. Effects of air gaps and saturated voids on accuracy of neutron moisture measurements. Soil moisture Measurement. A Troxler neutron soil moisture meter was used to measure the moisture content at pre- determined depths in each tank under condi- tions of changing water levels. Thirteen water levels, measured in inches from the surface of the sand, were selected for this study (fig. 5). A one-minute counting period (Merriam 1962) was used at each of these 13 water levels. The center of measurement for the probe was as- sumed to be the center of the detector tube. After a set of 13 one-minute co
. Effects of air gaps and saturated voids on accuracy of neutron moisture measurements. Soil moisture Measurement. A Troxler neutron soil moisture meter was used to measure the moisture content at pre- determined depths in each tank under condi- tions of changing water levels. Thirteen water levels, measured in inches from the surface of the sand, were selected for this study (fig. 5). A one-minute counting period (Merriam 1962) was used at each of these 13 water levels. The center of measurement for the probe was as- sumed to be the center of the detector tube. After a set of 13 one-minute counts, the water level was lowered or raised to the next water level and the neutron measurements were re- peated at all 13 water levels. Each set of read- ings was bounded by a set of 5 one-minute standard counts. The water which drained from the tank when the water level was lowered to the next stage was collected, measured, and compared with the weight of the tank before and after the change in water level. When the neutron measurements were completed on one tank (, from a saturated to a drained condi- tion), the process was repeated on the second tank. After all neutron measurements were completed, a series of bulk density samples were taken; the tanks were emptied and refilled with the fine sand. Three sets of bulk density measurements were made in each of the two tanks: (1) small (142 cc.) gravimetric samples were taken through the side of the tank; (2) measurements were made with a Troxler depth-density gage; and (3) large (6,300 cc.) gravimetric samples were taken adjacent to each void when the tanks were emptied. The small sampler consisted of a length of stainless steel conduit having an inside diameter of inches; it was machined on the outside to a diameter and had a flange acting as a stop to allow the sampler to penetrate 10 inches into the sand. After the tank had drained for 24 hours, a plug was removed from a sam- pling hole, and the small samp
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