Generalized Cross-correlation Technique Research Articles

Dynamic Adjustment of Weighted GCC-PHAT for Position Estimation in an Ultrasonic Local Positioning System.

Ultrasonic local positioning systems (ULPS) have been brought to the attention of researchers as one of the possibilities that can be used for indoor localization. Acoustic systems combine a suitable trade-off between precision, ease of development, and cost. This work proposes a method for measuring the time of arrival of encoded emissions from a set of ultrasonic beacons, which are used to implement an accurate ULPS. This method uses the generalized cross-correlation technique with PHAT filter and weighting factor β (GCC-PHAT-β). To improve the performance of the GCC-PHAT-β in encoded emission detection, the employment is proposed of mixed-medium multiple-access techniques, based on code division and time division multiplexing of beacon emissions (CDMA and TDMA respectively), and to dynamically adjust the PHAT filter weighting factor. The receiver position is obtained by hyperbolic multilateration from the time differences of arrival (TDoA) between a reference beacon and the rest, thus avoiding the need for receiver synchronization. The results show how the dynamic adaptation of the weighting factor significantly reduces positioning errors from 20 cm to 2 cm in 80% of measurements. The simulated and real experiments prove that the proposed algorithms improve the performance of the ULPS in situations with lower signal-to-noise ratios (SNR) than 0 dB and in environments where the multipath effect makes it difficult to correctly detect the encoded ultrasonic emissions.

Improved Direction-of-Arrival Estimation of an Acoustic Source Using Support Vector Regression and Signal Correlation.

The direction-of-arrival (DoA) estimation of an acoustic source can be estimated with a uniform linear array using classical techniques such as generalized cross-correlation, beamforming, subspace techniques, etc. However, these methods require a search in the angular space and also have a higher angular error at the end-fire. In this paper, we propose the use of regression techniques to improve the results of DoA estimation at all angles including the end-fire. The proposed methodology employs curve-fitting on the received multi-channel microphone signals, which when applied in tandem with support vector regression (SVR) provides a better estimation of DoA as compared to the conventional techniques and other polynomial regression techniques. A multilevel regression technique is also proposed, which further improves the estimation accuracy at the end-fire. This multilevel regression technique employs the use of linear regression over the results obtained from SVR. The techniques employed here yielded an overall improvement over the classical generalized cross-correlation technique.

Acoustic imaging with conventional frequency domain beamforming and generalized cross correlation: a comparison study

Nowadays, acoustic cameras have become a standard tool for visualizing sound sources. The main post-processing techniques for generating acoustic images are associated with beamforming in the time or frequency domain. While many advanced techniques have been developed for the latter in order to achieve high resolution, such as deconvolution or inverse methods, the former have been less investigated. Recent studies have shown that time-domain beamforming can provide a narrow main lobe with low side lobe levels in different situations. However, a comparison of both techniques in terms of acoustic imaging does not exist. This paper provides a detailed comparison of conventional frequency-domain beamforming (CBF) and time-domain beamforming based on the generalized cross-correlation technique (GCC). First, numerical data are used for assessing both techniques. Then, experimental tests are carried out in a hemi-anechoic room using loudspeakers or power tools. As expected, acoustic images provided by CBF and GCC are found to be very similar but with different computation times. In order to improve the acoustic image, advanced techniques are considered (Clean-SC and the GCC based on geometric mean). When dealing with low frequency, Clean-SC is not able to detect both sources while the GCC based on geometric mean provides an accurate source separation.

Optimization of a spherical microphone array geometry for localizing acoustic sources using the generalized cross-correlation technique

Abstract Many workers are exposed daily to excessive noise levels. In order to reduce the noise exposure at the workstation, the main noise sources have to be detected. This task can be done with a microphone array and a source localization technique. Previous studies have shown promising results with time domain beamforming based on the generalized cross-correlation technique. The objective of this work is to propose an optimal spherical microphone array geometry dedicated to this technique. A cost function based on the symmetry of the aperture angle maps is proposed and is maximized using a Nonlinear Optimization by Mesh Adaptive Direct Search. Numerical results show that the optimized geometry improves the noise source map by reducing the side lobe amplitude without increasing the main lobe surface. Experimental measurements are carried out in a semi-anechoic chamber with prototyped spherical microphone arrays confirming that the optimized microphone array improves the quality of the noise source map.

Identification of noise sources using a time domain beamforming on pneumatic, gas and electric nail guns

In the construction industry, many workers are exposed daily to harmful levels of impulsive noise from nail guns. Therefore, a better knowledge of the noise generated by these tools is required in order to propose noise reduction solutions. The objective of this work is to propose an approach for source identification using a microphone array together with a source identification algorithm based on recent development in the generalized cross-correlation technique. In addition to the pneumatic nail gun, for which sources have been partially identified in the literature, the proposed approach is applied to two other types of nail guns, an electric and a gas powered one. First, the standardized acoustic power spectrum of these three nail guns is measured for global comparison purposes and result in a ranking of the three nail guns. Second, the generalized cross-correlation technique applied to nail gun noise source identification is presented. Third, acoustic maps for successive small time segments are presented, providing a fine identification of noise sources for the three nail guns and an explanation of the observed sound power level ranking.

Online monitoring of furnace exit gas temperature in power plants

Furnace exit gas temperature (FEGT) is an important physical parameter of energy conservation and environmental protection in a coal-fired boiler furnace; however, to date, there is no effective method for monitoring it continuously online. The recently developed acoustic pyrometry is a comparatively advanced method of temperature measurement which possesses the essential characteristics of traditional temperature measurement approaches. We experimentally implemented online FEGT monitoring using acoustic pyrometry, and we could successfully replace the flue gas temperature probes successfully. Two key problems of the acoustic pyrometry technique, i.e. the acoustic signal and time delay estimation, were solved. We adopted the linear sweeping frequency signal as a sound source signal; its sweeping frequency ranged from 500 to 4000 Hz and the sweeping cycle was 0.1 s. We used a generalized cross-correlation technique with PHAT (Phase Transformation) and ML (Maximum Likelihood) as the time delay estimation method when the boiler was in different states. The actual operation of the monitor indicated that the acoustic pyrometry system was accurate and reliable.

Locating Leaking Buried Pipes Based on Ground Microseismic Records in 3D Space

Pipelines are a safe energy-efficient mode of transporting fluids and gases. However, risks of pipe leaks still exist. Various pipe leak detection methods are in use; some traditional methods rely on acoustic receivers that must be located on the pipe, thereby restricting their implementation. Microseismic monitoring resolves this restriction because the ground rather than the pipe is monitored. However, microseismic monitoring has, thus far, only been applied using 2D methods for pipeline leak detection, and its accuracy is limited. To address this problem, a new 3D leak detection and location method for buried pipelines is proposed. First, using a 3D staggered-grid finite-difference method for acoustic equations, we simulated a microseismic wave field generated by a leaking pipeline, and recorded it with a ground surface geophone array. Then, a generalized cross-correlation technique was used to extract the time difference. Finally, the simulated annealing method was used to obtain the leak location in 3D space. Simulation and field data results show that the proposed method can locate the leakage point and has good anti-noise capability. Accurate 3D leak location requires at least two survey lines. Non-parallel survey lines can locate the approximate plane position of the leakage. Parallel line and orthogonal line pairs can be used to obtain the leak position accurately; the parallel line pair is the most accurate. The proposed method was concluded to be effective and accurate at detecting and locating leakages in buried pipeline networks.

Acoustic source localization using a polyhedral microphone array and an improved generalized cross-correlation technique

Millions of workers are exposed to excessive noise levels each day. Acoustic solutions have to be developed to protect workers from hearing loss. The first step of an acoustic diagnosis is the source localization which can be performed with a microphone array. Spherical microphone arrays can be used to detect the acoustic source positions in a workplace. In this study, a spherical microphone array, with polyhedral discretization, is proposed and compared with a spherical array with a slightly different geometry. The generalized cross-correlation technique is used to detect the source positions. Moreover, two criteria are introduced to improve the noise source map. The first is based on the geometric properties of the microphone array and the scan zone whereas the second is based on the energy of the spatial likelihood function. Numerical data are used to provide a systematic comparison of both geometries and criteria. Finally, experiments in a reverberant room reveal that the polyhedral microphone array associated with both criteria provides the best noise source map.

Continuous broadband digital interferometry of lightning using a generalized cross-correlation algorithm

The VHF Broadband Digital Interferometer developed by Osaka University has been improved to allow continuous sampling over the entire duration of a lightning flash and to utilize a generalized cross-correlation technique for determining the lightning source directions. Time series waveforms of 20–80 MHz signals received at three orthogonally located antennas are continuously digitized over multisecond intervals, as opposed to sequences of short-duration triggers. Because of the coherent nature of the measurements, radiation sources are located down into the ambient receiver and environmental noise levels, providing a quantum leap in the ability to study lightning discharge processes. When postprocessed using cross correlation, the measurements provide angular uncertainties less than 1° and time resolution better than 1 μs. Special techniques have been developed to distinguish between actual lightning sources and noise events, with the result being that on the order of 50,000–80,000 radiation sources are located for a typical lightning flash. In this study, two-dimensional interferometer observations of a classic bilevel intracloud flash are presented and combined with three-dimensional Lightning Mapping Array observations to produce a quasi 3-D map of lightning activity with the time resolution of the interferometer. As an example of the scientific utility of the observations, results are presented for the 3-D progression speed of negative leaders associated with intracloud K-leaders.

A Signal-processing Scheme for Passive Acoustical Mapping of Breaking Surface Waves

An acoustical system is described with emphasis on its signal-processing scheme. The system consists of a small broadband hydrophone array of span 8.5 m and 5-kHz bandwidth, which is able to track individual breaking surface waves by passive detection of the naturally generated sound of wave breaking. The generalized cross-correlation technique is used to determine time differences of acoustical signals from breaking waves arriving at the array. Breaking events are identified in correlation time sequences, and the identification is aided by image enhancement and pattern recognition. Determination of source positions from the estimated time delays is also discussed. The instrument was first employed during the Surface Wave Program (SWAPP), and preliminary results clearly demonstrate the ability to track individual breaking events. This system can be used to measure some spatial and temporal characteristics of breaking waves, such as frequency of breaking, lifetime, velocity, and spatial distributions.