Distributed dynamic strain sensing in coherent Φ-OTDR with a pulse conversion algorithm
Heng Qian, Bin Luo, Haijun He, Yin Zhou, Xihua Zou, Wei Pan, Lianshan Yan
Abstract
In this Letter, a chirped-pulse conversion algorithm (CPCA) is proposed to convert a normal probe pulse into an equivalent chirped probe pulse by convolving a chirp factor on the received signal in coherent phase-sensitive optical time-domain reflectometry ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mi mathvariant="normal">Φ</mml:mi> </mml:math> -OTDR). With this algorithm, the Rayleigh interference pattern (RIP) demodulation once applied to chirped-pulse <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mi mathvariant="normal">Φ</mml:mi> </mml:math> -OTDR can be adopted to quantify the dynamic strain in the traditional coherent <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mi mathvariant="normal">Φ</mml:mi> </mml:math> -OTDR. Since the equivalent chirped pulse is generated by digital processing, complex and costly chirp modulation is not required. The proposed scheme is capable of fully quantifying perturbations with spatial resolution of 4 m, a sensing range of 8 km, frequency response of 5 kHz, and strain resolution of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>56</mml:mn> </mml:mrow> <mml:mspace width="thickmathspace"/> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">p</mml:mi> </mml:mrow> <mml:mtext>ε</mml:mtext> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>/</mml:mo> </mml:mrow> <mml:mo stretchy="false">√</mml:mo> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi mathvariant="normal">z</mml:mi> </mml:mrow> </mml:mrow> </mml:math> .