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United States Department of Agriculture

Agricultural Research Service

Research Project: HYDROLOGIC PROCESSES, SCALE, CLIMATE VARIABILITY, AND WATER RESOURCES FOR SEMIARID WATERSHED MANAGEMENT

Location: Southwest Watershed Research

Title: Measuring soil moisture content non-invasively at intermediate spatial scale using cosmic-ray neutrons 1986

Authors
item Zreda, M. - UNIVERSITY OF ARIZONA
item Desilets, D. - UNIVERSITY OF ARIZONA
item Ferre, T. - UNIVERSITY OF ARIZONA
item Scott, Russell

Submitted to: Geophysical Research Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 26, 2008
Publication Date: November 1, 2008
Citation: Zreda, M., Desilets, D., Ferre, T., Scott, R.L. 2008. Measuring soil moisture content non-invasively at intermediate spatial scale using cosmic-ray neutrons. Geophysical Research Letters, 35, L21402. doi:10.1029/2008GL035655.

Interpretive Summary: Moisture in the soil moderates regional climate, much as the ocean does, and measuring soil moisture is crucial for weather and short-term climate forecasting. But soil moisture measurements useful for these applications are difficult to make.We present a novel technique that uses the dependence of the low-energy cosmic-ray neutron intensity above the ground surface on the hydrogen content of soil. The measurement with a standard neutron detector placed a few meters above the ground takes minutes to hours, permitting high-resolution, long-term monitoring of undisturbed soil moisture conditions. The large area of measurement makes the method suitable for weather forecast models and for calibration of satellite sensors, and the measurement depth makes the probe ideal for studies of atmosphere, plant, and soil interactions.

Technical Abstract: Soil moisture content on a horizontal scale of hectometers and at depths of decimeters can be inferred from measurements of low-energy cosmic-ray neutrons that are generated within soil, moderated mainly by hydrogen atoms, and diffused back to the atmosphere. These neutrons are sensitive to water content changes, but largely insensitive to variations in soil chemistry, and their concentration above the surface is inversely correlated with hydrogen content of the soil. The measurement with a standard neutron detector placed a few meters above the ground takes minutes to hours, permitting high-resolution, long-term monitoring of undisturbed soil moisture conditions. The large footprint makes the method suitable for weather and short-term climate forecast initialization and for calibration of satellite sensors, and the measurement depth makes the probe ideal for studies of plant/soil interaction and atmosphere/soil exchange.

Last Modified: 9/10/2014
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