Location: Soil and Water Management ResearchTitle: Time domain reflectometry waveform analysis with second order bounded mean oscillation Author
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2014
Publication Date: 6/30/2014
Citation: Wang, Z., Kojima, Y., Lu, S., Chen, Y., Horton, R., Schwartz, R.C. 2014. Time domain reflectometry waveform analysis with second order bounded mean oscillation. Soil Science Society of America Journal. doi:10.2136sssaj2013.11.0497. Interpretive Summary: Accurate measures of soil water are needed for making appropriate and timely crop management decisions. Time domain reflectometry (TDR) is a standard method used to measure soil water content. This method requires the evaluation of the velocity of signals in waveforms recorded by instruments. Current computer programs used to interpret TDR waveforms can yield large water content errors, especially for short TDR probes. A new algorithm (second order bounded mean oscillation (BMO), was developed to evaluate water contents for short TDR probes and compared to other methods. For some waveforms, second order BMO was able to more reliably estimate water contents for short probes. Automatic implementation was challenging for the second order BMO because it was difficult to set a default threshold suitable for all waveforms, thus manual adjustments are often required.
Technical Abstract: Tangent-line methods and adaptive waveform interpretation with Gaussian filtering (AWIGF) have been proposed for determining reflection positions of time domain reflectometry (TDR) waveforms. However, the accuracy of those methods is limited for short probe TDR sensors. Second order bounded mean oscillation (BMO) may be an alternative method to determine reflection positions of short probe TDR waveforms. For this study, an algorithm of second order BMO is developed. Example waveforms are analyzed with tangent-line methods, AWIGF method and second order BMO, to illustrate the difference among the three methods. For some waveforms, second order BMO appears be able to give more plausible results. Automatic implementation was challenging for the second order BMO. With second order BMO, it is difficult to set a default threshold suitably for all TDR waveforms. Thus, manual adjustment may be required to select suitable threshold for second order BMO analysis.