Field Measurements of Moisture Content in Black Spruce Logs with Unilateral Magnetic Resonance

Abstract

Abstract The development of portable unilateral magnetic resonance (UMR) devices permits nondestructive characterization of wood moisture content (MC) in the field. In this study, six Picea mariana Mill. logs were measured. UMR measurements of MC were taken in four different spots displaced 15 cm from the end of each log. UMR measurements were also taken at the midpoint longitudinally for three of the six logs. The end goal of this study was to demonstrate a viable approach to estimating the whole-sample MC in the field. In the case of the species studied, there is a significant difference in MC between sapwood and heartwood regions. The sapwood MC is approximately three times greater than the heartwood MC. However, the volume of heartwood is greater than sapwood in wood logs. The sapwood region contains most of the water; therefore a measurement in the sapwood, coupled with sapwood-to-heartwood volume proportions and an estimate of heartwood MC, provide a viable estimate of bulk MC of logs. Results indicate that both measurement spots (15 cm displaced from the end and at the midpoint longitudinally) give good predictions of log MC. The UMR measurement signal-to-noise ratio decreases and variability in the total sapwood signal of the four spots, displaced 15 cm from the end, increases as drying progresses. The increase in variability is because of the appearance of a drying front at some measurement spots. The UMR device and technique provide a good tool to measure MC of logs in the field.