Soil Moisture Measurement with Ultrasonic Energy1
- A. R. Mack and
- E. J. Brach2
Low energy ultrasonic waves were propagated readily at specific megacycle frequencies through samples of water and moist soil. At these frequencies, the propagated energy varied with the moisture content of the soil. Energy propagated at frequencies near 15.9 and 19.8 Mcycle/sec was sensitive to a change in moisture over a narrow range (0 to 12 g H2O/130 cm3 soil), whereas that propagated near 114 and 142 Mcycle/sec was related to moisture over a wider range (0 to 56 g H2O/130 cm3 soil). Results obtained when salts were added to the soil indicated that ultrasonic waves near 15.9 and 19.8 Mcycle/sec were affected markedly by the ionic concentration of the soil. Waves near 114 and 142 Mcycle/sec were not affected by ionic concentrations of 1 mmhos cm-1 as measured in 1:5 soil-water extracts. Change in texture and in organic matter content of 8 soils and 2 other materials had no significant effect on propagation at the higher frequencies (114 and 142 Mcycle/sec). Propagation of energy (114 Mcycle/sec) through moist samples changed little between 0C and about 30C, increased somewhat above 30C and decreased sharply below 0C. These higher ultrasonic frequencies appeared suitable for a nondestructive method of determining moisture content of soils.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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