Traffic sensing and monitoring apparatus
First Claim
1. Traffic sensing and monitoring apparatus comprising a length l of optical fibre, a light source arranged to introduce a series of pulse pairs into an input end of the length, each of the pulse pairs comprising first and second pulses of radiation having a frequency difference Ω
- and the second pulse being delayed with respect to the first by a delay τ
, and the apparatus further comprising a photodetector arranged to detect radiation which is Rayleigh-backscattered within the length of fibre towards the input end and to generate an output signal in response thereto said apparatus further comprising an interrogation system arranged to obtain a set of signal samples by sampling the photodetector'"'"'s output signal and to process the signal samples to generate an output signal corresponding to the frequency or phase of a signal composed of said samples, wherein sets of signal samples are obtained by sampling the photodetector output signal at times t0−
Δ
t, t0 and t0+Δ
t after the first pulse of each pulse pair enters the length l of optical fibre and to process the set having samples corresponding to the largest signal with a frequency of approximately Ω
.
2 Assignments
0 Petitions
Accused Products
Abstract
Traffic sensing and monitoring apparatus (100) comprises a length of optical fiber (112), means (102, 103, 104, 106, 107, 109, 119) arranged to introduce a series of pulse pairs into an input end of the length, each of the pulse pairs comprising first and second pulses of radiation having a frequency difference Ω and the second pulse being delayed with respect to the first by a delay τ, and the apparatus further comprising a photodetector arranged to detect radiation which is Rayleigh-backscattered within the length of fiber towards the input end to generate an output signal in response thereto. Apparatus of the invention allows sensing and monitoring of traffic at any position along a long length of road (e.g. 5 km) with lower installation and maintenance costs per unit length compared to prior art systems providing the same spatial resolution.
-
Citations
14 Claims
-
1. Traffic sensing and monitoring apparatus comprising a length l of optical fibre, a light source arranged to introduce a series of pulse pairs into an input end of the length, each of the pulse pairs comprising first and second pulses of radiation having a frequency difference Ω
- and the second pulse being delayed with respect to the first by a delay τ
, and the apparatus further comprising a photodetector arranged to detect radiation which is Rayleigh-backscattered within the length of fibre towards the input end and to generate an output signal in response thereto said apparatus further comprising an interrogation system arranged to obtain a set of signal samples by sampling the photodetector'"'"'s output signal and to process the signal samples to generate an output signal corresponding to the frequency or phase of a signal composed of said samples, wherein sets of signal samples are obtained by sampling the photodetector output signal at times t0−
Δ
t, t0 and t0+Δ
t after the first pulse of each pulse pair enters the length l of optical fibre and to process the set having samples corresponding to the largest signal with a frequency of approximately Ω
. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
- and the second pulse being delayed with respect to the first by a delay τ
-
11. A method of sensing and monitoring traffic, the method comprising the steps of
(i) providing a length of optical fibre on or below a surface for carrying vehicles such that the weight of a vehicle using the surface may act on said length; -
(ii) introducing a series of pulse pairs into an input end of the length, each of the pulse pairs comprising first and second pulses of radiation having a frequency difference Ω and
the second pulse being delayed with respect to the first by a delay τ
;(iii) detecting radiation which is Rayleigh-backscattered within the length of fibre towards the input end to generate an output signal in response thereto; (iv) sampling he photodetector'"'"'s output signal at times t0−
Δ
t, t0 and t0+Δ
t after the first pulse of each pulse pair enters the length l of optical fibre to generate respective sets of samples;(v) processing samples obtained in step (iv) to generate an output signal corresponding to the frequency or phase of a signal composed of said samples; and (vi) processing the set having samples corresponding to the largest signal with a frequency of approximately Ω
. - View Dependent Claims (12, 13, 14)
-
Specification