VTEM ET: An improved helicopter time-domain EM system for near surface applications

Abstract

Sampling the earliest possible transient EM decay in time-domain airborne electromagnetic data (TDEM) is critical for shallow near surface applications. In an effort to further improve near-surface resolution, starting in late 2015 and into 2016, Geotech continued by developing its new VTEM ET system that uses a re-designed broadband receiver sensor, a re-configured transmitter system, and a new digital acquisition system to achieve precise, distortion free measurements of the time-domain EM decay as early as 0.005 msec after the transmitter turn-off. The new receiver features a much larger frequency bandwidth for lower distortion measurements. The new transmitter delivers a sufficiently high dipole moment, a long pulse-width and faster turn-off time than previous systems, but similarly using a single transmitter pulse. The new digital acquisition system operates at a much higher sampling rate, with significantly more decay channels, particularly in early times, and with low noise levels. The result is a new category of VTEM system that is specifically is designed for precise near-surface applications, such as groundwater and environmental problems, but also with sufficient depth of investigation. We present forward modelling and field survey test results comparing the VTEM ET system with our standard VTEM Plus system with full-waveform processing over a groundwater project with ground geophysical and borehole controls in the upper 30-50 metres.