As GMKA Defense, we develop the technologies needed by the Turkish Armed Forces to detect terrorist caves and bunkers, as well as to be used for many preliminary reconnaissance in the field of military defense.
Underground imaging is provided by various sensor waves emitted from magnetometer, manometer, gradiometer, GPR radar, Doppler radar devices.
Underground imaging devices have been produced with different features and capabilities. Underground imaging can be performed with devices of technologies and operating logics. For example, the structures and working systems of GPR radar devices and magnetometer devices are very different from each other. GPR radar underground imaging devices consist of electromagnetic transmitters-receivers and comparators operating at frequencies such as 25 MHz, 50 MHz, 100 MHz, 250 MHz. Low frequencies can penetrate deeper underground. However, there is an inverse relationship between frequency and object dimensions. The larger the frequency, the smaller the detected object size. This means that the resolution increases.
Magnetometer underground imaging devices, on the other hand, consist of only a magnetic field sensor and a microcontroller unit. It has no similarity with the GPR radar system. However, it is mostly preferred in underground imaging works. The magnetic field sensor forms the heart of the magnetometer.
Gradiometer devices are also used in underground imaging works. A gradiometer consists of two or more magnetometer sensors. The reason for using more than one magnetometer is to try to reduce the probability of error. Gradiometers and magnetometers are extremely useful and can detect magnetic metal objects at long distance depths.
There is a difference in the number of sensors between the magnetometer and the gradiometer. Systems using two or more sensors are called gradiometers. Gradiometers are usually mounted side-by-side in rows, and a large area can be scanned at once. In gradiometer devices, the margin of error is minimized compared to the magnetometer. It allows data collection from multiple points.
After the system collects data from all sensors that can operate selectively, as thermal or magnetic, it sends the data via bluetooth to the computer software along with the direction it is looking at.
The camera in the center of a sphere in the computer environment looks at the shell of the sphere from the inside and paints the inner surface of the shell of the sphere with the relevant color according to the sensor information received. This creates an image as the color equivalent of the thermal or magnetic field intensity in the direction of view.
This situation is met as a separate value for each metal in the software environment, which offers the possibility of differentiation.
In addition to lidar and thermal sensors, it has multiple cesium magnetic multi-sensors and lidar sensors. It penetrates 0-80 m depth in range in good soil conditions and correct use. They are systems that calculate metal differentiation, depth detection, distance information and target pinpointing.
The device magnetic sensor consists of three axes. It scans automatically on these axes (a, b, c), while visual touch on the control screen of the device is used when desired.
For example, scanning can be done by unidirectional c-axis scanning or by adjusting different axes such as a, b. The signal strength can be seen on the controller at the back of this scanning device and there is a rising and falling signal oscillator. It rises upwards for metallic objects and represents it with a color. It is a smooth instantaneous signal processing.
It represents a void or loose ground with one color and a complete void (room, tunnel or passage) with a different color. The oscillator also descends and renders a smooth instantaneous image.
Digital data is processed by the thermal sensor.
Visualization and identification are very accurate.
These scans may vary, but the ground temperature difference of the scan is visible at its exact value with an exact measure. In night scans and in wet ground, snowy, swampy ground, thermal mode scanning will be superior for gap detection.
UNDERGROUND IMAGING AND ANALYSIS
- It is a geophysics-based measuring device used in the investigation of shallow layers of the underground (first 0-80 m).
- The extraordinary developments in the electricity industry in the last 30 years and the ability to measure the travel times of electromagnetic waves traveling underground at a speed close to the speed of light in the order of nanoseconds have made significant contributions to shallow geophysical imaging methods.
It is a concrete result of these developments mentioned above.
METHOD
- The principle is to observe the echoes of high-frequency EM waves (radio waves) sent into the ground by a transmitting antenna with an electric field vector in the horizontal direction (TE: Transverse Electricity).
- It was first developed to measure ice thickness. As a result of processing the data obtained in the studies carried out in the regular ground environment with the data processing techniques used in seismic methods, it has been observed that the research depth of 10-20 m has been reached.
Today, the GPR method is widely used in shallow ground surveys and archeometry studies.
Examples of uses include the following:
- Ground survey: Road, airport, dam, water canal, power plant, residential area ground surveys
- Tunnel surveys: Railway, highway, water tunnels, tube passages, mine gallery surveys
- Building research: Examination of ceilings, floors and walls, restoration research
- Archaeogeophysical research: Finding ancient cities, temples, tombs, walls, foundations, corridors, and similar historical remains
- Investigation of industrial waste, leakage and environmental pollution: Finding old or unregistered industrial waste sites, identifying leaks, and leakages from factories, fuel stations, waterways, etc., site investigations of garbage disposal areas
- Investigation of old or unregistered city infrastructures: Finding old sewers, waterways, canals, pipes, bunkers, electricity, and telephone lines
- Judicial and forensic medicine: Detection of prison escape tunnels, locating corpses, and mass graves
- Mining exploration on the surface and in the galleries: Exploration of mines near the surface and development of reserves, mine (coal) research by drivage, first aid in cave-ins and mine accidents
WORKING PRINCIPLE
• Relative permittivity K is synonymous with the dielectric constant of a capacitor. The larger the dielectric constant of a capacitor, the more electromagnetic energy it can accumulate through polarization. The neutral molecules that make up the structure of a substance become polarized under the influence of the electromagnetic wave passing over them and store electromagnetic energy.
• Immediately afterward, they give back this energy as electromagnetic waves. This is how electromagnetic waves travel from one molecule to another in matter. In this respect, the phenomenon is very similar to the progression of seismic waves in matter. But electromagnetic waves can also travel in the vacuum of space without matter. For seismic waves to propagate, the medium must be composed of matter (the reason for the intensity parameter in the definition of the seismic reflection coefficient).
• The electromagnetic signal sent into the ground is in a harmonic structure and contains an effective frequency. The value of this frequency determines the depth of penetration, the amount of absorption, and the degree of scattering.
• At frequencies lower than 10 MHz, the penetration depth increases, but with two negative consequences:
1. Decrease in vertical resolution with decreasing frequency
2. The polarizable elements in the material leaving their original positions instead of being polarized at low frequencies and causing electrical conductivity (current)
• The conversion of electromagnetic energy into electrical conductivity at low frequencies is the main reason for absorption. At frequencies higher than 300 MHz, the polarizing elements in the matter will not have the opportunity to leave their original places, hence they will not be affected by the absorption caused by electrical conductivity. However, there will be an action-reaction delay problem at high frequencies, and as a result, there will be a frequency-dependent decrease in the relative permittivity with increasing frequency.
On the other hand, as the frequency increases, the vertical resolution improves, while the penetration depth decreases. High frequencies also cause the appearance of a large number of scattering hyperbolas in ground penetrating radar cross-sections.
• As can be understood from the above items, the more resistant (less conductive) the subsurface is, the higher the quality of the ground penetrating radar images. Where penetration depth is important, the environment should be as dry (moisture-free) as possible.
• When electromagnetic waves reach the groundwater level, they enter a relatively more conductive environment. At this wet level, both a significant relative permittivity differentiation (contrast) occurs and there is a significant decrease in the amplitude and high-frequency content of the electromagnetic signal reflected onto the earth due to absorption because of the sudden increase in electrical conductivity at this level.
• As a result, amplitude and high frequencies decrease in the ground penetrating radar cross-sections starting from the groundwater level to the depth due to absorption as one goes deeper, and the energy in the parts below the groundwater level presents a swept appearance in the cross-section.
• It is a device that images the subsurface by reflecting the electromagnetic waves that looks at the change in the reach (dielectric) coefficient of the ground.
• The depth at which it looks varies according to the sensor frequency (50, 100, 200, 400 MHz) and ground resistivity. The number of measurements per trace ranges from 128 to 2048, the stacking ranges from 1 to 32768, and the sampling frequency ranges from 300 to 600 MHz.
• It displays 50 tracks per second and has a scanning speed of 3 km to 50 km per hour. Sensor lengths are 0.8 cm for 400 to 100 MHz, and 3 meters for 50 MHz. The sensors can be moved along traces to measure distance and time by holding them in one place.
APPLICATION AREAS
It is used in underground engineering for mines, coal, sand, clay, groundwater, archaeological remains, burials, metals, pipes, underground cavities, cables, canals, tunnel exploration, old landfills; in subway excavations, landslide planes, sedimentation patterns, shallow underground discontinuities, water leaks, geotechnical, geophysical environment and engineering geology applications.
- Our device is equipped with a control unit and a high depth antenna.
- Control unit
- It is an excellent choice for deep and medium range applications. It is compatible with all types of antennas between 20 MHz and 1200 MHz, and you can achieve results with super-fast data acquisition and broadband options by simply changing the antenna.
- It is a system where you can get maximum efficiency in the field in minimum time with its low energy consumption and easy-to-use interface.
- It can be operated from the air by helicopter.
- It can be applied operated from the air by helicopter.
APPLICATIONS
• Deep geological and geotechnical survey
• Earth dam safety inspection, detection of structures or voids
• Fault line detection, mining
• Mapping
• Sand and gravel deposit surveys
• Geo – hydrological and ice thickness surveys
• Underground walls, basement and concrete reinforcements
• Hidden voids, tombs and shrines
• Water level, underground rivers and underground water basins
• Buried pipelines, canals and cable installations
• Embankment wells, galleries, trenches and underground bunkers
• Septic tanks, distribution boxes and drainage pipes
• Hidden tunnels, bunkers and shelters
ALTERNATIVE GPR ANTENNAS
60 MHz GPR antenna: The 60 MHz antenna, which is an extremely sturdy antenna, allows geophysical measurements at great depths. This alternative GPR antenna penetrates much deeper than a 100 MHz antenna and is particularly used for detecting larger objects lying deep beneath the ground.
100 MHz GPR antenna: Sturdy and balanced, it also has the ability to make high-resolution measurements. In contrast to the 60 MHz antenna, this antenna is particularly good at finding small objects underground.