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GPR is a short notation for ground penetrating radar

January 29, 2019 0 Comment

GPR is a short notation for ground penetrating radar. And it’s basically uses radio wave frequency in range of the electromagnetic spectrum to detect the location of an object. And these radio waves travel at the speed of light, which is 3E10^8 m/s in vacuum, and it makes the two wave travel time to burial depth to become extremely short. The wavelength of the wave associated in ground penetrating radar are 6-8 cm, and it considered short compared to seismic wavelength. Ground penetrating radar system contains a generator, transmitting antenna, receiving antenna, and receiver shows the output data. Transmitting antenna is the part that generates radio waves and sends off the signal, where the receiving antenna receives the energy that bounce back. Talking about the applications of ground penetrating radar, GPR can be used to detect historical and modern graves that are unmarked or to detect for unknown location of graves. The data are collected by moving the ground penetrating radar along a straight marked line, usually over the space that might have graves. As the GPR moves, the transmitted antenna (300-500MHz) will emit energy signals down the ground and then the receiver antenna will receive the refracted energy. The attached receiver or the digital device will project the data observed in a cross section of time and distance. Looking at the cross section, a person can get most of the information whether there are graves under the tested area or not by the hyperbola that appears in the digital device. However, the results of refraction hyperbola can be corrected and analyze to row data. This data acquisition method is called reflection profiling, which is basically gathering the data by walking the GPR at the speed of slow walk and the reflection hyperbola will immediately appear at the digital device screen. This method is commonly used at horizontal interface. Ground penetrating radar can also be used to detect layers in the soil. For this application, the best method to use is the common midpoint technique (CMP) or the common depth point technique (CDP); however, reflection profiling method can be used too. A person will use common depth technique for detecting the layers in the soil because this method is used for velocity analysis than as a stacking tool, and is combining the waveforms that have the same depth between transmitters and receivers. In common depth point technique, the transmuting antennas(1-2GHz) and the receiving antennas are moved away from each other by a certain amount each measurement. This method apply over a horizontal reflector and it produce diffraction hyperbola. GPR is used for Searching for pipes, buried drums, and the location of hazards that might affect the environment. Ground penetrating radar allows a person to visualize what is beneath the earth’s surface by using the profiling method with 200MHz antennas which is the same process as stated previously. One other method of ground penetrating radar is Transillumination method (zero offset profiling), which uses a setup where the transmitter antenna and receiver antenna are placed on either sides of the tested area. This method is usually applied to locate anomalies. Three dimensional displays of a time slice of depth vs. cross section are the best way to display GPR data and interpret them. 3D displays are mainly block views of GPR recorded data that are registered at different positions on the surface in different times. Data are usually recorded along profile lines, where the transmitting antenna and the receiving antenna are separated by fixed distance in each measurement. To obtain a good 3D display, a person needs to eliminate the noises from the objective or the target to be identified easily. Some of the factors that need to correct for are topography, radio towers, and cell phones. Moreover, to get a good image of data interpretation a person need to display only the peak values of the GPR signal, minimize the size of the data set, and display a limited time range (finite thickness time slice).