Proposed Processing Procedure Research Articles

Uncertainty Estimation for Ultrasonic Inspection of Composite Aerial Structures

Components made of polymeric composite materials, such as wings and stabilizers of aircrafts, are periodically inspected using non-destructive testing methods. Ultrasonic testing is one of the primary inspection methods applied in the aircraft/aerospace industry. Image processing methods have been developed for the purpose of ultrasonic data analysis and increasing the inspection efficiency. A critically important factor in damage sizing is appropriate processing of ultrasonic data in order to extract the damage region properly before calculation of its extent. The paper presents a comparative analysis of various image segmentation methods in the light of accuracy of damage detection in ultrasonic C-Scans of composite structures. A brief review of image segmentation methods is presented and their usefulness in the ultrasonic testing applications is discussed. The selected methods, namely the threshold-, edge-, region-, and clustering-based ones, were tested using ultrasonic C-Scans of a specimen with barely visible impact damage and aircraft panels with delamination, all made of CFRP composites. A problem with the selection of appropriate input parameters using most of the segmentation methods is discussed, and non-parametric histogram-based approaches are proposed. A quantitative analysis of the accuracy of damage detection using the segmentation methods is presented and the most suitable approaches are introduced. The proposed processing procedures may significantly improve the objectivity of inspections of composite elements and structures using ultrasonic testing.

Modeling of socially significant respondents' behavior: analytical and numerical rate estimates based on the episodes near interview in case of information deficiency

The paper offers a method for respondents' behavior modeling based on data about last episodes adjacent to interview and proposes improved techniques of modeling and processing of initial data uncertainty based on hybrid probabilistic and fuzzy approaches. This paper provides analytical (including asymptotic) analysis of these estimates and numerical behavior rate estimates according to the model. Software supplements enabling to fulfill numerical experiments realizing the proposed processing procedures were worked out.

An Adaptive Allocation Scheme in Multiuser OFDM Systems with Time-Varying Channels

Previously, a scheme in [1] is proposed for the subcarrier, bit, and power allocation problem to minimize the total transmit power for multiuser orthogonal frequency division multiplexing systems in downlink transmission. However, it is a batch mode which may not be so efficient in terms of computational complexity for slowly time-varying channel environments. The solution of the current frame can be obtained with slight modification from that of the previous frame in an adaptive fashion. By utilizing this property, we propose a scheme to obtain the solution in the adaptive fashion, which offers comparable performance with a reduced complexity compared to the previously proposed method and other existing suboptimal methods. Based on a derived expression composed of the channel gains, the numbers of assigned subcarriers, and the data rates along with the new proposed processing procedures, the proposed adaptive scheme is able to track the channel variation for the solution adjustment in a faster speed compared to the original batch mode method. Simulation results reveal that the proposed adaptive scheme has the competitive performance compared with those of the optimal and the existing schemes while the computational complexity and the number of iterations are both reduced.

Modeling and Processing L-Band Ground Based Radar Data for Landslides Early Warning

L-band radars have been proposed as possible way for monitoring landslides. In this paper, we examine and solve the principal difficulties arising in modeling and processing radar data, evidencing differences with more usual SAR imaging. Numerical examples in support of the proposed processing procedure are finally provided.

Range Cell Migration Correction for Bistatic SAR Image Formation

Range cell migration (RCM) correction (RCMC) is the key process in the imaging formation of bistatic synthetic aperture radar (SAR) (BiSAR). Due to the existence of double square root in the bistatic range equation, the RCMC in the general BiSAR configuration is more complicated than the traditional monostatic method. In this letter, the RCM of BiSAR system is analyzed in detail, and a novel data transformation is derived. From the derivation, we find that the original keystone transform (KT) is only a special case of our proposed transformation, so that we called it the generalized KT (GKT). Compared with the original KT, this generalized method can correct more complex RCM nicely. After the GKT processing, the RCM is eliminated closely, and the focused image with full range and Doppler resolution can be obtained using the fast Fourier transform. Finally, a hybrid spaceborne/airborne BiSAR numerical simulation is performed to validate the proposed processing procedure.

APPLICATIONS OF COMPRESSED SENSING FOR MULTIPLE TRANSMITTERS MULTIPLE AZIMUTH BEAMS SAR IMAGING

High speed analog-to-digital (A/D) sampling and a large amount of echo storage are two basic challenges of high resolution synthetic aperture radar (SAR) imaging. In this paper, a novel SAR imaging algorithm which named CS-MTMAB is proposed based on compressed sensing (CS) and multiple transmitters multiple azimuth beams (MTMAB). In particular, this new algorithm, which respectively reconstructs the targets in range and azimuth directions via CS technique, simultaneously provides a high resolution and wide- swath two-dimensional map of the spatial distribution of targets with a signiflcant reduction in the number of data samples beyond the Nyquist theorem and with an implication in simpliflcation of radar architecture. The simulation results and analysis show that this new imaging scheme allows the aperture to be compressed and presents many important applications and advantages among which include reduced on-board storage constraints, higher resolution, lower peak side-lobe ratio (PSLR) and integrated side-lobe ratio (ISLR), less sampled data than the traditional SAR imaging algorithm, and also indicate that it has high robustness and strong immunity in the presence of serious noise. Finally, the real raw airborne SAR data experiment is performed to validate the proposed processing procedure.

Refractor velocity analysis: a signal processing procedure

ABSTRACT This paper presents a signal processing procedure to perform refractor velocity analysis. The procedure enables one to obtain the seismic velocity from the refracted wavefield without the picking of refracted arrival times. Two processing procedures are derived, one starting from a seismic interferometric approach and another, from the conventional reciprocal method and generalized reciprocal method approaches. The theoretical equivalence of the two approaches is also demonstrated. The proposed processing procedure is applied to synthetic data in order to test the influence of some procedural parameters and its capability to reconstruct a known velocity model starting from refracted signals, without and with perturbations, in arrival times and noise; finally, it is applied to a field data set.

Focusing Spaceborne/Airborne Hybrid Bistatic SAR Data Using Wavenumber-Domain Algorithm

This paper focuses on the bistatic synthetic aperture radar (SAR) data processing in a spaceborne/airborne hybrid bistatic configuration. Due to the extreme differences in platform velocities and slant ranges, the airborne system operates in the inverse sliding-spotlight mode, while the spaceborne system works in the sliding-spotlight mode to achieve a tradeoff between azimuth scene size and azimuth resolution. In this extreme bistatic configuration, our original bistatic formula shows a limitation of accurately describing the bistatic point-target reference spectrum, owing to the assumption of equal contributions of transmitter and receiver to the total Doppler spectrum. We extend our previous formula using the weighting operation where the weighting factor is the ratio of the azimuth time-bandwidth product (TBP) of the platform to the total azimuth TBP. In this paper, the bistatic-deformation and azimuth-dependent range-cell-migration terms were removed with phase multiplications performed blockwise in range-azimuth subsections. The remaining quasi-monostatic term shows the characteristic of the conventional monostatic SAR besides an additional azimuth-scaling term. For the monostatic characteristic, any precision monostatic SAR processing algorithms can handle. In this paper, we prefer the wavenumber-domain algorithm (also known as Omega-K), since it can accurately correct the range dependence of the range-azimuth coupling, as well as the azimuth-frequency dependence. For the azimuth-scaling term, an inverse scaled Fourier transformation is performed to correct it. Finally, a hybrid spaceborne/airborne simulation experiment is conducted to validate the proposed processing procedure.

On the mechanism of gray scale patterning of Ag-containing As 2S 3 thin films

We demonstrate an application of photo-induced silver diffusion into chalcogenide glass thin film for gray scale lithography. The gray scale chalcogenide glass masking layer generated in the present experiments was dry etched using reactive ion etching. The etching rate increases almost linearly with the total dose of absorbed light, thus forming the basis of gray scale lithography. Chemical composition as well as electronic structure on the surface of chalcogenide glassy film has been determined by high-resolution X-ray photoelectron spectroscopy (XPS) of the film at different stages of the patterning process. Influence of thermal annealing of chalcogenide film before Ag deposition has been investigated using scanning electron microscopy (SEM) and XPS techniques. It is observed that thermal annealing of the chalcogenide film slows the process of silver diffusion during the proposed processing procedure. A mechanism is proposed to explain the stages of gray scale lithography based on chalcogenide glass photoresists.

Binaural speech enhancement by complex wavelet transform based on interaural level and argument differences

Binaural information might enhance speech signals in noisy environments. Most precedent studies in this area have implemented signal processing in time and frequency domains. For this study, an enhancement method using complex wavelet transform (CWT) was proposed. The CWT has a scale domain whose bandwidth is inversely proportional to the scale level and may therefore be well compared to auditory filters. The proposed processing procedure is the following: (1) By computing CWT for a sound signal at every direction of arrival (DOA), a database (DB) of the scale domain wavelet coefficients is prepared for every DOA. (2) For binaural input signals from an unknown direction, the scale domain wavelet coefficients are calculated using CWT. (3) The DOA of the input signal is estimated as the direction for which interaural level and argument differences calculated from wavelet coefficients are the most similar to those in the DB. (4) The input signal is segregated similarly to FDBM (Nakashima et al., 2003) based on the estimated DOA. Experiments with a directional target signal and an interference sound source calculated from real HRTFs were conducted to show the effectiveness of the proposed algorithm. [This research was partially supported by Sendai Intelligent Knowledge Cluster.]