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Ground-Penetrating Radar

      Ground-Penetrating Radar (GPR) must use low frequencies to penetrate the ground, achieve high resolution in both depth and cross-range to discriminate targets, and have a way to efficiently couple radar signals into the ground. METRATEK has conducted four years of  internal research on GPR to solve these problems. High attenuation clay soils and moisture-laden soils continue to be problematic except for very shallow depths. The Model 200 radar, using a wideband step-chirp waveform, SAR processing,  and antennas specially designed for ground penetration, have been applied to these problems as shown below. 

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      The Real-time Man-Portable Synthetic Aperture Radar (SAR) for Detection of UXO was developed and demonstrated for the Army Research Office via a contract with the Navy EOD Tech Center. The backpack contains the radar transceiver and a laptop computer that provides real-time SAR processing. The antenna module contains a pair of METRATEK planar log-periodic antennas that provide excellent ground penetration due to their close proximity to the ground. The support vehicle contains a generator and the heavier portions of the Model 200 radar. 

     As the operator pushes the GPR over the surface, his VGA goggles display the SAR strip-map in real-time, as shown at right. The top display shows the radar return without SAR processing and can be turned of to provide a larger SAR image. The SAR image is shown in the lower panel. The yellow line is a boundary between hard clay soil which has high radar attenuation. Note that the targets  (a 50-gallon drum at 10 feet and an artillery  shell at 6 feet) are much more detectable in the SAR image due to the higher resolution and better focusing. 

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 The image below is a composite of 7 real-time GPR data runs from left to right in very difficult clay soil. The circles indicate two mortar shells detected by the radar.

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      UXO Detection System - After the Model 200 GPR participated in preliminary tests for detection of Unexploded Ordnance (UXO) at Jefferson Proving Ground, Indiana, METRATEK was competitively up-selected to perform live-site demonstrations of the system at Yuma Proving Grounds and McChord Air Force Base. The 4-wheel drive vehicle tows a polyvinyl carpet sled that contains three pairs of Model 200 GPR antennas and three Electromagnetic Induction (EMI) sensors to provide a 3-m swath. The vehicle contains the Model 200 radar and real-time processing systems for the radar and the EMI sensors. This unit's performance at McChord was ranked best in performance (in terms of highest detection probability and lowest false alarm rate) of all sensors tested at all sites. For more information on this system, including EMI sensor and radar signatures of an 8-inch shell, please click UXO.

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Model 200-G Ground Penetrating Radar Parameters

Frequency

 200-2000 MHz

Antennas

2 to 16 depending on swath required

Pulse Width

4 - 1000 nanoseconds, 1-nanosec. steps

Pulse Repetition Rate

500-500,000 PPS

Peak Power

1 Watt

Range

0 - 25 feet, soil-dependent

Waveforms

 Pulsed step-chirp

Resolution       n=refractive index

  • Range: 15 cm / (n  x  Waveform Bandwidth in GHz)
  • Cross-Range: Range x Wavelength / (2n x Track Length)

Dynamic Range

66 dB single pulse, > 90 dB after integration

A/D Conversion

12-bit I,Q with DSP Integration to 16 bits

Real-time Processing

  • Downrange:  FFT or Coherent Integration    
  • Cross range: Real-time SAR

Display  Modes

Real-Aperture,  Strip map, or both

Data Storage

Removable Disk

Calibration

Built in autocal for every frequency

Other

Tests, HELP, Instant setup recall, Range Walk

 Copyright  METRATEK, Inc. 1998, all rights  reserved    

Phone METRATEK at (703)-293-9040