“…The NEI (i.e., Number density of Electrons by Impedance probe) measures the upper hybrid resonance (UHR) frequency in the ambient plasma surrounding the 1.2-m cylindrical electrode deployed from the rocket body. The impedance-probe measurement technique, developed in the 1960% [Oya and Obayashi, 1967;Oya, 1967]; is capable of determining N• from the measured UHR frequency (fum0 with an accuracy of +3 %, which is independent of probe shape, electric potential of rocket body, and plasma temperature. The basic advantage of the NEI is its ability to eliminate the stray capacitance associated with the impedance-measuring probe circuit by using a capacitance bridge [Oya, 1967].…”