On hydrogeological noise in superconducting gravimeter data

Abstract

ABSTRACTThe purpose of this research was to gain a better knowledge of the signals contained in superconducting gravimeter data at the Metsähovi station in southern Finland. Because superconducting gravimeter data are very sensitive to various environmental effects, we must first identify and understand the characteristics of these effects and only after that are we able to correct for them if necessary. In this study we used the continuous wavelet transform to analyse correlations between the gravity residuals, precipitation, and groundwater level. As a result, we determined and isolated the source of a long‐term effect, i.e. the varying flow rate of groundwater in an inhomogeneous ground. The causes of this flow‐rate variability are changes in the porosity of the ground due to changes in the type of medium, and the amount of fracturing in the bedrock. Topography is also a cause of the flow‐rate variation. Therefore, a single observation well to determine the groundwater level at the study site is not sufficient to provide coefficients that are precise enough to reduce the gravity effect due to variations in the groundwater level, and several access tubes will be needed to assess the correction coefficients accurately.