Frequency Management for Electromagnetic Continuous Wave Conductivity Meters
Przemyslaw Mazurek 1,2,†,* and Grzegorz Putynkowski 2,†
1 Department of Signal Processing and Multimedia Engineering, West Pomeranian University of Technology Szczecin, 26. Kwietnia St., Szczecin 71126, Poland 2 CBRTP SA, Zlota 59 St., Warsaw 00120, Poland † These authors contributed equally to this work.
* Author to whom correspondence should be addressed.
Academic Editor: Vittorio M. N. Passaro
Received: 2 December 2015 / Revised: 25 February 2016 / Accepted: 29 February 2016 / Published: 7 April 2016
(This article belongs to the Section Physical Sensors)
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Ground conductivity meters use electromagnetic fields for the mapping of geological variations, like the determination of water amount, depending on ground layers, which is important for the state analysis of embankments. The VLF band is contaminated by numerous natural and artificial electromagnetic interference signals. Prior to the determination of ground conductivity, the meter’s working frequency is not possible, due to the variable frequency of the interferences. Frequency management based on the analysis of the selected band using track-before-detect (TBD) algorithms, which allows dynamical frequency changes of the conductivity of the meter transmitting part, is proposed in the paper. Naive maximum value search, spatio-temporal TBD (ST-TBD), Viterbi TBD and a new algorithm that uses combined ST-TBD and Viterbi TBD are compared. Monte Carlo tests are provided for the numerical analysis of the properties for a single interference signal in the considered band, and a new approach based on combined ST-TBD and Viterbi algorithms shows the best performance. The considered algorithms process spectrogram data for the selected band, so DFT (Discrete Fourier Transform) could be applied for the computation of the spectrogram. Real–time properties, related to the latency, are discussed also, and it is shown that TBD algorithms are feasible for real applications.
Keywords: track-before-detect; ground conductivity meters; frequency management; radio interferences; frequency estimation; spectrogram; tracking; VLF
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