1 1 2 Fiber Bragg Grating: FBG 1 2 2.1 FBG FBG FBG Special Issue In recent years, heavy rainfalls have caused many urban ß oods and serious damage all over Japan. As countermeasures, a real-time measurement system is needed that grasps a sewer's ß ow rate over a wide area. We researched and developed a ß ow-rate measurement system that uses optical Þ ber sensors. Our system is reliable and does not require a power source to measure a sewer's ß ow rate with high density over a wide area. In this

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... paper, we introduce our new optical ß ow-rate measurement system using FBG sensors and present the result of our Þ eld tests. Our system makes it possible to connect sensors in a series and to conduct long-distance optical Þ ber transmission using FBG sensors.