Geophysics Forum

What do they do ERT survey for?

How deep was the tunnel? How big was it?

The link doesn't work -> file not found.

10KHz gives you better resolution and 3.5KHz gives you better penetration depth. I prefer 10Khz since clayey and silt sediments are more friendly than sands for penetration.

6pm in your local time? What's your time zone?

I took another look at the file. Now I realize it might be an underground wall with a slope. I think it's safe to say the mystery is mostly solved.

Kknq, please see a void model and its gpr data simulation below. You can see there are apparent different responses between the two sides and the middle of the void. When the void spacing (depth wise) is small, you can easily get the "ringing" effect as shown at the two sides due waves bouncing betw...

I still tend to believe it might be some kind of diffraction from something close to the ground surface, but it doesn't look like any diffractions I usually see. I haven't really think it through.

This is a GPR profile I collected close to a storm drain catch basin. The catch basin is at the ground surface between 13 to 16 ft in this profile. The strong "slope" signals to its left look very unusual. 270 MHz antenna.

Shielded or not, aboveground objects can show up in GPR data. GPR waves will be bounced back to the ground surface anyway -- they will keep travelling upward and then coming back down if there are aboveground objects.

To be honest, the anomalies do look like voids. I just realize that your tunnel might not be in a regular shape. I mean the top and walls of the tunnel might not be smooth at all. The GPR signals will bounce around inside the tunnel and show the signatures like the anomalies shown in your GPR profil...

At least you can see some anomalies. If the anomalies were caused by a tunnel, the tunnel might have collapsed. I think the more important question is, how large the area have you scanned. If you see this kind of anomalies everywhere, it's probably not a tunnel. If it's the only anomaly area you see...

If you drop a rock into a lake, the whole surface of the water becomes the wavefield as the water wave propagates. Each circle around the center where the wave starts is a wavefront. A wavefront is an interface (a straight line, a plane, a circle (as in this case)) or a ball, etc in the wavefield, o...

It probably means the wave velocity in the model doesn't change, such as a homogeneous media. If you provide more context, probably we can understand better about the question.

This is bad news for the survival of seismic operations. It could be the final straw for certain companies if North Carolina win.

In geophysics, a model space can be divided into a number small "boxes". Each box shares boundaries with adjacent boxes. Fore example, in 2D you can divide the model into rectangular shape boxes using parallel lines in box X and Y directions. Now you can see the "grid" formed by the dividing lines. ...

Although no sinkholes were found, it's good to see ERT was used instead of GPR for underground void locating. ERT should be used more often.

Very interesting. They built their own instruments. I wish someday I have some budgets to build my own tools.

It sounds great. Do you have some processed data examples? What kind of functions are available for data processing? Hi Geophix; There are examples of output on the website. In terms of processing, all typical functions used in GRED, RADAN, SLICE, etc are available, but the key here is speed. For e...

RockHound wrote: ↑

Tue Jul 21, 2020 11:42 pm

SOLD!

Congratulations!

It sounds great. Do you have some processed data examples? What kind of functions are available for data processing?

Nice!