The Sodankylä Geophysical Observatory (SGO) is one of the most versatile observatories in the world. The first measurements at Sodankylä took place already during the 1st International Polar Year between 1882 and 1884. Today SGO looks back on a long tradition of ground-based geophysical routine observations, which started in 1914 with the monitoring of the geomagnetic field. In the more recent past, instrument development and research based on the available data have become an essential part of SGO's activities. All activities are tightly linked to those of the Space Physics Group (SPG) at the University of Oulu.
All of the most important research and development activities at SGO chain of stations comprises 6 instruments between 60°N and 69°N, as well as one station on Crete, Greece. The instruments are capable of recording ULF waves in the whole Pc/Pi frequency range. SGO has constructed sophisticated VLF receivers, which are operated during campaigns. Fast algorithms for computing polarisation parameters were developed in order to study the link between whistler activity and auroral substorms as well as powerline harmonic radiation. Currently a new instrument measuring the vertical electric field is in test use near Oulu. Preliminary results show that it is able to register at least the lowest three Schumann frequencies. During the IGY in August 1957, the Sodankylä ionosonde started regular half-hourly soundings of the high-latitude ionosphere. The ionograms, which have entirely been scaled by the same person throughout, are used for studies of long-term changes of the ionosphere. Since the mid-1960s, SGO has carried out continuous measurements of cosmic radio noise by riometers in Finland and Northern Scandinavia. Today the network of 9 riometers covers L-values from 3.7 to 13.2 between 62°N and 77°N, and includes the 49-beam imaging riometer IRIS of the University of Lancaster, UK. In the 1980s, SGO became one of the sites of EISCAT, which operates powerful incoherent scatter radars and a heating facility. These observations are complemented every winter by optical observations with all-sky cameras and photometers.
All of the most important research and development activities at SGO are based on the same fundament: mathematical modelling of measurements and stochastic inversion theory. Exploiting these methods lead to completely new, revolutionary radar measurements, which gradually are being employed by a number of international radar facilities. Scientists of SGO and SPG are leading in the world concerning radar measurements as well as tomographic applications. Currently, a permanent chain of receivers for satellite tomography of the ionosphere is under development. Furthermore, a meteor radar is under construction and will be operational in 2001.
In the present work, some examples of available data and recent results are presented briefly. SGO welcomes the scientists of SPECIAL to work with these data. Additional information is available on-line at www.sgo.fi.