Backscattered lightwaves from an optical fibre are used to realise distributed fibre optic sensing (DFOS) systems for measuring various parameters. Rayleigh. Brillouin. and Raman backscattering provide different sensitivities to different measurands and have garnered the attention of researchers. https://www.roneverhart.com/Pure-27-Blemish-Correcting-Purifying-Fluid/