Comparison between Capacitive and Microstructured Optical Fiber Soil Moisture Sensors

Abstract

Soil moisture content has always been an important parameter to control because it is a deterministic factor for site-specific irrigation, seeding, transplanting, and compaction detection. In this work, a discrete sensor that is based on a SnO2–FP (Fabry-Pérot) cavity is presented and characterized in real soil conditions. As far as authors know, it is the first time that a microstructured optical fiber is used for real soil moisture measurements. Its performance is compared with a commercial capacitive soil moisture sensor in two different soil scenarios for two weeks. The optical sensor shows a great agreement with capacitive sensor’s response and gravimetric measurements, as well as a fast and reversible response; moreover, the interrogation technique allows for several sensors to be potentially multiplexed, which offers the possibility of local measurements instead of volumetric: it constitutes a great tool for real soil moisture monitoring.

Optical Fiber Sensors Based on Microstructured Optical Fibers to Detect Gases and Volatile Organic Compounds—A Review

“…The device showed a linear behavior from 20% to 90%RH in which the sensitivity was 0.14 rad/% and the humidity resolution was 0.0026%RH. This sensor was also used by the same authors for real soil moisture measurements in [124]: its performance was compared with a commercial capacitive soil moisture sensor in two different soil scenarios during two weeks. The authors inferred that the MOF sensor showed a great agreement with capacitive sensor response and gravimetric measurements, as well as a fast and reversible response making it very interesting for this type of measurement in real time.…”

Adaptive Nonlinearity Compensation System for Integrated Temperature and Moisture Sensor

“…Manufacturers perform huge numbers of tests under various temperatures and moisture levels in order to construct LUTs. However, the accuracy of this nonlinear mapping relationship depends on the precision of the measurements and the size of the LUT [7,8]. LUT-based adjustment can be highly accurate; however, a sensor unit can potentially be used in a huge range of temperatures, thus requiring a huge LUT to accurately provide moisture level readings.…”