First results from a time domain impedance probe for measuring plasma properties in the ionosphere

A new Time Domain Impedance Probe (TDIP) 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 microseconds, which yields an instantaneous spatial resolution of 0.1 meters for sounding rocket experiments. A prototype of this instrument was integrated into the payload of a NASA USIP sounding rocket launched out of Wallops Island on March 1 2016. The sounding rocket launched at 8:50 am and reached an reached an altitude of 170 km, passing through the D and E and F layers of the ionosphere. The TDIP was active for 206 seconds during the flight. Here we describe the instrument, and present some time domain data obtained from the sounding rocket experiment. A 6 Volt 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 what appeared to be a highly nonlinear response of the plasma because of the large input voltage signal applied. These are the first measurements of this type of response, to our knowledge. Post-flight laboratory calibration indicated that the instrument worked correctly through the flight. Further modeling, simulation and theoretical work needs to be performed to understand and interpret the measurements.