Challenges and Perspectives for Lowering the Vertical-Component Long-Period Detection Level

2021 ◽  
Author(s):  
Thomas Forbriger ◽  
Walter Zürn ◽  
Rudolf Widmer-Schnidrig
Keyword(s):  
Normal Mode ◽  
Atmospheric Correction ◽  
Detection Threshold ◽  
Vertical Component ◽  
Low Noise ◽  
Detection Sensitivity ◽  
Noise Model ◽  
Detection Level ◽  
Broadband Seismometer ◽  
First Case

Abstract For observations of vertical-component acceleration in the normal-mode band (0.3–10 mHz), the detection sensitivity for signals from the Earth’s body can be improved to levels below the Peterson low-noise model (PLNM). This is achieved by deterministic procedures that (at least partly) remove the accelerations originating from atmospheric mass fluctuations. The physical models used in such corrections are still too simple and fail at frequencies above 3 mHz. Anticipating improved atmospheric correction procedures, we explore the prospects of lowering the detection level. From recordings of excellent vertical-component sensors operated under exceptional site conditions at the Black Forest Observatory, we select time windows of very low background signal, for which all of the contributing broadband seismometers showed their best performance. Streckeisen seismometers of type STS-1, STS-2, and STS-6A, a Nanometrics Trillium T360, and the superconducting gravimeter (SG) SG056 manufactured by GWR Instruments take part in this comparison. Because of their low level of self-noise, the STS-1 and the SG056-G1 benefit the most from a correction with the best currently available improved Bouguer plate model for atmospherically induced signals at frequencies below 1 mHz. As far as we know, this is the first case in which the background level of a broadband seismometer could be lowered below the PLNM. At signal periods beyond the normal-mode band (investigated up to 12 hr), the gravimeters show the lowest level of self-noise, directly followed by the STS-6A. In the band from 0.3 to 10 mHz, the STS-1 has the lowest level of self-noise, which is at least 4 dB below the PLNM, directly followed by the T360 and the STS-6A. Sensors of lower self-noise than the currently manufactured STS-6A or T360 are needed before improved atmospheric correction procedures lead to a significantly lower vertical-component detection threshold.

Flowing water decreases hydrodynamic signal detection in a fish with an epidermal lateral-line system

2006 ◽  
Vol 57 (6) ◽  
pp. 611 ◽  
Author(s):  
Daniel K. Bassett ◽  
Alexander G. Carton ◽  
John C. Montgomery
Keyword(s):  
Lateral Line ◽  
Detection Threshold ◽  
Low Noise ◽  
Detection Sensitivity ◽  
Lateral Line System ◽  
Flowing Water ◽  
Background Flow ◽  
Line System ◽  
Water Conditions ◽  
The Common

The lateral-line system of the common bully, Gobiomorphus cotidianus, is unusual in that it possesses an extensive array of superficial neuromasts. Fish were trained to orientate to a small vibrating bead (50 Hz). By manipulating the amplitude of vibration to determine the threshold level for the behaviour, the hydrodynamic detection capabilities of the common bully were characterised in both still- and flowing-water. In still water, the common bully attained a detection threshold (calculated as the amplitude of water particle displacement at the snout) of 3.3 × 10−5 cm at 50 Hz. Successive elevations in the background flow caused a 10-fold decrease in detection sensitivity. At a background flow of 4.5 cm s–1 the detection threshold increased to 3 × 10−4 cm. These findings demonstrate that a lateral-line system that lacks sub-surface canal neuromasts is most sensitive in still-water conditions (low-noise). However, this system is compromised under flowing-water conditions such that sensitivity is reduced at current velocities >1.5 cm s–1.

A High- and Low-Noise Model for High-Quality Strong-Motion Accelerometer Stations

2013 ◽  
Vol 29 (1) ◽  
pp. 85-102 ◽  
Author(s):  
Carlo Cauzzi ◽  
John Clinton
Keyword(s):  
Urban Areas ◽  
Strong Motion ◽  
Low Noise ◽  
Noise Model ◽  
Accelerometer Data ◽  
High Quality ◽  
Broadband Seismometer ◽  
Instrument Noise ◽  
Low Amplitude ◽  
Noise Models

We present reference noise models for high-quality strong-motion accelerometer installations. We use continuous accelerometer data to derive very broadband (50 Hz–100 s) high- and low-noise models. The proposed noise models are compared (1) to the broadband seismometer Peterson (1993) noise models; (2) the datalogger self-noise and background noise levels at existing Swiss and Southern California strong-motion stations; and (3) typical earthquake signals recorded in Switzerland and worldwide. The accelerometer low-noise model (ALNM) is dominated by instrument noise from the sensor and datalogger. The accelerometer high-noise model (AHNM) reflects (1) at high frequencies the acceptable site noise in urban areas, (2) at mid-periods the microseismal peaks and (3) at long periods the maximum noise observed from well-insulated sensor/datalogger systems placed in vault quality sites. This study also provides confirmation of the remarkable capability of modern strong-motion accelerometers to record low-amplitude ground motions with seismic observation quality over a broad frequency range.

scholarly journals Analysis of Noise and Velocity in GNSS EPN-Repro 2 Time Series

2021 ◽  
Vol 13 (14) ◽  
pp. 2783
Author(s):  
Sorin Nistor ◽  
Norbert-Szabolcs Suba ◽  
Kamil Maciuk ◽  
Jacek Kudrys ◽  
Eduard Ilie Nastase ◽  
...  
Keyword(s):  
Time Series ◽  
Visual Inspection ◽  
Flicker Noise ◽  
Vertical Component ◽  
Likelihood Estimation ◽  
Noise Model ◽  
Noise Amplitude ◽  
Allan Deviation ◽  
Power Spectral ◽  
Position Time Series

This study evaluates the EUREF Permanent Network (EPN) station position time series of approximately 200 GNSS stations subject to the Repro 2 reprocessing campaign in order to characterize the dominant types of noise and amplitude and their impact on estimated velocity values and associated uncertainties. The visual inspection on how different noise model represents the analysed data was done using the power spectral density of the residuals and the estimated noise model and it is coherent with the calculated Allan deviation (ADEV)-white and flicker noise. The velocities resulted from the dominant noise model are compared to the velocity obtained by using the Median Interannual Difference Adjusted for Skewness (MIDAS). The results show that only 3 stations present a dominant random walk noise model compared to flicker and powerlaw noise model for the horizontal and vertical components. We concluded that the velocities for the horizontal and vertical component show similar values in the case of MIDAS and maximum likelihood estimation (MLE), but we also found that the associated uncertainties from MIDAS are higher compared to the uncertainties from MLE. Additionally, we concluded that there is a spatial correlation in noise amplitude, and also regarding the differences in velocity uncertainties for the Up component.

scholarly journals Seismic Vertical Component Effects on the Pathology of a Historical Structure, Xana, Located in Greece

2021 ◽  
Vol 7 ◽  
Author(s):  
Vasiliki Terzi ◽  
Asimina Athanatopoulou
Keyword(s):  
Seismic Analysis ◽  
Near Field ◽  
Three Dimensional ◽  
Vertical Component ◽  
Element Model ◽  
Material Behavior ◽  
Initial State ◽  
Tensile Cracks ◽  
First Case ◽  
Three Dimensional Finite Element

The present study aims to investigate the effects of the seismic vertical component on the pathology of Xana monument which is a typical caravanserai, constructed circa 1375–1385 and is located in the archeological site of the municipality of Trainapoulis, Greece. The monument’s plan is rectangular and the three-leaf masonry circumferential walls support a hemicylindrical dome constructed by bricks and mortar. The structure consisted of two consecutive parts: one for the travelers and one for the animals. Nowadays, the triangular roof, that covered the structure, and the first part of the monument do not exist. Xana suffers tensile cracks along the interior surface of the dome, a vertical fracture located on the northern wall and vertical tensile cracks located at the openings. A three-dimensional finite element model of the initial state of Xana is constructed. Non-linear material behavior is taken into account as well as soil-structure interaction effects. An adequate number of near-field earthquake events has been used, taking into account that they are related to significant vertical components. The structural seismic analysis is conducted for two cases. The first case refers to the action of the two horizontal-component of ground motions while the second one takes into account the three translational seismic components. The pathology estimation reveals important information concerning the structural effects due to vertical accelerations.

Establishing a Detection Threshold for Acoustic-Based External Leak Detection Systems

2020 ◽  
Author(s):  
Mathew Bussière ◽  
Mark Stephens ◽  
Marzie Derakhshesh ◽  
Yue Cheng ◽  
Lorne Daniels
Keyword(s):  
Sensitivity Analysis ◽  
Detection Threshold ◽  
Leak Detection ◽  
Detection Sensitivity ◽  
Sensitivity Threshold ◽  
Detection Systems ◽  
Threshold Measure ◽  
Full Scale Tests ◽  
Parameter Values ◽  
Very High

Abstract A better understanding of the sensitivity threshold of external leak detection systems can assist pipeline operators in predicting detection performance for a range of possible leak scenarios, thereby helping them to make more informed decisions regarding procurement and deployment of such systems. The analysis approach described herein was developed to characterize the leak detection sensitivity of select fiber optic cable-based systems that employ Distributed Acoustic Sensing (DAS). The detection sensitivity analysis consisted of two steps. The first step involved identifying a suitable release parameter capable of providing a defensible basis for defining detection sensitivity; the second step involved the application of logistic regression analysis to characterize detection sensitivity as a function of the chosen release parameter. The detection sensitivity analysis described herein provides a means by which to quantitatively determine the leak detection sensitivity threshold for each technology and sensor deployment position evaluated in a set of full-scale tests. The chosen sensitivity threshold measure was the release parameter value associated with release events having a 90% probability of being detected. Thresholds associated with a higher probability level of 95% were also established for comparison purposes. The calculated sensitivity thresholds can be interpreted to mean that release events associated with release parameter values above the sensitivity threshold have a very high likelihood (either 90 or 95%) of being detected.

Radiation modes of propeller tonal noise

2021 ◽  
pp. 1-25
Author(s):  
Hanbo Jiang ◽  
Siyang Zhong ◽  
Han Wu ◽  
Xin Zhang ◽  
Xun Huang ◽  
...  
Keyword(s):  
Spherical Harmonics ◽  
Sound Field ◽  
Low Noise ◽  
Noise Model ◽  
Sound Waves ◽  
Tonal Noise ◽  
Noise Sources ◽  
Separate Source ◽  
Radial Forces ◽  
Flow Variables

Abstract This paper focuses on the radiation modes and efficiency of propeller tonal noise. The thickness noise and loading noise model of propellers has been formulated in spherical coordinates, thereby simplifying numerical evaluation of the integral noise source. More importantly, the radiation field can be decomposed and projected to spherical harmonics, which can separate source-observer positions and enable an analysis of sound field structures. Thanks to the parity of spherical harmonics, the proposed model can mathematically explain the fact that thrusts only produce antisymmetric sound waves with respect to the rotating plane. In addition, the symmetric components of the noise field can be attributed to the thickness, as well as drags and radial forces acting on the propeller surface. The radiation efficiency of each mode decays rapidly as noise sources approach the rotating centre, suggesting the radial distribution of aerodynamic loadings should be carefully designed for low-noise propellers. The noise prediction model has been successfully applied to a drone propeller and achieved a reliable agreement with experimental measurements. The flow variables employed as an input of the noise computation were obtained with computational fluid dynamics (CFD), and the experimental data were measured in an anechoic chamber.

scholarly journals Non-informative vision improves spatial tactile discrimination on the shoulder but does not influence detection sensitivity

2020 ◽  
Vol 238 (12) ◽  
pp. 2865-2875
Author(s):  
Fabrizio Leo ◽  
Sara Nataletti ◽  
Luca Brayda
Keyword(s):  
Tactile Stimulation ◽  
Detection Threshold ◽  
Receptive Fields ◽  
Judgment Task ◽  
The Body ◽  
Detection Sensitivity ◽  
Body Parts ◽  
Tactile Acuity ◽  
Tactile Stimuli ◽  
Numerosity Judgment

Abstract Vision of the body has been reported to improve tactile acuity even when vision is not informative about the actual tactile stimulation. However, it is currently unclear whether this effect is limited to body parts such as hand, forearm or foot that can be normally viewed, or it also generalizes to body locations, such as the shoulder, that are rarely before our own eyes. In this study, subjects consecutively performed a detection threshold task and a numerosity judgment task of tactile stimuli on the shoulder. Meanwhile, they watched either a real-time video showing their shoulder or simply a fixation cross as control condition. We show that non-informative vision improves tactile numerosity judgment which might involve tactile acuity, but not tactile sensitivity. Furthermore, the improvement in tactile accuracy modulated by vision seems to be due to an enhanced ability in discriminating the number of adjacent active electrodes. These results are consistent with the view that bimodal visuotactile neurons sharp tactile receptive fields in an early somatosensory map, probably via top-down modulation of lateral inhibition.

scholarly journals Noise Modeling and Simulation of Giant Magnetic Impedance (GMI) Magnetic Sensor

Sensors ◽  
2020 ◽  
Vol 20 (4) ◽  
pp. 960
Author(s):  
Fang Jin ◽  
Xin Tu ◽  
JinChao Wang ◽  
Biao Yang ◽  
KaiFeng Dong ◽  
...  
Keyword(s):  
Modeling And Simulation ◽  
Noise Spectrum ◽  
Low Noise ◽  
Noise Model ◽  
Magnetic Noise ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Noise Modeling ◽  
Noise Characteristics ◽  
Spectrum Curve

The detection resolution of a giant magneto-impedance (GMI) sensor is mainly limited by its equivalent input magnetic noise. The noise characteristics of a GMI sensor are evaluated by noise modeling and simulation, which can further optimize the circuit design. This paper first analyzes the noise source of the GMI sensor. It discusses the noise model of the circuit, the output sensitivity model and the modeling process of equivalent input magnetic noise. The noise characteristics of three modules that have the greatest impact on the output noise are then simulated. Finally, the simulation results are verified by experiments. By comparing the simulated noise spectrum curve and the experimental noise spectrum curve, it is demonstrated that the preamplifier and the multiplier contribute the most to the output white noise, and the low-pass filter plays a major role in the output 1/f noise. These modules should be given priority in the optimization of the noise of the conditioning circuit. The above results provide technical support for the practical application of low-noise GMI magnetometers.

MODELING OF NOISE BEHAVIOR OF GRADED BAND GAP CHANNEL MOSFET AT GHz FREQUENCIES

2007 ◽  
Vol 07 (04) ◽  
pp. L507-L517
Author(s):  
ALI ABOU-ELNOUR ◽  
OSSAMA ABO-ELNOR ◽  
HAMDY ABDELHAMEED ◽  
ADEL EL-HENAWY
Keyword(s):  
Band Gap ◽  
High Frequency ◽  
Noise Figure ◽  
Low Noise ◽  
Noise Model ◽  
Superior Performance ◽  
Model Parameters ◽  
Short Channel ◽  
Suggested Structure ◽  
Graded Band Gap

A novel graded band gap channel Si - SiGe MOSFET structure has been suggested and its characteristics have been investigated. The investigations indicated that the suggested structure reduces the short-channel effects, increases the cut-off frequency, and hence makes its usage at high frequency and Low noise applications possible. To show the superior performance of the suggested structure at GHz frequencies, and as an example, the noise behavior of the structure is determined. First the device noise model parameters are calculated from D.C. and A.C. characteristics. The extracted noise model parameters are then used to determine the minimum noise figure at GHz frequencies. The effects of the different device parameters on the noise performance are determined. Finally, the results are compared with those of conventional MOSFET structure to show the superior performance of graded band gap Si - SiGe MOSFETs at high frequency ranges.

A Statistical Low Noise Model of the Earth

2012 ◽  
Vol 83 (1) ◽  
pp. 39-48 ◽  
Author(s):  
S. Castellaro ◽  
F. Mulargia
Keyword(s):  
Low Noise ◽  
Noise Model ◽  
The Earth
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