Effectiveness of a polarized lazer light for measuring soil moisture content

A polarized He-Ne laser light was used in a laboratory environment to measure soil moisture content. Depolarization of the light beam was used as an indicator of dielectric constant, which, in turn, indicated soil moisture content. Fourier analysis was used to analyze the signals. The DC component and the second harmonic of the Fourier spectrum were used to calculate the degree of depolarization. This method greatly reduced the effects of noise from various sources on the measurement of degree of depolarization. Three soil types (silt-loam, loam, and loam-sand) were tested. For all three soil types, degree of depolarization decreased with an increase of moisture content. The change was most significant for loam, followed by silt loam and loam sand.