Ionograms are an image of frequency versus time delay (virtual height) of HF echoes from the ionosphere recorded by an ionosonde. An ionosonde is a swept frequency HF pulsed radar used to monitor the ionosphere. SWS WDC has archived ionogram data from 30 stations, 16 of them are still active at present. The most active ionosondes in Space Weather Network (SWN) are IPS 5D ionosonde.
The 5D vertical sounding ionosondes normally sweep in frequency from about 1 to 21.5 MHz. Frequency step resolution for the 5D is 5kHz, with up to 4095 steps available. The step interval is variable, becoming more coarse at higher frequencies as ionograms are generally displayed on a logarithmic scale. Every five minutes, a Ionogram data file is recorded, cleaned and the cleaned ionogram is transfered to SWS Sydney head office for autoscaling and further analysis. The raw ionogram file is recorded in a DVD monthly, which will be posted to Sydney SWS head office every month. SWN also operates a few other digital ionosondes, they are IPS 4D in SCott Base, Antarctic, Canadian Advanced Digital Ionosonde (CADI) in Casey, Macquarie Island and Mawson, Lowell digisonde in Davis station.
In the past, the former IPS also used IPS 4c, 4d, 5a and 5c ionosondes. SWS WDC archives all raw digital ionogram files and cleaned ionogram files. The clean ionogram data is available since 1991, and digital raw ionogram data since 1992. The scaled hourly ionospheric data include parameters of foF2, foF1, FoE, foEs, fbEs, fmin, fxl, f'scaling F/s, M(3000)F2, h'F2, h'F, h'E, h'Es, h'Scaling R/S and Type Es. They are avalable since 1938. The median data of foF2 and M(3000)F2 are also available since 1938.
Data frequency: every 5 minutes file;