The Study of E-Region Ion Concentration and Composition by Incoherent Scatter Radar


  • J. V. Evans,

  • W. L. Oliver


This paper reviews the use of the incoherent scatter radar technique for studies of the E-region ion concentration and composition. A number of existing incoherent scatter radars are capable of securing profiles of ion concentration in the E region with a height resolution of 1 or 2 km by integrating the signals for several minutes. The advantage of these measurements is the ease with which a continuous time history may be secured. The height resolution is probably open to improvement by using coded pulses, but this remains to be attempted. The technique is of less value in studying the ion composition; and to date, only the relative abundance of atomic (O+) to molecular (principally NO+ and O2+) ions has been deduced from incoherent-scatter measurements. Even here it has usually been necessary to adopt a model for the ion temperature as a function of altitude. Nevertheless, these composition measurements clearly show a seasonal variation of the O/N2 ratio in the thermosphere which is believed to be responsible for the seasonal anomaly in F-region density. Recently, the accuracy of the measurements and the data reduction procedures have been improved to the point where the relative ion abundance can be determined over the altitude interval 120–200 km, given only that this be a continuous smooth function.