Question

Briefly explain the working principles and the main advantages of pulsed and frequency hopping GPR types. What is the advantage of using broadband GPR? What parameter of the GPR bandwidth pulse signal is set? What is the advantage and disadvantage of increasing PRF?

Answer 1

A. Working principle of GPR:

GPR stands for ground penetrating radar. GPR technology makes uses of energy waves in the microwave band whose frequency ranging from 1 to 1000MHz.

GPR is basically a geophysical identification method that makes use of radio waves to capture images below the surface of the ground in a modestly invasive way. It basically consists of two major parts, a transmitter and a receiving antenna.

GPR works by sending penetrating pulses into the ground and recording the echoes from the target objects.

B. Advantages pulsed and frequency hopping GPR:

1. Accuracy: The main advantage of GPR is that it allows technicians to identify the target locations of underground utilities with pinpoint accuracy without disturbing the ground.

2. GPR is very safe to use in public space and a wide variety of project sites.

3. Can be used to detect metal and non- metal objects.

4. The object dimensions, depth, and thickness can be found.

5. Data detection is very quick and it can be used to cover a wider space.

6. Frequencies can be varied to obtain a range of resolution and penetration depths.

7. It is highly cost-effective when compared with other methods.

8. Digging, excavating, or drilling the site areas is not necessary in this method. Quietly the search can be executed.

9. During the survey process, lawn, structures, monuments, etc, need not be disturbed.

C. What is the advantage of using broadband GPR?

In broadband GPR system, dipole antennas are used, which can be made more broadband by increasing the width of the conductive rods or by using extended conductive plates. By making the antennas sufficiently broadband, one can more efficiently transmit the entire frequency content contained within the source wavelet signal. This antenna type is a best fit for operating frequencies below 250 MHz.

D. What parameter of the GPR bandwidth pulse signal is set?

Frequency: Frequencies can be varied to obtain a range of resolution and penetration depths.

E. What is the advantage and disadvantage of increasing PRF?

Advantages:

Pulse Repetition Frequency (PRF) operation is commonly used for maximum range detection. It typically requires a high-power transmit unit, to receive returns of sufficient power for detection at a long range

To get the highest power, long transmit pulses are sent, and correspondingly long-matched filter processing is used. This mode is useful for accurate range determination. Strong sidelobe returns can often be found by their comparatively close ranges and filtered out.

Disadvantages:

Doppler processing is comparatively unproductive due to so many overlapping Doppler frequency ranges. This limits the ability to detect moving objects in the presence of heavy background clutter, such as moving objects on the ground.

This can also be a problem for identifying low-flying aircraft because of ground terrain clutter at similar ranges in the main lobe of the radar.

High PRF operation spreads the frequency spectrum of the receive signals, allowing a full Doppler spectrum without aliasing Doppler measurements.