Recent studies have employed a new device to measure beach “surface” moisture content, the Delta-T Theta probe. A key weakness of the device for this application is that the sensor length (6.0 cm) exceeds the desirable depth for “surface” measurements in the context of coastal-aeolian processes. This study investigated the reliability of the Delta-T Theta probe when modified to restrict measurement depths to 0.5–1.5 cm. Field investigations were conducted at two beaches in Texas and North Carolina to allow assessment of the influence of different sediment sizes. Results demonstrated that sensor output becomes less sensitive as the sensor length is decreased. However, R2 values reveal very strong relationships between probe output and laboratory-measured moisture content, with virtually all sampling runs exceeding 0.90. Further, although the standard error approximately doubled (from ±1% to ±2%) for the modified versions of the probe, the error remained within the accuracy ranges reported in the literature and did not appear to consistently increase as the sensor length was shortened. Grain size was found to have no consistent influence on sensor performance. Comparisons of multiple runs and multiple probes indicated that it is possible to achieve high levels of repeatability both between runs and between probes, but several instances of significant departures were identified that suggest caution with this application and that other environmental parameters may influence results.
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Vol. 27 • No. 3