Performance of Rayleigh-based phase-OTDR with correlation-based diversity combining and bias removal
View Patent ↗Aspects of the present disclosure describe systems, methods and apparatus for improving the performance of Rayleigh-based phase-OTDR with correlation-based diversity combining and bias removal.
1. A distributed acoustic sensing (DAS) system using phase optical time-domain reflectometry based on Rayleigh scattering comprising:
an optical interrogator unit that generates optical pulses at one or more optical frequencies and introduces them into an optical fiber under test;
a receiver unit that detects Rayleigh backscatter from the optical fiber under test, and
a data processor unit that determines acoustic vibrations experienced by the optical fiber under test by computing a plurality of delay interferometric products based on different combinations of polarizations and/or frequencies of the detected Rayleigh backscatter, adding the interferometric products in phase by aligning their vectors using correlation, followed by bias removal wherein phase rotations φ l,k are determined by first choosing an appropriate window size of M samples and then determining a b k [l, m] term according to the following relationship:
k
0
=
max
k
(
∑
m
=
1
M
b
k
[
l
,
m
]
2
)
;
; and
subsequently determining the phase rotations by correlating remaining terms according to b k [l, m] according to the following:
φ
l
,
k
=
angle
(
∑
m
=
1
M
b
k
[
l
,
m
]
b
k
0
*
[
l
,
m
]
)
where b k [l, m] are delay interferometric products, l is a position index and m is a time index.
2. The system of claim 1 wherein the receiver unit detects the Rayleigh backscatter at each optical frequency of the one or more optical frequencies using a plurality of coherent receivers.
3. The system of claim 1 wherein the receiver unit detects the Rayleigh backscatter at each optical frequency of the one or more optical frequencies using a plurality of optical delay interferometers.
4. The system of claim 1 wherein the optical pulses are introduced into the optical fiber under test at regular intervals (pulse repetition rate) and the Rayleigh impulse response is sampled at the pulse repetition rate.