Detection of soil gravity water with hetero-core optical fiber sensor

It is well known that soil water at a farm land seriously affects on growth and quality of crops. Therefore, although several methods for monitoring of soil water have been developed. We developed a hetero-core structured optical fiber Surface Plasmon Resonance (SPR) sensor coated with gold thick layer for sensing a drop of soil gravity water. We set the sensor at 5 cm in depth from the top of soil and connected it to both a LED light source and a power meter. As the result, the loss in light going through inside of the optical fibers became from 0.06dB to 1.21dB in 10-60 seconds after watering, and the gain in light became from 0.03dB to 0.17dB in a matter of time after detection. According to the result, it was proved that to detect soil gravity water is possible and in soils the detection ability of the sensor can return which is caused by evaporating of water on the surface of the sensor by air in a soil.