gpr-forum.com

Forum dedicated to Ground Penetrating Radar technology
It is currently Fri Nov 24, 2017 2:45 pm

All times are UTC




Post new topic Reply to topic  [ 5 posts ] 
Author Message
PostPosted: Thu Aug 10, 2017 3:17 pm 
Offline

Joined: Mon Apr 24, 2017 3:38 pm
Posts: 6
Hello, My name is Chris. Recently, I conducted grid scanning at an old petro-station in North Carolina, USA. The objective was to locate the USTs and associated fuel piping. My LMX200 worked quite well to complete the task. However, while processing/interpreting the data in the field, I was curious why my 3D-Slice imagery displayed the USTs as an outline - see attached mapview. Is that because the tank was empty, or filled with air? Also note, the construction of the UST was suspected to be metal encased in a plastic shell.
Best


Attachments:
File comment: Note outline of UST in south portion of mapview.
1300 N Patterson_GPR Depth Slices_edited.jpg
1300 N Patterson_GPR Depth Slices_edited.jpg [ 413.73 KiB | Viewed 268 times ]
Top
 Profile  
 
PostPosted: Mon Aug 28, 2017 6:44 am 
Offline

Joined: Tue Nov 30, 2010 3:21 pm
Posts: 28
Dear CHDenvironmental,
if the tank is made of metal (coated with plastic or not) the EM waves from the GPR can not penetrate into the tank.
Now as for the outline...what happens if you observe the slices shallower than the one posted?
Is there a depth level where you have a strong response in between of the current outlines?
If it is a cylinder tank you should notice a strong response starting in the center of the current outline at one shallower depth. After that as you go deeper, there should be two lines that are getting more spaced till the level you have shown.
BR


Top
 Profile  
 
PostPosted: Thu Aug 31, 2017 7:39 pm 
Offline

Joined: Mon Apr 24, 2017 3:38 pm
Posts: 6
BR,
I appreciate your response. It is hard to assess the shallower slice in middle of outlines because there are several metal lids at the driving surface over top of the UST. Back to the point you make, if the tank is metal, the signal cannot penetrate metal. So if the top of the tank is say 2 ft deep, there should be a strong reflection at 2 ft. If all the signal is absorbed at 2 ft, will the deeper slice appear to have no signal, or be blank - such as the case in the image I provided?
Cheers,
C


Top
 Profile  
 
PostPosted: Tue Sep 05, 2017 2:11 pm 
Offline

Joined: Tue Nov 30, 2010 3:21 pm
Posts: 28
Dear CHD,
since the signal can not penetrate the metal there can not be other responses beneath a metal object, but there could be a reverbration/multiple/repeating response from the same metal object (signal trapped between surface and metal and bouncing up and down). Observing just the 3D map could be misleading in this case - one can not know what the 3D interpolated objects are, first or repeating reflection, so I would suggest to always take a peek into the 2D profiles at the corresponding locations.
Best regards,


Top
 Profile  
 
PostPosted: Mon Sep 11, 2017 1:37 pm 
Offline

Joined: Mon Apr 24, 2017 3:38 pm
Posts: 6
Danne,
That's a great suggestion. Thanks!
CHD


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 5 posts ] 

All times are UTC


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group