| Summary: | Recent studies have reported on the use of a new device to measure beach 'surface' moisture content, the Delta-T Theta Probe. However, the sensor length (6.0 cm) is too long for measurement of true surface moisture conditions. This study investigated the reliability of the Theta Probe as sensor length is reduced to lengths of 1.5, 1.0, and 0.5 cm. Field investigations were conducted at sites in Texas and North Carolina, in order to evaluate the influence of differing sediment sizes on probe output. It was found that calibration R^2 values remained high and only a minimal increase in standard error occurred as the length of the sensor rod array was shortened. However, the sensitivity of the Theta Probe response to changes in moisture content was influenced by the length of the sensor rod array, weakening as sensor length was reduced. Sediment size does not influence the calibration strength or accuracy of the Theta Probe, as the R^2 values and SE values are not significantly different at the 95% confidence interval between grain sizes. Comparison of multiple calibration repetitions and different probes showed that the Theta Probe is reliable and the probe units are interchangeable.
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