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 26 stations, 12 of them are still active at present. An Lowell Digisonde-Portable-Sounder-4D (DPS4D) has been sounding since 18/12/2001 at Davis. The Lowell vertical sounding ionosondes normally sweep in frequency from about 0.5 to 30 MHz. Frequency step is selectable to 1kHz. The step interval is variable, becoming more coarse at higher frequencies as ionograms are generally displayed on a logarithmic scale. Every ten 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. During 02/06/1994 to 06/01/2000, Davis also had an IPS 4D ionosonde, and during 07/02/2000 to 01/12/2001, an IPS 5D ionosonde. SWS WDC archives all raw ionogram files and cleaned ionogram files. The Davis digital clean ionogram data is available since 01/08/1994, and digital raw ionogram data since 02/06/1994. The Davis 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 01/01/1985. The Davis median data of foF2 and M(3000)F2 are available since 03/1985.

Frequencies used to sonde ionopshere

The apparent height of an ionospheric layer deduced from the time delay of a reflected radio pulse upon the assumption that it travelled at the speed of light over its entire path. However, the radio wave actually slows down as it is refracted so that the virtual height is greater than the true height of the refracting layer. Lowell DPS4D height range is 0-1200KM ( 0 KM used for self-calibration).