Inversion method for soil moisture content based on a distributed fiber optic acoustic sensing system

The traditional measurement method can't achieve real-time monitoring of soil moisture content (SMC) within a two-dimensional area. To solve the above problems, we propose a rapid SMC monitoring method for two-dimensional area based on distributed acoustic sensing (DAS). DAS demodulates the backward Rayleigh scattering signal containing seismic wave sound velocity information from the active seismic source. The folding ruler approximation is employed to calculate the sound velocity of the soil, which is then inverted to determine the soil moisture content. The experiment measured the soil within a two-dimensional area formed by the seismic source and the acoustic sensing optical cable. The sensing optical cable and the active seismic source are organized into a two-dimensional area and the measurement range is 3 × 10 m with 33 points. The SMC ranges from 15% to 40%. The experiment shows that the absolute error between the measured values obtained by DAS and the water cut meter is 7%. This experiment verifies the feasibility of using the Rayleigh scattering properties to invert SMC and provides a new method for real-time monitoring of SMC in a large area.