3d Radar Principle of Operation

The GeoScopeTM GPR is designed for high-resolution 3-dimensional subsurface mapping using innovative radar and antenna technology.

Figure 1

Figure 1

Figure 1: 3d-Radar Geoscope GPR Control Unit.

The fastest step-frequency system available

The GeoScopeTM GPR is the fastest step-frequency radar on the market. By using a digital frequency source instead of traditional phase-locked loop technology, the GeoScopeTM can generate waveforms from 100 MHz up to 2 GHz with as much as 1000 frequencies with waveform lengths of 0.5-10 milliseconds. The step-frequency radar has a coherent receiver which means that the whole waveform length (typically a few milliseconds) is used as 100% efficient integration time. By comparison impulse GPRs use stroboscopic sampling with significant loss of energy. Figure 2 shows an overview of the GeoScope system.

Figure 1

Figure 2

Figure 2: GeoScope GPR system overview.

What is step-frequency?
How does step-frequency data differ from data from impulse radars?
What are the benefits using step-frequency?

  • 100% efficient integration time.
  • Fully programmable frequency source signature with full spectrum control.
  • The frequency range can be programmed and optimized to each measurement problem. There is no need to waste energy at high frequencies if the soil attenuation is high and medium to low resolution is sufficient for the job.
  • The raw measurement data can be stored as frequency domain data. This allows the user to reprocess data with different frequency weighting to enhance the features of interest. It is also possible to perform frequency domain absorption analysis to study phenomena related to concrete detoriation.
  • The frequency domain data is perfectly suited for fast FK-migration for image focusing.
  • The step-frequency signal is a low peak-power signal with low probability of interference with other radio systems. The 3d-Radar step-frequency system only transmits a burst of energy only when it is performing a scan.
  • Due to the self-calibration of the system, there is no time-drift in the system eliminating the warm-up time.

The step-frequency waveform gives optimum source signature with a uniform frequency spectrum. The computer control allows the user to set the dwell time on each frequency as well as the start and stop frequencies as shown in Figure 3.

Figure 3

Figure 3

Figure 3: Step-frequency waveform.

The radar system performs real-time time domain conversion through Fast Fourier Transform allowing the user to view B-scans from one antenna at a time. Raw data can be stored on 3DR data format either in time-domain or frequency-domain for post-processing. These data can be imported into either ReflexW from Sandmeier or RoadDoctorTM from Roadscanners OY.

The radar is controlled from a laptop computer through an ethernet cable. The system can also be configured with GPS / Total Station interface (RS232C) to allow recording of position data.

Collect up to 32 survey lines simultaneously

The GeoScopeTM GPR is designed to operate with an electronically scanned antenna array containing up to 31 antennas. The antennas are scanned sequentially by the radar unit. The unique antenna system consists of air-coupled bow-tie monopole pairs as shown in Figure 4. This gives a quasi-monostatic antenna configuration with practically zero-offset distance. The air-coupled antenna array can be operated at elevations up to 30 cm off the ground allowing high-speed surveys.

Figure 4

Figure 4

Figure 4: Ultra-wideband bow-tie antenna pair (cross section).

In opposition to traditional octave-band GPR antennas the ultra-wideband bow-tie monopoles have continuous frequency coverage from the 100 MHz range up to 2 GHz as illustrated in Figure 5. In practice this allows the user to collect data from 100 MHz to 2 GHz without changing antennas. By comparison, a similar survey using impulse GPR would require use of 200 MHz, 400 MHz, 800 MHz and 1600 MHz antennas.

Figure 4

Figure 5

Figure 5: Wideband coverage of the antenna array compared with traditional GPR antennas.

The antenna elements are arranged in an interleaved pattern consisting of antenna elements with different sizes to fulfill both the Nyquist spatial sampling criterion for high-resolution imaging and sufficient low-frequency radiation for deep penetration. Depending on the application the system can be programmed to use all the antennas in the array for full 3-D imaging mode. For regular road survey, the system can be programmed to use fewer elements for depth sounding on a sparse spatial grid.

Figure 6 illustrates the differnet survey modes ranging from high-speed surveys collecting 3 profiles to high-resolution surveys collecting data on all 31 antennas for full 3-dimensional imaging.

Figure 6

Figure 6

Figure 6: Data Collection modes

User friendly data acquisition and control

The GeoScopeTM is controlled by a Windows XP laptop or panel PC using standard 1Gbit/s Ethernet connection. The user software allows you to configure the frequency range, integration time, number of active antennas, and sampling interval for each survey. You can also create arbitrary scan sequences with arbitrary offsets, as well as using pre-defined Common Mid-Point sequences. During data acquisition, the users can view data from one channel at the time and define their own range of markers to be introduced into the data.  DMI (Distance Measurement Instrument) calibration is also easy conducted using the step-by-step guidance. Figures 7, 8 and 9 contain screenshots of the user interface.

GPR waveform setup

Figure 7. GPR waveform setup

Figure 7. GPR waveform setup

Figure 8. GPR data acquisition

Figure 8. GPR data acquisition

Figure 8. GPR data acquisition

<TBD Antenna array configuration screenshot>

Figure 9.  Antenna array configuration

Accessories & Options

The GeoScopeTM GPR unit (19” rack) can be integrated in a rock solid flight case with wheels and telescopic handle for easy shipping and travelling.

 The GeoScopeTM can be used in combination with Digital Video Camera using RoadCamTM software from RoadScanners for simultaneous recording of video, GPR data and GPS data. Each video frame is tagged with GPS position and GPR scan number.

 For easy surveying of large areas the Automatic Spray Painting Marker is very useful for marking the survey swaths during acquisition. This device can be programmed to paint a dashed line on the surface when it is mounted on the edge of the antenna array.

 The antenna array can be equipped with a 4-wheel lightweight trailer assembly (Figure 10) that fits into the antenna container during transportation. The trailer connects to a standard 50 mm ball hitch used on cars. For railway operation we can provide railway wheels with adjustable gauge.

Figure 9: GPR setup with 4-wheel trailer

Figure 10. GPR setup with 4-wheel trailer

Figure 10. GPR setup with 4-wheel trailer.

For high-speed surveys we recommend to mount the array directly to the vehicle’s front or rear bumper as shown in Figure 11.

Figure 10. Front mounted antenna array & DMI wheel adapter

Figure 11. Front mounted antenna array & DMI wheel adapter

Figure 11. Front mounted antenna array & DMI wheel adapter.