A new method of measuring the ion-neutral collision frequency using incoherent scatter radar

Abstract

A new method of measuring the ion-neutral collision frequency using the Doppler shift instead of the shape of the incoherent scatter spectrum is introduced. The method is based on the fact that, in the absence of neutral wind, the relation between electric field and ion velocity is determined by collision frequency. If both the electric field and the ion velocity are measured, the collision frequency can be solved from the equation of ion motion. The method is tested using the EISCAT radar. The applied experiment gives profiles of vertical ion velocity in the E-region and electric fields in the lower F-region. Data from a period with a weak neutral wind and a sufficiently strong electric field are analysed and the results are compared with those obtained using the conventional method. It is found that, under favourable conditions, the new method allows the determination of the collision frequency up to 130 km altitude. This is a considerable improvement as compared to the conventional method, which usually gives the collision frequency profile no higher than to the 110 km level. At altitudes where both methods can be used, a good agreement is found. The main drawback in the new procedure is that it can be used only during periods of negligible neutral wind. It is suggested that this difficulty can be avoided by using an experiment with at least two transmitter beam directions.