A filtered convolution method for the computation of acoustic wave fields in very large spatiotemporal domains

The full-wave computation of transient acoustic fields with sizes in the order of 100x100x100 wavelengths by 100 periods requires a numerical method that is extremely efficient in terms of storage and computation. Iterative integral equation methods offer a good performance on these points, provided that the recurring spatiotemporal convolutions...

Estimating and correcting the amplitude radiation pattern of a virtual source

In the virtual source (VS) method we crosscorrelate seismic recordings at two receivers to create a new data set as if one of these receivers were a virtual source and the other a receiver. We focus on the amplitudes and kinematics of VS data, generated by an array of active sources at the surface and recorded by an array of receivers in a...

Tracking of Nonstationary Noise Based on Data-Driven Recursive Noise Power Estimation

This paper considers estimation of the noise spectral variance from speech signals contaminated by highly nonstationary noise sources. The method can accurately track fast changes in noise power level (up to about 10 dB/s). In each time frame, for each frequency bin, the noise variance estimate is updated recursively with the minimum mean-square...

Noise Tracking Using DFT Domain Subspace Decompositions

All discrete Fourier transform (DFT) domain-based speech enhancement gain functions rely on knowledge of the noise power spectral density (PSD). Since the noise PSD is unknown in advance, estimation from the noisy speech signal is necessary. An overestimation of the noise PSD will lead to a loss in speech quality, while an underestimation will...

On the Estimation of Complex Speech DFT Coefficients Without Assuming Independent Real and Imaginary Parts

This letter considers the estimation of speech signals contaminated by additive noise in the discrete Fourier transform (DFT) domain. Existing complex-DFT estimators assume independency of the real and imaginary parts of the speech DFT coefficients, although this is not in line with measurements. In this letter, we derive some general results on...

Time-domain modeling of electromagnetic diffusion with a frequency-domain code

We modeled time-domain EM measurements of induction currents for marine and land applications with a frequency-domain code. An analysis of the computational complexity of a number of numerical methods shows that frequency-domain modeling followed by a Fourier transform is an attractive choice if a sufficiently powerful solver is available. A...

Fourier reconstruction of marine-streamer data in four spatial coordinates

Many methods exist for interpolation of seismic data in one and two spatial dimensions, but few can interpolate properly in three or four spatial dimensions. Marine multi-streamer data typically are sampled relatively well in the midpoint and absolute offset coordinates but not in the azimuth because the crossline shot coordinate is...

Measurements of shock-induced guided and surface acoustic waves along boreholes in poroelastic materials

Acoustic experiments on the propagation of guided waves along water-filled boreholes in water-saturated porous materials are reported. The experiments were conducted using a shock tube technique. An acoustic funnel structure was placed inside the tube just above the sample in order to enhance the excitation of the surface modes. A fast Fourier...

Design reuse in product shape modeling: A study of freeform feature reuse by signal processing techniques

Lack of facilities in supporting design reuse is a serious problem in product shape modeling, especially in computer-aided design systems. This becomes a bottleneck of fast shape conceptualization and creation in consumer product design, which consequently prohibits creativity and innovation. In the past, several efforts have been made in order...

Some aspects of aircraft response to atmospheric turbulence

Aspects of the requirements for and the calculation of design loads due to atmospheric disturbances are discussed. Special attention has been paid to the relation between discrete gusts and continuous turbulence. It is recommended that a worst case gust model, as described in this report, be further developed.

Worst case gust shapes for atmospheric turbulence with known spectrum

A worst case gust shape has been derived for turbulence or gust patches, assuming only that the average spectrum of such patches is known. The maximum value of the response can be calculated quite easily. The result differs from the PSD-method. Some examples of worst case inputs and outputs are given, also for nonlinear systems.

Atmospheric turbulence spectra and correlation functions

The derivation of one- two- and three-dimensional spectra and correlation functions for isotropic (atmospheric) turbulence and the mutual relations have been collected from various sources. Aircraft loads usually are determined using a one-dimensional turbulence description. In some cases a two- or even three-dimensional description might be...

Onderdrukken van lek naar zijlobben bij het berekenen van auto- en kruisspectra mb.v. fast fourier transforms

Bij het bepalen van auto- en kruisspectrale vermogensdichtheidsfunklies (in het vervolg van deze notitie: spectra) van tijdreeksen ult een meetreeks van beperkte duur, onstaat in het algemeen lek van vermogensdichtheid bij een bepaalde frequentie naar andere frequenties. Dit wordt veroorzaakt door het feit, dat als het signaal periodiek wordt...

Channel coding with the (255,255-2T) Reed-Solomon codes over CF(256)

The class of (255, 255-2T) Reed-Solomon codes over CF(256) is studied in detail. In particular the encoding and decoding algorithms are elaborated. Main computational elements are the discrete Fourier transform for syndrome and error locator computation, Euclid's algorithm for solving the key equation and Horner's scheme for determining the...