Author
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PAIGE, G. - UNIVERSITY OF WYOMING |
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Keefer, Timothy |
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Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 6/7/2007 Publication Date: 2/1/2008 Citation: Paige, G.P., Keefer, T.O. 2008. Comparison of field performance of multiple soil moisture sensors in a semi-arid rangeland. Journal of the American Water Resources Association (JAWRA) 44(1):121-135. DOI: 10.1111/j.1752-1688.2007.00142.x Interpretive Summary: Various types of soil moisture sensors have been developed for automated and unattended use for scientific and land management applications. These sensors are being installed and used for a wide range of soil moisture applications such as drought forage prediction or validation of large scale remote sensing instruments. The convergence of three different research projects at the USDA-ARS Walnut Gulch Experimental Watershed in southeastern Arizona facilitated the evaluation and comparison of three commercially available soil moisture probes under field application conditions. Previous studies have compared multiple sensors under laboratory or controlled field conditions, or compared individual sensors to physically measured soil moisture, however, few have directly compared the performance of different probes under field applications as they are being employed for long term monitoring of soil moisture. The sensors all use an electronic technique to indirectly measure the soil moisture content. Sensor responses are evaluated over a range of conditions using water balance and infiltration simulation models. Each of the sensors responded to the majority of precipitation events; however, they varied greatly in response time and magnitude from each other. The results of a soil moisture computer simulation model were compared to the measured sensor values, but no distinct or consistent trend was detected. The results of this analysis underscore the need to recognize the limitations of soil moisture sensors and the factors that can affect their accuracy in predicting soil moisture in situ. Technical Abstract: Automated electronic soil moisture sensors such as time domain reflectometry (TDR) and capacitance probes are being used extensively to monitor and measure soil moisture in a variety of scientific and land management applications. These sensors are being installed and used for a wide range of soil moisture applications such as drought forage prediction or validation of large scale remote sensing instruments. The convergence of three different research projects facilitated the evaluation and comparison of three commercially available soil moisture probes under field application conditions. Previous studies have looked at the performance of soil moisture probes as compared with gravimetric measurements or used TDR to calibrate other capacitance probes; however, few have directly compared the performance of different probes under field applications as they are being employed for long term monitoring of soil moisture. The sensors are all installed in shallow soil profiles in a well instrumented small semi-arid shrub covered sub-watershed in Southeastern Arizona. The sensors all use either a TDR or a capacitance technique; both of which indirectly measure the soil dielectric constant to determine the soil moisture content. Sensor responses are evaluated over a range of conditions using water balance and infiltration simulation models. Each of the sensors responded to the majority of precipitation events; however, they varied greatly in response time and magnitude from each other. No distinct or consistent trend was detected when comparing the responses from the sensors or the model to individual precipitation events. The results of this analysis underscore the need to recognize the limitations of soil moisture sensors and the factors that can affect their accuracy in predicting soil moisture in situ. |
