Soil Moisture Estimation Using Inexpensive Radios
Abstract
Technological advances and changes in licensing have made small, inexpensive radio modules commonplace. Today, these radios are used in a large number of wireless data- and control applications. A novel approach is to view such radio modules not only as communication devices, but also as small, inexpensive sources of radio frequency (RF) energy, which are useful for devising unconventional sensors. We have explored the possibility of using buried radios and the resulting RF links as distributed soil moisture sensors. We conducted a number of experiments that record the RF attenuation of the links over time. Estimating RF attenuation is straightforward, since the radio modules provide a received signal strength indication (RSSI). To provide reference data, we installed several time-domain reflectometry (TDR) soil moisture probes with accompanying temperature probes to monitor changes in soil moisture and soil temperature. We collocated tipping bucket rain gauges for monitoring rain events. We employed RF modules that operate at 900 MHz. Rather than burying the radios, we lowered the antennas into 2.5 cm PVC pipes that we drove into the ground to a depth of 60 cm. We seal both ends of the PVC pipe to prevent water from entering the tube. Our experimental data shows a clear relationship between soil moisture and RF attenuation. We developed a simple, yet effective, mathematical model to relate changes in RF attenuation to changes in soil moisture. One can easily achieve reliable links 2-3 m long, and we believe the technique holds promise as an economical method for distributed/integrated soil moisture estimation.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.H11G1150N
- Keywords:
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- 1866 HYDROLOGY / Soil moisture;
- 1895 HYDROLOGY / Instruments and techniques: monitoring;
- 6994 RADIO SCIENCE / Instruments and techniques