Optimal site selection for Choutuppal geomagnetic observatory, based on geophysical evidence

Abstract. The phases of development of Choutuppal magnetic observatory over the last 15 years have enabled the effects of the natural environment like groundwater changes and lightning activity on the magnetic data to be evaluated. A high-resolution survey of total field anomalies led to the construction of a 2D model of the shallow surface. Constrained by conductivity depth slices from previous electrical resistivity tomography and electrical vertical resistivity imaging surveys, the distribution of sandy regolith, saprolite and granitic layers in the shallow subsurface is delineated. The pattern of lightning strikes in a 10 km area around the observatory is correlated to modulations and disruptions in the magnetic data. The analysis as a whole provides information for selecting a location to install a secondary variometer room by taking into account topography, lightning effect, soil resistivity, low magnetic anomaly and distance from the recharge pond, which can produce continuous data of higher quality and consistency than at present.