The use of conventional single channel instrumentation requires either a significant investment of time for data acquisition or a compromise between sampling methodology and the area of coverage. The recent development of multi-channel, vehicle towed GPR arrays offers the potential to obtain very detailed data sets across a wide frequency bandwidth that combines the full resolution of near-surface targets together with the investigation of a site to a significant depth of penetration.
Along with improved imaging software, datasets recorded with multi-channel systems can be processed at similar speeds to coarsely spaced single-channel data. With the cross-line spacing approaching a fraction of the wavelength of the transmitted microwaves into the ground, multi-channel systems have the advantage of complete coverage of a site with no need for interpolation. Multi-channel systems do require additional (radargram signal processes) in order to balance the channels and to condition the data prior to imaging.
EVEREST GEOPHYSICS uses state-of-the-art technology in our GPR surveys. Our system uses a stepped-frequency unit with a very wide range of frequency from 100 MHz to 3000 MHz, hence repeated surveys with different antenna frequencies are no longer necessary.
The 3D-GPR system emits a step-frequency continuous-wave (SFCW) waveform, which is a sinewave with constant amplitude and stepwise frequency variation. The waveform is specified by determining a start frequency, a stop frequency, a frequency step (∆f), and a dwell time. The frequency spectrum of the time-domain system is bell-shaped with the center frequency of antenna. In contrast, the stepped frequency-domain system transmits same power and time of each frequency step, which produces a rectangular shaped frequency spectrum. The time-domain signal is then calculated from frequency information using the inverse Fourier-transformation. The uniform frequency spectrum in frequency-domain systems enables the efficient signal analysis for the measured data. The wider bandwidth of this system ensures a better resolution at most depth levels.
Lastly, it is important to point that the GPR results are worthless if a bad positioning system is used. EVEREST GEOPHYSICS uses a triple positioning system composed by an odometer, three GPS receivers (one internal inside the GPR antenna for accurate time synchronization plus two external ones, -SBAS aided-) and an IMU to provide coverage in case of GPS signal loss. The combination of all three systems yields excellent positioning accuracy to our GPR images.