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GPR Technique for Near Surface Geological Investi

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Information about GPR Technique for Near Surface Geological Investi
Science-Technology

Published on July 21, 2008

Author: alaageo

Source: authorstream.com

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Fourth Year Graduation Project GPR Technique for Near Surface Geological Investigation : Fourth Year Graduation Project GPR Technique for Near Surface Geological Investigation Prepared by  Alaa Mohammed Omar Cario University, Faculty of Science , Geophysics Department, EGYPT. Slide 3: The analogy between GPR and seismic reflection method. GPR operational requirements according to Daniels, 1988: Efficient coupling. Adequate penetration of the EM waves with respect to target depth. Obtaining a sufficiently scattered signal. An adequate bandwidth in the recovered signal with regard to the desired resolution. Slide 4: MAXWELL’S EQUATIONS: Slide 5: CONSTITUTIVE EQUATIONS: There are 3 quantities affecting the propagation of EM waves through materials : Electric conductivity Dielectric permittivity Magnetic permeability Slide 6: EM FIELD PARAMETERS: The velocity of electromagnetic wave in the ground is defined as: In low-loss (resistive) materials the velocity become: In non-magnetic materials the velocity is reduced to: Slide 7: The attenuation coefficient can be expressed as: In low-loss materials the attenuation coefficient is reduced to: reflection coefficient, K, at a half space for a normal incident signal is given by: Slide 8: The general topography of the area is a nearly peniplained desert with low relief and the average altitude is about 199m above the sea level. Slide 9: The sedimentary cover was deposited in the Holocene age (Recent). The studied area is mainly composed of three successive layers; the first layer is friable sands and gravels (Wadi-fill deposits). the second is cohesiveless soil composed of coarse-grained sands. and the third layer is consolidated sediments which is equivalent to the bed rock of the studied site. Slide 12: Types of antennae ( Shielded and unshielded). Modes of operation (Bistatic and Monostatic). Time window. Triggering. Antenna frequency vs. investigation depth. Stacking No. Survey Design. Slide 14: The data was processed by “RAMAC Ground Vision”, as we applied the following filters on the raw data: Automatic gain control (AGC). Time – Gain filter. Running Average filter. Band pass filter. The final step is data editing to correct mistakes in the field as well as reversing profile directions, merging files, etc . Slide 15: After applying AGC. Slide 16: After applying time-gain. Slide 17: After applying running average filter. Slide 18: After applying Band Pass filter. Slide 19: After data editing, reversing, and merging. Slide 20: Processing Parameters: Slide 21: Interpretation of GPR data involves the following steps: Identification of reflections and noise. Determination of velocity. Picking two-way times of reflection events, and trying lines with events that occur on the intersecting lines, which was made using “Golden software surfer”. Conversion of reflection times to depths, also done by “Golden software surfer” . Integration of the information from different lines to identify the type of the target causing the reflection. Slide 22: Data interpretation showed that the GPR results are analogous to the geological background of the studied area. The subsurface succession is composed of: the surface layer is friable sands and gravels (Wadi-fill deposits) with an average thickness of (1 m) , this layer is underlined by the second layer which is cohesiveless soil composed of coarse-grained sands with an average thickness of (2 m), this layer overlay the third layer which is the bed rock of this area, and composed of consolidated sediments. Slide 24: This study has shown one of the most important geophysical techniques GPR has the following advantages over other geophysical techniques: Very high resolution imaging technique. Non-destructive and non-intrusive way of collecting data. Can detect non-metallic as well as metallic objects. It provides a three dimensional pseudo-image that can easily be converted to depths that are accurate down to a few centimeters and reached to some meters. Data can be displayed and interpreted almost instantly if necessary – other techniques require various degrees of processing. GPR can often see through surface disturbances. GPR surveys are fairly easy to conduct and provide the results during the field survey. THANK YOU : THANK YOU

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