Automated and antidispersive coherent and incoherent noise reduction of waveforms that contain a reference pulse

Abstract

Fully automated and antidispersive noise reduction of a waveform containing a reference pulse is often necessary for more efficient, accurate, and reliable interpretation of signals – such as highly attenuated waves in ultrasonic NDE. We propose two methods, pulse specification (PS) and coherent enhanced pulse specification (CEPS), for improving the signal-to-noise ratio (SNR) of coherent pulse amplitudes against both incoherent and coherent noise, as well as apply complementary antidispersive pulse generation (APG) to localise the pulse upon reception. We have demonstrated PS and CEPS effectiveness, with and without APG, using two examples of ultrasonic inspection, by comparison with established methods and demonstrated improvements in SNR up to a factor of 2 (6.02 dB) and never less than 1 (0 dB) for favoured pulse specifications. This has benefits in applications such as NDE, medical ultrasonics, seismology, and acoustics.We deconvolve waveforms using a reference pulse time windowed from said waveforms. These waveforms are convolved with pulses that have centre frequencies and bandwidths that are optimally and automatically specifiable for that unprocessed waveform. We combine independent measurements of the waveforms using PS and CEPS to maximise the coherent pulse amplitude of known scatterers and minimise the noise content. CEPS also enhances the coherent scatterer amplitude to significantly greater than achieved using an established filtered time shift method – where the time shift is subjective. Unlike such time shift methods, PS and CEPS do not reduce the amplitude of the coherent pulse signals when reducing noise.Automated and antidispersive coherent and incoherent noise reduction by pulse specification has been demonstrated to be effective in ultrasonic NDE of both damping and scattering media. Suggestions for further applications of this method have already included application to ultrasonic NDE of composite media, application to ultrasonic guided wave NDE, ultrasonic NDE imaging that can include ultrasonic B-scans, and more. This is greatly encouraging regarding the potential immediate applicability of noise reduction by pulse specification.