Tangent line/second order bounded mean oscillation waveform analysis for short TDR probe
Tangent line (TL) methods and the second order bounded mean oscillation (BMO) method have been proposed for determining the reflection positions of time domain reflectometry (TDR) waveforms, especially for short probe TDR sensors. However, the accuracy of TL methods is limited by the multi reflection effects of the short probe TDR sensor, and an automatic implementation of the second order BMO is challenging because of the superimposition of the TDR waveforms. In this study, we combined a TL method with second order BMO to develop a tangent line/second order bounded mean oscillation (TL BMO) method. Laboratory and field data were used to evaluate the TL BMO method. Separate tests were performed on laboratory data to compare the TL BMO method with the TL method and the second order BMO method. For selected waveforms, the TL BMO was more accurate than the TL method (the RMSE of TL BMO was 0.0197 m 3 m 3 and the RMSE of the TL method was 0.1071 m 3 m 3 The TL BMO was able to avoid calculation errors associated with automatic analysis by the second order BMO (RMSE of TL BMO automatic analysis was 0.0199 m 3 m 3 and the RMSE of second order BMO automatic analysis was 0.1414 m 3 m 3 For analyzing field measurements, the TL BMO method was able to determine soil water contents accurately during a 3 wk long measurement period. Conclusively, the new TL BMO method was more accurate than the TL method, and it demonstrated the stability necessary for automatic analysis of short probe TDR sensors.