Zhong Huasen

The Hilbert–Huang Transform-Based Denoising Method for the TEM Response of a PRBS Source Signal

The denoising process is critical in processing transient electromagnetic (TEM) sounding data. For the full waveform pseudo-random binary sequences (PRBS) response, an inadequate noise estimation may result in an erroneous interpretation. We consider the Hilbert–Huang transform (HHT) and its application to suppress the noise in the PRBS response. The focus is on the thresholding scheme to suppress the noise and the analysis of the signal based on its Hilbert time–frequency representation. The method first decomposes the signal into the intrinsic mode function, and then, inspired by the thresholding scheme in wavelet analysis; an adaptive and interval thresholding is conducted to set to zero all the components in intrinsic mode function which are lower than a threshold related to the noise level. The algorithm is based on the characteristic of the PRBS response. The HHT-based denoising scheme is tested on the synthetic and field data with the different noise levels. The result shows that the proposed method has a good capability in denoising and detail preservation.

Understanding of Grounded-Wire TEM Sounding with Near-Source Configuration

In order to understand the near-source TEM sounding method, the topic on the time domain electromagnetic exploration of deep targets is addressed using a grounded dipole source. At first, the development of the near source TEM is reviewed in this paper, then a new kind of technique capable of detecting geological targets located at deeper levels in the subsurface is proposed using the short-offset transient electromagnetic method (hereafter referred to as SOTEM). The detection abilities of this system, such as the feasibility of near-source detection for SOTEM, the investigation depth of SOTEM and the sensitivity of SOTEM, have been analyzed. The conclusion has been achieved that the proposed method is more applicable and convenient for exploration and could be used to obtain a greater detection depth with higher detection accuracy.