The Whistling Elk
Subsurface Imaging Project

by Kenneth L. Kvamme

Instrumentation

  1. Electrical resistivity survey was performed using the RM-15 resistance meter by Geoscan Research. A twin probe array was employed with probe separation (prospection depth) set at 1.0 m. A current of 1 mA at 40 v was injected for each reading. The automatic logging speed of this instrument averaged about 15 measurements/min. at a resolution of 0.1 ohms. Resistivity data were sampled every 0.5 x 1.0 m. Resistivity survey is sensitive to soil type and moisture differences.

  2. Electromagnetic conductivity data were acquired using the EM-38 by Geonics, Ltd. This instrument uses radio energy to induce a temporary magnetic field in the earth that is proportional to soil conductivity. It measures an average conductivity through a depth of 1.5 m, with peak sensitivity at 0.4 m. The EM-38 logs up to 2 measurements/sec. at a resolution of less than 1.0 milliSiemen/m. Conductivity data were sampled every 0.5 x 1.0 m. EM measurements represent the inverse of resistivity: poor soil conductivity implies high resistivity.

  3. Magnetic survey was accomplished through a fluxgate gradiometer, the FM-36 by Geoscan Research. This instrument automatically logs up to 8 measurements/sec. at a 0.1 nT resolution. Magnetic data were sampled every 0.25 x 1.0 m. Magnetic survey is sensitive to iron-bearing artifacts, variations in the type and density of iron compounds in the soil, and fired areas, which cause large magnetic signatures.

  4. Ground penetrating radar (GPR) data were obtained in 1999 only in limited areas using a Geophysical Survey Systems SIR 2000 with a 400 MHz transducer. This instrument transmits a radar pulse into the earth, set at every 2 cm along transects in this project. Changes in subsurface soils return reflections to the antenna. The strengths of these reflections are recorded and their timing gives indications of depth. Separation between adjacent transect was maintained at 0.5 m.

The RM-15, EM-38, FM-36, and GSSI 400 MHz antenna, respectively

This project was supported by a technology transfer grant from the National
Center for Preservation Technology and Training, National Park Service.

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