Fiber optic sensor for distributed liquid content quantification in subsurface

A novel fiber-optic sensor assembly for continuous monitoring of moisture over extended subsurface environments, such as road embankments, wall backfills, and landfills is presented. This sensor meets the requirements of subsurface monitoring by distributed measurements over linear positioning of a single fiber. The sensor assembly is composed of a communication optical fiber and a hydrophilic polymer. A phenomena associated with the backscattering of light, namely Brillouin scattering, correlates to the velocity of acoustic wave within the fiber, and in turn its elastic response. A hydrophilic polymer is coupled with the optical fiber at discrete locations along the fiber. Upon exposure to moisture, the swelling polymer exerts stress on the fiber. The resulting Brillouin shift response is then calibrated to determine the moisture level in the surrounding environment.