Trends in waterborne electrical and EM induction methods for high resolution sub‐bottom imaging

Abstract

Shallow water applications of electrical and electromagnetic geophysical methods have grown in recent years with recognition of the information these methods can provide regarding groundwater‐surface water interaction, geotechnical engineering, exploration, marine geology and other fields. In many applications, spatial variations in resistivity are useful as a proxy for variations in another bulk material property such as pore water salinity, clay content, porosity, or temperature. Applications of galvanic resistivity methods have been buoyed by the development of marine configurations that are now commercially available. In contrast, with two notable exceptions, most applications of EM induction methods have involved experimental adaptations of instruments originally designed for use on land. Methods for shallow water resistivity and EM induction surveys are at an exciting stage of development where several promising applications have been demonstrated but the suite of tools and components commercially available and widely tested remains relatively small.

Water- and land-borne geophysical surveys before and after the sudden water-level decrease of two large karst lakes in southern Mexico

“…It is worth mentioning that previous shallow-water TEM studies (Butler, 2009;and references therein;Hatch et al, 2010;Mollidor et al, 2013) employed in-loop configurations with an outer transmitter loop and a smaller receiver loop or coil in the centre, while we used a single-loop configuration, which is quicker to assemble and easier to handle while navigating on the lake. We also showed that it is sensible to constrain the interpretation of the sounding data by incorporating water depth and eventually water resistivity into the inversion process as a-priori information.…”

“…In particular, low-frequency echo sounders (e.g., Dondurur, 2018), also referred to as sub-bottom profilers (SBP), allow to quickly map sediment deposits of several tens of meters based on single-channel seismic data. Nevertheless, electrical-resistivity data provided by electrical resistivity tomography (e.g., Binley and Kemna, 2005) or electromagnetic soundings (e.g., Kaufman et al, 2014) can complement the mostly geometrical information obtained from reflection-seismic or sub-bottom profiling measurements (Butler, 2009). Under certain conditions such as high lake-bed reflectivity and/or low reflectivity of targeted boundaries, seismic methods may, however, provide insufficient results and therefore alternative methods are needed.…”

“…Hatch et al (2010), for example, used an in-loop configuration with a ~7.5 m x 7.5 m transmitter and a ~2.5 m x 2.5 m receiver to map river bed salinization in an Australian river with an average water depth of 5-10 m. Mollidor et al (2013) used a similar but slightly larger setup (~18 m x 18 m transmitter, ~6 m x 6 m receiver) to map a thick conductive sediment layer below the bottom of a 20-m deep maar lake in Germany. Some older relevant case studies with shallow-water applications of both techniques, DC resistivity and electromagnetic soundings, were reviewed by Butler (2009).…”

Magnetic, electrical, and GPR waterborne surveys of moraine deposits beneath a lake: A case history from Turin, Italy

“…A review of the existing methods and recent case histories can be found in the Special Issue of Near Surface Geophysics on Waterborne Geophysics (Butler, 2009;Sambuelli and Butler, 2009).…”

Case history: A 5 km long waterborne geophysical survey along the Po river within the city of Turin (northwest Italy)

“…Among the available geophysical techniques, the use of nonseismic methods with this aim has received growing attention in recent years. A detailed review on the topic can be found, for example, in the special issue of Near Surface Geophysics specifically devoted to waterborne geophysics (Butler, 2009;Sambuelli and Butler, 2009).…”