The ionosonde was situated on Shetland, within the grounds of the Met. Office station at Lerwick. The site used a series of digital ionosondes culminating in a Digisonde DPS 1. This consisted of a crossed delta transmitting antenna (converted into a crossed arrowhead by the addition of outer support towers) and an array of four crossed loop receive antennas. With this equipment, it is possible to measure not only electron density profiles, but also location, Doppler shifts and polarisation of any ionospheric echoes.
The transmitter was located on a headland, and the receivers are placed approximately 100 metres down the hill.
Lerwick is a thriving fishing port and during the summer months attracts many East-European fishing vessels known as Klondykers. Although recently introduced laws concerning the seaworthyness of such vessels has dramatically reduced their number, HF transmissions from these vessels still accounted for a significant amount of radio noise in the ionospheric data.
Lerwick is quite an exposed site and the equipment had to withstand quite a beating from the natural elements. As an example, look at the images of the transmitter support towers before and after a period of extremely dense freezing fog. Ice formed on the transmitter cables to a diameter of several centimetres. From the direction in which the two support towers bent (inwards) it is clear that it was the weight of this ice, and not the accompanying wind that caused the damage. These towers were subsequently replaced with steel equivalents. When using ionosonde data, it is important to keep in mind that some of it has been obtained under extreme weather conditions.
