Summary
A Lowell DPS-4 digital ionosonde has operated at the Australian Antarctic polar cap station of Casey (-80.6 deg CGM latitude) since early 1993. During that time the DPS-4 has been operated in routine modes to obtain an extended database of Doppler ionograms and background ionospheric drift measurements. Special campaigns have also been conducted in which the instrument has been operated in special new modes to study, for example, polar patches or the formation of sporadic E. This paper will review the experimental and data analysis techniques developed, and the database of high latitude ionospheric measurements available. Several campaigns were undertaken with the DPS-4 during 1997 and early 1998 with the aim of identifying the occurrence and motion of polar patches over Casey. Polar patches identified from ionosonde records were compared with other geophysical data sets. Initial results show good correlations between group range and critical frequency ionosonde measurements, and Total Electron Content derived from GPS observations. The field-of-view for GPS observations allows patches to be observed over large distances, providing some insight into their origin.