Hey Bigman, It's been 3 years pass I am still going learning new things, but als back some of your channel following your video. So please keep updating new things. Appreciated!
Hello, thank you for the videos. I am new to GPR Aplications. I am aware of its limitations but your videos are very helpful. I own an OERAD formerly as EASYRAD out of Bulgaria. it's a dipole antenna unit. We purchased it in hopes of locating voids. Specifically tunnels, and air vents coming to the surface. I have an 8' shaft that the first 16" is sealed with plywood and dirt. After playing with the settings and the background colors I am getting pretty good images. Unfortunately the manufacturer doesn't provide much operational information, so it kind of like you are on your own. thanks again, I subbed and will be watching everything you post.
How do we understand the underground space? Do we understand such gaps by looking at the signal amplitude? eg rock hole? or the burial space under the ground? thanks
Metal is special - it actually absorbs the radar pulse and re-transmits it back to the antenna. That is why you typically get such a strong response from metal (and usually ringing as well). The non-reversal of polarity (sorry for the double-negative!) is important for its own sake. I think new FRP bars might also be a higher dielectric than concrete, and so would be expected to give a non-reversal of polarity, but the response won't be as strong as metal. So the basic concept - higher dielectric gives non-reversal, lower dielectric gives reversal - holds. I just get a little picky at the use of the word "reflection" when it comes to metal (although the word otherwise pertains for all other materials). If the metal is very, very thin (as in wire mesh), then you won't necessarily get the strong response I've seen from rebar, but that is, presumably, a more advanced topic. Having just written these sentences, I guess I'm more comfortable with "response" than I am with "reflection"... :)
Sir i am trying to study how to use GPR to find moisture content ...while reading some articles i found that we can use ground waves (clearly mentioned not reflected wave) for the purpose ............. or can you pls make a video about finding moisture content of soil by using bi-static shielded antennas
Hi. The articles may have been distinguishing between surface and buried as reflected and nonreflected. Bit I think I understand what you were asking now. If you are looking for moisture content at the ground surface you will see different amplitudes in the ground wave response. Or you can map variation in signal attenuation below ground surface to get a relative measure of moisture
Hi Omar. Thanks for the great question! Yes, The GPR records the polarity of the signal. This can be inferred from the color sequence of the signal in 2D or from the actual polarity from the 1D wiggle trace.
Hi Thanks for this vedio. Could you please provide me some knowledge about concrete scanning interpretation (rebar distribution, slab thickness and concrete cover thickness over rebar)? Mostly i'm confuse if i see a layer below the rebar patter it will be slab bottom but which of the polarity should be picked for the thickness of the slab.
pranjal maurya hi. You asked a bunch of questions. Check out my other videos. I recently did one on finding depth to target. All of the questions are answered in my online program at learngpr.com.com.
Hi Anatolii! Thanks for watching and commenting. Here are two resources that are useful: 1. A basic overview article about GPR for rebar mapping. There is a small section that discusses polarity. This paper is curated on the Penn State University website... citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.522.4134&rep=rep1&type=pdf 2. Here is a book written by Conyers. It is not about rebar or void detection, but in the chapter about graves and cemeteries he gives an incredible discussion on polarity shifts of voids. Here is a link to the book on Amazon...amzn.to/2ctOJWE Hope this helps!
hmmmm, I'm sorry Dan, but I am going to have to disagree with you on one section of this video. Firstly, everything you have gone through on here is spot on, and it amazes me how many people that use GPR, regardless what sort of antenna and application they are using it for, do not know this simple process, to determine what material the object you have found is made from. But can I just pull up you one point? You said "does it matter if your radar is set for positive or negative" and you said, "absolutley it does". I'm sorry, (now maybe I am just being too critical) but I am going to say "no it doesn't matter what your radar is set up for" so long as you actually know what it is set up for. If you know it is set for negative positive or set for positive negative then you will be fine out in the field. So long as you know and you can read it and more so understand it. Sorry mate, I'm probably just being too critical, you do go through and explain it perfectly throughout the rest of the video, so regardless of that bit at the start, if someone is watching this and paying attention then they should get it and understand it. But anyway, well done on doing a great video for everyone to learn from. Keep up the good work. Regards Ben
Hey Geelong! Thanks for another comment. I agree with you here, but I think I asked does it matter if the reflection is positive or negative and it does. Certainly you are correct. It matters what your GPR settings are, but that is a little more detail than I was shooting for. The point of the video, which I think you agree, was to show that the polarity will be different if the wave moves from a high dielectric to a low dielectric compared to the other way around. Understanding that the polarity will be different depending on the materials is important for interpretation and can help many surveyors that currently don't use this important fact to develop better understanding. Thanks again for the comment and please keep watching. I'd love to hear more from you on future videos. PS, I like the critical! :)
If parallel scans show that your "void" is repetitive and forms a nice line, then you are actually looking at an air (or water?) filled PVC pipe. I'd be reluctant to call that a "void".
bdrogin Thanks so much for the comment. I would say it's semantics, but no doubt you are correct. The ultimate purpose of the video is to show that wave transitions from concrete into different kinds of materials will produce different responses. That would be the response for air whether a pipe, crack, or a void below a concrete slab, or an air pocket of a grave. Understanding this point should allow, I hope, beginners to take this info and use it in many different circumstances ultimately enhancing his or her ability to make interpretations. Thanks again and I really appreciate the interaction. Keep the comments coming :)
I agree, this is a great video for beginners. I don't have as much experience in using GPR on soil, which can get quite complex in interpretation, and I have great respect for those with expertise. In concrete, the purpose of the scan is usually very specific, and locating a non-metal pipe or conduit run can typically be part of the assignment, which is why calling it that is an important semantic. Except in an episode of Law & Order (SVU), finding a grave embedded in a building interior is not so common... ;)
bdrogin Thanks for the compliment and you do make a good point about the wording. p.s. I have located 1000s of graves...but I'm still waiting to find that one below the building. ONE DAY!!
There's an episode where they used GPR to find a suitcase embedded in a wall, and in the suitcase was a body. The filmmakers showed a technician holding up a tablet which appeared to be giving a live 2D picture of the wall! I thought, got to get my hands on one of those! Unfortunately, a TV fantasy, as you know, it takes several line scans in both directions for software to create a 2D or 3D representation. But the industry shout-out was still appreciated...
Hey Bigman, It's been 3 years pass I am still going learning new things, but als back some of your channel following your video. So please keep updating new things. Appreciated!
@@BGIS2000 thanks so much! I'll try to take some time to make new videos soon.
Hello, thank you for the videos. I am new to GPR Aplications. I am aware of its limitations but your videos are very helpful. I own an OERAD formerly as EASYRAD out of Bulgaria. it's a dipole antenna unit. We purchased it in hopes of locating voids. Specifically tunnels, and air vents coming to the surface. I have an 8' shaft that the first 16" is sealed with plywood and dirt. After playing with the settings and the background colors I am getting pretty good images. Unfortunately the manufacturer doesn't provide much operational information, so it kind of like you are on your own. thanks again, I subbed and will be watching everything you post.
Thanks so much for the sub and im glad the videos are helpful. Good luck!!
How do we understand the underground space?
Do we understand such gaps by looking at the signal amplitude?
eg rock hole?
or the burial space under the ground?
thanks
Great explanation......as always!
Prospekteur thanks so much! I really appreciate the comment.
Metal is special - it actually absorbs the radar pulse and re-transmits it back to the antenna. That is why you typically get such a strong response from metal (and usually ringing as well). The non-reversal of polarity (sorry for the double-negative!) is important for its own sake. I think new FRP bars might also be a higher dielectric than concrete, and so would be expected to give a non-reversal of polarity, but the response won't be as strong as metal. So the basic concept - higher dielectric gives non-reversal, lower dielectric gives reversal - holds. I just get a little picky at the use of the word "reflection" when it comes to metal (although the word otherwise pertains for all other materials).
If the metal is very, very thin (as in wire mesh), then you won't necessarily get the strong response I've seen from rebar, but that is, presumably, a more advanced topic.
Having just written these sentences, I guess I'm more comfortable with "response" than I am with "reflection"... :)
Hi,is there any sensor we can use for building a diy?
Sir
can you pease tell me how defferentiate between ground wave and reflectd wave by taking an example radargram
Vishnu Manoj Thanks for the comment. A ground wave can be a reflected wave. Can you be a little more specific?
Sir i am trying to study how to use GPR to find moisture content ...while reading some articles i found that we can use ground waves (clearly mentioned not reflected wave) for the purpose
.............
or can you pls make a video about finding moisture content of soil by using bi-static shielded antennas
Hi. The articles may have been distinguishing between surface and buried as reflected and nonreflected. Bit I think I understand what you were asking now. If you are looking for moisture content at the ground surface you will see different amplitudes in the ground wave response. Or you can map variation in signal attenuation below ground surface to get a relative measure of moisture
+LearnGPR can you please release a video on that please sir
Hello, How does GPR know the polarity is negative or positive? It is recorded in the data?
Hi Omar. Thanks for the great question! Yes, The GPR records the polarity of the signal. This can be inferred from the color sequence of the signal in 2D or from the actual polarity from the 1D wiggle trace.
Hi
Thanks for this vedio.
Could you please provide me some knowledge about concrete scanning interpretation (rebar distribution, slab thickness and concrete cover thickness over rebar)?
Mostly i'm confuse if i see a layer below the rebar patter it will be slab bottom but which of the polarity should be picked for the thickness of the slab.
pranjal maurya hi. You asked a bunch of questions. Check out my other videos. I recently did one on finding depth to target. All of the questions are answered in my online program at learngpr.com.com.
Dear author! Share please references on scientific publications or books which are used as a resourse of information to prepare these videos
Hi Anatolii! Thanks for watching and commenting. Here are two resources that are useful:
1. A basic overview article about GPR for rebar mapping. There is a small section that discusses polarity. This paper is curated on the Penn State University website... citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.522.4134&rep=rep1&type=pdf
2. Here is a book written by Conyers. It is not about rebar or void detection, but in the chapter about graves and cemeteries he gives an incredible discussion on polarity shifts of voids. Here is a link to the book on Amazon...amzn.to/2ctOJWE
Hope this helps!
hmmmm, I'm sorry Dan, but I am going to have to disagree with you on one section of this video.
Firstly, everything you have gone through on here is spot on, and it amazes me how many people that use GPR, regardless what sort of antenna and application they are using it for, do not know this simple process, to determine what material the object you have found is made from.
But can I just pull up you one point?
You said "does it matter if your radar is set for positive or negative" and you said, "absolutley it does".
I'm sorry, (now maybe I am just being too critical) but I am going to say "no it doesn't matter what your radar is set up for" so long as you actually know what it is set up for.
If you know it is set for negative positive or set for positive negative then you will be fine out in the field. So long as you know and you can read it and more so understand it.
Sorry mate, I'm probably just being too critical, you do go through and explain it perfectly throughout the rest of the video, so regardless of that bit at the start, if someone is watching this and paying attention then they should get it and understand it.
But anyway, well done on doing a great video for everyone to learn from.
Keep up the good work. Regards Ben
Hey Geelong! Thanks for another comment. I agree with you here, but I think I asked does it matter if the reflection is positive or negative and it does. Certainly you are correct. It matters what your GPR settings are, but that is a little more detail than I was shooting for. The point of the video, which I think you agree, was to show that the polarity will be different if the wave moves from a high dielectric to a low dielectric compared to the other way around. Understanding that the polarity will be different depending on the materials is important for interpretation and can help many surveyors that currently don't use this important fact to develop better understanding. Thanks again for the comment and please keep watching. I'd love to hear more from you on future videos. PS, I like the critical! :)
If parallel scans show that your "void" is repetitive and forms a nice line, then you are actually looking at an air (or water?) filled PVC pipe. I'd be reluctant to call that a "void".
bdrogin Thanks so much for the comment. I would say it's semantics, but no doubt you are correct. The ultimate purpose of the video is to show that wave transitions from concrete into different kinds of materials will produce different responses. That would be the response for air whether a pipe, crack, or a void below a concrete slab, or an air pocket of a grave. Understanding this point should allow, I hope, beginners to take this info and use it in many different circumstances ultimately enhancing his or her ability to make interpretations. Thanks again and I really appreciate the interaction. Keep the comments coming :)
I agree, this is a great video for beginners. I don't have as much experience in using GPR on soil, which can get quite complex in interpretation, and I have great respect for those with expertise. In concrete, the purpose of the scan is usually very specific, and locating a non-metal pipe or conduit run can typically be part of the assignment, which is why calling it that is an important semantic. Except in an episode of Law & Order (SVU), finding a grave embedded in a building interior is not so common... ;)
bdrogin Thanks for the compliment and you do make a good point about the wording. p.s. I have located 1000s of graves...but I'm still waiting to find that one below the building. ONE DAY!!
There's an episode where they used GPR to find a suitcase embedded in a wall, and in the suitcase was a body. The filmmakers showed a technician holding up a tablet which appeared to be giving a live 2D picture of the wall! I thought, got to get my hands on one of those! Unfortunately, a TV fantasy, as you know, it takes several line scans in both directions for software to create a 2D or 3D representation. But the industry shout-out was still appreciated...