A Time-Domain Impedance Probe for Fast Measurements of Electron Plasma Parameters in the Ionosphere

Abstract

A new time-domain impedance probe is presented in this paper. The new instrument is able to make measurements of absolute electron density and electron-neutral collision frequency in the ionosphere at temporal and spatial resolutions not previously attained. A single measurement is made in $100~\mu \text{s}$ , which yields an instantaneous spatial resolution of 0.1 m for sounding rocket experiments. A prototype of this instrument was integrated into the payload of a NASA Undergraduate Student Instrument Program sounding rocket launched out of Wallops Island on March 1, 2016. Here, we describe the instrument, and present the data obtained from the sounding rocket experiment. A 6-V amplitude Gaussian derivative excitation was applied to a dipole probe structure, and the current through the probe terminals measured with a balanced active bridge circuit. The time-domain current response was sampled at 5 MS/s, at 12-bit resolution. In the course of the flight, the instrument measured a highly nonlinear response of the plasma because of the large input voltage signal applied. The linear theory cannot explain this response, which obscured interpretation of the data. As a result, we used time- and frequency-domain trend analysis to obtain the variation of electron density over the upleg and downleg of the rocket trajectory. The obtained time and fast Fourier transform trends showed enhanced electron densities in the F layer, which confirmed that the instrument was able to measure the density variations during a significant portion of the flight.