Data repeatability and acquisition techniques for time‐domain spectral induced polarization

Abstract

ABSTRACTThe Time Domain Induced Polarization (TDIP) technique is widely used in applied geophysics, particularly for environmental issues, for instance for delineating landfills or detecting leachate percolation. Because the reliability of IP data remains an issue at the field scale, this paper deals with the factors controlling data quality and compares different arrays and acquisition parameters for optimal collection of data in the field.The first part focuses on repeatability experiments carried out in the former Hørløkke landfill (Denmark), in order to infer the degree of which a signal can be reproduced over time. Results show a good repeatability, with on average less than 10% of difference in raw data. Also, from the results it is inferred that the paramount parameter controlling repeatability is the IP signal level; a value of 2 mV is a sufficient threshold to ensure repeatability within 10% of data difference, although system dependant.The second part focuses on survey design and underlines the importance of keeping the geometrical factor low. This points to the choice of a relevant measurement protocol, which depends on the threshold of the geometrical factor, again depending on expected chargeability and resistivity, threshold voltage and injected current. Furthermore, acquisition parameters such as the duration of the pulse injection and data sampling have a significant effect on both the signal‐to‐noise ratio and resolution. A comprehensive comparison between three protocols, the gradient array, the linear grid and the dipole‐dipole array, is shown and the choice of an acquisition sequence is discussed.