Fiber-optic seismic sensing of vadose zone soil moisture dynamics

Area of Science:

• Earth and Environmental Sciences
• Hydrology
• Geophysics

Background:

• Vadose zone soil moisture is a critical water reservoir in semi-arid regions, linking surface and groundwater systems.
• Understanding soil moisture dynamics is vital for ecological and agricultural resilience, especially under changing climate patterns.
• Current limitations in high-resolution, large-scale soil moisture monitoring hinder accurate quantitative assessments.

Purpose of the Study:

• To demonstrate a novel fiber-optic seismic sensing principle for capturing vadose zone soil moisture dynamics.
• To quantitatively characterize soil moisture fluctuations and water loss in response to meteorological forcing.
• To assess the potential of this technology for water resource management in semi-arid environments.

Main Methods:

• Utilized pre-existing fiber-optic cables repurposed as seismic sensors to monitor subsurface conditions.
• Collected high-resolution data on vadose zone soil moisture dynamics in Ridgecrest, California.
• Compared observational data with a zero-dimensional hydrological model and validated evapotranspiration estimates with eddy-covariance measurements.

Main Results:

• Successfully captured sub-seasonal precipitation events and identified a prolonged drought period in the vadose zone.
• Estimated significant evapotranspiration water loss of 0.25 m/year, consistent with independent measurements.
• Observed discrepancies between model predictions and seismic sensing data highlight the need for further in-situ validation.

Conclusions:

• Fiber-optic seismic sensing is a promising, non-invasive technology for robustly monitoring vadose zone soil moisture.
• The findings provide crucial insights into water dynamics in semi-arid regions, essential for climate change adaptation.
• This method can significantly enhance water resource management strategies, particularly in drought-prone areas.