FAQ

 

 
  1. What is GPR?
 

 The OKO-2 GPR is a portable lightweight low-prices system designed for non-destructive environmental monitoring. The OKO-2 GPR includes control unit or control processing unit and antennas. All antennas are interchangeable and meet the needs of a broad range of applications.

 

  2. Applications
 

 OKO-2 is device designed for a geotechnical, geoecological, hydrological, hydrogeological, archeological applications such as:

  • Search for buried small objects;
  • Examination of buildings and structures;
  • Exploration of facilities;
  • Mapping geological structures;
  • Defining thickness of ice floe;
  • Basin exploration and sediments mapping;
  • Detecting thickness of temporary freezing/defrostation and mapping perpetually frozen soils and taliks;
  • Special applications.
 
  3. Advantages
 
  • High accuracy GPR data
  • Compatible with all antennas
  • Removable rechargeable batteries
  •   Rugged and weather resistant
  • GPS integration
  •  Several languages option (Russian, English, Chinese), 
  • Synchronization of GPR sounding and video recording
  • Horn antennas which can be mounted on a vehicle and a railway car (the speed up to 80 km/h)
  •  Advanced multi-channel multi-frequency system
  • Technical support and assistance
  • After sales service
  • Free training
  • 2-year warranty
  • CE certificate
  4. What about the price?
 

 Please send your request to info@geotech.ru

 

  5.  What about the training?
   Three-days Training course (Moscow, Russia) is provided to Customers who purchase the  GPR The training program includes:
  1. GPR positioning basics;
  2. GPR survey methods training;
  3. Field operations on a test range;
  4. Basics of GPR scanning results interpretation with GeoScan32 software.
Upon completion of the training program the trainees receive a package of the documents:
  1. OKO GPR Technical Description;
  2. GeoScan32 Illustrated Users Manual;
  3. CD with GeoScan32 software and personal password of software user that allows download of software updates from LogiS Ltd. web-site;
  4. Course of lectures of the three-day training program.

The training is provided by specialists of Geotech Ltd. having significant practical experience in application of GPRs for addressing a wide range of tasks beginning from surveying to complex geological and engineering explorations.

 

  6. Do you lease OKO GPRs?
 

 We do not lease GPR. Operations can be done by our specialists.

 

  7. Is it easy/difficult to learn how to interpret GPR positioning data?
 

 As any skill interpretation of GPR positioning data can be divided into several levels: basic, advanced and professional. GPR Positioning Basics course provides fundamentals of interpretation. This knowledge is sufficient for independent operation but is just basic knowledge and corresponds to beginner’s level. For improvement of your skills practical experience is of primary necessity. It is desirable to work independently at the sites where almost everything is known. Participation in GPR-positioning workshops and conferences regularly held in Russia and abroad will significantly push your skills upward. People with basic geological or geophysical education for sure have absolute advantage over people without special education. However, it is not a reason to lose heart and refuse purchase of a GPR.

 

  8. How is antenna unit selected for addressing a specific task?
 

 Antenna unit first of all depends on the task that you plan to address as well as a depth of exploration. Scanning depth and resolution data of different antenna units can be found in the Antenna Unit section. But we strongly recommend you to consult with sales specialist before purchasing a GPR as to take into account all possible aspects.

 

  9. What is the accuracy of depth testing and sizing of objects?
 

 Depth testing accuracy to 99% depends on the accuracy of evaluation of dielectric permeability of layers. Error per unit in the value of dielectric permeability of layers can produce error of up to 10% of depth. Sizing of object is possible only if dimensions of objects exceed wave length. Accuracy of sizing of object in lateral plane directly depends on accuracy of surveying of traces of chart. Reliability of evaluation of vertical size of object as well as reliability of depth testing depends on the accuracy of evaluation of dielectric permeability. However, if the target object is metal it is not possible to determine its vertical dimensions due to 100% reflection of a signal from the upper surface of such object which results in failure of the electromagnetic wave to scan the environment below this surface. Such objects form screens for GPR observation. When dimensions of objects are less or comparable to a wave length the object is recognized as a point – diffraction of an electromagnetic wave occurs. In this case it is impossible to size the object.

 

  10. Which software products can be used for processing and interpretation of GPR data?
 

 GPR OKO-2 basic package includes Professional version of GeoScan32 software designed for recording, processing and interrupting GPR data. GPR exploration data obtained by GPR OKO-2 can be saved in international data format SEG-Y and subsequently processed with any software product designed for interpretation of seismic or GPR data that supports this format, for example, RadExplorer or RadExProPlus.

 

  11. What feedthrough signal time shift shall be set in GeoScan32 scan window prior to scanning?
 

 During manufacturing of antenna unit an optimum feedthrough signal time shift is programmed in the memory of antenna unit, so when you enter the scanning window of GeoScan32 software and press the Connect button, software defines an antenna unit and the feedthrough signal time shift for connection of antenna is set automatically. Shift of feedthrough signal is set at a level of 10-20% from the beginning of time scale of the connected antenna.
If after connection with antenna unit the feedthrough signal shift is set at a level below 20% from the beginning of the time scale it is necessary to adjust position of the feedthrough signal by pressing the Connect button. After that the feedthrough signal is positioned at the required level automatically or by hand by pressing the Smooth button. Detailed information can be found in GeoScan32 Description software in Appendix 2. 

 

  12. What scanning step shall be set in parameters of GeoScan32 software scan window?
 

 Optimum step between samples for each antenna unit is specified in Table 2.4.1. of the Description of GPR OKO-2. The value of this parameter can be increased but when it exceeds the recommended values more than two times, objects can be missed between two samples.

 

  13. What stack value shall be set in parameter of GeoScan32 software scan window?
   Stack determines the value of repeated reception of each trace and its subsequent summing-up. Increase of this parameter allows detection of weaker signals, deepens the actual scanning depth and improves quality of image but at the same the recommended antenna unit scroll speed goes down during the profile recording.
Our
recommendations:
  • 1,4 – fast scanning for shallow depth exploration (asphalt thickness evaluation, road bed survey, etc.);
  • 8,16 – detection of different objects, engineering and geological tasks in light and medium ground environment;
  • 32 and more - operation under strong attenuation of signals in tight ground (clay loam, clay), explorations of fresh water surface. In case of stack ranging from hundreds to dozens of thousands it is recommended to perform the step-by-step scanning.
  • for maximum scanning depth it is possible to go to high stack value up to 100 thousand. With that scanning will be performed in the step-by-step mode.

 

  14. What is the purpose of Threshold Value parameter and what is the function of its value?
 

 Threshold value parameter is used for automatic localization of a feedthrough signal position. GeoScan32 determines place of a feedthrough signal for binding zero point of the depth scale.
GeoScan32 records the time when the signal first time exceeds the reference threshold value set by the Threshold Value parameter by averaging the numbers of records obtained from each trace of the profile. GeoScan32 obtains position of a feedthrough signal in the given profile and respectively positions the zero depth point.
It can be necessary to change Threshold Value for scanning very weak or very strong signals when automatic positioning of a feedthrough signal does not function correctly.
To change the Threshold Value, open the “Profile Properties” panel in the Options menu of GeoScan32 software. To save the changes close the “Profile Properties” panel by pressing the OK button and save the profile. After closing of the profile the Threshold Value set by you will be applied to new profiles created for GPR surveying.

 

  15. How airborne noises received during GPR scanning can be distinguished from signals reflected from real boundaries in section?
 

 Inclination procedure from the Options menu can be used if profile has at least one hyperbola branch for identification of airborne noise. Position the cursor on the top part of the inclined line, press and hold the left button of the mouse and move the cursor to the lower part of the inclined line. Speed of electromagnetic wave in this environment will be displayed in the left bottom corner of the screen. If speed exceeds 30 cm/ns then airborne noise is recorded in profile.

 

  16. Why does the value of feedthrough signal shift set in the scan window of GeoScan32 software differ from the shift value displayed in “Profile Properties” window?
 

 To obtain the shift value was set in the scan window of GeoScan32 software it is necessary to divide feedthrough signal shift value displayed in the “Profile Properties” window by 256. The obtained integer number will correspond to the Rough direct signal shift value in the scan window and remainder of the division further divided by 8 (for single point antennas) or by 64 (for multiple point antennas) will be equal to the Smooth feedthrough signal shift value. “S” letter is added to multiple point antennas – e.g., AB-90S.

 

  17. Does GPR OKO-2 feature godograph capability?
 

 Godograph scanning mode of GPR OKO-2 is provided by GeoScan32 software. Design of the AB-90, -250 and -150 antenna units allows disconnection of transmitter from receiver and scanning in the godograph mode with distance reference to the receiver movement.

 

  18. What is the procedure for setting zero point of depth scale when processing scanning files?
  

The following shall be done for setting zero point of the depth scale:

  1. Set depth gain to 1 for better visualization of feedthrough signal by pressing the button on the tool panel of the main window of software (or by pressing Ctrl+K on the keyboard), open the “Gain” window, set value of the “Gain Factor” to 1 and press the OK button. 
  2.  Press the button on the tool panel (or press the space button on the keyboard) to open the Trace Window. Position the horizontal line at the first passage of feedthrough signal as shown in Fig. 1. 
  3.  Press the pp button in the right top part of the Trace Window after positioning the horizontal line on the first passage of the feedthrough signal. Depth scale zero point will be set to proper position.
There is a second method for setting zero of the depth scale. Set the horizontal line of the Trace Window to maximum of the second half-period (Fig. 2) of feedthrough signal and press the pp button in the right top part of the Trace Window. Depth scale zero point will be also set to proper position. Remember when using the second method for setting depth scale zero:
  1. division of layers will also fall on the positive half-wave of the reflected signal.
  2.  Reflection from dielectric environment results in inversion of the reflected signal.