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I have contour maps showing conductivity and in-phase data from an electromagnetic survey done on a ground, where, supposedly, an underground sewer system is running horizontally across the survey area. The In-phase data shows a clear indication of it, but the conductivity data is just blank.

Can anyone help me under stand why? Shouldn't the conductivity data show at least something? The survey was carried out both vertically and horizontally on the survey area using a CMD.

And what exactly does the in-phase data show in a electromagnetic survey? On the manual it just says that 'It is closely related to magnetic susceptibility of measured material.' Does this mean it's measuring the magnetic susceptibility?

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  • $\begingroup$ Are you measuring the earth magnetic field or various electric potentials such as caused by cathodic protection applied to pipelines , etc ? $\endgroup$
    – blacksmith37
    Commented Aug 26, 2021 at 15:14
  • $\begingroup$ @blacksmith37 Sorry. I don't really understand your question. My guess is that it'd be the electric potentials since the goal of the survey was to map out the underground pipelines. $\endgroup$
    – ggraann
    Commented Aug 26, 2021 at 21:30
  • $\begingroup$ Depending on location a voltage survey could be complicated and change. Gas and oil lines will have cathodic potential . Water pipe may by protected, sewer probably not . Electric transmission lines can induce voltage in pipe, etc. Surface and underground electric rail affect the voltage . Pipelines are also electrically bonded to each other and this may switched on and off. Maps at oil and gas companies would be a better way to find pipelines; Municipalities will also have maps for water and sewer. USGS maps show larger oil and gas lines. $\endgroup$
    – blacksmith37
    Commented Aug 27, 2021 at 0:49
  • $\begingroup$ Suggesting maps are a good way to find pipelines is a not a helpful comment. The reality on the ground is that many services were never 'mapped', many services aren't where the map says they are, and maps may, or may not, be accessible. Geophysical surveys are an appropriate tool for localizing services. $\endgroup$
    – Andy M
    Commented Aug 27, 2021 at 8:55
  • $\begingroup$ It will depend on what "pipe lines" he is looking for. For water, sewer and gas to an individual house , a local electric survey tool is great . For gas and oil transmission lines ,the operators know where they are ; it is likely illegal not to know. That being said there are rare instances where a second operator lays pipe in the same right-of-way and makes minor moves of existing pipes. $\endgroup$
    – blacksmith37
    Commented Aug 27, 2021 at 18:48

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