Development and performance evaluation of a novel OTDR-based distributed optical fiber sensor using superabsorbent polymers for precision soil moisture monitoring

As the global population grows and climate change intensifies, sustainable water management and agricultural practices face serious challenges. This paper introduces an innovative distributed optical fiber sensor based on Optical Time Domain Reflectometry (OTDR) and employing superabsorbent polymers (SAPs) as humidity-sensitive materials. SAPs, known for their high water absorption and retention capacities, are utilized here not only to amend soil properties but also to facilitate precision in soil moisture and water retention monitoring. The sensor system comprises an OTDR device connected to fiber optics integrated with SAPs through a novel structural setup where each node contains a SAP humidity-sensitive materials formed after SAP solidifies and is tightly installed in the groove structure above the optical fiber. This design can detect humidity changes through the expansion or contraction caused by the SAP humidity-sensitive materials, thereby driving the pressing or releasing of the optical fiber, changing the bending of the optical fiber, and thus affecting the attenuation characteristics of the optical signal. These changes are precisely recorded by the OTDR, with different attenuation levels translated into moisture levels via a calibration chart. The sensor demonstrates high accuracy and spatial resolution in laboratory settings, achieving moisture monitoring with a resolution up to the meter-level, suitable for detailed field applications. Additionally, the system's real-time data transmission capabilities allow for rapid response to moisture changes, supporting real-time decision-making for precision irrigation. This technology shows potential in enhancing irrigation strategies, improving crop yields, and conserving water resources, indicating a promising avenue for broader application in precision agriculture.