The most recent VTEM system development is designed to achieve fully calibrated time-domain EM decay for better near-surface mapping than was possible with previous VTEM systems. The new design, known as the “full waveform VTEM system” uses the streamed half-cycle recording of transmitter and receiver waveforms to obtain a complete system response calibration throughout the entire survey flight that helps to precisely eliminate the effect of the data acquisition system response on the recorded signals. The full waveform technology can be added to either the standard VTEM or VTEM early time systems. In addition to improving the system bandwidth and the complete system response calibration, newly developed digital signal processing techniques have been applied that are aimed at reducing the effect of the input transmitter waveform and time-varying injected current using both a parasitic loop capacitance correction and a transmitter drift correction, as well as ideal waveform deconvolution. These implementations have helped improve the accuracy of the measured earth-response particularly in the earliest portions of the off-time EM decay. Results of the full waveform VTEM helicopter system implementation over the Spiritwood Valley aquifer, in southern Manitoba, have shown a significant improvement in quantitative VTEM data at earlier times than previously achieved - as early as 18 μs after the current turn-off. This has resulted in improvements in the model space that include better definition of the near-surface heterogeneity and also a more compact resistive anomaly associated with the buried valley aquifer that is in good agreement with previous seismic and resistivity results.


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