Multiwavelength Optical Sensing of Water-Level Stratification in Closed Plastic Pipelines Using Signal Attenuation and CIR Analysis

This paper presents an optical sensing technique for estimating water fill levels and stratification states inside closed plastic pipelines using multiwavelength visible light. Four LEDs (475, 528, 583, and 625 nm) and a photodiode receiver with automatic gain control (AGC) are deployed across a PVC pipe section to monitor the effects of air–water stratification on signal attenuation and channel impulse response (CIR). Experimental results and ray-tracing simulations reveal wavelength-specific optical losses and CIR variations that correspond to fill ratios from 0% to 100%. Compared to conventional water-level sensors, which often rely on float mechanisms, capacitive probes, or ultrasonic pulses, this method enables contactless, inline assessment of water distribution in sealed, non-transparent geometries. Unlike prior optical approaches applied mainly to open tanks or homogeneous media, this work demonstrates that stratified layers in confined pipelines can be resolved through spectral and time-domain features. The system offers a compact and mechanically simple sensing alternative for embedded monitoring or mobile robotic inspection platforms.