'Free Line Sensing', a new method for soil moisture measurements using high-voltage power lines

摘要

Large area integrated soil moisture measurement results are often required for meteorological studies as well as for geological, agricultural and natural disaster research. Commonly used sensors measure the soil moisture locally and exhibit a strong spatial variability due to the heterogeneity of most land surfaces.The new 'Free Line Sensing' technology uses existing high-voltage power lines to detect variations in soil moisture below the lines. The electromagnetic field of an additional radio-frequency signal in the range of 50-500 kHz on the line is influenced by changes in the electric properties of the soil, e.g., after rainfall. This has been simulated using high-frequency software, the result being that variations of electrical conductivity or dielectric coefficient of the soil will lead to a measurable effect with power line sections extending over several kilometres.Measurements have been conducted on a 13 km long high-voltage power line. The resulting signal is evaluated with respect to amplitude and phase. Measurement data demonstrate the capability of the 'Free Line Sensor' to monitor the integrated soil moisture of the Earth's surface and near subsurface over the area covered by the power line. The resulting signal of the 'Free Line Sensor'strongly responds to precipitation events and the following drying of the soil. Comparison with soil moisture data obtained from gravimetric drying of soil samples reveals a good agreement.