Continuous ionospheric sounding has been carried out at the Appleton Laboratory, Ditton Park, Slough since 1931. When the Appleton Laboratory moved to the Chilton site in 1982, sounding continued at Ditton park, but it was realised that eventually the ionosonde would have to be moved to Chilton.
As can be seen from the map, the new Chilton site is almost exactly fifty kilometres due west of the old site. In order that the Chilton data could continue the Slough data sequence, it is important to understand the effects of the location of the instruments on the data. If the two sites are to be paired, it is desirable to determine any differences between the ionospheric soundings at the two sites. As a result, it was decided to run an ionosonde at both sites for a period of at least a year.
Ideally, the two ionosondes should have been identical, as then any differences would be entirely due to the change in location. Unfortunately, before the study began, on the 23rd of October 1992, the Slough ionosonde was struck by lightning, damaging the hardware of the DGS 256 (a similar, if older, version of the DPS now at Chilton) beyond repair. In order to maintain the continuous records at Slough, a replacement ionosonde was used. This was an older, KEL IPS42 ionosonde, quite different from the DPS at Chilton. On the 1st December 1993, the new ionosonde at RAL, Chilton, started to make continuous soundings and these were compared with the replacement KEL at Slough. These comparisons form the basis of this report.
Since it was not possible to make a comparison between the two Slough ionosondes, any differences between the soundings as a result of the hardware change there are unknown. If an experiment could be envisaged where the KEL and the DPS observed side by side with no interference between them, any number of things could be responsible for a difference in the recorded data. The most obvious are the transmitter power and the receiver sensitivity, although other causes, such as the processing algorithms could also contribute. The fact that this experiment can not be carried out complicates the comparison of the RAL and Slough sites.
For the current study, data from the two different sites is used. It may never be clear whether any difference in this data is a result of the instrumentation, or the change in location. All that can be safely determined are any systematic differences in the parameters measured by the two instruments.