Estimation of the influence of facilities removed from the Memambetsu Magnetic Observatory site on geomagnetic field measurements at the absolute observation point
Shin ARITA, Takeshi OWADA, Fujio MUROMATSU, Tetsuo TOKUMOTO, Kenji MORINAGA & Takashi OHKAWA
Eleven unnecessary facilities identified as magnetic sources (eight buildings and three storerooms) were removed from the Memambetsu Magnetic Observator y site during September and October 2014. These were one residential building and one storeroom (about 115 m east-northeast of the absolute observation point), another one residential building and two storerooms (about 160 m east-northeast of the absolute observation point), and another six buildings (about 105 to 245 m north of the absolute observation point). To evaluate the amount of artificial magnetic noise caused by the facilities we removed, we specially arranged monitoring magnetometers. In addition, we carried out magnetic surveys around the observatory before and after their removal. In past, when the absolute observation point had been permanently influenced by an artificial disturbance from a single magnetic source, we had estimated the influence using the traditional method. However, in this case, the absolute observation point was influenced by several sources of artificial disturbance. Therefore, it was difficult to separate the individual influences of the various sources of artificial disturbance by the traditional method. Nonetheless, we have now developed a new software to estimate the individual influences of the various sources of artificial disturbance, and estimated the influence on geomagnetic field measurements to the absolute observation point.