Imaging near surface formation using TEM and ERT methods: A case study from the western coast of India

The paper presents comparative performance of airborne electromagnetic (EM), ground-based EM and electrical resistivity tomography (ERT) methods for characterization of near-surface hydrogeological units of the Western coast of India. The electromagnetic data was acquired in time domain mode employing dual (low and high) moments technology, while the ERT data was obtained using multi-gradient arrays with 10 m electrode spacing. The early time gates of low moment (LM) data provide near-surface geological knowledge, whereas late time gate measurements of high moment (HM) data provide deeper information. Early time gate measurements of LM data corrected by primary field and system response help in utilizing a very early time gate starting from ∼4 μs that enhances near surface resolution. Formation resistivity derived from LM airborne transient electromagnetic (aTEM) data has been compared with ground-based transient electromagnetic (gTEM) and ERT data for resolving very near-surface features, especially the upper few meters, including soil. The study revealed that the performance of aTEM with system response corrections and on-time modelling is effective in comparison to gTEM, and consistent with those results from ERT of 10 m unit electrode spacing in resolving near-surface features. Thus, aTEM survey can contribute to hydrogeological applications dealing with shallow processes such as infiltration, and aquifer recharge studies.