High-Frequency and Very-high-Frequency (HF&VHF) above-groundelectromagnetic impedance measurements

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We have field-tested an apparatus for measuring the electromagnetic impedance above the ground at a plurality of frequencies in the 0.3 - 30 MHz range. This window in the frequency spectrum, which lies between frequencies used for GPR and those used for conventional loop-loop EM soundings, has not been used because of difficulties in fielding equipment for making absolute and accurate measurements. Model and physical parameter studies however confirm that data in this frequency band can be used to construct high-resolution maps of electrical conductivity and permittivity of near-surface material. Our equipment was assembled using commercial electric and magnetic antennas. ... continued below

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Frangos, William; Becker, Alex & Lee, K.H. September 20, 2002.

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We have field-tested an apparatus for measuring the electromagnetic impedance above the ground at a plurality of frequencies in the 0.3 - 30 MHz range. This window in the frequency spectrum, which lies between frequencies used for GPR and those used for conventional loop-loop EM soundings, has not been used because of difficulties in fielding equipment for making absolute and accurate measurements. Model and physical parameter studies however confirm that data in this frequency band can be used to construct high-resolution maps of electrical conductivity and permittivity of near-surface material. Our equipment was assembled using commercial electric and magnetic antennas. The magnetic loop source is excited by a conventional signal generator - power amplifier assembly. Signal detection is accomplished using RF lock-in amplifiers. All system elements are appropriately isolated by optic - fiber links. We estimate a measurement accuracy of about {+-} 10% for an 8-m separation between source and detector. Field tests were done at the University of California Richmond Field Station where the near surface electrical structure is well known. The experimental data at this site are mainly a function of electrical conductivity. In this context, we have obtained good agreement with the known local variations in resistivity both with depth and with position along a 35-m traverse. Additional tests in more resistive regimes where dielectric permittivity is not negligible yield spectral data compatible with the less well known near-surface electrical properties.

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  • Journal Name: Journal of Environmental&EngineeringGeophysics; Journal Volume: 9; Journal Issue: 2; Related Information: Journal Publication Date: 06/2004

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  • Report No.: LBNL--51672
  • Grant Number: DE-AC02-05CH11231
  • Office of Scientific & Technical Information Report Number: 917521
  • Archival Resource Key: ark:/67531/metadc888219

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  • September 20, 2002

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  • Sept. 22, 2016, 2:13 a.m.

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  • Sept. 30, 2016, 2:26 p.m.

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Frangos, William; Becker, Alex & Lee, K.H. High-Frequency and Very-high-Frequency (HF&VHF) above-groundelectromagnetic impedance measurements, article, September 20, 2002; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc888219/: accessed August 20, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.