The problem of offset in measurements made using acoustic pulse reflectometry

Li, Aijun and Sharp, David B. (2005). The problem of offset in measurements made using acoustic pulse reflectometry. Acta Acustica united with Acustica, 91(4) pp. 789–796.



Acoustic pulse reflectometry is a useful non-invasive technique for measuring the input impulse response, input impedance and internal dimensions of ducts. A sound pulse is injected into the duct under investigation and the resultant reflections are recorded. Suitable analysis of the reflections then yields the input impulse response, from which both the input impedance of the duct and its cross-sectional area as a function of distance can be calculated. However, an input impulse response measurement made using acoustic pulse reflectometry generally contains an offset. Unless this offset is removed, the application of a bore reconstruction algorithm results in a calculated duct profile which expands or contracts spuriously. In this paper, the offset introduced into reflectometry measurements is shown to consist of both constant and time-varying components. The origins of these DC and time-varying offsets are examined and methods of preventing or removing them are investigated. Finally, improved accuracy bore reconstructions, calculated from input impulse response measurements where any offset has been eliminated, are presented.

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