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Thread: The missing link? FDEM & TDEM

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    Junior Member Waikibz's Avatar
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    Default The missing link? FDEM & TDEM

    Aloha,
    I've been in the Utility locating/ SUE industry, for about 17 years (mostly East Coast).
    I am trying to find the connection between: Time Domain Electro Magnetic (TDEM) , and/or Frequency Domain Electro Magnetic (FDEM), mostly used in the field of Geology, and how it can contribute to mapping utilities. The way I see it, FDEM is like GPR that you can hold at "waist high" and navigate terrain that any of todays GPR units could not think about. The data is collected by a Geonics EM-31 or 61, (there are other companies that make similar instruments) and thru post-priocessing, you get a beautiful picture of everywhere the earth has been disturbed, showing vitreous clay sewer laterals and plastic pipe irrigation (just to name a couple). OK, now you have an idea of what I'm thinking. What do you guys think?

    Mahalo,
    Waikibz

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    Senior Member ProfessionalLocator's Avatar
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    Default Re: The missing link? FDEM & TDEM

    Quote Originally Posted by Waikibz View Post
    Aloha,
    I've been in the Utility locating/ SUE industry, for about 17 years (mostly East Coast).
    I am trying to find the connection between: Time Domain Electro Magnetic (TDEM) , and/or Frequency Domain Electro Magnetic (FDEM), mostly used in the field of Geology, and how it can contribute to mapping utilities. The way I see it, FDEM is like GPR that you can hold at "waist high" and navigate terrain that any of todays GPR units could not think about. The data is collected by a Geonics EM-31 or 61, (there are other companies that make similar instruments) and thru post-priocessing, you get a beautiful picture of everywhere the earth has been disturbed, showing vitreous clay sewer laterals and plastic pipe irrigation (just to name a couple). OK, now you have an idea of what I'm thinking. What do you guys think?

    Mahalo,
    Waikibz
    I came in on the end of some TV show where such technology was used to find now buried building foundations and such. Was unable to find what I was searching for as I did not know the names. Worth checking out as GPR is still in development and has many limitations.

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    Junior Member Aquaman's Avatar
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    Default Re: The missing link? FDEM & TDEM

    It is my understanding that GPR maps the reflection of waves off structures in the soil while FDEM and TDEM are methods to measure the conductivity in the soil, ie for mapping groundwater, oil and natural gas pockets. I could be off on my research, if so apologies.

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    Senior Member ProfessionalLocator's Avatar
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    Default Re: The missing link? FDEM & TDEM

    Quote Originally Posted by Aquaman View Post
    It is my understanding that GPR maps the reflection of waves off structures in the soil while FDEM and TDEM are methods to measure the conductivity in the soil, ie for mapping groundwater, oil and natural gas pockets. I could be off on my research, if so apologies.
    At a quick look this technology sends an electric pulse into the earth. The the signals are processed through a computer. The signals are measured by their intensity and time to return to the surface. Different things give different returns and the signal does not stop where it is reflected back like a radar signal sriking a first object. The electric pulse keeps traveling so the returned signal can be measured below the first objects reach.

    Sounds like a computer processing these signal can make a three dimensional representation of what is below the ground for depths greater than current GPR is capable of.

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    Default Re: The missing link? FDEM & TDEM

    OK now that I have a headache from reading all that tech bs I'm sold how much? It seems that fdem seems more suited to our industry. I could not find any mention of price any ideas.

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    Junior Member Waikibz's Avatar
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    Default Re: The missing link? FDEM & TDEM

    I think I may not have made my point. Is there anyone out there, who has used these instruments and imaged utilities,regardless if that was the goal.

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    Junior Member gfox's Avatar
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    Default Re: The missing link? FDEM & TDEM

    Does the M in FDEM stand for Marimba?

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    Senior Member sauroke's Avatar
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    Default Re: The missing link? FDEM & TDEM

    I have seen it tested years ago, but it was inconclusive. It depends on how much salinity is in the ground as well. The show you are thinking about, Pro was on the Discovery Channel, and was the same company I saw. Here is where the problem is, this will show DISTURBED earth, but will not show directional bores. They use it in conjunction with GPR, and can make a 3d image of something based on the diameters they can see.

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