Techniques for understanding anomalous radar spectra.

This thesis concerns the investigation of the Earth's upper atmosphere, ionosphere and magnetosphere. In particular, it involves a study of the F region, using EISCAT Svalbard Radar data. Anomalous ion line spectra have been identified in many of the radar experiments which have been conducted at that site. Such spectra are defined as deviations from the standard symmetric "double-humped" spectra derived from incoherent scatter radar echoes from the upper atmosphere. Some anomalous spectra --- where there are sharp enhancements of power over restricted height ranges --- have been attributed to satellite contamination in the beam path. Here we outline a method for detecting such contamination, and review in detail a few cases where the method enables the identification of anomalous spectra as satellite echoes, subsequently ascribed to specific orbital objects. The methods used here to identify such satellites provide, a useful way of distinguishing anomalous spectra due to satellites from those of geophysical origin. Analysis of EISCAT Svalbard Radar data reveals that an average of 8 satellites per hour are found to cross the beam. Based on a relatively small sample of the data set, it appears that at least half of the occurrences of anomalous spectra are caused by satellite contamination rather than being of geophysical origin.Those anomalous spectra which cannot be explained by satellite contamination appear to occur most frequently during or immediately before magnetic storms, as can be seen when compared with the Dst index and magnetometer data. A model of the chemical structure of the ionosphere is proposed; This gives predictions for the intensity ratios of the 6300A and 5577 A emission lines and these are compared with readings from the meridian scanning photometer at Adventdalen.