Improved data segmentation method for EM excited by m-sequence: A new approach in powerline noise reduction.

Electromagnetic (EM) data obtained by using an m-sequence source is typically segmented with an m-sequence cycle, and the random noise is suppressed by stacking the earth impulse responses recovered from each data segment. However, the stack cannot suppress the powerline noise, which is normally several orders of magnitude greater than the random noise. In this paper, the powerline noise reduction with different data lengths were compared by numerical simulation; the results show that there is always an optimal data length, not a single cycle but several cycles that can achieve maximum powerline noise suppression. The concept of an identification system was proposed and the identified earth impulse response is obtained by measuring the system output with the input of the voltage response. The optimal data length was summarized in two cases by analyzing the identification system with different data lengths. Coding frequency optimization was proposed to shorten the optimal data length to increase the stacking times. Finally, the validity of the theory described in this paper was verified by field data processing. Different from the traditional subtraction method and notch filter, the powerline suppression method presented here does not need a noise record or filter design; the powerline noise is suppressed accompanied by the identification processing without any additional workload; the simple and practical method provides a new insight into the powerline noise reduction. With this method, the utilization of field data is improved and the anti-noise performance of the m-sequence is also fully exploited. [ABSTRACT FROM AUTHOR]