Long-range OFDR distributed strain sensing based on optimized deskew filter and image denoising methods

A method combining an optimized deskew filter based on a peak-seeking algorithm and an image denoising based on Gaussian filtering was proposed, enabling a strain sensing with a spatial resolution of 5 cm over a measurement range of 1.68 km. In the optimized deskew filter method, the accurate estimation of the nonlinear phase was improved by third-order Taylor expansion and high-accuracy estimation of the time delay in the auxiliary interferometer using a peak-searching method. By employing an optimized deskew filter based on the peak-searching method, the amplitude and width of the peak located at 1212.16 m were improved from 5.9 dB and 45 cm to 14.4 dB and 7 cm, respectively. The strain distribution at 1212 m could be clearly identified at a spatial resolution of 5 cm with the Gaussian filtering-based image denoising method, when the strain was increased from 500 to 2000 µε.