Tom Richard Parker

A fully distributed simultaneous strain and temperature sensor using spontaneous Brillouin backscatter

We report here the first simultaneous measurement of strain and temperature using Brillouin backscatter in an optical fiber. A new sensor arrangement is presented which allows the distributed measurement of Brillouin spectra. Simultaneous measurement of spontaneous Brillouin power and Brillouin shift distributions are made from these spectra, and from this information, we obtain fully distributed measurements of strain and temperature. Our sensor achieves a 100-/spl mu//spl epsiv/ strain and 4/spl deg/C temperature resolution, with 40-m spatial resolution, over a sensing length of 1200 m.

Simultaneous distributed measurement of strain and temperature from noise-initiated Brillouin scattering in optical fibers

The simultaneous determination of strain and temperature distributions from the measurement of noise-initiated Brillouin scattering (NIBS) power and frequency shift in optical fibers is discussed. Equations governing the growth of the NIBS signal are derived and from these, we calculate the dependence of the Brillouin power on temperature and strain. We study the potential problem given by the need to normalize the nonlinear Brillouin signal and present a new technique that solves this problem by mathematically combining the values of the Stokes and anti-Stokes powers to produce a linear effective power. Experimental results are presented that support this theory and allow the verification of the coefficients governing the dependence of the Brillouin power and frequency shift on temperature and strain. The signal-to-noise ratio of the sensor is discussed, and it is found that the noise associated with the field statistics plays a limiting role in the sensor performance and that an optimum value for the Brillouin gain factor can be determined. A simultaneous distributed temperature and strain sensor is demonstrated; preliminary results show a strain resolution of 100-/spl mu/m strain, a temperature resolution of 4/spl deg/C, and a spatial resolution of 40 m, over a sensing length of 1200 m.

Power measurement of noise-initiated Brillouin scattering in optical fibers for sensing applications

We discuss the measurement of noise-initiated Brillouin scattered power in optical fibers and its application to distributed sensing systems. In particular, we consider the use of Brillouin scattering in the nonlinear regime, demonstrating a novel processing technique that compensates for the nonlinear growth of the scattered signals. The signal-to-noise ratio performance of this technique is evaluated, highlighting the importance of the noise contributed by the random statistics of the scattered field and yielding the conditions for optimum system operation.

Advances in distributed optical fibre sensing

The ability to make distributed measurements on extended structures is of increasing importance. For example, the measurement of strain distribution on aircraft operating close to their performance limits, the distribution of temperature in boilers, pressure vessels, high voltage transformers etc.,

The intelligent distributed acoustic sensing

Distributed Acoustic Sensing (DAS) technology has progressed rapidly from being capable of event detection only to faithfully capturing the full acoustic signal (amplitude, frequency and phase) at all points along the sensing fibre. In this paper we demonstrate the performance of one such sensor and describe how the unique nature of DAS data enables a range of ground-breaking industrial applications.

Distributed temperature and distributed acoustic sensing for remote and harsh environments

Advances in opto-electronics and associated signal processing have enabled the development of Distributed Acoustic and Temperature Sensors. Unlike systems relying on discrete optical sensors a distributed system does not rely upon manufactured sensors but utilises passive custom optical fibre cables resistant to harsh environments, including high temperature applications (600°C). The principle of distributed sensing is well known from the distributed temperature sensor (DTS) which uses the interaction of the source light with thermal vibrations (Raman scattering) to determine the temperature at all points along the fibre. Distributed Acoustic Sensing (DAS) uses a novel digital optical detection technique to precisely capture the true full acoustic field (amplitude, frequency and phase) over a wide dynamic range at every point simultaneously. A number of signal processing techniques have been developed to process a large array of acoustic signals to quantify the coherent temporal and spatial characteristics of the acoustic waves. Predominantly these systems have been developed for the oil and gas industry to assist reservoir engineers in optimising the well lifetime. Nowadays these systems find a wide variety of applications as integrity monitoring tools in process vessels, storage tanks and piping systems offering the operator tools to schedule maintenance programs and maximize service life.

Tracking system developed using an optical fiber-based distributed acoustic sensor

This work will present a system for acoustic source tracking and imaging developed using a novel distributed acoustic sensor. This sensor, the intelligent Distributed Acoustic Sensor (iDAS), uses standard off-the-shelf optical fiber as a transducer to capture the audio-frequency acoustic field (both phase and amplitude) simultaneously along the entire length of a fiber with a spatial resolution of about 0.5 m. iDAS was used to track the bearing of acoustic sources in a reverberant environment, with localization being performed in two stages. First, the received signal was preprocessed for the mitigating effects of calibration errors and multipaths. Then tracking was performed via particle filters. These filters can track multiple acoustical sources and are efficient enough to run in nearly real time. The output from this system is presented in the form of an acoustic camera-type video.

The intelligent distributed acoustic sensor (withdrawal notice)

Distributed Acoustic Sensing (DAS) technology has progressed rapidly from being capable of event detection only to faithfully capturing the full acoustic signal (amplitude, frequency and phase) at all points along the sensing fibre. In this paper we demonstrate the performance of one such sensor and describe how the unique nature of DAS data enables a range of ground-breaking industrial applications.

The strain of success

Paul arrives with a big box. Salesmen of physics instruments are very popular; they lend you equipment that you have no money to pay for, let you use it to attract research funds and then take it back. If you find the money, you may well buy it – although there is no guarantee that you will. But salesmen know the system: without loans there would be no sales. Mahmoud arrives and shakes Pauls hand. We all know each other very well.