High-amplitude Noise Research Articles

Sparse representation of complex-valued fMRI data based on spatiotemporal concatenation of real and imaginary parts

BackgroundSpatial sparsity has been found to be in line with the intrinsic characteristic of brain activation. However, identifying a sparse representation of complex-valued fMRI data is challenging due to high noise within the phase data. New methodsWe propose to reduce the noise by combining real and imaginary parts of complex-valued fMRI data along spatial and temporal dimensions to form a real-valued spatiotemporal concatenation model. This model not only enables flexible usage of existing real-valued sparse representation algorithms but also allows for the reconstruction of complex-valued spatial and temporal components from their real and imaginary estimates. We propose to select components from both real and imaginary estimates to reconstruct the complex-valued component, using phase denoising to recover weak brain activity from high-amplitude noise. ResultsThe K-SVD algorithm was used to obtain a sparse representation within the spatiotemporal concatenation model. The results from simulated and experimental complex-valued fMRI datasets validated the efficacy of our method. Comparison with existing methodsCompared to a magnitude-only approach, the proposed method detected additional voxels manifest within several specific regions expected to be involved but likely missing from the magnitude-only data, e.g., in the anterior cingulate cortex region. Simulation results showed that the additional voxels were accurate and unique information from the phase data. Compared to a complex-valued dictionary learning algorithm, our method exhibited lower noise for both magnitude and phase maps. ConclusionsThe proposed method is robust to noise and effective for identifying a sparse representation of the natively complex-valued fMRI data.

GROUND ROLL NOISE ATTENUATION IN 3D LAND SEISMIC DATA IN PARTS OF NIGER DELTA, NIGERIA

Three-dimensional (3D) land seismic datasets were acquired from Central Depobelt in the Niger Delta region, Nigeria, with with the aim of attenuating ground roll noise from the dataset. The Omega (Schlumberger) software 2018 version was used along with frequency offset coherent noise suppression (FXCNS) and Anomalous Amplitude Attenuation (AAA) algorithms for ground roll attenuation. From the results obtained, Frequency Offset Coherent Noise Suppression (FXCNS) attenuates ground roll while AAA algorithm attenuates the residual high amplitude noise from the seismic data. Average frequency of the ground roll in the seismic data is 10.50Hz which falls within the actual range of ground roll frequency which is within the range of 3.00 – 18.00Hz. The average velocity of the ground roll in the seismic data is 477.36ms-1 while the velocity of ground roll ranges between 347.44 and 677.37ms-1. The wavelength of ground roll in the seismic data is 50.28m. The amplitude of the ground roll of -6.24dB is maximum at 4.2Hz. Frequency of signal ranges between 10.21 and 25.12Hz with an average of 17.67Hz. Signal amplitude of -8.32dB is maximum at 6.30Hz, while its wavelength is 57.12m. The results of this work can be used in the seismic source-receiver design for application in the area of study. Moreover, with ground roll noise attenuated, a better image of the subsurface geology is obtained hence reducing the risk of obtaining a wild cat drilling.

Data-adaptive harmonic analysis of oceanic waves and turbulent flows.

We introduce new features of data-adaptive harmonic decomposition (DAHD) that are showcased to characterize spatiotemporal variability in high-dimensional datasets of complex and mutsicale oceanic flows, offering new perspectives and novel insights. First, we present a didactic example with synthetic data for identification of coherent oceanic waves embedded in high amplitude noise. Then, DAHD is applied to analyze turbulent oceanic flows simulated by the Regional Oceanic Modeling System and an eddy-resolving three-layer quasigeostrophic ocean model, where resulting spectra exhibit a thin line capturing nearly all the energy at a given temporal frequency and showing well-defined scaling behavior across frequencies. DAHD thus permits sparse representation of complex, multiscale, and chaotic dynamics by a relatively few data-inferred spatial patterns evolving with simple temporal dynamics, namely, oscillating harmonically in time at a given single frequency. The detection of this low-rank behavior is facilitated by an eigendecomposition of the Hermitian cross-spectral matrix and resulting eigenvectors that represent an orthonormal set of global spatiotemporal modes associated with a specific temporal frequency, which in turn allows to rank these modes by their captured energy and across frequencies, and allow accurate space-time reconstruction. Furthermore, by using a correlogram estimator of the Hermitian cross-spectral density matrix, DAHD is both closely related and distinctly different from the spectral proper orthogonal decomposition that relies on Welch's periodogram as its estimator method.

Hardware Efficient Solutions for Wireless Air Pollution Sensors Dedicated to Dense Urban Areas

This paper proposes novel solutions for the application of air pollution monitoring systems in so called ‘smart cities’. A possibility of the implementation of a relatively dense network of wireless air pollution sensors that can collect and process data in real time was the motive behind our research and investigations. We discuss the concept of the wireless sensor network, taking into account the structure of the urban development in cities and we present a novel signal processing algorithm that may be used to control the communication scheme between particular sensors and an external network. We placed a special emphasis on the computational complexity to facilitate the implementation directly at the transistor level of particular sensors. The algorithm was verified using real data obtained from air pollution sensors installed in Krakow, Poland. To ensure sufficient robustness of the variability of input data, we artificially added high amplitude noise to the real data we obtained. This paper demonstrates the performance of the algorithm. This algorithm allows for the reduction of the noise amplitude by 23 dB and enables a reduction of the number of wireless communication sessions with a base station (BS) by 70%–80%. We also present selected measurement results of a prototype current-mode digital-to-analogue converter to be used in the sensors, for signal resolutions up to 7 bits.

Small target detection and window adaptive tracking based on continuous frame images in visible light background

Due to the difficulty in distinguishing the target and the noise in the visible light background and the loss of the target for a short period of time, a scheme of track association and target tracking for the small target in the sky is carried out. Multi-feature similarity is taken into account, such as the maximum intensity, the maximum brightness, the size and the moving speed. Firstly, the trajectory prediction is carried out by the least square prediction method. By updating the real-time data to deduce the trajectory parameters, the target position in the next frame image is predicted. Based on the trajectory confidence test, all current recorded trajectories are traversed. The over-confidence trajectory is detected and the trajectories of continuous lost points are deleted, as well as the trajectories below the threshold of confidence. For the trajectory of the over-confidence, the target trajectory without the significant motion feature is deleted by judging the magnitude of the moving speed, so that the effective trajectory can be displayed while the false target is eliminated. Then, the target tracking is carried out, which is based on the LOG filter and the constant false alarm rate segmentation. Considering the temporal and spatial continuity of the target trajectory and the randomness of the amplitude and position of the noise, the false alarm rate can be reduced by eliminating the high amplitude noise by using the difference between the two in terms of temporal and spatial correlation. Owing to that the setting of the division threshold is not less than 5 times the background variance of the window image, the generation of the noise by the constant false alarm rate segmentation can be avoid when there is no target. In addition, the target coordinates may be abrupt due to sudden changes in target speed and the jitter of the image acquisition equipment. Therefore, we propose a dynamic adjustment scheme for the tracking window size to enable window adaptive tracking, which can set the length and width of the rectangular window to k times of the original size according to actual needs. At the same time, the number of points of the relatively stationary target in each frame of the image can be counted in real time. Finally, the reliability of the method is verified by simulation experiments, and the running speed is relatively fast and the recognition accuracy is relatively high.

AMBIENT SEISMIC NOISE FOOTPRINTS AND SPECTRA IN THE MIDDLE BENUE TROUGH, NIGERIA

Ambient noise was analysed from a two-dimensional (2D) seismic data acquired in the Middle Benue Trough, Nigeria for the purpose of characterizing the ambient seismic noise. Sercel 428XL recording instrument was deployed on 3 traverse lines where dynamite explosive sources and geophone detectors were used. The acquired data was processed using frequency wavenumber (FK) and wild amplitude attenuation (WAA) algorithms. The dominant amplitude of the primary reflection ranges between -20dB and -10dB, while those of the ambient seismic noise varies between -42dB and -3dB. The primary reflections have dominant frequency varying from 6Hz to 75Hz while that of ambient seismic noise varies between 4Hz and 70Hz. Analysis of the noise shows two distinct ground roll modes with velocities between 400 ms-1 and 810 ms-1 both of which are dispersive with wavelength (λ) of 61.5m and peak frequency at 6.5Hz. Analysis of passive noise records acquired showed that ambient seismic (background) noise level excluding source-generated noise average of 91.56% are below 25µV, which is the tolerance noise level limit. The combination of frequency wavenumber FK and WAA filters effectively attenuated the surface waves especially ground rolls and other high amplitude noise making the primary reflection very visible and better enhanced. The filtered amplitude values estimated from signal-to-noise (SNR) analysis using cross correlation (XC) method are much higher than the values of the unfiltered amplitudes indicating that SNR are highest when noises are attenuated from the data than when noise algorithm is not applied to the data. The attributes of these seismic noises will provide further information and solution for their suppression during seismic data acquisition and processing.

Impact of previous work in the conditions of industrial noise on the development of sensorineural hearing loss in the outcome of a military injury.

The results of a survey of militia members - industrial workers aged 35-39 years who had previously worked in the conditions of industrial noise are presented. As a result of a military trauma (combined head injury, acutrauma, barotrauma) they developed sensorineural hearing loss. The level of hearing loss and the degree of involvement in the pathological process of the sound-perceiving apparatus is related to the length of work experience in the conditions of industrial noise. For persons who worked in conditions of constant low-amplitude broadband noise (n=30), hearing loss is more pronounced compared to persons (n=30) who worked in conditions of pulsed high-frequency high-amplitude noise. In the control group (35-39 years, n=30), who previously worked outside of industrial noise, the level of hearing loss is determined by the frequency of traumatic brain injury and is associated with the formation of post-traumatic osteochondrosis and vertebrobasilar insufficiency.

Experimental testing of semirigid corrugated baffles for the suppression of tube waves in vertical seismic profile data

Multichannel borehole hydrophone strings are a low-cost, low-risk, alternative to borehole clamping geophones. Vertical seismic profile (VSP) data collected with hydrophones, however, suffer from high-amplitude coherent tube-wave noise. This reduces the usable data to the first arrivals and traveltimes for check-shot surveys. To significantly reduce tube-wave noise from VSP data acquired with hydrophones, we have designed and tested a novel tube-wave attenuation baffle. The effectiveness of the baffle was first verified in a laboratory-scale experiment and then in a borehole drilled into a hardrock environment. The laboratory experiments tested the performance of four different baffle topologies, whereby the best performing topology was the semirigid corrugated pipe baffle. This design reduced the amplitude of the tube wave with more than 40 dB and was logistically easy to deploy. The field experiment investigated the effectiveness of three different semirigid corrugated pipe baffle topologies in a PQ (123 mm) diamond drillhole in Western Australia. Here, we found that the semirigid corrugated pipe baffle was effective in disrupting tube-wave propagation. The 100 mm diameter baffle achieved an impressive 60 dB of tube-wave attenuation, whereas the 50 mm baffle had a modest attenuation of 10–15 dB. This suggests that the performance of this new type of baffle is best when the diameter of the baffle is closely matched to the diameter of the borehole. The results of these experiments have significant implications because hydrophone arrays with a large number of receivers are comparatively inexpensive and simpler to deploy than borehole geophone counterparts. The development of hydrophone arrays that are free of interfering borehole modes could allow VSPs to be acquired in situations in which seismic-polarity information is not required and could help VSP gain traction in cases in which the cost of acquisition has precluded its use until now.

Passive Microseismic Monitoring of CO2 EOR and Associated Storage Using a Downhole Array in a Noisy Subsurface Environment

A passive microseismic monitoring study of CO2 enhanced oil recovery operations at the Bell Creek Field was conducted. Two distinctive low signal-to-noise ratio environments were observed: a diurnal, dominated by high-amplitude coherent noise in the same frequency band as the signal, and a nocturnal, characterized by weak signals buried in random noise. Using estimations from a synthetic microseismic model as a reference and applying conventional, relatively simple event detection, picking and location estimation algorithms to nocturnal seismograms, we were able to identify microseismicity. We propose and demonstrate a low-cost tool correction method to simplify logistic field and data processing operations.

Noise in urban land seismic surveys

Land seismic surveys are most often acquired in remote areas, thus the predominant noise source is often the wind. In urban areas, however, noise sources abound, including electrical cables, mechanical equipment, aircraft, and traffic. We recorded seismic data continuously over three days at a test site located in suburban Perth, Western Australia (32° 0’ 40”S, 115° 53’ 22”E). and found that the highest amplitude noise was mechanical (centred on 75 Hz), but the most consistent noise was traffic related (10-25 Hz). Electrical noise was identified but given its moderate amplitude and relatively consistent frequency it should be easily removed in processing. Aircraft flying over the test site resulted in moderately high level of noise with a wide bandwidth (30-200 Hz) but the noise generally lasted only a minute.Based on these results we recommend that: acquisition should be carried out during the late night/early morning; receiver locations should be chosen with care to avoid sources of noise; analogue cabling should be as short as possible to avoid electrical noise; real-time QC should be in place to identify short-duration high-amplitude noise periods during which acquisition should cease.

POSSIBILITY AND APPLICABILITY OF PSEUDO-RANDOM CODE FUNCTIONS IN IMPULSE-CODE SEISMIC CONCENTRATION TO OIL AND GAS SEISMOLOGY PROBLEM-SOLVING RESEARCH

The applicability of pseudo-random code functions in impulse-code seismic concentration to oil and gas seismology problemsolving has been assessed through the comparative analysis of correlation functions in compliance with pseudo-random pulse sequences and linear change in pulse repetition sequences. The research shows that the correlation functions’ main peaks spectrums of pseudo-random pulse sequences are almost equal to the single impulses’ spectrums used for the sequences development. The given circumstance reflects the general possibility of pseudo-random sequences applicability to oil and gas seismology problemsolving. However, pseudo-random sequences are characterised by the increased interference level of correlative transformation, which makes the use of pseudo-random code functions in oil and gas seismology inappropriate. It is noted that not only are impulsecode pseudo-random signals characterised by high-amplitude correlation noise, but also all the other pseudo-random complex signals, e.g. random quasi-harmonic signals, contained in modern vibroseis management systems.

A large area detector for thermal neutron flux measurements at the KamLAND site

A large area (0.5 m × 0.5 m) thermal neutron detector was developed based on 0.32 mm-thick 6LiF:ZnS(Ag) scintillator sheets. The detector was constructed for measurements of seasonal variations in low intensity thermal neutron flux at deep underground sites. The detector response to neutrons was studied using a low intensity 241Am/9Be(α,n) neutron source. The digital pulse shape discrimination technique was applied to separate neutron capture events from the background caused by traces of α-emitters from Uranium and Thorium decay chains in scintillator components. The thermal neutron detection efficiency was 0.368 ± 0.018 (0.155 ± 0.009) before (after) event selection based on the digital pulse shape discrimination method. The measured α-particle background event rate in the 6LiF:ZnS(Ag) scintillator was (4.88 ± 0.06(stat))×10−6α cm−2 s−1. As a test of detector performance we measured the thermal neutron flux at the KamLAND area of the Kamioka neutrino observatory and compared it with result of the neutron flux measurement carried out at the Super-Kamiokande site. The thermal neutron flux at KamLAND was (6.43 ± 0.50)×10−6 n cm−2 s−1 that included ∼10% contribution from neutrons with energies above 1 eV. During the detector construction we identified a source of high amplitude noise pulses generated by 5-inch R1250 photomultipliers manufactured by Hamamatsu Photonics K. K.

Octave Spanning Coherent Supercontinuum Comb Generation Based on Er-Doped Fiber Lasers and Their Characterization

Wideband, octave spanning, coherent supercontinuum (SC) with high flatness is very useful for many applications, but it has been difficult to achieve such ideal SC. In this paper, we investigated the octave spanning, coherent SC generation based on Er-doped ultrashort pulse fiber laser system. First, we developed a high power ultrashort pulse system using a single-wall carbon nanotube fiber laser and similariton amplifier. A 1.0–2.2 μ m octave-spanning coherent supercontinuum was successfully generated. Next, by use of a stabilized fiber laser comb system as the seed pulse, an octave spanning SC comb was demonstrated. An octave spanning, highly coherent comb with high flatness was generated with normally dispersive highly nonlinear fiber. The characteristics of the generated supercontinuum comb were examined via balanced heterodyne beat measurements with stable continuous-wave laser diodes. The SC comb was confirmed to have high coherence and low amplitude noise at the observed wavelengths. Finally, the SC generation in two kinds of highly nonlinear fibers with different dispersion properties and the characteristics of the generated comb were examined. The dependence on fiber length, wavelength, and dispersion properties were discussed.

Improving the Positional Accuracy of the Airborne Vehicle during Its Motion along the Predetermined Path

The method of improving the positional accuracy of the airborne vehicle that moves along a great circle path is considered due to the analytical three-dimensional projection of its current coordinate position, determined from the measurements of the satellite navigation system under the conditions of high-amplitude noise to the true guide path.

The effects of mining machinery noise of different amplitudes on the behaviour, faecal corticosterone and tissue morphology of wild mice (Mus musculus)

Mining noise has been identified as a source of stress for wildlife but the effects on the behaviour and physiology of individuals are largely unknown. We evaluated the effects of exposing wild mice to mining machinery noise for 3 weeks at two amplitude ranges: high (HA; 70–75 dB (A)) and low (LA; 60–65 dB (A)) on their behaviour, organ properties and faecal corticosterone levels, when compared with a control treatment (no extra auditory stimuli, below 55 dB (A)). Both noise treatments increased circling to the left, compared to the control (P = 0.001) which corresponds to right hemispheric processing of the stress response; however only the high amplitude noise increased circling to the right (left hemisphere activation; P < 0.0001), which may inhibit stress arousal by right hemisphere. Total circling behaviour (to the left and right) was just increased in mice exposed to high amplitude noise, compared with those in the control and low amplitude noise (P < 0.0001), but in the low amplitude noise faecal corticosterone was increased (P = 0.003). We hypothesize that dopamine-related stereotypies during high amplitude mining noise were a coping mechanism that prevented a physiological response. Noise-exposed males tended to have smaller spleens (P = 0.003) and females in the HA treatment tended to have a smaller adrenal cortex/medulla ratio (P = 0.007). Mining machinery noise produced amplitude – dependent stress responses in wild mice that probably required the generation of coping mechanism.

3D forward modeling of upgoing and downgoing wavefields using Hilbert transform

The separation of upgoing and downgoing wavefields is an important technique in the processing of vertical seismic profiling data and ocean bottom cable data. It is also used in reverse time migration (RTM) based on the two-way wave equation to suppress low-frequency, high-amplitude noises and false images. Therefore, we model upgoing and downgoing wavefields directly in the wavefield propagation. There are several methods to obtain separated wavefields. The methods using the Fourier transform require storage of the wavefields, which is not practical due to the extremely high disk-space requirements. Methods using Poynting vectors have an ambiguity problem when crossing a peak or a trough of the wavefields. To improve the accuracy and stability of the modeled upgoing and downgoing wavefields in a complicated velocity model, we evaluate an efficient forward-modeling approach purely based on the Hilbert transform in 3D acoustic wavefield simulation. This method is implemented by the Hilbert transform along the time and depth axis, instead of the Fourier transform. We explicitly derive the formulas for upgoing and downgoing wavefield propagation and attach reproducible source codes. Applications to synthetic models indicate that this method can forward propagate upgoing and downgoing wavefields effectively and improve the imaging quality in migration. This method has various potential applications, e.g., 3D seismic imaging with high computation efficiency.

Noise reduction with complex bilateral filter.

This study introduces a noise reduction technique that uses a complex bilateral filter. A bilateral filter is a nonlinear filter originally developed for images that can reduce noise while preserving edge information. It is an attractive filter and has been used in many applications in image processing. When it is applied to an acoustical signal, small-amplitude noise is reduced while the speech signal is preserved. However, a bilateral filter cannot handle noise with relatively large amplitudes owing to its innate characteristics. In this study, the noisy signal is transformed into the time-frequency domain and the filter is improved to handle complex spectra. The high-amplitude noise is reduced in the time-frequency domain via the proposed filter. The features and the potential of the proposed filter are also confirmed through experiments.

Frequency-constrained robust principal component analysis: a sparse representation approach to segmentation of dynamic features in optical coherence tomography imaging

Sparse representation theory is an exciting area of research with recent applications in medical imaging and detection, segmentation, and quantitative analysis of biological processes. We present a variant on the robust-principal component analysis (RPCA) algorithm, called frequency constrained RPCA (FC-RPCA), for selectively segmenting dynamic phenomena that exhibit spectra within a user-defined range of frequencies. The algorithm lacks subjective parameter tuning and demonstrates robust segmentation in datasets containing multiple motion sources and high amplitude noise. When tested on 17 ex-vivo, time lapse optical coherence tomography (OCT) B-scans of human ciliated epithelium, segmentation accuracies ranged between 91-99% and consistently out-performed traditional RPCA.

A Novel Signal Regeneration Technique for High Speed DPSK Communication Systems

In long haul communication systems, the signal regeneration is frequently used technique that provides the long reach for high-speed transmission and reception systems. During high speed and distance transmission signal fades below a definite level due to transmission impairments; Bit error rate (BER) increases rapidly that degrades the system performance. In this work, a novel signal regeneration technique is proposed for 60 Gb/s differential phase shift keying transceiver system that transmits and receives the high-speed signal over single mode fiber at transmission distance of 300 km. The designed system is modeled mathematically and its real time simulation are demonstrated. It is examined that novel proposed technique is significantly regenerating the signal for 300 km fiber length. The proposed technique has achieved the BER of 10−19 with eye open diagram in the presence of high amplitude noise, phase noise and dispersion per kilometer in optical fiber transmission. At the receiver, the proposed system has adequately mitigated the amplitude noise up to 88% and phase noise up to 89% from the transmitted signal. The proposed system will be helpful for system design engineer to design high-speed communication with required BER before its physical realization to provide quality performance for future generation high-speed communication system.

Effects of modifications of the crackle percept in high-amplitude noise on sound quality and statistical metrics

Three methods of altering a waveform that exhibits the crackle percept in high-amplitude noise were previously considered [Swift, Gee, Neilsen, 2014]. Two alterations—expanding shocks and transforming the derivative of the waveform to a Gaussian distribution—were found to eliminate crackle, while a third modification—transforming the waveform pressure to exhibit a Gaussian distribution—did not eliminate the crackle percept. In this paper, a fourth alteration, altering the phase of a crackling signal in the frequency domain in the manner of an all-pass filter in selected frequency bands, is considered and its effects on the crackle percept is compared to the previous methods. In addition to waveform playback, metrics such as skewness of the pressure waveform derivative and loudness and sharpness, along with their time-varying forms, are used in the comparison. [Work supported by AF SBIR.]