부산대학교 도서관

A High Temperature Superconductor (HTS) SQUID magnetometer is located at the INTERMAGNET Hermanus Magnetic Observatory (HER) site in South Africa. The LN2-cooled SQUID is operated unshielded and records the geomagnetic field continuously. If validated, the SQUID may be used as a space weather instrument. The SQUID records small geomagnetic variations such as pulsations, which are short period fluctuations of the geomagnetic field at ULF frequencies. Although the SQUID magnetometers are about 10× more sensitive than fluxgate magnetometers, it is running in an urban environment contaminated by anthropogenous noise. It was also found that one of the SQUIDs is prone to thermally induced oscillations due to thermo-acoustic oscillations in the dewar. To distinguish pulsations from uncorrelated noise, the SQUID data is correlated with fluxgate data from the two closest INTERMAGNET observatories, Hartebeesthoek (HBK) and Keetmanshoop (KMH), both located more than 1000 km away. Man-made noise and SQUID oscillations should give low coherence between SQUID/KMH and SQUID/HBK pairs. Coherence higher than 0.9 was found when pulsations were present in the data and the algorithm has also proven effective on data contaminated with the thermal SQUID oscillations.