 8lN/f2, where N is the electron concentration per cubic centimeter and f is the exploring frequency in kilocycles per second.