ASTM D6639-01(2008)
Standard Guide for Using the Frequency Domain Electromagnetic Method for Subsurface Investigations
- Standard No.
- ASTM D6639-01(2008)
- Release Date
- 2001
- Published By
- American Society for Testing and Materials (ASTM)
- Status
- Replace By
- ASTM D6639-18
- Latest
- ASTM D6639-18
- Scope
Concepts:
This guide summarizes the equipment, field procedures and interpretation methods used for the characterization of subsurface materials and geological structure as based on their properties to conduct, enhance or obstruct the flow of electrical currents as induced in the ground by an alternating electromagnetic field.
The frequency domain method requires a transmitter or energy source, a transmitter coil, receiver electronics, a receiver coil, and interconnect cables (Fig. 5).
The transmitter coil, when placed on or near the earth''s surface and energized with an alternating current, induces small currents in the near earth material proportional to the conductivity of the material. These induced alternating currents generate a secondary magnetic field (Hs), which is sensed with the primary field (Hp) by the receiver coil.
Under a constraint known as the “low induction number approximation” (McNeill, 1980) and when the subsurface is nonmagnetic, the secondary magnetic field is fully out-of-phase with the primary field and is given by a function of these variables.
where: σa = apparent conductivity in siemens/meter, S/m, ω = 2πf in radians/sec; f = frequency in Hz, µo = permeability of free space in henrys/meter 4π × 10–7, /m, s = intercoil spacing in meters, m, and Hs/Hp = the ratio of the out-of-phase component of the secondary magnetic field to the primary magnetic field, both measured by the receiver coil. Perhaps the most important constraint is that the depth of penetration (skin depth, see section 6.5.3.1) of the electromagnetic wave generated by the transmitter be much greater than the intercoil spacing of the instrument. The depth of penetration is inversely proportional to the ground conductivity and instrument frequency. For example, an instrument with an intercoil spacing of 10 m (33 ft) and a frequency of 6400 Hz, using the vertical dipole, meets the low induction number assumption for earth conductivities less than 200 mS/m.
Multi-frequency domain instruments usually measure the two components of the secondary magnetic field: a component in-phase with the primary field and a component 90° out-of-phase (quadrature component) with the primary field (Kearey and Brook 1991). Generally, instruments do not display either the in-phase or out-of-phase (quadrature) components but do show either the apparent conductivity or the ratio of the secondary to primary magnetic fields.
When ground conditions are such that the low induction number approximation is valid, the in-p......
ASTM D6639-01(2008) Referenced Document
- ASTM D420 Standard Guide to Site Characterization for Engineering Design and Construction Purposes
- ASTM D5730 Standard Guide for Site Characterization for Environmental Purposes With Emphasis on Soil, Rock, the Vadose Zone and Ground Water
- ASTM D5753 Standard Guide for Planning and Conducting Borehole Geophysical Logging
- ASTM D6235 Standard Practice for Expedited Site Characterization of Vadose Zone and Ground Water Contamination at Hazardous Waste Contaminated Sites
- ASTM D6429 Standard Guide for Selecting Surface Geophysical Methods
- ASTM D6431 Standard Guide for Using the Direct Current Resistivity Method for Subsurface Investigation
- ASTM D653 Standard Terminology Relating to Soil, Rock, and Contained Fluids
ASTM D6639-01(2008) history
- 2018 ASTM D6639-18 Standard Guide for Using the Frequency Domain Electromagnetic Method for Subsurface Site Characterizations
- 2001 ASTM D6639-01(2008) Standard Guide for Using the Frequency Domain Electromagnetic Method for Subsurface Investigations
- 2001 ASTM D6639-01 Standard Guide for Using the Frequency Domain Electromagnetic Method for Subsurface Investigations
