Estimation of harmonic interference parameters of surface-NMR signal using an adaptive method and residual signal power

Surface nuclear magnetic resonance (surface-NMR) method is a well-known tool for determining the water-bearing layers and subsurface resistivity structure. Harmonic interference is an inevitable interference in surface-NMR measurements. Accurate estimation of harmonic interference parameters (i.e., fundamental frequency, phase and amplitude) leads to better retrieval of power-line harmonics and consequently, more effective suppression of harmonics from surface-NMR recordings. To that end, two algorithms are addressed for isolation and then subtraction of harmonic interfering noise based on modeling of power-line harmonics by a modified version of Nyman-Gaiser estimation (NGE) and residual signal power (RSP) technique. Then, the results derived from the proposed algorithms are analyzed and compared through the modeling of some synthetic signals embedded in simulated noise and real recordings obtained from multi-channel surface-NMR measurements. The numerical experiments on simulated and real surface-NMR signals show that the application of the proposed procedures results in significant decline of the level of the standard deviation of imaginary part of the detected signal and consequently, relatively accurate recovery of the harmonic signal components with an accompanying enhancement in estimation of the surface-NMR signal parameters.