Measuring duff moisture content in the field using a portable meter sensitive to dielectric permittivity*
P. R. Robichaud A G , D. S. Gasvoda B , R. D. Hungerford C , J. Bilskie D , L. E. Ashmun E and J. Reardon FA Rocky Mountain Research Station, Forestry Sciences Laboratory, U.S. Department of Agriculture Forest Service, 1221 South Main St, Moscow, ID 83843, USA.
B Retired, Missoula Technology and Development Center, U.S. Department of Agriculture Forest Service, Missoula, MT 59808, USA.
C Retired, Rocky Mountain Research Station, Fire Sciences Laboratory, U.S. Department of Agriculture Forest Service, Missoula, MT 59807, USA.
D Campbell Scientific, Inc., Logan, UT 84321, USA.
E Rocky Mountain Research Station, Forestry Sciences Laboratory, U.S. Department of Agriculture Forest Service, Moscow, ID 83843, USA.
F Rocky Mountain Research Station, Fire Sciences Laboratory, U.S. Department of Agriculture Forest Service, Missoula, MT 59807, USA.
G Corresponding author. Telephone: +1 208 883 2349; fax: +1 208 883 2318; email: probichaud@fs.fed.us
International Journal of Wildland Fire 13(3) 343-353 https://doi.org/10.1071/WF03072
Submitted: 13 October 2003 Accepted: 2 March 2004 Published: 16 November 2004
Abstract
Duff water content is an important consideration for fire managers when determining favourable timing for prescribed fire ignition. The duff consumption during burning depends largely on the duff water content at the time of ignition. A portable duff moisture meter was developed for real-time water content measurements of non-homogenous material such as forest duff. Using circuitry developed from time and frequency domain reflectometry (TDR and FDR) technologies, this sensor measures a change in frequency that is responsive to the dielectric permittivity of the duff material placed in a sample chamber and compressed. Duff samples from four forest cover types—Douglas fir, larch, lodgepole pine and spruce/alpine fir—were used to calibrate the frequency output to volumetric water content. A second-order polynomial (R2 = 0.97) provides the best fit of the data to volumetric water content. The accuracy of the duff moisture meter is ±1.5% at 30% volumetric water content and ±4% at 60% volumetric water content. The volumetric water content can readily be converted to gravimetric water content, which is used more frequently by fire managers and as an input to predictive models of duff consumption.
Additional keywords: duff moisture meter; forest floor; frequency domain reflectometry (FDR); prescribed fire; time domain reflectometry (TDR).
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* This manuscript was written and prepared by U.S. Government employees on official time and therefore is in the public domain and not subject to copyright.
† The use of trade or firm names in this publication is for reader information and does not imply endorsement by the U.S. Department of Agriculture of any product or service.
