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Source text - English Georadar
Co to jest georadar?
Jeszcze do niedawna nie istniały obiektywne metody pozwalające na ciągłe badanie gruntu, pokazujące całą jego strukturę wraz ze wszystkimi "wtrąceniami" w postaci rur, kabli, konstrukcji betonowych itd. Mimo, iż pierwszy georadar działał już 1929 roku (!) w Austrii, to pierwsze modele pojawiły się na rynku dopiero w latach 70-tych.
Metoda działania
Georadar impulsowy jest precyzyjnym nadawczo-odbiorczym urządzeniem pomiarowym, wykorzystującym fale elektromagnetyczne. Jedna antena wysyła przerywany impuls sinusoidalny, o długości półtora okresu, a druga identyczna antena, zamontowana tuż obok, odbiera odbite sygnały, które są opóźnione w stosunku do sygnałów nadawanych o pewną wartość od kilkudziesięciu do kilku tysięcy nanosekund.
Procesing
Georadar dostarcza nam surowe falogramy, na których mamy setki ponakładanych na siebie informacji, zniekształceń, szumów i zakłóceń. Obróbka danych staje się więc kluczowym zadaniem operatora georadaru. W celu uzyskania z nich interesujących nas informacji dane można obrabiać na wiele sposobów.
Interpretacja
Wspomagając się wspomnianymi procesami (filtrami) oraz swoim doświadczeniem, operator georadaru jest w stanie prawidłowo zinterpretować odczyt georadaru.
3D i georadar
Georadar daje nam możliwość uzyskania liniowego obrazu anomalii pod powierzcznią ziemi, wody czy w innym ośrodku np. w betonie, asfalcie czy drewnie, czyli dwuwymiarowego obrazu przekroju np. gruntu.
Translation - Polish What is a goeradar?
Up to recently there existed objective methods that allowed for a constant examining the ground showing its’ complete structure with all “inclusions” like pipes, cables, concrete constructions and so on. Although the first georadar worked already in 1929 in Austria, the first models appeared on the market in the 70’s.
All of the used measuring methods are better or worse images of reality. The opening method, considered as the best one, reflects real orogen structure only in a measure because it is a punctual method. We have 100% of information only in the points where drills were made but not between them.
When georadar found its’ way to a wider group of users, scientists and practitioners received a tool which allowed them for very precise obtaining of linear (and not punctual) cross-sections with information about objects situated near surface of the ground (cables, pipes, tunnels). These qualities together with the fact that georadar makes constant indestructive measurements, showing exact profile of the orogen are the reasons for georadar to be an indispensable tool with limitless number of applications. Out of the profiles, we can read depth, size, and shape of the objects and define material, which was used to make these objects. We can also learn about the level of earth water and much, much more.
Examination using the goeradar method- also called GPR (ground penetrating radar) can also be done on land, from air, on water, under water, on ice, and on slimy ground, on snow and on steep slopes- wherever a man is able to walk or swim through and where it is possible to stretch through the georadar antenna e.g. on a pontoon.
Formation of a hyperbole on georadar
Because georadar (through antenna) receives signals already reflected from some distance, the time needed for passing the way back to the object and forth is longer than in a case when the antenna is situated slightly above the examined object. Because of this, the cross-section of a pipe will be presented in the reading as a hyperbole.
GEORADAR – how does it work?
An impulse georadar is a precise radio- transceiving gage device using electromagnetic waves. While one antenna sends out discontinuous sine signal one and half interval length long, the second identical antenna installed right next to the first one, receives reflected signals which are delayed to related beamed signals from about tens up to a few thousand nanoseconds.
A recording of the signal is a single track, which can be compared to a single drill. It was that kind of an image being watched on oscilloscopes. After rendering tracks one by one, we get two-dimensional image where x is sojourned interval in the time of a profile and y is the time of georadar’s “monitoring”, which in an environment of known and constant dielectric allows for a precise qualification of depth of obstacles, which reflect transmitted signals.
Single recording registered by georadar…
…and one by one – make a 2D wave-guide
2D wave-guide without colour
Palette of colours from black to white
A palette, and its’ biggest amplitudes are marked black, zero, is white
Wave-guide in colours set by the author
Georadar works, depending on needs, in wide range of frequencies from 10 MHz to 2 GHz. Selection of the working frequencies depends on the depth of penetration because electromagnetic waves are stifled in the ground (especially in loams and clay- dry sand and gravel do not limit the scope so much).
The waves with the highest frequencies are stifled the most. That is why if there is a need to explore lithological layers, which are situated deeper, antennas working in the lower range of frequencies are used, namely from 20 up to 300MHz.
Reaching for deeper depths means lower resolution. It means that at the greatest depths we can perceive only the biggest objects like caves, tunnels, downcasts, and the structure of lithological layers. It is not a shortcoming of these antennas but their advantage because at great depths we are not looking for cables, pipes, or rock bits. Their presence on the wave-guide would only darken the image.
If there is a necessity to make precise analysis at great depths we can make it not from the ground but from drilling gap after setting special antenna in it, which transmits the smallest and the most interesting details relevant to us.
Antennas for middle and high frequencies enable detecting middle and small objects. Antennas with the frequency of 1-2GHz detect even single armament bars in a concrete construction.
Following examples show differences in frequencies of profiles depending on the frequency used. In order to simplify the comparison each profile shows the same depth (although the antennas with lower frequencies reach far deeper). Big anomaly (about 4 meters up) is a beautifully seen inclusion of different material- it is marble in this case.
Examples show differences
Georadar profile 900MHz
Profile made with georadar
With un-screened antenna 900MHz
Georadar profile 500 MHz
...500 MHz
georadar profile 300 MHz
...300 MHz
georadar 75 MHz
...and dipolar 75 MHz
Processing- working with georadar’s data
Georadar supplies raw wave-guides on which there are hundreds of information put one on another, distortions, noises, and disturbances. Working with the data becomes the main task for a georadar’s operator. In order to get information relevant to us the data can be worked with in many ways.
Direct image does not have to be readable well (especially when we are looking for subtle anomalies or when there are many disturbances caused by other objects), that is why we can enhance its’ particular fragments and other stifle. We need to know what the goal of our research is and which signals are the sources of the information needed.
An example of a scan from polish cathedral made with the use of unscreened antennas 250 MHz by Dr. Adam Szynkiewicz from Wroclaw University. Well known crypt visible on the left. Further on an area with many reflections.
After indicating the illustration with a cursor, a wave-guide after tooling will appear.
After long tooling of the data six anomalies appeared (smaller crypts?) next to the first visible anomaly on the left side of the profile. The anomalies are indicated with a blue colour.
We can notice an anomaly at the first sight shown by georadar. Without using a filter, only with a change of colors’ palette we can make a given object be more visible (example in the middle). Next after an “envelope” filter and cosmetic re-correction of colors’ palette, we receive a much-contrasted reading.
Following example illustrates, gradually, a process of filtering the file in order to stifle or delete completely the disturbances and to raise weak signals. The goal of the research is to find a place where a metal pipe with 90 cm diameter and at depth of 3 meters ia buried.
The research, because of needs, is conducted with 900 MHz antenna.
In order to see the progress of filtering the data please indicate the number of each phase of processing.
The outlook of rigour data saved by georadar. Numerous disturbances are visible, e.g. so called ringing, possibly from metal just by the surface of the ground (vertical streak on the right side).
The filter removing constant horizontal disturbances so called background removal; direct signal and all unchangeable disturbances occurring on each track disappear.
Filtering out the unwanted frequencies. Thanks to this filter, it is possible to stifle any range of frequencies. Here, we get rid of a disturbance caused by metal detected just by the surface of the ground.
Amplification of weak signals (gain). The deeper the signal reaches, the weaker it comes back; that is the reason for amplification of deep signal in order to receive correct reading. Very characteristic but weak signal of the pipe we are looking for emerges from the background.
Raising the contrast in colours’ palette shows us weaker signals.
The change of the palette into colourful. The result shows us a biggish metal pipe at 3 meters depth, drains visible on top, cuts, and cables. The arrangement of contour lines below.
INTERPRETATION
The data from georadar should be properly read which is not always.
Helping with processes mentioned before (filters) and my own experience, the georadar’s operator is able to define for e.g. how deep is specific pipe located, to define rough diameter and material used for its’ production. In some cases, it is possible to define if there is water in it.
Georadar finds a bunker- phase I
Analysis of a prism on the left. The question is if it is a buried bunker or not? We will improve topography
Georadar fins bunker- phase II
Now, when the shape of the prism examined was brought in we can look “inside”. Well seen reflex ion is a repulse from medium of different kind- it is bunker’s ceiling. After examination that is more exact, we can also see the armourment (small but regular accidents). Lower there is next reflex situated, not so strong as before. It is bunker’s sill this time.
Georadar finds the bunker- III phase.
We have an answer. The concave shape of the ceiling may be the evidence for its’ cracking and settlement, different penetrability or size of the bank on bunker’s sides. The only unknown is the red spot and strong signal in the middle on the level of bunker’s ceiling. It is probable that the ceiling is cracking.
Georadar hyperbole
We can see here on the left strong signal even without processing.
After slightly strengthening, the signal two weaker signals appear.
The pipe
The migration filter changes hyperboles into points...
The pipe after gpr processing
...next after fixing another effect- envelope and changing colours, we get very sharp view. Two smaller pipes were filtered by the change of colours. A place of burying the metal pipe was indicated.
3D and georadar
Georadar gives us possibility to receive lineal image of anomaly in the subsurface, water or in a different centre like concrete, tarmac or wood; so it is two-dimensional image of ground’s cross-section.
We can still go further and get full 3-dimensional model of technical infra-structure situated in the ground (cables, pipes, culverts, pieces of walls) through putting together many two dimensional profiles, made one after another in equal interspaced.
What is more, we can spin this 3-dimensional model and cut it in every possible way. We can also change a coefficient of transparently In order to see signals chosen by the operator. Short film below illustrating cross-section through the ground with buried pipes (from the example discussed before, only there are all three pipes visible here). We will be looking into the ground along the pipes. The pipes’ movement is a result of ground’s shape and its’ qualities.
Georadar animation
Click on the picture to download animation (~465 Kb).
There is no need to make many examination drills because the completely lithological structure and technical infrastructure are visible very well. Sometimes two or three holes are enough for precise identification of layers and for collecting the samples to delve physical and chemical examination of ground. In case of searching for elements of underground infrastructure, there is no need to make any drills...
Georadar gpr 2d
2D image
georadar gpr 3d
...and the way of making profiles for 3D model. Technologically advanced, technical programmes are able to complete the model in “empty places” between the profiles. The thicker the profiles are made the more precise model we can get.
Copyright (C) 2004 Highland Systems
GEORADAR – samples of working
Examples of examination’s readings below. Georadar has been working with screened antenna 900 MHz and unscreened antenna 500 MHz.
Processing the data takes time, experience and professional software. Nevertheless, an experienced operator is able to filter this data out so it will be the answer for questions asked by clients.
Examination of bastion on Jasna Mountain showed a piece of wall buried under the surface of ground at depth of 1 up to 3 and a half meter.
The rest of examination soon.
Click on the image to download additional explanations.
Georadar is able to show the location of different centres very precisely. Here, the examination of bunker’s floor shows different materials used in its’ construction.
Click on the image to download additional explanations.
Simple example illustrating different way of presenting another kind of centre by georadar. Hollowness in this case.
Click on the image to download additional explanations.
Perfect example of seller’s fraud who sold an allotment and unreliability of the brigade pulling down previously standing building (early post-war years). Georadar defines depth and shape of ruble covered with one-meter wide bank very precisely.
After indicating the profile, another profile after data processing will appear. Click on the image to download zoom.
A decline in the embankment detected by georadar
Georadar shows big, mediaeval walls (centre of the scan) among others, smaller and contemporary.
The depth of seating the walls is ~3, 5 meter. Profile without filtered processing.
Click on the image to download zoom.
Georadar shows mediaeval walls
Georadar detects damages of anti-inundation banks very accurately. On this example, a bank made of impenetrable materials is visible (right at the beginning on the left) and a gap covered with another grounding.
After indicating the profile, another profile after data processing will appear. Click on the image to download zoom.
A gap in the anti-inundation bank detected by georadar
It took more time for interpretation of the first and the third profile. Profiles 2 and 4 were worked with, only to present more contrasting readings.
GPR interpretation of the profiles:
1. Locating the hollowness at the depth of 1.8 (sill about 2.4m). Georadar usually reacts on hollowness with a very strong signal.
2. Searching for pipes below 1.5m. By this kind of works, georadar does not have any problems.
3. Locating the ceiling of a big channel-tunnel. The channel was located at the depth of 2.9m.
4. This example illustrates an interesting feature of the georadar. Pipe at the depth of 0.7m is surrounded by grounding with different kind of qualities- an excavation is visible (structure of the ground is injured)
Hollowness examination with georadar georadar locates the pipes georadar – Examination of the tunnel with GPR georadar gpr image
Copyright (C) 2004 Highland Systems
Bastion on the Jasna Mountain- site under construction
The goal of the investigation was to prove whether the bastion was built around already existing rock or is it filled up with ordinary grounding.
By the way of examining the bastion we found a piece of wall buried in the ground. We present you a model made of 16 parallel scans, which made it possible to hale a look from above (more about creating 3D models).
In order to see next cross-sections please indicate next numbers by the description.
Anomaly seen from above – 0.5m under ground
About 1m under ground
About 1.5m under ground
About 2.2m under ground
3m under ground, the shape disappears
3.7m under ground only irregular shapes are visible
Examination of the bunker.
The goal of the examination was to present bunker’s floor structure.
Signals slightly enhanced show disposition of anomalies.
Two kinds of fulfillments are distinctly visible. They are divided with a very precise border (vertical anomaly indicates a place where two materials are connected). We can also see horizontal isolation in concrete (black arrow). There are small but characteristic signals reflected from armourment above the hollowness indicated with a green arrow.
The last image introduces the interpretation of examined object. Grey area is the concrete, blue line is the water table, bright blue area is the hollowness, red line is the isolation.
Copyright (C) 2004 Highland Systems
On the profile above – georadar denotes two big granite mediaeval walls. There were two slight outlines visible on the surface (much thicker). The wall reaches~3.5m into the ground.
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* - new film showing 3D model ~1.6MB
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Years of experience: 25. Registered at ProZ.com: Feb 2009.
