Frequency-drift compensation in chirped-pulse-based distributed acoustic sensing
AssigneeNEC Laboratories America, Inc.
InventorsEzra IP, Yue-Kai HUANG
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Abstract
Aspects of the present disclosure directed to frequency drift compensation for coded-DAS systems that use chirped pulses as a probe signal. Our inventive approach estimates timing jitter by correlating the amplitude of the estimated Rayleigh impulse response of every frame with a reference frame, and then re-aligns each frame by the estimated timing jitter. As the amount of timing jitter varies within a frame, every frame is divided into blocks where all samples have similar timing jitter, and perform timing jitter estimation and compensation on a block-by-block, frame-by-frame basis using an overlap-and-save method. Tracking of a slowly changing channel is enabled by allowing the reference frame to be periodically updated.
Claims6
A method for frequency-drift compensation in a chirp-pulse-based distributed acoustic sensing system (DAS) comprising:
- a length of optical fiber sensor cable;
- a DAS interrogator in optical communication with the length of optical fiber sensor cable, the DAS interrogator including:
- a seed laser;
- and
- a coherent receiver;
- the interrogator configured to:
- produce probe signals including chirped pulses at a given frame rate, chirp duration and chirp slew rate and launching the probe signals into the length of optical fiber sensor cable;
- and
- recover Rayleigh backscatter from the optical fiber sensor cable using the coherent receiver;
- wherein the seed laser exhibits a non-negligible frequency drift such that a frequency of a local oscillator is different from a frequency which generated the chirped pulses resulting in timing jitter of a Rayleigh impulse response determined from a correlation of received backscatter with known chirp;
- the method comprising:
- compensating timing jitter in an estimated Rayleigh impulse response by
- dividing each received frame of Rayleigh backscatter into overlapping blocks wherein the first frame received is a reference frame from which timing jitter of subsequent frames are estimated by correlating amplitude profiles of the subsequent frames with an amplitude profile of the reference frame and;
- re-aligning the frames by the estimated jitter.
Dependencies are inferred from the claim text.