Ground Penetrating Radar System
As the name indicates ground penetrating radar referred as GPR is a type of radar developed to analyze the internals of the ground. It helps to map ground structures and ground features. GPR systems use range of frequencies for different applications and depth penetration requirments from low frequency (25 to 200 MHz), mid frequency (200 to 1000 MHz) and high frequency (1-3 GHz and above).
The diagram depicts typical components used in the ground penetrating radar system. Similar to other wireless system this radar will be composed of transmitter and receiver part. The transmitter part consists of source signal generation, modulation and RF upconversion before feeding the signal to the antenna for transmission into the solid ground. This is opposite to wireless systems where in signals are transmitted into the air.
The receiver part consists of signal sampling, signal digitization, data storage, signal processing to display and radar scope for displaying relevant information as needed.
GPR working principle
Ground penetrating radar system works as follows:
• Transmitter emits the RF (Radio Frequency) signal into the solid ground as per application requirements from Low, Mid and High range options. Some advanced GPR systems use multi-frequency arrays which allow users to collect data at different frequencies simultaneously or sequentially.
• Detects and records the different time instance of the echoes and utilizes these information to construct the image.
• Provide this image information on the scope in terms of signal time delay and signal strength.
Following are applications of this radar:
• to measure snow and ice sheet thickness in arctic region and other places
• to locate utilities buried within the ground
• to evaluate mine site
• for forensic investigation
• Digging archeological sites
• to search buried land mine
• to predict avalanche
• for environmental studies including soil stratigraphy, groundwater levels and other factors.
• to assess pavement and road analysis
• Concrete assessment
• Search and rescue operations
• Geological and geophysical studies
• Quality control and inspection
GPR Depth range
Following table provides ground penetrating radar depth. This data is specific to the site. It may vary depending upon many factors. One can refer this for basic comparison between different materials as well as to have rough estimate of the values.
|Material description||Depth (meters)|
|sea water||between 0.01 to 0.1 meter|
|Concrete||About 1 meter|
|Asphalt||About 3 meters|
|Clay,shale||About 6 meters|
|Silt,mudstone||About 7 meters|
|wood||About 8 meters|
|Fresh water||About 40 meters|
|Sand, Gravel||About 60 meters|
|Limestone||About 70 meters|
|Salt (Dry)||About 80 meters|
|Granite||About 100 meters|
|Ice, Air||About 1000 meters|
From the table, we can derive that ground penetrating radar can go as deep as possible based on materials in the ground. Typically depth range of ground penetration radar system is from 0.01 to 1000 meters. This depth varies based on several factors such as operating frequency of radar, dielectric properties of the materials being scanned and the specific GPR system being used.
Advantages of Ground Penetrating Radar (GPR)
Following are the benefits or advantages of Ground Penetrating Radar (GPR).
➨It is a non-destructive testing method which provide subsurface investigation without the need for excavation, drilling or any other invasive methods.
➨It can be used in variety of applications including archaeology, geology, environmental studies, civil engineering, utility mapping and more.
➨GPR systems can rapidly collect data over large areas to offer comprehensive view of subsurface features and structures below the ground.
➨GPR produces subsurface images that allow us to visualize location, depth and shape of buried objects, structural elements and geological layers.
➨GPR is commonly used to locate buried utilities such as cables, pipes and conduits. It helps to prevent accidental damage to underground infrastructure during excavation and construction activities.
Disadvantages of GPR
Following are the drawbacks or disadvantages of GPR.
➨The penetration depth of GPR is influenced by various factors such as radar frequency, electrical properties of subsurface materials etc.
➨Interpretation of GPR data requires expertise and experience.
➨The effectiveness of GPR can vary depending on geological and soil conditions of survey area.
➨GPR signals can be attenuated or reflected by various subsurface features. This can sometimes obscure desired subsurface information.
➨It may struggle to accurately image complex subsurface structures.
➨GPR systems are typically better at vertical resotion (i.e. depth) than horizontal resolution.
➨Rough or uneven terrain as well as poor surface conditions can affect quality of GPR data and may require additional survey preparation.
➨GPR signals can be affected by EM interference, ambient noise and other adverse weather conditions.
➨GPR equipment can be expensive to purchase or rent.
Despite these disadvantages, GPR remains a valuable tool for non-destructive subsurface investigations in various applications. Careful consideration of these drawbacks and proper planning can help maximize the effectiveness of GPR surveys and mitigate potential challenges.
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