Lecture 37 - Field Demonstration of GPR - Part 2

[Music] welcome back so in our previous lecture we have uh discussed about the how what is the basic principle behind the GPR technique and uh different components of GPR the penetration depth of GPR and uh now I will be discussing about how you can acquire the data into the field so uh currently we will do a 2d profile uh so it is very important uh before getting into the 3D profile it is very important that we should uh take uh several 2D profiles to get the overall idea of the region uh so that we can accurately decide the uh 3D grid uh where we have to take the uh data where we have to uh map these subsurface near subsurface region so uh so now as you can see we have adjusted the parameters so now as you can see we have adjusted the parameters uh the mode is 2D and now we will just click on the start scan so uh we will be taking a profile of around 10 m uh from here uh so we will take uh there is a vacant space uh uh uh chamber is there vant chamber is there within the subsurface so uh we will try to Target that uh currently so we will take a 2d profile while going from here and while coming back from here so from there so there will be two profiles so that we can correlate the data of both the profile and uh we can verify that if uh the data is not due to some any other kind of noises or uh or any kind of another uh feature so uh we will uh uh we will take two profiles while going from here and from by while coming from back from there uh so uh now uh as so uh I will uh you can start the profile by pressing the start scan so you can see now uh the real time uh mapping of the subsurface has been stopped and you can see this is the uh horizontal distance that is the distance of the ground that we can see this is 0 1 2 3 4 that will be the data that we'll be acquiring while uh creating the uh while taking the profile and this is the depth uh so uh depth we have taken it up to the 4 M so uh now I will you have to always keep in mind that you have to uh push or uh take the uh GPR unit very slowly so that the transmitted and the received data can be uh catched by the receiver uh otherwise if you will move it very quickly or fast uh then the transmitted uh electromagnetic waves will not be able to detect by the receiver so it is uh very important that you move very slowly while taking the uh GPR survey so now I am just so now you can see as I moving the uh wheel uh the cart the data has is being acquired yeah as I'm moving the uh GPR unit uh the data is being getting acquired so uh this is the real real time data that you are able to visualize and uh as we will cross this chamber you can see so uh as soon as we have crossed uh the vacant chamber you can see that this is uh this is the portion where the uh empty chamber is present uh so uh you can see in the screen green that whole part this air fill chamber that is vacant uh that is shown by a black region uh throughout the depth uh so we will repeat the profile by uh taking it once again uh in the reverse manner so I will stop the scan here here the where there was the start scan there is also a tab of stop stop scan we can uh I will press this so This profile has been stopped so we have taken uh one profile while coming uh from the initial Point uh it is very important that you should uh Mark the initial and the final position while taking uh the profile so now I will uh play back the profile that we have taken so we will click on the playback mode and you can see that we have taken one profile uh so I will check I will check on this uh folder and uh press the take button so uh you can see the overall profile has been taken so uh from there from the initial point to the final point it is around of 9 M profile and uh uh at the uh horizontal distance of around uh 5.2 so if you will touch the screen so it you can uh just uh the a crossair will be uh shown and you can easily uh know the depth and height uh depth and the horizontal distance that you want to see so the horizontal distance from the initial Point uh is 5.15 for the this uh Airfield chamber and uh the uh the width of the chamber is around uh 3 m uh approximately and uh other than uh the chamber we can also uh identify identify few other uh utilities uh so as you can see there is a hyperbola that is getting uh that we can see over here so so you can see uh a hyperbola that is uh this is the hyperbola so this hyperbola actually uh gives the signature of the uh underground pipe that is that we can encounter so uh similar hyperbola we can also find here this is also a hyperbola which is also uh for this we can also interpret as a pipe so there are two pipes that I can uh see as of right now and there is a gas fi chamber uh so uh the hyperbola signature for the uh cylindrical pipe is uh like uh when uh so the hyper the the logic behind the hyperbola signature for the cylindrical metallic metallic pipe is that when the electromagnetic uh waves propagate uh from the pipe so suppose this is our cylindrical pipe and we are crossing the GPR unit across this so the electromagnetic waves at the side of this pipe will take the higher time uh time duration than the central portion so uh this will uh this will be this will take more uh travel time to reach to the receiver and the the the crest part of the uh pipe will take a short time so the travel time is uh based on the travel time you can get a hyperbola uh symbol uh on the radar gr so that's why we we are uh we are getting a hyperbola signature for the we can interpret as a hollow uh cylindrical pipe uh within the radarr and this hole this is a chamber that we can encounter so now I will repeat the same profile uh while going from the final position to the initial position and uh this uh the profile that we will correlate from uh the profile that we take uh previously uh so uh to to confirm the uh presence of the utilities so I will stop the playback and uh now we can go to the collect mode so we will get back to the collect mode in which we can acquire the 2D data so this is collect mode so you can see that now a real time data uh will be taken uh through this mode so now as soon as I will uh uh press the start scin the uh uh scanning the the uh scanning will be for for the 2D profile will start so gently slowly I will take the unit and I will move it at the same path that we choose so now you can see on the display once again the Holo chamber has been encountered and here the chamber was there and it it has been now or so you can as I have seen that with while taking the profile also you can see that there is a hyperbola that is coming so we can mark the position over here uh for the interpretation part that uh we have encountered a utility pipe over here so we can mark the location here uh by uh uh by putting some color on the ground or we can mark it manually and now I am moving for further away so the total profile was around 9 M and similarly the second hyperbola has also arrived here uh so that means in both the profile we are getting the correct data so 9 M has been completed so I will stop the scan so uh we have taken the second profile so to access the second profile we will once again go to the playback mode and uh you can see a second profile has been generated over here second file has been generated and so there is a check box that we have to select and we have to click on the this part so you can see to to go to the full screen once again you have to uh click on the playback file so you can see the chamber was there over in this portion and so the profile total was of 9 M that we took while going from from the initial position to the final position and uh the uh chamber that we encountered was uh from 5 m at the horizontal distance from the initial point from the first profile and uh so uh by back calculating it was around 3 m so uh our uh chamber was uh of uh from 5 m to 8 m in the uh initial profile and from by looking at that the profile should start at 1 M from here uh uh uh the the chamber should start from one 1 M and it should get over at the 4 M so as we can easily see that it is starting from 1 M and it it is getting over at 4 M and other than that we can clearly see the hyperbola structure over here and over here so similar kind of profile has been uh generated so that means uh uh the uh the there the noise value of uh the the the signal that we have encountered that is from the utility and not from other kind of noise so uh now I will show you how we can see uh how we can uh uh acquire the 3D so we have done the uh 2D uh 2D 2D acquisition of the data uh now we will uh acquire the 3D data using the uh uh using the 3D mode which I have mentioned earlier so uh to go to the uh 3D mode I will just uh stop playback stop playback and system options uh then system shutdown and I will close this application and go to the start screen so this will close our 2D data profiles and now we are back to the start screen so in uh once again I will press A1 and I can change the mode uh using this tab so initially it was 2D now it is 3D as you can see and now I will create a new project and uh I will create a new data path and give it a DAT name lab practice 3D so now you can see the file has been generated and uh the name of this is lab practice 3D grid 1 so uh we can take several grids uh so I will design a 3D grid for uh our 3D AC data acquisition so signal process is same as 2D that I have discussed earlier we have to just Define the uh 3D grid so uh you can see there is one mode that has been uh added over here so uh I will go to the 3D mode and in 3D mode we can configure the grid so you can see that we have to configure the grid so uh this uh the the the grid mode that we can see that uh there is X start X and Y start y end and uh the spacing between the X line and the spacing between the Y Line so uh what we can imagine is like so for 3D mode what we can imagine uh a greed like a coordinate system a two 2D uh two dimensional coordinate system in which we have x coordinate and y coordinate so suppose if we want to create a grid of 2x2 M so for that and and and and the interval for each meter should be one the the offset between the uh grid should be 1 M so uh the grid size will be we will give the x is equal to 2 and Y is = to 2 and the offset will be of 1 M so it will create a 2x2 grid with having a mark between 1 1 M so uh that is the spacing that that is how it is it is getting uh configured so uh I want to create a 2x2 grid so X start will be zero X end will be 2 y start will be zero and Y end will be 2 so now you can see uh the system has generated a 2x2 grid having a uh spacing of 1 M the X spacing and Y spacing is 1 m so as you can see this is the 0 0 coordinate that means X is0 Y is Z over here so we have configured the uh two uh 3D grid of uh 2x2 M having a spacing of 1 M on the system and similar kind of greed we have also gener we have also marked on the ground as you can see uh this is also a uh 2x2 meter grid having a spacing of 1 m in X and Y Direction so uh now so now uh we will keep this unit uh on the uh initial 0 position and uh it is very important to uh know that uh the the the the the initial Point always should be correlated to this point this is the initial starting point of the profile this Mark has been given so this is the center point of our transmitter and the receiver so our profile should always start from this point and not from the uh initial of the cart but it should be from the center point of the uh C the Mark has already been given on the cut so I will adjust so that our central part on is on is matching with the marking and we will start the scan so as soon as I will start the scan it will show that we are going to cover this this this part of the uh profile so as soon as I I I I uh as soon as I uh click on the Run pad so uh Run tab so it will you can see the profile is getting generated and as soon as 1 M will be completed this this 1 M has been completed and we can correlate it with the ground also and as soon as the 2 m will get completed it will automatically get over so now you can see this profile has been taken we have taken one grid so now I will go to the second position so now I have moved the uh unit to the our second uh profile and I will uh press the Run tab and it will start taking the second profile from the X Direction so now it has been completed now initially I will once again take the profile to the final X position and I will press the Run tab so it will take the this is this uh we have uh completed the X Direction profiles now I will get back to the 0 location of the profile so now we will take profile in the y direction so now the y direction profile is being shown so as soon as I so I have brought uh the unit to the 0 uh initial location now we will take the profiles along the Y Direction so uh as you can see in the screen the Y Direction has been uh now uh shown so uh now we will uh press the Run tab and this profile is getting captured so one profile has been taken we will get back to the second y position and press the Run tab so this will start taking the second profile and now we will take the third profile third and final profile which will complete our 3D total grid so I will press the Run tab and so now we have seen that we have taken the so now uh till now we have taken uh so we you can uh see over here that uh in the grid 4 total six in the grid 4 gr number four total file uh number are six that means we have taken six uh files so I will go to the playback mode and uh we have so uh uh we have uh we have taken the data into the grid number four so we will select it and uh as we can see there are total six profiles that is getting loaded and uh you can uh uh playback files so uh individual files you can go uh you can select so this is uh file number one and next file this is file number two next file file number three next file file number four similarly we can go we can see that we have taken six total files of 2 m each so uh now uh I will go to the playback mode now if we want to uh see the uh to overall animated profile so we can go to the Z slice and we can uh it will get load and you can see that overall profiles that has been taken it has been uh it is uh now you can see from 0 to 2 m it is getting vary and uh from uh 0 0 m to uh 2 m it is getting uh animated uh on the screen so you can visualize the data and you can also uh see the you can also take the uh X slice or white as we have taken the Z slice we can also uh take the X and uh y slices uh we can animate the X and Y slices so if you want want to go to the Y slice you can see so you can uh animate all the layers using this similarly you can go to the X slice so you can uh see all the profiles are getting uh animated and and you can uh visualize the same uh individually and using the uh grid mode so uh we have seen how we can uh acquire 2D and 3D data uh through uh using the GPR technique and you can uh easily detect or uh image the near subsurface uh region uh up to a me uh depth of 4 M and if uh we will reduce the frequency so there are other units uh that is of 100 MHz and 200 MHz from that you can attain a depth of around 20 to 30 m uh and similarly you can uh go to the deeper level of the uh data so uh now uh further we can also process the uh data using the radan 7 so if time will be there so we will also show if if there will be time so we will show you how we can process the 2D and 3D data on the radan 7 software uh to Pro to reduce the noise and uh to enhance the data uh so I will stop here and uh we will get back to the next Lab [Music] [Music] thank [Music]