SOIL IMPEDANCE MEASUREMENTS BY AN ACOUSTIC PULSE TECHNIQUE

Impules generated by the discharge of a rifle cartridge have been used to determine the complex acoustic impedance of grassland, cultivated earth, a layered forest floor, and highly reflecting stone impregnated ground. The length of the grass coverage had a marginal effect on the impedance while measurements over broken soil indicate that only the first centimeter of earth influences the reflected pulse. Alterations to the impedance of the base material of a forest floor are clearly demonstrated as layers of pine needles or leaves are applied, while a limitation of the pulse technique is demonstrated by measurements over stony ground. Calculated impedance values are not consistent with predictions based on measured flow resistivity.