Recent observational techniques for incoherent scatter plasma line observations

The Incoherent Scatter (IS) plasma line is the part of the IS spectrum scattered from Langmuir waves. It contains only a small portion of the scattered power. The offset of the plasma line from the transmitter frequency varies with electron density. As a result, the signal has a large bandwith, even though the line itself is very narrow. As a result of these complications, plasma line observations are hard compared to ordinary IS measurements, and plasma line observations are not made as part of the ordinary experiment schedule at any of the world's IS radar sites. In the last decades we have seen significant improvements in the observational techniques used in Incoherent Scatter radars. However, for plasma line observations, these techniques have not seen widespread use. The recently developed MIDAS-W data acquisition system (J. M. Holt, P. J. Erickson, A. M. Gorczyca and T. Grydeland, MIDAS-W: A workstation-based incoherent scatter radar data acquisition system, accepted for publication in Ann. Geophys., 2000) puts us in a position where we can quickly and easily employ new techniques to plasma line and other IS observations. Since MIDAS-W is primarily a software system, modifications and new methods can be implemented and tested quickly, and we will be in a better position to compare different experimental techniques. In addition to the MIDAS-W based work, and as an example of the plasma line measurements possible with existing systems today, we present plasma lines from the auroral E-region observed using Barker-coded alternating codes at the EISCAT UHF radar, natural and HF-enhanced F-region plasma lines observed using plain alternating codes at EISCAT VHF and an alternating code plasma line experiment for the EISCAT Svalbard Radar.