Carl K. Frederickson
Jim S. Sabatier
Richard Raspet
Univ. of Mississippi, University, MS 38677
Level difference measurements have been used to determine three properties of air filled porous media; porosity, tortuosity, and flow resistivity [Soil Sci. Soc. Am. J. 54, 658--672 (1990)]. These can be used to find the characteristic acoustic impedance of a porous medium. It can be shown that the level difference measurement alone does not contain enough information to uniquely determine more than two of these properties. A second measurement is needed to determine one of the properties. A probe microphone can be used to determine either the flow resistivity or the tortuosity; either of which can then be used in the level difference calculation to determine the other two properties. An experiment has been performed to determine the viability of this combined technique for characterizing the ground. Probe microphone measurements were made in a container of 0.526-mm glass beads. This same size of bead was then used in level difference measurements. As the beads are spherical the porosity is known. Values of flow resistivity and tortuosity obtained from both the level differences and probe microphone measurements agree fairly well. [Work supported by the US Department of Agriculture.]