Plasma diagnostics with Langmuir probes in the equatorial ionosphere: I. The influence of surface contamination

The application of spherical Langmuir probes for measuring the electron temperature and density on ionospheric sounding rockets is discussed with respect to the influence of the geomagnetic field effects and probe contamination. The influence of the contamination layer is thoroughly analysed in the frame of a nonlinear equivalent circuit. When operating the probe in ramp mode, it is found that the distortion of the current-voltage characteristic is different for decreasing and increasing probe voltages. The resulting error of the electron temperature is determined for a range of capacitance (C) and resistance (R) values of the contamination layer. A method is described to determine the parameters R and C from the flight data. Further, a correction algorithm is discussed that allows the true probe characteristic to be retrieved from the measured distorted characteristic.