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The Dopplionogram was developed as a method of displaying Doppler shifts along the frequency axis of ionograms recorded using B-mode soundings of the Dynasonde, an early type of HF digital ionosonde. The basic idea of recording Doppler shifts in an ionogram format is applied and extended to the Doppler velocity mode of the Digisonde Portable Sounder-4 (DPS-4), a related and more recent type of digital ionosonde. In order to describe our mode of operation a Dopplionogram is redefined to mean a set of stepped-frequency soundings that yields a set of ionospheric Doppler shifts particular to the chosen transmission frequencies. Extension of the technique to include Doppler-sorted interferometry (DSI) analysis of the Doppler spectra facilitates a detailed analysis of ionospheric velocity variations in time and group height. This revitalized approach to DSI should prove useful for the study of ionospheric dynamics for which knowledge of the height profile of electric currents, drift velocity, and neutral winds is required. The technique is demonstrated using measurements of polar cap plasma winds obtained with a DPS-4 located at Casey, Antarctica (66.3°S, 110.5°E).

The seasonal, diurnal, and latitudinal variations of total electron content (TEC) were determined using Global Positioning System (GPS) satellite signals over approximately 5 days per month during almost half a sunspot cycle (July 1991 to June 1995) at Salisbury (latitude 34.77°S, longitude 138.63°E), South Australia. These are the only such extensive southern hemisphere data till 1995 that have been recorded and analyzed. A selection of the data is presented, discussed, and compared with other workers' observations. Examples of Australian Surveying and Land Information Group (AUSLlG) data in the Australian region are presented. Some model predictions for northern hemisphere ionospheric TEC are compared with the GPS southern hemisphere observations of the combined TEC of the ionosphere and protonosphere. (The two models employed are the international reference ionosphere (IRI-90) and the paramaterized ionospheric model (PIM)(version 1.4, February 1996)). They are considered to be global models, even though the IRJ model is based primarily, but not exclusively, on northern hemisphere TEC data, and PIM is based on a theoretical model and is thus not directly based on TEC data.

Ionospheric total electron content (TEC) and slab thickness (τ) have been determined for southern Australia from July 1991 to June 1995 using Global Positioning System (GPS) satellite reception and ionograms (at 5-min intervals) recorded at Salisbury, South Australia, and other Australian ionograms of the Ionospheric Prediction Service Radio and Space Services, Australian Department of Administrative Services. Seasonal, diurnal, and latitudinal variations in TEC and slab thickness are investigated. The removal of possible error sources in GPS measurements such as satellite and receiver biases is considered. Preliminary procedures are outlined in which protonospheric electron content is separated from GPS TEC measurements (up to 20,000 km height) by subtracting Navy Navigation Satellite System (NNSS) measurements (up to 1000 km height). Although slab thickness is substantially constant, there is a trend for increased values at times of reduced solar influence, such as when approaching sunspot minimum. A preliminary report is given of an extension of the current work at Salisbury by using Australian Surveying and Land Information Group GPS receivers at other Australian locations. A comparison is made between the experimental data and values derived from ionospheric models. The two models considered are the international reference ionosphere model (IRI90) and the parameterized ionospheric model ((PIM) version 1.4, February 1996). The GPS TEC measurements near solar minimum were consistently of the order of 5–10 TEC units greater than the model TEC predictions. This difference is attributed to the inclusion of protonospheric TEC in the GPS measurements but not in the model predictions.