Electromagnetic Induction and Ground-Penetrating Radar Surveys at Transportation Infrastructure Sites in New Hampshire, 2022

In 2022, the U.S. Geological Survey (USGS) New England Water Science Center, in cooperation with the New Hampshire Department of Transportation (NHDOT), surveyed four transportation infrastructure sites with frequency-domain electromagnetic induction (EMI) instruments and one site with ground-penetrating radar (GPR) to aid traditional geotechnical site characterizations performed by NHDOT. Information about subsurface physical properties is typically obtained through the use of borings during geotechnical site characterizations. Geotechnical site investigations that also include geophysical surveys (such as the EMI and GPR methods) between borings help provide more thorough characterizations. Integrated analysis of geophysical and boring data for transportation projects aids in the production of a more spatially comprehensive representation of geotechnical subsurface conditions than can be determined using conventional borings alone.
Two frequency-domain EMI instruments that measure electrical conductivity changes with depth in different ways were used:
·The GEM-2 (serial number 405, Geophex, Ltd.), with fixed transmitter-receiver (Tx-Rx) coil spacing, transmits waves at several logarithmically spaced frequencies (1530Hz, 3930Hz, 8250Hz, 13590Hz, 20370Hz, and 47970Hz). Lower frequencies are generally capable of imaging deeper, and higher frequencies provide increased resolution of the subsurface.
· The DUALEM-421 (serial number 335, DualEM, Inc.) uses a single frequency at 9-kHz with various Tx-Rx coil spacings and orientations, where larger coil spacings image deeper and shorter coil spacings provide increased resolution of the subsurface. Ground penetrating radar profiles used an antenna with a fixed Tx-Rx offset contained within a tow-body.
GPR transmits pulses of electromagnetic energy into the subsurface and records the amplitude and timing for the return of reflected signals (Keary and Brooks, 1991). The GPR data were collected using a MALA GX controller (ID:227603071) running software version 15.2.269.39 and GroundExplorer 80-MHz shielded antenna (ID:1513002).
This data release contains raw and processed EMI and GPR data and measurement locations. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. The data provided in this data release are: (1) raw GPR profile data in the *.RD3 and *.RD7 formats, (2) raw DUALEM-421 data in comma separated values (*.CSV) files, (3) raw GEM-2 data in Geophex Binary Format (*.GBF), and *.CSV file formats (Geophex software application, EMExport (Version 4.5.2) was used to export the raw binary *.GBF format to *.CSV), (4) processed DUALEM and GEM-2 files with ‘_dat’ in the filename, and (5) inverted DUALEM and GEM-2 profiles with ‘_inv’ in the filename. Readme files are available to explain the data contained within the data files
References:
Kearey, P., and Brooks, M., 1991, An introduction to geophysical exploration second edition: Blackwell Scientific Publications, Cambridge, Mass., 254p.

Tags: canterbury-nh, electromagnetic, environment, geophysics, geoscientific-information, geotechnical, ground-penetrating-radar-gpr, groundwater, lee-nh, location, new-hampshire, new-london-nh, society, transportation, troy-nh, usgs-b6d52933-502c-45da-949a-c21fba1bd36a
Organization: Department of the Interior