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Remote Sensing of Soil Moisture with RF Polarimetry
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.orgCitation: 2011 Louisville, Kentucky, August 7-10, 2011 1100017.
Authors: Thomas G Pratt, Mike Higginson, Qing Xue, Marc W van Iersel
Keywords: Remote sensing, radio frequency, polarization, soil moisture, saturation cue, dry soil cue
Motivated by the need for low-cost non-contact methods to continuously monitor soil moisture at various scales, a new method for sensing soil moisture is being developed. The approach involves use of a radio frequency (RF) transmitter and a receiver to estimate changes in polarization mode dispersion properties of the reflected signal. To test this method, trays of sand were placed between a transmitter and a receiver separated by 3 meters. The sand in the trays was uniformly wetted and then allowed to dry out over several days, and the process was repeated. In each case, five capacitance soil moisture sensors in one of the trays provided direct measurement of the soil moisture level during the evaporation cycles. Measured changes in the polarimetric properties of the reflected signal correlated well with capacitance sensor readings, and cues for both saturation and dry soil conditions were evidenced. Using one of the cycles for calibration, absolute soil moisture levels could be inferred from the polarimetric signatures using minimum distance estimation techniques.