At NGI there has been a continuos activity in developing and testing Ground Penetrating Radar (GPR) for different subsurface mapping tasks since 1989. The work has included development of hardware and software for data acquisition and algorithms for data processing and interpretation.

In parallel with the development work, NGI has carried out more than hundred service jobs, gaining a lot of practical experience. The NGI Ground Penetrating Radar (GPR) employs an HP8714 Network analyser as the transmitter and receiver. It uses step frequency radar signals instead of the impulse signals that most of the commercial GPR use.  NGI GPR has been successfully used for over 100 field tests in around 20 countries since 1989.  The NGI radar systems have been exported to USA, South Korea, France, Taiwan, Malaysia, India, Denmark and Bhudan.

The advantages of using a network analyser based GPR system are:

  • The system can work within the frequency band 0.3 MHz to 3000 MHz, which has a  wider bandwidth coverage than most of the commercial GPR systems.
  • The radar signal bandwidth can be adjusted by software at the test site in order to best match the ground conditions to the antenna resonance frequency. Conventional GPR systems, which use impulse signals, need to change hardware to modify radar signals.
  • The frequency step number can be adjusted by software to make the best use of signal power for target detection under different ground conditions.
  •  The receiver has a higher processing dynamic range than conventional GPR systems.
  • A perfect frequency response, flat and non-dispersion within the assigned bandwidth. It is in itself a good tool for measuring ground material parameters and antenna response.
  • The NGI system makes it simpler to employ frequency-domain signal processing method such as filtering, deconvolution, Hilbert transform, etc.

Spesifications:

Transmitter:

  • Frequency range: 0.3 - 3000 MHz;
  • Frequency steps: 201 (typical value);
  • Average power: 0.1  Watt  (without amplifier) 1.0  Watt  (with power amplifier)

Measurement mode:

  • Operator controlled acquisition (discrete mode) and time controlled acquisition (continuous mode)
  • Speed: 1.5 sec per measurement (250 Hz noise bandwidth) 0.2 sec per measurement (3700 Hz noise bandwidth)

Size and weight for the main unit (transmitter and receiver): Size: 43 cm W, 18 cm H ,48 cm D, Weight: 20.5 kg

Receiver:

  • Dynamic range: 105 dB (for 250 Hz noise bandwidth) 90 dB (for 3700 Hz noise bandwidth)
  • Receiving sweep time: 7.2 msec per step frequency (250 Hz noise bandwidth) 0.6 msec per step frequency (3700 Hz noise bandwidth)

 Antennas:

  • Type: Flat plate resistively loaded wide bandwidth dipoles;
    Borehole antennas and high frequency horn antenna;
  •  Frequency coverage:
    - Dipole antennas:
    300 - 1300 MHz (center 800 MHz): 15 cm
    100 - 900 MHz (center 400 MHz): 30 cm
    50 - 350 MHz  (center 200 MHz): 60 cm
    30 - 180 MHz  (center 100 MHz): 120 cm
    - Horn antenna: 800 - 3000 MHz (center 1500 MHz): 10 cm
    - Length variable borehole antenna