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Basics Of Ground Penetrating Radar


Alex_Sor

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Greetings to all!

My name is Alexander, I am from Ukraine (Eastern Europe).

I represent myself and my friends, we developed a portable type GPR many years ago and gave it the name EasyRad.

We have developed a georadar and software for it. We would like to get in touch (get contact) with those people or organizations who need to search for gold in the United States and Alaska.

To my regret, on forums of gold prospectors and forums of archaeologists there are no sections "georadars", there are only metal detectors. I would like to convey to the searchers the information that GPR is not expensive and it allows you to explore underground spaces quickly and with great interest 🙂

We produce this GPR equipment, so we can answer all your questions. Our radar has a very affordable price for individual use, unlike other radars.

See the web link below for examples.

EasyRad GPR is a portable multi-purpose scanning ground penetrating radar of sub-surface probing for the problems of engineering geology, hydrogeology, archeology, ecology, field engineering as well as for search and rescue operations.

https://www.easyrad.com.ua/index.php?r=index_en

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Welcome to the forum!

I have long been intrigued by ground penetrating radar for prospecting. They are generally useless for finding individual gold nuggets unfortunately, as these items are too small to stand out on a GPR screen.

My interest was in Alaska where stream channels are buried and hidden deep below tundra and organic materials. GPR is good at picking up dramatic changes, and in this case the goal would be to simply trace and map buried channels. Depth to bedrock and in particular looking for drop offs or bends in the channel that might be a good drilling or pit excavation sample sites.

A few links....

http://www.groundradar.com/wp-content/uploads/J.Francke_FirstBreak_July09.pdf

https://www.researchgate.net/publication/27667687_Application_of_ground_penetrating_radar_in_placer_mineral_exploration_for_mapping_subsurface_sand_layers_A_case_study

https://ui.adsabs.harvard.edu/abs/2020E3SWC.19204005F/abstract

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thanks!

I would like to start by presenting our technology of work.

Start over.

I will be oversimplifying complex things so that ordinary readers (not engineers with higher education) can understand "how it works". There are radars on the market that work according to a primitive method: sending a signal and receiving a reflection. This method is described in most "scientific manuals". As a result of this work, the simplest radarograms are obtained. For example, you see such pictures on echo sounders that see fish:

fish-arches.jpg

As you can see, each fish is seen as a small hyperbola (math curve).

The more hyperbole, the bigger the fish.

But what if we don't have fish underground? 🙂 If what we are looking for does not give a clear response-reflection?

This is where an unusual theory comes to our rescue, which is called "Spiral Wave Geometry" (SVG). I will not overload you with mathematics, I will explain it simply.

The main postulate of the theory: "Everything is a wave." Any micro or macro object interacts with the World at certain frequencies.

Let's say you have a closet with opaque doors at home. You do not know what is inside it. Maybe there are dishes for guests? maybe there are glass glasses? How to find out ? You walk up to the closet and hit it with a sharp, quick blow. The entire contents of the cabinet are hit and begin to ring (make sounds). Every plate, every glass, every shelf is making sounds. The human ear receives these sounds, and the human brain decodes them. You can tell for sure after hitting: there are dishes in this cabinet! And it stands on the top shelf, and on the shelf in the middle there is glass, and at the bottom of the cabinet there are iron pans. What changed ? The approach to understanding has changed. I could take an ultrasonic emitter in my hand and separately receive a response-reflection from each part of the plate, from each pan. I would be able to see the reflection of the signal, but I will never understand from the reflection what exactly was the reflection? glass? metal? Spiral Wave Geometry gives us mathematical methods for processing the signal of reflected and excited vibrations from various objects in the earth below us.

Our Ukrainian engineers decided to use the SVG for the operation of the GPR. This required a lot of mathematical processing, a lot of experiments on real objects. Ukrainian engineers do not receive $ 250,000 a year like Silicon Valley engineers 🙂 we do not have such salaries in Ukraine ... But this does not mean at all that our engineers do not have encyclopedic knowledge and thirty years of experience in radio and radio electronics 🙂 Equipment for georadar surveying in the world costs a lot of money, and software costs hundreds of thousands of dollars. This makes it inaccessible to ordinary people. Starting work on our radar, we wanted to make a tool accessible to an ordinary person, which would allow working with a GPR as with a conventional metal detector, i.e. visualize very complex signals in a simple and accessible way. We did it. And we managed to create an inexpensive solution.

 

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The principle of operation of the GPR.

The device belongs to the class of monopulse ground-penetrating radars (GRLPZ) of the category of ultra-wideband devices (UWB) and is one of the tools for sounding the soil structure to a depth of several tens of meters in order to detect and determine the spatial boundaries of the occurrence of various subsurface inhomogeneities (objects that differ from the surrounding environment electrical characteristics: dielectric constant and conductivity, for example, areas of high humidity, soil decompaction - voids, inclusions of less / more dense substance, etc.).

The principle of operation of the GRLPZ is based on sensing the physical environment with electromagnetic pulses with an amplitude of 5-10 KV and a duration of about 2-8 nanoseconds and recording the amplitude and time delay of reflected signals from the interfaces between media with different dielectric permittivities.

The GRLPZ is capable of sounding the ground to a depth of 15 (30-50, Pro version) meters. The sounding signal emitted by the GRLPZ antenna propagates under the earth's surface, attenuating as it propagates, and, encountering an inhomogeneity, is partially reflected in different directions, including in the direction of the receiving antenna.

The level of received signals depends on the reflection coefficient of the signal from the subsurface heterogeneity. The reflection coefficient depends on how much the electrical parameters of the inhomogeneities differ from the parameters of the environment. The larger the difference, the larger the reflected signal. Part of the signal goes further and is reflected from the next discontinuity, etc., until the signal is completely attenuated.

The GRLPZ can be equipped with various types of antennas for solving various problems.

Dipole antennas are the simplest in a low-budget configuration. As a radiating system for professionals, a specialized antenna (option, version -Pro) has been developed, which has less radiation into the upper half-space and lowered lobes of the radiation pattern along the earth's surface. The antenna is based on a magnetic slot antenna based on an open resonator structure. The directional pattern of the GRLPZ antenna has a width not exceeding 25 degrees.

The use of this type of probing signal made it possible to relatively easily apply methods that lead to a gain in the signal-to-noise ratio and, ultimately, achieve a much greater sounding depth.

The radar software allows us to visualize a picture of what is below us. It is possible to build a 3D picture.

For example, here is a 3D picture of a river bed:

prognoz_voda.gif

 

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a little fun 🙂

Here in the photo - a man walks with our radar in his hand.

Please note, it comes without shoes 🙂 The metal parts of the boots add unnecessary signals to the profile of the shoot, and on this expedition we could not find shoes without metal parts.

 

work_rad.jpg

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Technique for sounding the GRLPZ.

The sounding technique is as follows. The operator moves the device along the surface of the earth along the selected profile, based on the required resolution in the horizontal direction. At each discrete point, a probe signal is emitted, and signals reflected by the inhomogeneities of the subsurface structure are received, which are processed and stored in the computer memory.

The main form of presentation of the results is the construction of radar images of soil sections along the profiles of the device movement, in which the depth is plotted along the Y-axis, and the distance in meters along the selected profile along the X-axis.

When constructing radar images, special signal processing algorithms are used to display the result on the screen. When displaying an image on a monitor screen, the degree of darkening and the color gamut of image areas corresponding to the inhomogeneities of the subsurface structure is directly proportional to the amplitude of the radar signals reflected from these objects. Since the amplitude of the radar signals reflected from subsurface objects is proportional to the reflection coefficients from the boundaries of these objects, and the reflection coefficients themselves are determined by the degree of difference in the physical properties of these objects from the environment, then in this case we can observe the degree of difference between the observed objects and the environment. The greater the indicated difference (the larger the radar signals), the greater the degree of difference between the image areas corresponding to the indicated objects. Thus, the degree of reflectivity of the boundaries of subsurface objects (for example, the boundaries of layers of different soil) is represented by a color gamut and darkening (blackening) or color saturation of the areas of the picture corresponding to inhomogeneities. Weakly contrasting boundaries of some objects or layers in this case are suppressed by reflections from objects with strongly pronounced differences in their physical properties from the environment.

1-5.jpg

In fig. Figure 1.5 shows the mechanism for the formation of radar images of soil cross-sections using the example of a small section of a profile where reflected signals from two pipelines are observed.

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Several examples of work.

Archeology.

Search for underground passages.

The primary readings on the radar profile look like this:

arh_1.thumb.jpg.9b26d1b8a382dc8ddcd082bae95eee6c.jpg

Left and right - two pictures with different processing (primary simple processing).

On the left, an envelope of the hyperbola is automatically drawn (blue line) over the intended object.

Well, now - mathematical processing using our visualization program:

arh_2.thumb.jpg.5a79bb6e4cb61b75e028b441828a519d.jpg

Left and right - two pictures with different processing (more complex mathematical filters).

Well, in conclusion, this is what the object itself looks like after archaeologists unearthed it:

arh_3.thumb.jpg.a18a3d6614d555cd87d49b83192c5f74.jpg

I draw your attention: there is no metal inside the object!

Only stones, emptiness (air) and earth rocks (clay).

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Math can work wonders.

Here in the picture on the left is the "primary radar screen".

and the second part (on the right) is the result of mathematical processing.

The object is visible - it is a cavity-decompaction under the ground (on the right).

 

___Example_M.thumb.png.01a97c15e5f69d8bafb5f911261df8b8.png

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Technogenic (human) objects.

in the picture below, a pit filled with earth and a ditch dug and then covered with earth (the radarogram was filmed across the ditch).

The pit on the left is surrounded by a white oval, the moat on the right is surrounded by a white oval.

The radar allows you to distinguish "mixed land" from untouched land.

arh_4.thumb.jpg.70248e2d89968e20249a0f48d2a20b89.jpg

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We have a test site where we test radars.

Look at the photo.

this is a long hole, inside which we placed a plastic bottle wrapped in aluminum foil.

As a result of our mathematical processing, the hole itself (voids) and the metal object inside are visible.

0-02-0a-eb328552d693f13c837c32ede0ae1d4071b8d8f2476503e8d5a9f15d38f9b9d1_3452791c.thumb.jpg.c965026325f34c343f7d2ab8cfc32126.jpg

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