Additonally, the presence of solutes or other substances which increase the electrical conductance of groundwater and have the same attenuation and penetration results. The objective of GPR surveys is to map near-surface interfaces. For many surveys, the location of objects such as tanks or pipes in the subsurface is the objective. Dielectric properties of materials are not measured directly. The method is most useful for detecting changes in the geometry of subsurface interfaces.
Geologic problems conducive to solution by GPR methods are numerous and include the following: bedrock configuration, location of pipes and tanks, location of the groundwater surface, borrow investigations, and others. Geologic and geophysical objectives determine the specific field parameters and techniques.
Delineation of the objectives and the envelope of acceptable parameters are specified in advance. However, as the results cannot be foreseen from the office, considerable latitude is given to the field geophysicist to incorporate changes in methods and techniques. The following questions are important considerations in advance of a GPR survey. What is the target depth?
Though target detection has been reported under unusually favorable circumstances at depths of m or more, a careful feasibility evaluation is necessary if the investigation depths need to exceed 10 m. What is the target geometry? Size, orientation, and composition are important. As with all geophysical methods, a contrast in physical properties must be present. Dielectric constant and electrical conductivity are the important parameters.
Conductivity is most likely to be known or easily estimated. Both the electrical properties and homogeneity of the host must be evaluated. Attenuation of the signal is dependent on the electrical properties and on the number of minor interfaces that will scatter the signal.
Radio frequency transmitters, extensive metal structures including cars and power poles are probable interfering effects for GPR. The physics of electromagnetic wave propagation are beyond the scope of this manual. However, there are two physical parameters of materials that are important in wave propagation at GPR frequencies. This property is related to how a material reacts to a steady-state electric field; that is, conditions where a potential difference exists but no charge is flowing.
Such a condition exists between the plates of a charged capacitor. Physically, a great deal of the energy in an EM field is consumed in interaction with the molecules of water or other polarizable materials. Thus, waves propagating through such a material both go slower and are subject to more attenuation. The roles of two earth materials that cause important variations in the EM response in a GPR survey need to be appreciated.
The ubiquitous component of earth materials is water; the other material is clay. At GPR frequencies, the polar nature of the water molecule causes it to contribute disproportionately to the displacement currents that dominate the current flow at GPR frequencies.
Clay materials with their trapped ions behave similarly. Additionally, many clay minerals also retain water. The physical parameters in table 18 are typical for the Characterization of earth materials. The range for each parameter is large; thus, the application of these parameters for field use is not elementary. Simplified equations for attenuation and velocity at low loss are:. A common evaluation parameter is dynamic range or performance figure for the specific GPR system.
The performance figure represents the total attenuation loss during the two-way transit of the EM wave that allows reception; greater losses will not be recorded.
The above equations indicate a velocity of 0. A GPR system with dB of dynamic range used for this material will cause the signal to become undetectable in 2. These large variations in velocity and especially attenuation are the cause of success target detection and failure insufficient penetration for surveys in apparently similar geologic settings. I am working on modifying the code to work with different LCDs, I will post in a week or so when I have things working Thank you, sir, for your response and attention But is it possible to download some pictures of antennas from inside the plastic box.
Thanks Mirel. Also would it be possible to upload some photos of your existing antennas inside the box plastic? Especially where the TX and RX feeds are connected. GPRino is very good - please help send me pictures of electronic boards from top and bottom. I am struggling to see how it works. The system seems to fall between stepped frequency and frequency modulated techniques. If the former then my understanding is that quadrature information is required from the mixer and an inverse FT performed.
If the latter then the return signal will be received within the period of a single frequency step so a beat frequency will not be generated. Am I missing something? Okay, could someone in this "discussion" confirm if I'm reading this correctly or just completely wrong. I'm new to ALL of this Do The J connections all connect to the arduino including the connection in the RF sch?? Granted it won't work with the Gerber prints so you would probably need to get creative. Can I use adf eval board as freq generator controlled by arduino uno and hackrf one as receiver instead of most items?
Marcio Yamagushi. Become a member to follow this project and never miss any updates. About Us Contact Hackaday. By using our website and services, you expressly agree to the placement of our performance, functionality, and advertising cookies. Learn More.
Yes, delete it Cancel. You are about to report the project " GPRino ", please tell us the reason. Sign up Log in. Following Follow project. Liked Like project. Become a Hackaday. Remember me. Sign up. Forgot your password? Just one more thing To make the experience fit your profile, pick a username and tell us what interests you. Would expect low frequencies would work much better than 2 gig. Obviously it would change the specs on the components and filters. A GPR is so fascinating to read about.
Thinking about all the things that are still buried deep in the ocean, is just exciting. Excellent write up! Keep in mind that GPR has quite significant limitations in conductive surfaces such as clay soil, wet soil, and salt water will cause significant signal attenuation.
Can this be used to find water reservoirs underground or it only for detecting objects of other densities? GPR looks for differences in the RF propagation characteristics, like any radar. How can this possibly work? I would guess all that you are seeing is the atmospheric conditions above your angle of incidence. To make a much simpler analogy, imagine pointing a bright flashlight into a dirty mirror, and looking for reflections.
How can you pernitrate the earth with anything in the MHz range? It seems to me that this would best be served with large acoustical impulses into the dirt, exactly how the oil prospectors do it? And sonar has the same problems as GPR. GPR works just like radar in air. RF does penetrate into the ground, and it does reflect off features that are different than the surrounding medium. The attenuation is much greater than air, and it works both ways, so you are greatly limited in range.
But the attenuation varies with frequency, so you can penetrate deeper with lower frequencies. But … the resolution is proportional to bandwidth, so at lower frequencies your resolution gets worse.
If you are looking for a tank 3 feet down, or a salt dome feet down, you use different frequencies. Another big problem is isolation. If you use an FMCW radar, and your transmitting antenna is near your receiver, you need a lot of dynamic range to cancel out the transmitted signal from your received signal, so you can see those targets waaaay down in the mud electrically, and physically.
Simple pulsed radars are used to find buried tanks, pipes, and the like. Ground contact is commonly used to reduce ground bounce. Designing antennas for these is not fun. So pointing a long log periodic down is not going to work right. Bow ties flat on the ground are good, but for wide bandwidth they need to be electrically long.
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