Onshore CSEM > In frequency domain
  • Step 1: Back to signal processing
    Measurement of the secondary field (in-phase and quadrature component) leads to a relevant discrimination of conductivities.

  • Step 2: Airborne Field equipment
    Basic concept of AEM in frequency domain (FDAEM) relies on matched pairs of transmitters and receivers, each pair working for a specific frequency (i.e. the resonance frequency) to increase the system response (Hodges, 2010).
    Constraint about measurement accuracy could be fulfilled with rigid systems. And one should not forget AEM requires low weight equipment. Consequently, FDAEM requests use of small coils (about 50-cm diameters).
    http://www.bgr.bund.de

  • Step 3: EM 31 ground conductivity meter
    The EM 31 ground conductivity meter, designed by Geonics (www.geonics.com), is portable by an operator and does not require contact with the ground. It consists of two coils, one transmitter and the other receiver, connected by a bar of 3.7 m in length. The measurement of the conductivity (expressed in mS / m) is obtained by the ratio between the magnetic field emitted by the apparatus and the magnetic field received after propagation in the ground. Depending on the orientation of the coils, it is theoretically possible to prospect at a depth of 3 or 6 m. In addition, this device makes it possible to record the phase between the emitted field and the recorded field, signaling the location of electromagnetic or metallic disturbances (pipes, fences, cladding, etc.).

  • Step 4: EM 34 ground conductivity meter
    The EM-34-3 ground conductivity meter, designed by Geonics (www.geonics.com), consists of two coils, one transmitter and the other receiver, connected to each other by a cable fixing the spacing of the device (10, 20 or 40 m). The depth of investigation depends mainly on the geometry of the device. It increases with increasing transmitter-receiver distance and varies according to the arrangement of the coils. The coils are kept horizontal to obtain the maximum depth of investigation, or vertical for a lower depth of investigation. Depending on the chosen configuration (spacing of the coils, vertical or horizontal dipole), different theoretical depths of investigation are obtained.