A spin stabilized probe was constructed to make three component vector measurements of dc electric fields in the auroral ionosphere. The resolution of an electric field component was found to be as high as ≃ 0.5 mV/m in magnitude and ≃ 20 msec in time, while the total vector was resolved in ≃ 0.5 sec. This miniaturized instrument was mounted on the exterior skin of sounding rockets and, containing its own telemetry and magnetometer system, was ejected into the ionosphere. The floating double Langmuir probe detector was designed to have a high input impedance of ≃ 8 × 103 Ω at 60 Hz. Spin rates from 10 to 100 Hz allowed the dc offset errors, normally measured by other techniques, to be removed by ac coupling of the electronics. A simplified data reduction procedure is obtained by an envelope analysis of the amplitude modulated electric and magnetic field signals.
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